1st test drive with the new turbo

[70vert]

Slightly unrelated, but I did look through both threads for the info - I can tell you went through the passenger side engine compartment sheet metal to intake air, but you didn't by any chance tap into our beautiful but "faux" air inlets next to the headlights, did you? I have always thought those fake air inlets need to be made honest, either by ducting leading to the front brakes, an air intake, or both. I think eventually I'd love to make those into mesh "screens" that let air in.

Amazing, and inspiring, project. I'm specifically getting my stroker down at a low 9.0-9.5 compression ratio should I ever go nuts and do a supercharger or turbo. Turbo is preferred, of course - it's more efficient and the top end horsepower complements the low end torque.

 

[red65]

I am regretting my pre-turbo gear choice tho. The 3.73's are just too damn low... 1st is a joke and it's honestly a bit of a pain to drive like that.

I went to a 3:25 rear gear in my S/C 306 for the same reason. Just a data point - the 3:25 rear with a 2.94 first makes a reasonably usable combination. Keep up with the updates as you make improvements! Interesting project.

 

[10secgoal]

... lots of spark energy but still allows me to control timing via the megasquirt. It's cheap too.

You should still be able to control the timing through MS with a box no ? Comparing yours to mine. Haven't got to read a lot yet since we talked last.

 

[ForceFed70]

Slightly unrelated, but I did look through both threads for the info - I can tell you went through the passenger side engine compartment sheet metal to intake air, but you didn't by any chance tap into our beautiful but "faux" air inlets next to the headlights, did you? I have always thought those fake air inlets need to be made honest, either by ducting leading to the front brakes, an air intake, or both. I think eventually I'd love to make those into mesh "screens" that let air in.
.

I considered it, but couldn't justify the work for no benifit.

Getting access to the location isn't easy because the the fender extension piece. Plus you need to fit a filter in there somehow, so I don't know how it would be possible to create a Ram-air effect or anything like that.

I agree tho... it would be neat location.

 

[ForceFed70]

You should still be able to control the timing through MS with a box no ? Comparing yours to mine. Haven't got to read a lot yet since we talked last.

You can definately control the timing with an ignition box. In your case, I'd probably stick with the MSD box... you already own one and with EDIS you can't use MS's launch control features, or ignition based rev-limiting. Not a concern for me as I'm rarely at the drag strip... but your car sounds like it spends most of it's driving time at the track. With EDIS you can't drop ignition events, etc because of the limp home mode that's built into the module. If your megasquirt stops sending ignition signals, the EDIS module uses a flat 10* BTDC to "limp" the car home. Great for a street car, but can be a problem for a racer.

Now.. if you want the ultimate igniton control with MSII.. you could use the MSII-extra code and do Coil over plug in a wasted spark configuration. This involes modifying your MSII so that it has 4 coil drivers. They're still the same coil drivers, but since you've got 4 of them instead of 1 you can still provide lot's of spark energy and use all of the fancy features. You'd also need to install a trigger wheel and VR sensor.

 

[ratio411]

That is so cool!
I missed this one. I haven't been around much...

Quick question you might have looked into when researching your project:

What do you need to modify if you decide to blow through a Holley carb?
Will a regular double pumper get the job done, or does it need special mods?

I have seen turbos that pump into a plenum below the carb. Does anyone know how that works?
Seems like it would confuse the carb to have pressure below the throttle blades.:huh:
GM did this in the 70s on some turbo Trans Ams.

I have heard you must run a bigger turbo with an intercooler because of the increased
displacement of air before the pressure reaches the engine. Pressure drop? How much of an issue is this?
Do you have to go way larger on the turbo?
Or do you just use the same turbo with a different wastegate adjustment?

Thanks!
Dave


Edit:
I just figured something out... I bet the carb fed the suction side of the turbo on the setup I mentioned.
A 'wet' turbo? That has to be hard on the turbo to have the fuel/air mix going through it. Hard on the
fuel/air mix too! It doesn't sound right, but it sound better than the pressure being forced under an open carb.

 

[65ShelbyClone]

1.) What do you need to modify if you decide to blow through a Holley carb?
Will a regular double pumper get the job done, or does it need special mods?

2.) I have seen turbos that pump into a plenum below the carb. Does anyone know how that works?
Seems like it would confuse the carb to have pressure below the throttle blades.:huh:
GM did this in the 70s on some turbo Trans Ams.

3.) I have heard you must run a bigger turbo with an intercooler because of the increased
displacement of air before the pressure reaches the engine. Pressure drop? How much of an issue is this?

1.) A regular double pumper can be modified for use as a blow-through. I don't know off the top of my head what needs to be done, but there are sites that outline how to do it.

2.) As you figured out, that is a draw-through turbo setup. The compressor must have a carbon positive seal to cope with the vacuum. This style of turbocharging is easy to set up, but that convenience comes at the cost of degraded throttle response and not being able to use an intercooler.

3.) It's a non issue. Compressor sizing is not affected by the use of an intercooler at the non-professional/ultra maximum effort level. I'm not sure it even affects the compressor size at all. If the intercooler is such a bottleneck that the turbo must be sized to work at a higher pressure ratio, then the whole setup needs some serious reevaluation.

All the large intake tract volume does is slightly increase lag. I'm talking maybe a tenth of a second, not something noticeable.

 

[ForceFed70]

That is so cool!
I missed this one. I haven't been around much...

Quick question you might have looked into when researching your project:

What do you need to modify if you decide to blow through a Holley carb?
Will a regular double pumper get the job done, or does it need special mods?

I have seen turbos that pump into a plenum below the carb. Does anyone know how that works?
Seems like it would confuse the carb to have pressure below the throttle blades.:huh:
GM did this in the 70s on some turbo Trans Ams.

I have heard you must run a bigger turbo with an intercooler because of the increased
displacement of air before the pressure reaches the engine. Pressure drop? How much of an issue is this?
Do you have to go way larger on the turbo?
Or do you just use the same turbo with a different wastegate adjustment?

Thanks!
Dave


Edit:
I just figured something out... I bet the carb fed the suction side of the turbo on the setup I mentioned.
A 'wet' turbo? That has to be hard on the turbo to have the fuel/air mix going through it. Hard on the
fuel/air mix too! It doesn't sound right, but it sound better than the pressure being forced under an open carb.

65Shelby is on the money..

I also am not sure what's required to modify a carb for blow-thu. Like mentioned, there's lots of info out there... I went the EFI route. You definately need to make mods to the carb for a blow thru setup. 10secgoal can probably answer this with much more info.

THere are also draw-thru (wet turbo) applications. Again, like mentioned the turbo needs to be a special design with a "carbon seal". I'm not sure how a blow off valve works on these setup's as the vented air would have fuel mixed in.

You don't need to run a bigger turbo or more boost with an intercooler so long as your intercooler is big enough. Buy a large enough intercooler and it doesn't act as a restriction. The intercooler I went with is supposed to be good up to 800Hp.

 

[mrmustangman357]

ideal pressure drop across an intercooler is .5-1.0 psi. any more and you have issues. Any less and you aren't transferring out as much heat as you should be

 

[ForceFed70]

Any less and you aren't transferring out as much heat as you should be

I'm curious about this statement. From what I know.... pressure drop has no effect on heat transfer.

Can you explain why a pressure drop is required for proper heat transfer?

Thanks.

 

[bnickel]

I'm curious about this statement. From what I know.... pressure drop has no effect on heat transfer.

Can you explain why a pressure drop is required for proper heat transfer?

Thanks.

you have to have a slight restriction to allow the heated air enough time to cool off, if it goes out as fast as it comes in it won't have enough time in the intercooler to draw off sufficient heat to do anything.

 

[ForceFed70]

you have to have a slight restriction to allow the heated air enough time to cool off, if it goes out as fast as it comes in it won't have enough time in the intercooler to draw off sufficient heat to do anything.

That doesn't make sense to me at all. Pressure does not mean more time in the intercooler. The air is comming out the other side at the same rate it's being fed in at. The only thing that will effect "time in the intercooler" is the total volume of the intercooler. The volume doesn't change with pressure.

Sure a pressure drop would mean less flow.. so yeah, if there's less air to cool of course it's going to cool more... but it doesn't explain why the pressure drop is needed. With a big enough intercooler you could have 0 pressure drop and nearly ambient intake air temps.

 

[mrmustangman357]

a pressure drop implies there is a friction factor inside the intercooler. In an idealized case there would be no delta p. however, in actuality you need the pressure drop because it implies the flow through the fins is turbulent.the flow needs to be turbulent in nature in order to promote heat transfer. no delta p implies no odd boundary layer conditions of the system (laminar flow), which means only the boundary layer of the flow has its energy (temp) reduced. This is actually inefficient because not all the fluid (air) is exposed to the cooling fins of the intercooler. some delta p is needed in actual applications in order to maintain efficient heat transfer. Most good intercoolers have fin designs that promote this turbulence. More turbulence means better heat transfer. The key is limiting delta p so it doesn't get excessive. Thermodynamics of fluid flows II at work:SNSign:

 

[65ShelbyClone]

THere are also draw-thru (wet turbo) applications. Again, like mentioned the turbo needs to be a special design with a "carbon seal". I'm not sure how a blow off valve works on these setup's as the vented air would have fuel mixed in.

A blow off valve is not used because the throttle butterflies are upstream from the compressor. When they close, it is impossible for the turbo to surge because the compressor is spinning in a vacuum. This has the added benefit of reducing lag as well. Some of the turbo F1 teams put a throttle body on the compressor inlet just for that purpose even though they were using EFI.

As for air "not spending time" in the intercooler, this too is a non issue for the reasons mrmustang alluded to. It's the same argument that water flowing "too fast" through a radiator have enough time to cool off, when in fact flow over time has little impact on the effectiveness of the cooling system.

 

[ratio411]

What I have read, I am under the impression that the air shrinks with cooling.
Hot air expands, cool air shrinks, so you get less effective volume/pressure.

I know for a fact that exhaust gasses shrink as they progress through the exhaust
system. You can reduce the size of your exhaust as it heads to the back of the car,
and not lose any flow. Also, this is why it is best to put the mufflers as far back as
possible. The cooler the exhaust gasses, the less volume, therefore the muffler
poses less restriction that it would if put upstream. Make sense?

Anyway, cool air shrinks, so you get less at the heads with an intercooler. Therefore
you need to pump more air with an intercooler to get the same pressure as a system
without. This is what I heard and was going off of with my question. However, you
guys are far more experienced, so if this is wrong, I'll take your word.

 

[ratio411]

A blow off valve is not used because the throttle butterflies are upstream from the compressor. When they close, it is impossible for the turbo to surge because the compressor is spinning in a vacuum. This has the added benefit of reducing lag as well. Some of the turbo F1 teams put a throttle body on the compressor inlet just for that purpose even though they were using EFI.

Just a thought here...
By this description, the best way to do a turbo might be EFI, with the TB and
MAF installed upstream. This method would have multiple benefits, it seems to
me. You wouldn't have to use a special wet turbo with the dry TB. You wouldn't
have the need for a wastegate/blow off. Then, being dry, it seems to me that
you could run an intercooler just fine.

Are there any holes in my thinking?
For a budget build, this sounds awesome.

 

[mrmustangman357]

Anyway, cool air shrinks, so you get less at the heads with an intercooler. Therefore
you need to pump more air with an intercooler to get the same pressure as a system
without. This is what I heard and was going off of with my question. However, you
guys are far more experienced, so if this is wrong, I'll take your word.

not to hijack the thread, but for the exhaust it gets slightly cooler and becomes more dense. if pipe diameter stays the same, and density increases, velocity has to decrease (by the square) to compensate. Maybe less velocity would make for better sound cancellation? I dont know. its a bernoulli equation1/2*density*velocity^2.


for what we consider (air in a pipe) , its almost always turbulent but forces due to fluid flows are density*cross-sectional area*v^2. the force should be the same through the muffler and hence the backpressure, so i dont think thats the reason mufflers are placed late. I think its mostly due to packaging and weight distribution

 

[65ShelbyClone]

Anyway, cool air shrinks, so you get less at the heads with an intercooler. Therefore
you need to pump more air with an intercooler to get the same pressure as a system
without.

Yes, the volume and pressure changes with temperature, but the air mass does not. Since the pressure may be reduced yet the mass stays the same, that means that theoretically the engine should make the same power at a lower boost level. Don't think of it in terms of pressure, think of it in terms of mass airflow like how turbo flow is rated.

Just a thought here...
By this description, the best way to do a turbo might be EFI, with the TB and
MAF installed upstream. This method would have multiple benefits, it seems to
me. You wouldn't have to use a special wet turbo with the dry TB. You wouldn't
have the need for a wastegate/blow off. Then, being dry, it seems to me that
you could run an intercooler just fine.

Are there any holes in my thinking?
For a budget build, this sounds awesome.

This type of setup still needs the higher drag carbon seal. It's not the gasoline that is a problem, it's the high vacuum when the throttle is shut. I proved it to myself a few years ago with EFI by trying exactly what you described here. The turbo had a standard dynamic seal and lost a lot of oil past it. Putting the TB downstream of the turbo like is common these days eliminated the oil loss.

Also, a wastegate will be necessary no matter what. Without one, there is no way to regulate boost. It doesn't matter where the throttle is in relation to the turbo; the exhaust still goes through the turbine in the same fashion and it has to be bypassed in order to control turbo speed.

 

[ratio411]

It becomes dense because it shrinks in displacement.
This allows it to flow through smaller and smaller pipe, while retaining
the same level of flow. Another reason mufflers are placed downstream
is that heat destroys them quicker.

 

[ratio411]

65Shelbyclone...
You posted while I was responding to the previous thread.

Thanks for the info. I understand exactly what you mean now.
You just had to spell it out like I was a pre-schooler!

No so on the exhaust stuff. I have studied up on that hard
when picking headers, mufflers, x-pipe/h-pipe, etc... The exhaust
cools... shrinks... volume reduces... pipe size requirement reduces.