Cams! (valve event timing, resonance tuning, what's theory, what's fact)

FastDriver

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David posted some of the best tech I've read regarding resonance tuning in another thread comparing the TFS-R and Box-R intakes. This thread is meant to discuss some of the more technical details of cam design brought up in that thread.

Alright, I'm cracking my knuckles and might be out of my field of expertise here because I don't have a mechanical engineering undergrad or anything, but am inclined to go that direction in grad school. However, I do excel at physics related discussion. First, before going into the specific comments you've made, I'd like your recommended reading material regarding cams so I can up my game a little when it comes to the technical discussion concerning them. So far, you’ve mentioned John Heywood, and now Blair.

A large cylinder head + intake system may like a delayed intake opening (or at least slow beginning ramp rate) so when the piston speed increases on the intake stroke towards its peak speed, the draw on the intake runner (head + intake) is greater.

More important to me than numbers, at the moment, is an understanding of the physics concepts. Here, you speak of "greater draw" as a good thing. I've definitely heard this before. Explain why, please. I have extremely limited education regarding cams, and even less experience on engine simulations, so I might be way of base in some of my ideas. Allow me to elaborate a bit and see if I'm headed in the right direction:

Negatives
draw
It seems to me that the "draw" itself isn't all positive: First, it causes an increased pressure differential between the inside of the cylinder and the intake runner. The lower pressure in the cylinder is not in itself helpful as it increases the drag on the piston. So, first lets all recognize and agree that the the port velocity gained comes at a cost. Agreed?

The assumption that delaying the intake opening event increases drag on the piston on the intake stroke might only be invalid if there is still more pressure initially in the cylinder than in the intake runner as the piston begins to move downward. This is most likely to be the case in a turbocharged application with significant back-pressure in the exhaust, but could still be the case in n/a engines if the exhaust hasn't had time to completely evacuate, which I think would indicate that the cam wasn't timed correctly to begin with.

overlap
Another possible negative is that delaying the intake opening (IO) reduces overlap (given constant exhaust valve timing), which would most likely be a negative in an n/a engine where delaying the intake valve opening would reduce the benefits of exhaust scavenging.

Since I'm assuming that you're right about this delayed opening being an overall advantage, the positives must outweigh the negatives. Here are the possible positives that I can think of:

Before I get to the possible positive consequences of delaying the intake valve opening, let me define a term in the context that I will use it (though not technically correct, perhaps). 100% VE: air mass in the cylinder = the expected air mass in that cylinder at BDC at rest given atmospheric pressure and the air temp in the cylinder, or in a boosted motor given the applied boost and the in-cylinder air temp). This definition allows for a common reference whether we're talking about a boosted engine or n/a engine regardles of the ambient temperature, or intake air temperature (IAT). If any clarification is needed, please ask.

Positives
Port Velocity
First, delaying the IO, should result in the increase in initial force on the air mass, meaning that acceleration of that air mass will be higher, at least initially. Is it higher, overall? I don’t know. If you’re correct about resulting port velocity being higher, then the answer is yes. And, going with that assumption. It seems to me, that we’re reducing the time that we’re able to apply a force on the air mass. At low RPM, or in a low displacement engine, that’s not a problem because we still have enough time to fill the cylinder, but at high RPM or in a big engine, that may no longer hold true.

Given the earlier definition of VE, my first thought as to the biggest advantage regarding delaying the intake opening event has to do with both increasing intake port velocity, and also timing that velocity with the intake closing event. The only reason that I can see port velocity providing any advantage at all is if the momentum of the air causes an increase in cylinder filling. At the point where the net force acting on the air mass begins to decelerate it, the rate the cylinder is filled is higher because of the momentum of the air mass. One question I have concerning this is: Is that point going to be 100% VE? I think 100% VE should be the point where the pressure in the cylinder equals the pressure in the intake tract. Without accounting for other forces, it would also be the point of maximum port velocity because the net forces acting on the air-mass would be 0. There are other forces involved, like resistance due to friction in the port and when air approaches sonic, though I don’t know how significant an impact they make in normal conditions. Regardless, any air-flow at and beyond which air is no longer being accelerated by the pressure differential would be due solely to momentum of the air column caused by inertia (intake port velocity). The thing that leads me to believe it might be a benefit below 100% VE is that Ed Curtis always talked about the importance of port velocity even in street motors where it is unlikely 100% VE was being reached.

The second part of the port velocity thing is related to the Intake closing (IC) event. I think, theoretically, the optimum IC event without other compounding factors would be the point at which air speed through the port has stalled. Does that actually happen, or are we actually forced to close the intake before that point? In any case, at this point well after the piston has reversed direction but before the intake air reverses direction, you’d want the intake valve to shut. Problem is, the point will vary depending on engine speed. So in terms of crank degrees after BDC, at low RPM I believe the ideal IC would be sooner (in crank degrees) because the cylinder has more time (in seconds)to fill the cylinder, and at high RPM, ideal IC would be later (in crank degrees) because the cylinder has not had as much time (in seconds) to fill. So, choosing the right IC should play a significant part in the power band without even considering resonance tuning.

Now, IC timing should relate back to IO timing for two reasons that I can think of: cylinder filling due to air mass, and resonance tuning. I’ll discuss the first reason in this section. If we slap on bigger heads and do not delay the IO, then the cylinder might fill well more than 100%VE, and then because the intake valve is open too long for the large head, it could actually lose some of the air fuel charge back into the intake port before the valve closes (possibly dropping below 100% VE again. By retarding/delaying (in crank degrees) the IO event, and/or advancing the IC event, we can “tune” the bigger headed combination so that we’re still getting the full cylinder fill with the small engine or at lower RPM.

Here’s another question for you concerning the discussion above: What happens to resonance tuning if the air in the intake tract has stalled? After all, isn’t the pressure wave caused by the impact of the sudden closure in the intake valve on the moving column of air? No pressure wave would be created at the valve shutting because the air there is already not moving. However, I could still see there being a pressure wave that was created earlier by the pressure rise in the cylinder. Is resonance tuning still of any significance at this RPM? If no, then is this our peak torque rpm? Or, is this a non-starter because it doesn’t actually happen the way I’m imagining it?

Overlap:
less overlap = may actually be a good thing for boosted engines. Since you like to cite Bernoulli, you know that air flow causes a local decrease in fluid pressure, which should still help “draw” air from the intake as exhaust flows out. However, it should also be apparent that when the pressure in the exhaust is significantly greater than the pressure in the intake, then minimal overlap is preferred. Thus, delaying the intake valve opening is actually positive anyway. However, due to the increased cylinder pressure in this situation, I don’t think this would create the additional draw that it would in an n/a engine. Perhaps, in a turbocharged application, an even later IO might be called for than would be expected on an n/a motor with big heads.

Resonance tuning
Delaying the IO might result in proper timing to take advantage of the helmholtz effect. I imagine that this would also be of concern regarding the IC event. You seem to have the math figured out… please guide discussion here. I can’t imagine exhaust timing has anything to do with this effect, at least with regard to the intake, so only the IO and IC could. Please enlighten me. How large an effect can playing with this timing have? Is it possible to calculate when the advantages gained from resonance tuning do not outweigh other disadvantages (see port velocity comments regarding IC).

That's pretty much all I can think of at the moment. My brain is out of juice because it's after 4am here, now. What else did I forget to mention?

In any case, that’s enough for tonight. I’ll respond to the rest of your post below tomorrow in a subsequent post in this thread. I definitely want to ask some questions regarding that stuff, too. But the above is already enough for now, wouldn’t you agree?



This is when the curtain area should be maximized in a timely manner. The change in air pressure will increase the air speed (some call it velocity) and will bring inertia with it. You need less duration. Matched parts become crucial when you go with various parts, like small or larger intakes.

With a large port velocity profile (relative to the cylinder volume), you need to "limit" the camshaft valve activity, not try to feed the cylinder more air with longer/larger durations. Thinking about how a basic 4-stroke engine works, you also will benefit with larger exhaust parameters with a large induction system.

There is no perfect set-up (large induction + small cam or small induction + larger camshaft). They just need to be matched, as this dyno session was matched better and it had some strong results to back it up. :nice:

Anyways, back on topic. For sake of argument - let's take the aforementioned XE274HR on this 331. Given the specs of that camshaft, the TFS 185 heads, I get a optimized 3rd tuned harmonic of ~12.9". Well, low and behold, the TFS-R BOX (9.0") + TFS 185 (4.75") length equals 13.75". This is less than an inch from ideal. However, add the extra 2.00" on to create the TFS-R runner length + same cylinder head, you get 15.75" - even further from ideal. The TFS-R BOX fits much closer, compared to the previous dyno run using a tuned length an entire two inches off near optimal. I wonder why the power went up? :) Factor in the assumed increase in taper from the BOX upper to lower, and you get even closer to the needed harmonic for a 12.9" length runner.

It was not a coincidence that at those funny RPM's (3700 and 3200) that we saw variations in HP/FT LB numbers at the wheels - tuned length and other intake parameters played a big part in this.
 
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5spd GT

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I got to say, first - I am sorry for being late with this reply, just was working on other things like everybody else I suppose. :)

David posted some of the best tech I've read regarding resonance tuning in another thread comparing the TFS-R and Box-R intakes. This thread is meant to discuss some of the more technical details of cam design brought up in that thread.

Alright, I'm cracking my knuckles and might be out of my field of expertise here because I don't have a mechanical engineering undergrad or anything, but am inclined to go that direction in grad school. However, I do excel at physics related discussion. First, before going into the specific comments you've made, I'd like your recommended reading material regarding cams so I can up my game a little when it comes to the technical discussion concerning them. So far, you’ve mentioned John Heywood, and now Blair.

My degree is not in ME either, but it doesn’t keep us from enjoying bits and pieces of it! My brother is a ME and I usually have to refer to him for formula help, if they get to involved for dumb old me. By the way, I think this is a great topic. These kind of discussions take more time than I need to spend on it, so my long winded responses may be limited in the future. The two text books I look to are, as you said, by John Heywood and Gordon Blair.

Design and Simulation of Four-Stroke Engines by Gordon Blair - $100

Internal Combustion Engine Fundamentals by John Heywood - $200 (but the International version is cheaper)

These two text books are not about “cams”, but have a great deal of information on how an engine works down to very finite details, WAY above my head.:shrug: Heywood’s book is a bit easier to follow in some ways, while Blair’s book has more detail oriented information. I am still working on trying to figure out his intake ramming factor formulas completely.

I also like Buddy Rawls camshaft website gives a high level overview of the importance of camshaft timing, if it is still up.

More important to me than numbers, at the moment, is an understanding of the physics concepts. Here, you speak of "greater draw" as a good thing. I've definitely heard this before. Explain why, please. I have extremely limited education regarding cams, and even less experience on engine simulations, so I might be way of base in some of my ideas. Allow me to elaborate a bit and see if I'm headed in the right direction:

Negatives

draw
It seems to me that the "draw" itself isn't all positive: First, it causes an increased pressure differential between the inside of the cylinder and the intake runner. The lower pressure in the cylinder is not in itself helpful as it increases the drag on the piston. So, first lets all recognize and agree that the the port velocity gained comes at a cost. Agreed?

The assumption that delaying the intake opening event increases drag on the piston on the intake stroke might only be invalid if there is still more pressure initially in the cylinder than in the intake runner as the piston begins to move downward. This is most likely to be the case in a turbocharged application with significant back-pressure in the exhaust, but could still be the case in n/a engines if the exhaust hasn't had time to completely evacuate, which I think would indicate that the cam wasn't timed correctly to begin with.

I have very limited knowledge in camshafts as well, so I am in the same boat as you. I simply only believe I know more than the average enthusiast.
I agree with you that a late intake opening is not always a positive move and there is a pumping loop that the intake and exhaust stroke has to deal with. Now, here is what I said in the other thread:

A large cylinder head + intake system may like a delayed intake opening (or at least slow beginning ramp rate) so when the piston speed increases on the intake stroke towards its peak speed, the draw on the intake runner (head + intake) is greater. This is when the curtain area should be maximized in a timely manner. The change in air pressure will increase the air speed (some call it velocity) and will bring inertia with it.

This delayed intake valve opening I am speaking of is simply allowing the piston time to speed up, allowing for a stronger pull on the intake trac. This creates the higher cylinder pressure when the valve shuts well after BDC. More cylinder pressure equals more power! Peak piston speed occurs on my engine at ~75 degrees and of course that is when the piston in the cylinder creates some serious pull on the port. As you know, at this time, this is when the valve is open considerably, but not peaked yet. Of course, there is a balance here as you mentioned with your thoughts on the “draw.”

overlap
Another possible negative is that delaying the intake opening (IO) reduces overlap (given constant exhaust valve timing), which would most likely be a negative in an n/a engine where delaying the intake valve opening would reduce the benefits of exhaust scavenging.

Since I'm assuming that you're right about this delayed opening being an overall advantage, the positives must outweigh the negatives. Here are the possible positives that I can think of:

Before I get to the possible positive consequences of delaying the intake valve opening, let me define a term in the context that I will use it (though not technically correct, perhaps). 100% VE: air mass in the cylinder = the expected air mass in that cylinder at BDC at rest given atmospheric pressure and the air temp in the cylinder, or in a boosted motor given the applied boost and the in-cylinder air temp). This definition allows for a common reference whether we're talking about a boosted engine or n/a engine regardles of the ambient temperature, or intake air temperature (IAT). If any clarification is needed, please ask.

I’m not saying that the delayed intake opening is the only way or that it is “right”, it is just another way to skin a cat and minimize the potential negatives of a larger port. I believe the overlap period is very important to the performance of engine, due to the possibility of incorrect valve events causing a lot of problems. Obviously, if the cylinder pressure is too high because of a late exhaust opening, spent gasses can be shoved into the intake trac. On the contrary, to early of an exhaust valve opening for blowing out the hot exhaust gasses, can cause fresh air to exit straight out the exhaust valve as it closes.

With that said, I think effective exhaust scavenging still primarily deals with the timing of the exhaust valve opening and closing portions, as long as the piston + upward pressure continue to push with the negative wave, creating the suction in the exhaust runner to assist in removing all of the spent gasses. I think you want to try to get the exhaust gasses out as much as possible, BEFORE the intake valve opens to any significant degree (overlap). Of course, if timed right the negative pressure wave in the exhaust runner can create a bit more suction on the intake port, but will close before the clean air moves out the exhaust. I’m not too versed with the boosted portion of cam timing and its effects, but I’m quite sure there is less room for messing around. I am with you on the VE description so far.

Positives

Port Velocity
First, delaying the IO, should result in the increase in initial force on the air mass, meaning that acceleration of that air mass will be higher, at least initially. Is it higher, overall? I don’t know. If you’re correct about resulting port velocity being higher, then the answer is yes. And, going with that assumption. It seems to me, that we’re reducing the time that we’re able to apply a force on the air mass. At low RPM, or in a low displacement engine, that’s not a problem because we still have enough time to fill the cylinder, but at high RPM or in a big engine, that may no longer hold true.
Given the earlier definition of VE, my first thought as to the biggest advantage regarding delaying the intake opening event has to do with both increasing intake port velocity, and also timing that velocity with the intake closing event. The only reason that I can see port velocity providing any advantage at all is if the momentum of the air causes an increase in cylinder filling. At the point where the net force acting on the air mass begins to decelerate it, the rate the cylinder is filled is higher because of the momentum of the air mass. One question I have concerning this is: Is that point going to be 100% VE? I think 100% VE should be the point where the pressure in the cylinder equals the pressure in the intake tract. Without accounting for other forces, it would also be the point of maximum port velocity because the net forces acting on the air-mass would be 0. There are other forces involved, like resistance due to friction in the port and when air approaches sonic, though I don’t know how significant an impact they make in normal conditions. Regardless, any air-flow at and beyond which air is no longer being accelerated by the pressure differential would be due solely to momentum of the air column caused by inertia (intake port velocity). The thing that leads me to believe it might be a benefit below 100% VE is that Ed Curtis always talked about the importance of port velocity even in street motors where it is unlikely 100% VE was being reached.

Your definition of VE above, just makes me think that there is no pressure differential at that point, but not necessarily relating to 100% VE. However, I could EASILY be wrong. I believe that 100% VE occurs between the time you opened the intake valve and closed it, and if you trapped 100% of the potential air mass (assuming temp/atmosphere is constant) in the cylinder volume difference between BDC and TDC. I admit that is too simplistic. I got lost on your comments about the “forces acting on the air-mass would be 0” portion. About the port velocity, people hate that phrase, but it just means air speed into the cylinder. I am with you on the Ed Curtis comment. Like you said, at low RPM’s, these large intake tracs do not have a lot of piston speed to assist in pulling the air into the cylinder, so some cam manipulation has to occur, (ex. delaying the intake opening and matching the other valve timing components to it).

The second part of the port velocity thing is related to the Intake closing (IC) event. I think, theoretically, the optimum IC event without other compounding factors would be the point at which air speed through the port has stalled. Does that actually happen, or are we actually forced to close the intake before that point? In any case, at this point well after the piston has reversed direction but before the intake air reverses direction, you’d want the intake valve to shut. Problem is, the point will vary depending on engine speed. So in terms of crank degrees after BDC, at low RPM I believe the ideal IC would be sooner (in crank degrees) because the cylinder has more time (in seconds)to fill the cylinder, and at high RPM, ideal IC would be later (in crank degrees) because the cylinder has not had as much time (in seconds) to fill. So, choosing the right IC should play a significant part in the power band without even considering resonance tuning.

Now, IC timing should relate back to IO timing for two reasons that I can think of: cylinder filling due to air mass, and resonance tuning. I’ll discuss the first reason in this section. If we slap on bigger heads and do not delay the IO, then the cylinder might fill well more than 100%VE, and then because the intake valve is open too long for the large head, it could actually lose some of the air fuel charge back into the intake port before the valve closes (possibly dropping below 100% VE again. By retarding/delaying (in crank degrees) the IO event, and/or advancing the IC event, we can “tune” the bigger headed combination so that we’re still getting the full cylinder fill with the small engine or at lower RPM.

Air speed definitely stalls, due to the fact of the piston moving upwards, since intake closings happen well after BDC. Eventually this upward movement will stall and potential reverse the intake flow, if not closed off early enough. The “point will vary depend on engine speed” for sure; good observation, but that is where tuning for an RPM for peak power is where the cam timing should be if looking for performance. I agree with you 100%, just cam timing plays into the goals of the engine (or owner's wants…lol).

Again, I agree with your thoughts, but along those same lines the speed of the fill is important, so a large cylinder head /intake could create high cylinder pressure as well as a small cylinder head/intake. I know everyone hates to hear the buzz word “velocity”, but the air speed (velocity) has to be a balance between a small restrictive inlet and a large inlet port. This is why, delaying the intake opening MAY be a benefit on a larger inlet combination by creating a higher pressure differential when the intake valve does open. In response to the negatives about a late intake opening, the intake valve can open later by degree (7* BTDC vs. 9* BTDC), but shortly, it can pass the earlier opening valve camshaft, because the ramp rate on the camshaft is made sharper, thus negating some of the negatives of a late intake opening. Of course, a steep ramp rate to open the valve later/quicker needs more valvetrain stability and has its mechanical limits. I hope that makes sense. :shrug: I probably didn't describe that very well.

Here’s another question for you concerning the discussion above: What happens to resonance tuning if the air in the intake tract has stalled? After all, isn’t the pressure wave caused by the impact of the sudden closure in the intake valve on the moving column of air? No pressure wave would be created at the valve shutting because the air there is already not moving. However, I could still see there being a pressure wave that was created earlier by the pressure rise in the cylinder. Is resonance tuning still of any significance at this RPM? If no, then is this our peak torque rpm? Or, is this a non-starter because it doesn’t actually happen the way I’m imagining it?

Overlap:
less overlap = may actually be a good thing for boosted engines. Since you like to cite Bernoulli, you know that air flow causes a local decrease in fluid pressure, which should still help “draw” air from the intake as exhaust flows out. However, it should also be apparent that when the pressure in the exhaust is significantly greater than the pressure in the intake, then minimal overlap is preferred. Thus, delaying the intake valve opening is actually positive anyway. However, due to the increased cylinder pressure in this situation, I don’t think this would create the additional draw that it would in an n/a engine. Perhaps, in a turbocharged application, an even later IO might be called for than would be expected on an n/a motor with big heads.

Resonance tuning
Delaying the IO might result in proper timing to take advantage of the helmholtz effect. I imagine that this would also be of concern regarding the IC event. You seem to have the math figured out… please guide discussion here. I can’t imagine exhaust timing has anything to do with this effect, at least with regard to the intake, so only the IO and IC could. Please enlighten me. How large an effect can playing with this timing have? Is it possible to calculate when the advantages gained from resonance tuning do not outweigh other disadvantages (see port velocity comments regarding IC).

So here is what I know about resonance or wave tuning…

When the intake valve begins to open, it sends a negative pressure wave up the intake runner at the speed of sound, then it hits the higher pressure air (Bernoulli principle!) in the plenum, then reverberates back down the intake runner as a positive wave (intake + cylinder head) towards the opening valve. Depending on the length of the total runner, it could hit on the first round or the fifth. It will shove a bit more air into the cylinder, increasing the cylinder pressure (power). The intake ramming occurs primarily during the later portion of the intake events, after the piston has reached BDC on the intake stroke and is chasing the intake valve closing. This cycle of expansion and compression waves happen while the valve is closed up and down the runner, until the intake valve opens again. Having a nice compression wave hit as the intake valve opens is obviously a good idea.

Oh, and in Blair's book, he has an optimum intake length formula gets decently involved. He considers the simpler side of things like the speed of sound and RPM, but then he involves delivery ratios, atmospheric pressure, and air density, etc. Each length has particular intake ramming peaks and I got the formula to figure those out.

You just need the gas constant of air, ratio of specific heat for air, Kelvin temp converted to Fahrenheit, induction length (mm), peak power desired, and the velocity of a sound wave (acoustics) in m/s. I put it all in Excel to make it easier. Some may believe that the waves are not strong or “how strong can air pulsations be?”. I saw one test that showed a 7” of mercury increase over atmospheric pressure (29.92” Hg). Imagine adding that into the last little bit of intake push into the cylinder and increase the cylinder pressure (power). Ever see spikes (or dips) on a dyno run outside of mechanical issues? I’d be willing to bet you that it is due to intake ramming factors. :nice:

With a 7000 RPM intake tuning goal for peak power, 80* air temp in the runners, and a 13” runner length, this places the speed of sound at 347 m/s (based off temp). I get ramming peaks (positive waves) @:

6729 RPM (second harmonic), 5250 RPM (third harmonic), and 4231 RPM (fourth harmonic)

I get troughs (negatives waves) @:

7748 RPM (second harmonic), 5811 RPM (third harmonic), 4588 RPM (fourth harmonic)

It actually seems most cars use the second and third harmonic.

Reading his book, it made me rethink measurements of the intake trac too. I was looking at the pictures of the pressure waves into the cylinder, they kind of “curl” back about ½”-1” into the cylinder. In other words, add up to an inch on the measured intake length (head + intake from bellmouth at the plenum) to account for the “end” of the wave. So with that said, if I take the AFR 185 length that I measured + the average of the 8 runners in the SMII + .75” for the wave into the cylinder, I get very close to 20”. That drops the harmonics by 2000 RPM compared to the one above. Anyway, just some stuff I found interesting…:)

I think that exhaust tuning is probably just as important as intake tuning and timing of valve events and work very well together. The interesting thing in the Blair book, when you begin reading into the exhaust section, you see that he wants you to tune the exhaust valve timing/length on the troughs of the intake and vice versa. It will pick up the amplitude of the waves.

In the end, I have the same thoughts as you on this stuff – no real arguments here! Good stuff Chris!

I would love to hear other thoughts (right or wrong, etc.).
 

v8stang289

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This thread is an interesting read. I've never really put much thought into camshaft theory but you guys have really peaked my interest. I may have to start researching.
 

tmoss

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Consider what the differential pressure is across the valve (Cylinder depression with respect to the plenum) and then think about the difference in affect the valve timing will have. open the valve early and the diff-p across the valve is less than waiting longer, this leads to a lazy air speed build. If you have an unrestricted inlet, you want to get air speed built quickly to keep diff-p up to increase fill as your close event will be sooner than a restricted long runner inlet. Due to shorter runner length and possibly lower air speeds as well as shorter valve events, the unrestricted inlet makes better use of the mass in motion if builds speed faster (higher diff-p) and has the right length/taper as that builds pressure at the bottom of the air mass column (valve) as the diff-p decays earlier (less inlet restriction) and that valve closes earlier. Now think about how a restricted inlet acts differently. less cross section - air gets moving faster, you can open valve earlier and build air speed better/earlier. Cylinder depression (valve diff-p) can last longer due to slower fill rate and the faster air speed mass in motion to "ram" as the valve closes allows for longer IVC duration efficiency.

You can use either effectively, the trick is to know enough to get each case designed right.
 

FastDriver

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For the first time since I came back to germany, I've been able to get back online with my computer. I will respond in more detail when I can get my house back up and running on the internet. I'm in no hurry, and appreciate the responses Tom & David. I do plan on fleshing the rest of my thread out, and in responding to yours. I should have internet installed in my house around the 25th of November.

Chris
 

5spd GT

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Consider what the differential pressure is across the valve (Cylinder depression with respect to the plenum) and then think about the difference in affect the valve timing will have. open the valve early and the diff-p across the valve is less than waiting longer, this leads to a lazy air speed build. If you have an unrestricted inlet, you want to get air speed built quickly to keep diff-p up to increase fill as your close event will be sooner than a restricted long runner inlet. Due to shorter runner length and possibly lower air speeds as well as shorter valve events, the unrestricted inlet makes better use of the mass in motion if builds speed faster (higher diff-p) and has the right length/taper as that builds pressure at the bottom of the air mass column (valve) as the diff-p decays earlier (less inlet restriction) and that valve closes earlier. Now think about how a restricted inlet acts differently. less cross section - air gets moving faster, you can open valve earlier and build air speed better/earlier. Cylinder depression (valve diff-p) can last longer due to slower fill rate and the faster air speed mass in motion to "ram" as the valve closes allows for longer IVC duration efficiency.

You can use either effectively, the trick is to know enough to get each case designed right.

Great explanation Tom - I agree, I strongly believe there is NOT one method (large runners/narrow camshaft events or smaller runners/wider camshaft events). They both have their limits. Meaning, you cannot place just any cylinder head, large or small, on a 6000 RPM 302 and have a good broad powerband. It is a balance without a doubt.

Glad you made it back safe Chris.
 

Shaolin Crane

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For the first time since I came back to germany, I've been able to get back online with my computer. I will respond in more detail when I can get my house back up and running on the internet. I'm in no hurry, and appreciate the responses Tom & David. I do plan on fleshing the rest of my thread out, and in responding to yours. I should have internet installed in my house around the 25th of November.

Chris
Welcome back man!
:flag:
 

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Consider what the differential pressure is across the valve (Cylinder depression with respect to the plenum) and then think about the difference in affect the valve timing will have. open the valve early and the diff-p across the valve is less than waiting longer, this leads to a lazy air speed build. If you have an unrestricted inlet, you want to get air speed built quickly to keep diff-p up to increase fill as your close event will be sooner than a restricted long runner inlet. Due to shorter runner length and possibly lower air speeds as well as shorter valve events, the unrestricted inlet makes better use of the mass in motion if builds speed faster (higher diff-p) and has the right length/taper as that builds pressure at the bottom of the air mass column (valve) as the diff-p decays earlier (less inlet restriction) and that valve closes earlier. Now think about how a restricted inlet acts differently. less cross section - air gets moving faster, you can open valve earlier and build air speed better/earlier. Cylinder depression (valve diff-p) can last longer due to slower fill rate and the faster air speed mass in motion to "ram" as the valve closes allows for longer IVC duration efficiency.

You can use either effectively, the trick is to know enough to get each case designed right.

Great explanation Tom - I agree, I strongly believe there is NOT one method (large runners/narrow camshaft events or smaller runners/wider camshaft events). They both have their limits. Meaning, you cannot place just any cylinder head, large or small, on a 6000 RPM 302 and have a good broad powerband. It is a balance without a doubt.

Glad you made it back safe Chris.

See, I'm just not sure I'm on board with that. I think in the restricted inlet case, you're more limited than with the unrestricted inlet, and you're making more sacrifices along the way.

First off, it's clear that that "unrestricted inlet" requires/benefits from a late IV opening and an early IV closing. Side effect: milder cam profile. Better low speed operating characteristics. So now, we're making all the power we want, without giving up drivability.

Secondly, lets talk about the IV closing event. We know that in the "restricted inlet" design, the "ideal" IV closing occurs later. What is happening here? We've given the air mass more time to enter the cylinder, but we've also given the piston more time to come up in the bore. So we've comparatively reduced cylinder volume at the time of IV closing in the RI engine versus the UI engine. SO it would seem to me, that the RI engine needs more of a ram effect to get the same mass of air in, because it has a smaller volume to fill than the UI engine does (with the earlier IV closing). So, if we could achieve a strong ram effect with the UI engine with an early IV closing, that it would be a more ideal situation because: more cylinder volume with the same ramming effect = more air mass in.
 

5spd GT

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See, I'm just not sure I'm on board with that. I think in the restricted inlet case, you're more limited than with the unrestricted inlet, and you're making more sacrifices along the way.

First off, it's clear that that "unrestricted inlet" requires/benefits from a late IV opening and an early IV closing. Side effect: milder cam profile. Better low speed operating characteristics. So now, we're making all the power we want, without giving up drivability.

I would reread what Tom posted, because it talks about all of this at a high-level. In a nut shell, he is saying a (using your terminology) URI will have higher air speed if you delay the opening and speed up the close, but a RI will have the same attributes if you open the valve earlier and close it later, thus creating what appears to be a wide duration figure.

Less restricted example (paraphrasing Tom) - If you open the valve early the differential pressure across the valve is less, than waiting longer to open it up. If you open it up to early this leads to a lazy air speed build. If you have an unrestricted inlet, you want to get air speed built quickly, thus delaying the intake opening.

This paraphrased version of Tom's post above should remind you of what I stated earlier:

A large cylinder head + intake system may like a delayed intake opening (or at least slow beginning ramp rate) so when the piston speed increases on the intake stroke towards its peak speed, the draw on the intake runner (head + intake) is greater. This is when the curtain area should be maximized in a timely manner. The change in air pressure will increase the air speed (some call it velocity) and will bring inertia with it.

More restricted example - A restricted example compared to the above assumes less cross sectional area, thus the air gets moving faster (i.e. air speed, velocity, etc.), so you can open valve earlier and build air speed better and earlier.

Now I see the "mild cam" comment a lot about larger runner cross section head/intake combos. In short, the only mild thing about these camshafts are the NUMBERS, not the lobe. The lobe will require a more 'aggresive' valvetrain (stiffer/lighter valve springs, stronger lifters, stronger camshaft material). If you think how a large cross section intake system works, by opening the intake valve later + closing it earlier (less duration FIGURES), the valve has to open and close in LESS time. This gets you closer to a "square" or "dwell" lobe camshaft. This is MORE aggressive, not less because the URI needs a faster ramp rate for the decreased time for cylinder fill.

Secondly, lets talk about the IV closing event. We know that in the "restricted inlet" design, the "ideal" IV closing occurs later. What is happening here? We've given the air mass more time to enter the cylinder, but we've also given the piston more time to come up in the bore. So we've comparatively reduced cylinder volume at the time of IV closing in the RI engine versus the UI engine. SO it would seem to me, that the RI engine needs more of a ram effect to get the same mass of air in, because it has a smaller volume to fill than the UI engine does (with the earlier IV closing). So, if we could achieve a strong ram effect with the UI engine with an early IV closing, that it would be a more ideal situation because: more cylinder volume with the same ramming effect = more air mass in.

I agree with what you are saying here, however don't forget a large runner (cylinder head + intake runner) would benefit strongly from a ramming peak as well, due to potential slower air speed at points where the pressure differential is not high, due to the larger cross sectional area. By the way, the ramming effect peak occurs primarily AFTER BDC, so the piston is coming up either way and we are speaking of very small degree changes from RI to UR set-ups, assuming same powerband and same respective lobe profile ratio.

A quick caveat: A large cylinder head may not always want a early opening/late closing intake valve, depending on the combination. However, we are just talking in general here. Also, when we mention just the intake opening and intake closing points, we are leaving out those effects on the exhaust opening and closing points. I believe all the valve events are as equally important.

There is more than one way to skin a cat, ask Ed Curtis. It depends on the goal for the engine and other outlying deciders. Even Darin Morgan stated that he would rather be slightly restricted on the inlet side, than have to much cross section. He is probably the BEST head designer in the current industry right now at this moment. You will be hard pressed to find anyone that would disagree.

BTW if anyone is interested, I figured out ideal runner length formula calculation if looking to make peak power at a certain RPM. This is using Blair.

At 6600 RPM, it may like these TOTAL runner lengths:

18.42"
13.66"
10.66"
8.59"

At 5200 RPM it may like these TOTAL runner lengths:

23.38"
17.34"
13.53"
10.90"

The shorter the length, the higher harmonic (weaker wave) the ramming peak will use.

BTW Nik, what is your 1/8 mile MPH with that combination?
 

NIKwoaC

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Now I see the "mild cam" comment a lot about larger runner cross section head/intake combos. In short, the only mild thing about these camshafts are the NUMBERS, not the lobe. The lobe will require a more 'aggresive' valvetrain (stiffer/lighter valve springs, stronger lifters, stronger camshaft material). If you think how a large cross section intake system works, by opening the intake valve later + closing it earlier (less duration FIGURES), the valve has to open and close in LESS time. This gets you closer to a "square" or "dwell" lobe camshaft. This is MORE aggressive, not less because the URI needs a faster ramp rate for the decreased time for cylinder fill.

I guess it all depends on what you mean when you say "aggressive cam". When I say "mild" or "aggressive", I'm speaking solely on the duration/overlap of the cam and the resulting drivability, idle, manifold vacuum, etc. You are correct, the lobe profiles that an UI engine is going to want will have very steep ramp rates, and this will require a more capable valvetrain. On that note, my heads have some pretty nice dual springs and titanium retainers, but you don't feel the titanium retainers while you're driving... You feel the "aggressiveness" of the cam, and in that regard, UI engines tend to need fairly mild cams, comparatively.

I agree with what you are saying here, however don't forget a large runner (cylinder head + intake runner) would benefit strongly from a ramming peak as well, due to potential slower air speed at points where the pressure differential is not high, due to the larger cross sectional area. By the way, the ramming effect peak occurs primarily AFTER BDC, so the piston is coming up either way and we are speaking of very small degree changes from RI to UR set-ups, assuming same powerband and same respective lobe profile ratio.

I just jumped on Comp's website and the XE282HR intake valve closes at 70 deg ABDC (@ 0.006"). The XE266HR closes its IV at 61 ABDC.

If you crunch the numbers for a 302 with a 5.09" rod, it appears that the piston in the XE282HR engine comes up ~0.3" more than the XE266HR would have at the time of IV closing. That's 10% of the stroke, and accounts for a difference of ~3.77 cubic inches (per cylinder).

I don't know, in my feeble little mind, it seems like that's a significant number, and because of this, we would want to achieve cylinder filing as quickly as possible, rather than waiting and closing the IV later. :shrug:

BTW Nik, what is your 1/8 mile MPH with that combination?

Well, let me just cover my ass by saying that I'm still fairly new to the drag racing thing, and as of the end of last season, I still had not worked all of the bugs out of the car with the combo as you see it in my sig. :p

8.581 @ 86.16 mph 1/8 with a blazing 2.1 60', haha. That's the same run where I went 13.1 @ 109.33 as you see in my sig.
 

5spd GT

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I guess it all depends on what you mean when you say "aggressive cam". When I say "mild" or "aggressive", I'm speaking solely on the duration/overlap of the cam and the resulting drivability, idle, manifold vacuum, etc. You are correct, the lobe profiles that an UI engine is going to want will have very steep ramp rates, and this will require a more capable valvetrain. On that note, my heads have some pretty nice dual springs and titanium retainers, but you don't feel the titanium retainers while you're driving... You feel the "aggressiveness" of the cam, and in that regard, UI engines tend to need fairly mild cams, comparatively.

When I say aggressive, I am speaking of the cut of the camshaft and its relationship to the valvetrain. Now the duration FIGURE and therefore the overlap period (calculated from valve opening/closing numbers) on many UI engines appears smaller, but the actual lobe area and effective valve opening period over the lobe ramp is more aggressive. That is why I look at the actual camshaft to determine if it is aggressive or not, not the figures it spits out. I can see where the confusion happens and can see both sides of that debate.

I have titanium retainers as well and a good lightweight valvetrain, they work great don't that? :nice: In fact, if anyone is interested, here are some numbers I got when I removed and weighed many of the valvetrain parts on my gram scale.

AFR 165's - 11/32" stems - 1.90"/1.60" valve size configuration

106 grams - Intake valve
118 grams - Exhaust valve
32 grams - Retainer
131 grams - Total Valve Spring Weight, including inner spring
6 grams - Both valve keepers

AFR 185's - 8mm stems - 2.02"/1.60" valve size configuration

105 grams - Intake valve
100 grams - Exhaust valve
10 grams - Retainer
97 grams - Total Valve Spring Weight, including inner spring
3 grams - Both valve keepers

If you look at just the exhaust side, I lost 77 grams (17% of a lb) on ONE valve. Now take that multiplied by ~16 and some results start happening, to the tune of nearly 3 lbs :)

The lighter/stronger valvetrains, the more aggressive (talking at the lobe transferred to the valve) the camshaft can be and more power. :nice:


I just jumped on Comp's website and the XE282HR intake valve closes at 70 deg ABDC (@ 0.006"). The XE266HR closes its IV at 61 ABDC.

If you crunch the numbers for a 302 with a 5.09" rod, it appears that the piston in the XE282HR engine comes up ~0.3" more than the XE266HR would have at the time of IV closing. That's 10% of the stroke, and accounts for a difference of ~3.77 cubic inches (per cylinder).

I don't know, in my feeble little mind, it seems like that's a significant number, and because of this, we would want to achieve cylinder filing as quickly as possible, rather than waiting and closing the IV later. :shrug:

That sounds about right, but we are not thinking about a couple of things. However, if you were just trying to make a point, I get it and ignore the rest below.

You are comparing two camshafts that have a 16* spread on both sides. Also, these camshafts have a 1000 RPM difference in powerband. Not sure that is the best comparison, but I can admit that there is likely two similar camshafts (duration, ICL, etc.), with two totally different close points, but they are likely for different combinations.

Anyways, back to those camshafts. Due to the nature of the larger spread in duration, you are going to get an earlier opening and a later closing, with the XE282 HR. However, if you stick the larger XE 282 HR in a 306, you will rev it higher and make more power. But it closes even later? But according to you, this later closing is not good for power. The engine is complex (as you know) and way over our heads. Meaning, there is a lot more going on that just the opening and closing points. Another point we are missing is the piston speed and rpm difference between those camshafts. The 9* difference is about ~150 FPM difference in piston speed, but on a 6500 RPM engine (5300 FPM peak), it isn't so relative when the air has mass and is pushing into the engine at ~250-350 FPS and constantly compressing. On top of all of that, we can only guess at the lobe profile differences. Those valve events only tell us the beginning and the end, not the 99% of the action everywhere in between. You have brought up some really good points and honestly got me thinking. Keep that up; nice job!

Well, let me just cover my ass by saying that I'm still fairly new to the drag racing thing, and as of the end of last season, I still had not worked all of the bugs out of the car with the combo as you see it in my sig. :p

8.581 @ 86.16 mph 1/8 with a blazing 2.1 60', haha. That's the same run where I went 13.1 @ 109.33 as you see in my sig.

Haha, I understand man! I was just looking for a comparison point with your large runner set-up. That is still a good MPH - you should know I could care less about your elapsed time.

My small runner set-up on a 9.6:1 306 (AFR 165's)/Performer intake with 65 mm TB @ a verified 3400 lbs on certified scales went 8.2 @ 87.33 MPH (110-111 MPH in the quarter). It was NEVER tuned; just base timing and FP. I told Ed when I ordered that I was super conservative and it was a 110% daily driver for stock pistons. I was unaware at the time how much driveability would be impacted - I know different now. I am thinking this new combo on the 306 is going to be pushing over 90-92 MPH in the 1/8th and I drove 50,000 miles with the prior set-up before I got bored and sold it all. It is running in another guys ride right now, still moving right along. I still maintain, there is more than one way to skin a cat. :)
 

NIKwoaC

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Yea, I was just using those XE cams as an example, just some real-world cams with different IV closing points. I figure the valve events of the 282 at least somewhat represent what you'd be looking for in a restricted-inlet engine, and the 266 would be closer to what you'd be looking for in an unrestricted case.
 

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Dammit!!! Looks like you two already partied without me. Ok, internet is back up and running finally (customer service in Germany just ain't what it is in the US).

Alright, let me get back up to speed and I should be able to post something back up by the end of the week.

Was Shaolin Crane banned again, or does his just need a different title?