Heads: Let's air it out
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It's pretty common but it refers to and is referenced more when talking about carb sizing. Basically not too much or too little carb...you need it to be just right.
Personally, i think too much is always better than not enough. It may not be as good as just right, but it also gives you room to grow. I'm fairly sure my cam is a bit overkill for my heads, but i have room to grow if i get say some 205's.
Oh, and you CAN get good performance out of huge heads...but the catch is you have to run a huge cam and huge RPM to go with it. Demand has to match the supply..if the heads are capable of supplying huge amounts of air, and your engine can't suck it up, what you'll get is low numbers at low RPM and so-so numbers at higher RPM that'll get better and better the higher you rev it, but then you have to consider how high can you safely rev and will you actually use that RPM range?
Case in point...the Boss 302. That engine SUCKED ASS on the street, because nobody was driving it to 8k RPM where the 2.20 valved heads started to make real power.
Going into carbs opens a can of worms... Carbs depend on air speed and vacuum to work properly, and not only that, the fuel is carried for a longer distance by the air than in an EFI application. So a lot of these "big heads/small cams" stuff doesn't work as well with carb engines...
See, that is the misconception that I'm trying to pull apart. Big heads with a big cam IS a dog down low. But what happens when you run a "small" cam (short duration, minimum overlap) with a "big" head? You get the low-speed performance characteristics of a small cam (good low speed drivability, broad torque curve), and yet, since the head flows so much air, you're moving as much, if not more air, than a medium sized head with a "big" cam.
The big head/small cam concept is what makes the LS engines FAST. People think it's magic, but it's simple. I have yet to see an actual flow chart of the new Coyote heads, but I've heard rumblings that they move more than 340 CFM at peak lift... 340 CFM!
I've heard a few different theories about that engine, but I think it boils down to the fact that they didn't have the technology 40 years ago to really make the big heads/small cam thing work, at least not on the street.
I dunno about the small cam big head idea...i just don't think a small cam has the lift or duration to make near the power at low RPM as a big cam. I think with the thousands of engine builders that have been along since the 302 was born, this would've caught on by now if it had real potential. Those GM engines, sad to say, just have a better head design than the 302. What happens when you put a nasty cam in an otherwise stock LSx engine? It gets even nastier than it did with the stock cam.
I don't know if I'm totally sold on that but I see your point. I'm going back to my original point, for aluminum heads there are AFR, Trick flow, Edelbrok, Holley, Brodix, Dart, World, Patriot, Flotek and Ford racing off the top of my head. yet out all of these companies you will only see 2 maybe 3 get mentioned in threads for a recommendation. I would assume that all of them (exception maybe patriot and flotek since I don't know that much about them) would be in the same league. I totally agree 90lxcoupe on flow charts, I have seen some flow charts on certian heads and 1 flowed better than the other on the charts w/o being biased lets say brand X out flowed brand Y. yet brand Y with pretty close to the same engine setup handed brand X it's hat at the track.
Think about it. In a theoretical situation, let's say head "A" flows 250 CFM at .600" lift, and head "B" flows 300 CFM at .600" lift. Let's say head "B" is already flowing 250 CFM at only .450" lift. In theory, with all else equal, we could run the "B" head on an engine with a tiny little .450" inch lift cam, and get the same performance as the "A" head with a .600" lift cam.
Now what happens if we run a .600" lift cam on both engines, but we pull some duration and overlap out of the "B" headed engine? Now, the "B" engine has better idle vacuum, better drivability...
It IS catching on. It's out there, just pushrod Ford guys are slow to change their ways, haha.
See, this is that "magic" thing I'm talking about. "The LS engine gets away with it and we can't because the LS engine is just better." You don't think that aftermarket head companies like Trick Flow, AFR, Edelbrock have the same level of head design technology available to them that the fellas at GM do? Yes, the LS engines have 20 years of more technology and engineering in them than our old pushrod 302s do, but that doesn't mean we can't use the same concepts that they use to make our junk fast, too.
While sacrificing some low speed performance and drivability, just like any engine when you move to a bigger cam.
Hey, I'm sending you a link to a website I want you to take a look at.
one thing i never understood is why people consider afr heads to be top of the line in quality. the only thing they have on other heads out of the box is cnc porting(assuming the gibs on the cnc machine wern't loose). the set i bought had almost all of the studs wobbled when i pulled them, the guide plates have .015 clearance on pushrods, you cannot get 1.6 rockers to clear pushrod holes with the pushrods when rocker tips arn't half off the valvestem. and then when you chop up good guideplates to center the rocker arm on the valvetip the pushrods still hit the hole walls with 1.7 rockers. cylinder #2 and #7 had valve spacing different from the rest of about .025. the included valvesprings click because the damper spring get stuck between the coils of the outer spring and snaps back into place when the valve opens. after you get all of these deficiencies fixed and drive 1000 miles you discover the valve guides are worn out, and the valve stem tips are mushroomed. so you could buy a $1400 and put $500-$600 into fixing them out of the box or buy $1200 heads and spent $600 to have them ported.
:end rant
:end rant
I have heard bad things about AFR lately. I can't say anything other than that, since I've never owned a set myself.
I spent $750 on a lightly-used set of Performers w/1.7 roller rockers installed. No complaints. I wouldn't have wanted to spend nearly that on work to my stockers, nor would I want to spend over a grand or so for an aluminum aftermarket set.
fiveohwblow
Official Member
- Jul 21, 2005
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Well that's the casting flaws I have heard about. That's what air I also want cleared. Has ANYONE actually seen all of the heads and can give a fair assessment? I spent thousands on recommendation and review and can assume everyone reading this has as well.
Who and where is that guy who has seen em all? Do the patriot heads out do our beloved AFR and TW?? Are we wasting our money??
Who and where is that guy who has seen em all? Do the patriot heads out do our beloved AFR and TW?? Are we wasting our money??
HotFox
15 Year Member
Well I have had some issues with the AFR 185 CNC on my 331 currently. I bought a set of as cast 195 Darts. As cast according to Dart they flow 23cfm more ([email protected]") note that my AFR's were flowed on a 1020 Super Flow bench by me. I made 417hp at the wheels before she broke
. I am just going to do a clean up and flow before and after on the Darts and also cc them verifying they are 195cc ports (note the AFR measured 177cc). I will swap the AFR's for the Darts and change nothing else and go back to dyno to see what the difference is. Follow my progress thread for results.
One thing I would add on velocity…what is velocity? Velocity is the speed that air moves thru an orifice. So what is needed to see velocity? Volume or cross-section and air speed. A easy way to run some comparisons is take the cfm and divide by the port size (cc's). That will give you some idea on which head has more velocity. A more accurate way is measure cross section and use that instead of port volume. As an example of what I know the AFR have a 177cc intake port, I know they flow 265 cfm. 265/177=1.497 cfm per cc of volume. Darts are 288/195=1.477. So the AFR’s have a little more velocity. I guess my point here is you can’t just look at cfm you need to look at port size as well.
Low lift cfm come into play as well as cam ramps,duration and of course lift.
Scott
. I am just going to do a clean up and flow before and after on the Darts and also cc them verifying they are 195cc ports (note the AFR measured 177cc). I will swap the AFR's for the Darts and change nothing else and go back to dyno to see what the difference is. Follow my progress thread for results.One thing I would add on velocity…what is velocity? Velocity is the speed that air moves thru an orifice. So what is needed to see velocity? Volume or cross-section and air speed. A easy way to run some comparisons is take the cfm and divide by the port size (cc's). That will give you some idea on which head has more velocity. A more accurate way is measure cross section and use that instead of port volume. As an example of what I know the AFR have a 177cc intake port, I know they flow 265 cfm. 265/177=1.497 cfm per cc of volume. Darts are 288/195=1.477. So the AFR’s have a little more velocity. I guess my point here is you can’t just look at cfm you need to look at port size as well.
Low lift cfm come into play as well as cam ramps,duration and of course lift.
Scott
I'll keep my answer simple.
The better aluminum heads are always worth it.
No point in doing hundreds of dollars of work to your car, only to have it still be slower than almost all modern sports cars.
There was a day when mid 13's was plenty fast. Now with a mid 13 timeslip you stand to lose to suv's.
Economize by using better parts the first time.
And have all heads valve jobbed, new or used. That goes for afr's and TW's too. The valve job could make all the difference in how they run, and the extra work avoids variables.
The better aluminum heads are always worth it.
No point in doing hundreds of dollars of work to your car, only to have it still be slower than almost all modern sports cars.
There was a day when mid 13's was plenty fast. Now with a mid 13 timeslip you stand to lose to suv's.
Economize by using better parts the first time.
And have all heads valve jobbed, new or used. That goes for afr's and TW's too. The valve job could make all the difference in how they run, and the extra work avoids variables.
in terms of velocity, the first thing you need to know is the target port velocity. the next thing you need to know is the minimum cross section of the head. you also need to know the cylinder displacement. 
the problem with using port volume to evaluate heads is that some heads have different port lengths and assuming the same port length based on volume will mess up the equation.
the problem with using port volume to evaluate heads is that some heads have different port lengths and assuming the same port length based on volume will mess up the equation.
Hey, I stumbled across an interesting build on another board. Not actually a member myself, but I was following links around. The thread is actually 5 years old.
Check it out. 351 Windsor, EFI H/C/I. Makes 360hp and almost 400ft-lb at the tires. Not anything mind blowing, but respectable.
Now here's the clincher: It uses ported Eddie Victor heads that flowed 380 CFM peak, and on top of that, THE STOCK MUSTANG HO CAM!
Linky
Weird, right? Read on and you'll see the engine was already making 338rwtq at 3100rpm. The huge heads didn't seem to hurt it in the low-end torque department.
Like I said, this engine is nothing mind blowing, until you look at the parts used. According to him, it idles/drives like a stocker, and he was putting 90 miles on it a day. Imagine what would happen if he put a better cam in it!
I love when people are willing to experiment, and end up blowing the doors off of accepted "truths"!
Check it out. 351 Windsor, EFI H/C/I. Makes 360hp and almost 400ft-lb at the tires. Not anything mind blowing, but respectable.
Now here's the clincher: It uses ported Eddie Victor heads that flowed 380 CFM peak, and on top of that, THE STOCK MUSTANG HO CAM!
Linky
Weird, right? Read on and you'll see the engine was already making 338rwtq at 3100rpm. The huge heads didn't seem to hurt it in the low-end torque department.
Like I said, this engine is nothing mind blowing, until you look at the parts used. According to him, it idles/drives like a stocker, and he was putting 90 miles on it a day. Imagine what would happen if he put a better cam in it!
I love when people are willing to experiment, and end up blowing the doors off of accepted "truths"!
See, the thing i wanna see is, what happens with this 351 when you put a bigger cam in? I'm still not sold on this giant low end loss everyone talks about with big cams, because i myself get good power at 2500rpm which to me is plenty streetable. I think i can agree that maybe this idea that huge heads hurt power is a myth, but i'm not sold on the idea that a small cam with those big heads is any better than a huge cam or the right custom cam for that matter. The cam just effects the RPM and power range..simple as that. This engine made a lot of low end power because of the stock cam...if you wanted to make more power and at higher RPM (where those 380cfm heads are gonna show their true worth) then stick a big cam in and see what happens. It's all in the application and intended RPM range.
You're right, there probably could be a lot more performance to be had from those heads. The thing to take away from it, though, is this is an engine that makes respectable power with not just a "streetable" idle, but a completely STOCK idle.
Think about this, the car made about 1.026hp/ci at the tires. On a 302 that would be about 310hp to the tire. Can you imagine a bolt-on 302 that makes 310 to the tire, but sounds/acts like it is completely stock? No cam necessary! To me, that's just telling me that there is some legitimacy to this big head/small cam thing. So many people settle for "smallish" heads and justify it because "it's just a street car, needs to be drivable". This shows that you can have your cake and eat it too, more than 1hp/ci, without sacrificing even the smallest bit of drivability.
Think about this, the car made about 1.026hp/ci at the tires. On a 302 that would be about 310hp to the tire. Can you imagine a bolt-on 302 that makes 310 to the tire, but sounds/acts like it is completely stock? No cam necessary! To me, that's just telling me that there is some legitimacy to this big head/small cam thing. So many people settle for "smallish" heads and justify it because "it's just a street car, needs to be drivable". This shows that you can have your cake and eat it too, more than 1hp/ci, without sacrificing even the smallest bit of drivability.
