I'm going to totally make myself look like a moron here, but ahhh, it won't be the first time I guess. I get most of the basic concepts behind FI, but I'm still pretty fuzzy on the principles behind a turbo.

My question is, does the size of the turbo affect the power the car puts down or is it simply a matter of pressure? Obviously spool time will be affected, but ignoring that. At 10psi will a GT30 make the same power as a GT35? Is a GT35 able to make more power b/c it has the ability to create more boost, or b/c it makes more power at a given pressure?


To break it down a little further (purely ficticious numbers, just trying to give a reference):

Option A:
GT30 @ 10psi (maxed out turbo at 20psi) = 380hp
GT35 @ 10psi (maxed out turbo at 25psi) = 380hp

Option B:
GT30 @ 10psi (maxed out turbo at 20psi) = 360hp
GT35 @ 10psi (maxed out turbo at 20psi) = 400hp

Option C:
A combination of A and B, or something beyond what my tiny brain can conjure up.

 

It's not that simple. Turbos vary by efficiency, efficiency range, spool up, and so on.

Some turbos make more power with less psi because they are more efficient and heat the intake air less.

Learn to read compressor maps and you will be on your way.

 

I know there are 100's of other factors, I was just curious if someone could dumb it down, hypothetically eliminating the other factors for me. Thanks for the input though, I'll go check out some compressor maps and see if I get anything from them

 

1psi does not equal 1psi to simply state it.

As sideways said, if you can read a compressor map, you'll understand what I said a lot more.

But in another numb version a GT30R at 10psi is say 320rwhp but a GT35R at 10psi will be 360rwhp (or whatever the case is). Just becasue they are pushing the same pressure doesn't mean the CFM (cubic feet per minute) is the same, nor efficencies, etc etc.

 

Thanks for the replies. This forum is 9874962 times better than anywhere else I've found for people willing to help and explain things, you guys are awesome.

I found some additional explaination that really helped me piece together what sideways and spec_ops were saying. If anyone wants some more explaination check out this link.

 

all posts said above make alot of sense. Reading the efficiency maps of the turbos will allow you to see where a turbo, when attached to a motor will be most efficient.

The comparison of a gt30 and gt35 is one that many people want to see. The way i make myself understand how a turbo will work with a system is first the efficiency of the manifold. If the manifold is tubular, whatever turbo being used will make more power than if it was to be on a log manifold. So if you go for a tubular manifold, you'll probably be able to get away with a gt30r if you want 450-500whp. If you have a log manifold, you'll be hard-pressed to make 500 with one.

I then think about the air requirements of the motor, and the compressing efficiencies of the turbo. A gt30r will spool sooner than a gt35, but will not moving as much CFM's. So you will see a very strong midrange with the gt30r, where it is pumping alot more CFM's into the motor,(than the GT35) but as the rpms's increase and the CFM requirements to keep the same torque increase, (from the motor) the GT30r starts to run out of air. I saw a dyno graph of the two on the same motor. The gt30r made alot more power under the curve than the gt35, but the gt35 made more power at the top of rev range, because it was able to keep the CFM requirements and subsequent torque curve flat. Basically, the higher boost pressures you run on the gt30r, the higher the mid-range will be, but the greater the decrease of the torque curve as it reaches redline!

I wouldn't look at boost pressure as an understanding of power. I would first come up with what type of driving i wanted.... A nice DD with tons and tons of midrange response and still a pretty decent topend. Or a 1/4 or racetrack type car that will only see the top end of the rpm band. This will give you a good idea of what turbo to purchase!

 

Are you thinking of switching to turbo?

If you want over 500 rwhp (need to build block probably if you intend on keeping your motor for some time) or use a log manifold, you should go with a GT35.

If you're not building your block or use a tubular manifold, the 30 series turbo will be best.

 

Eh, you can hit 500rwhp with a log manifold without a built block and still be safe.

 

[QUOTE=afwfjustin,Jan 23 2008, 10:02 AM]

Are you thinking of switching to turbo?

 

absolutely true! But it will be much harder to do with a log manifold and a gt30! GT35 FTW with a log manifold!