Happy New Year!

Has anyone experimented with C3 cams and a turbo before? I know people have ran with the C1 series with a turbo, but what about the C3? Does this profile have TOO much overlap? What effect will a higher compression, say 10:1 provide with the Stage 5 turbo and C3's? I've got a crazy idea...

Originally posted by Big Boost
Happy New Year!

Has anyone experimented with C3 cams and a turbo before? I know people have ran with the C1 series with a turbo, but what about the C3? Does this profile have TOO much overlap? What effect will a higher compression, say 10:1 provide with the Stage 5 turbo and C3's? I've got a crazy idea...

AFAIK, no one has ever done this. Ben B has run C2's with the Stage V turbo.

I think that it could very well work, but you need to do a little homework first.

Since you are a clever monkey, I know you can handle this: rig yourself up an exhaust manifold pressure gauge. Make sure you use an old fuel filter or something equivalent as an expansion chamber to dampen out the pulses or else you'll fry your guage. Carefully monitor intake manifold pressure and exhaust manifold pressure. Make up a plot of engine delta P (Intake manifold pressure minus exhaust manifold pressure) as a function of engine speed, and send it to me (because I'm curious :-).

As long as you have positive engine delta P (crossover, or higher intake manifold pressure than exhaust manifold pressure), then there is really no such thing as too much overlap, and the C3's will be perfect.

What I really think is sick about the C3's in a positive engine delta P situation is that they have so much duration that you can really play around with cam timing and see all of the effects on the motor. If you are getting crossover out to high RPM's, then I would recommend running C3's with adjustable cam gears and running the car in on the dyno to find out exactly what kind of cam timing the car likes.

Hey Rob, thanks for your reply. My crazy idea is to run high compression, C3's, 72lb injectors and a turbo with an air to water intercooler coupled with the aquamist system.

As soon as I get the C3's, I'll do the test and email you the info.

Did you ever install your intake manifold yet?

Talk to you soon.
The "other" Rob

Originally posted by Big Boost
Hey Rob, thanks for your reply. My crazy idea is to run high compression, C3's, 72lb injectors and a turbo with an air to water intercooler coupled with the aquamist system.


I don't like the idea of the high compression, but the rest sounds good.


As soon as I get the C3's, I'll do the test and email you the info.


Take the data before you get the cams... if the car is getting pretty backpressured, don't run the C3's.


Did you ever install your intake manifold yet?


It's in my garage. I need to arrange payment with you, and discuss all the installation issues. Please email me privately.

Rob

In all of your vast experience, what are the limitations to high compression and boost? I understand that I would be limiting myself to a certain amount of boost. The car will see both street and track, but mostly used for straightline purposes. I know if I use a set of 8.5:1 pistons, I can safely run 30psi. Would a higher compression (10:1) only allow 20-22psi provided every detontation resistant technique is used. My reasoning is that I want to achieve a specific HP value with a lower boost figure. I remember a lo-o-o-o-o-ng topic on the SE-R list about, but I figured I would ask you first hand. Any help would be appreciated.

I ran a BB DET setup (t25) on a 10:1 motor for a few months, 2.5 mandrel downpipe into a 3inch crush cat back, stock boost.
I liked it.. except it ran rich (jwt tuned it for 'low boost' and 10:1 compression... I think they tuned it rather rich so that I would not have blown a motor and called them telling them their tuning blew my motor, which, I could see alot of people doing, but I could not convince them that I would not call and complain if I blew it up.. but, that's business)
it ran rich, and the engine was in good tune, I believe it was the ECU. It boosted FAST and kept the boost but it fell off at about 6krpm, that did not bother me though, I just shifted earlier and it was a blast to drive!

I am interested to see your progress on this project!
I would slap another t25 on my NX if I could, but, it was stolen, so scratch that plan :(

david lau

Originally posted by Big Boost
In all of your vast experience, what are the limitations to high compression and boost? I understand that I would be limiting myself to a certain amount of boost. The car will see both street and track, but mostly used for straightline purposes. I know if I use a set of 8.5:1 pistons, I can safely run 30psi. Would a higher compression (10:1) only allow 20-22psi provided every detontation resistant technique is used. My reasoning is that I want to achieve a specific HP value with a lower boost figure. I remember a lo-o-o-o-o-ng topic on the SE-R list about, but I figured I would ask you first hand. Any help would be appreciated.

Well, I don't know how much boost you can run on an SR20 with 10:1 compression, as I've never done it before. What I can tell you is this: all else being equal, an increase in compressor from 8.5:1 to 10:1 will increase your horsepower by about 4.6%. On a 400 hp motor, this will net you about 19 hp.

Every 2 psi of boost increase you run should net you about a 5.8% power increase, or about 23 hp. So, if increasing compression from 8.5:1 to 10:1 means you have to run 2 psi less boost, you've already lost.

I don't know what the difference will be, especially when we're talking C-16 and all of its wonderful properties. However, I think that the gains to be made from compression increases are modest, and the gains to be made from boost increases are quite huge. Given the choice, I'd run more boost rather than run more compression.

I also think that if you are running up against a boost limit, you are better off running more RPM rather than more compression. Running 8500 RPM instead of 7500 RPM will put 13% more air into your engine.

That means the following:

If you are running 400 hp at 20 psi of boost at 6500 RPM on an 8.5:1 compression ratio motor, you can get to 450 hp by doing the following:

Increasing boost pressure from 20 psi to 24.3 psi
Increasing compression ratio from 8.5:1 to 12.7:1
Increasing peak power engine speed from 6500 to 7310 RPM

All things considered, compression increases are about the weakest lever in increasing engine power.