well, for one, turbo size changes hp greatly, even when you are running the same psi on the two different turbos, you can see very different power outputs.

 

Originally posted by boardernr
well, for one, turbo size changes hp greatly, even when you are running the same psi on the two different turbos, you can see vary different power outputs.

Depends on the engine also...

 

too many factors for perfect condition theories to apply. higher compression will make more power on a given boost level all else equal, but the lower compression will take more boost before blowing to smitherines and result in higher output.

 

Go google on pressure ratios, density ratio, dynamic vs static compression ratios.

Roughly and simplistically speaking power appears to increase on the 1ZZ by 8% starting from the 1st pound of boost and continuing until thermal and flow limits start to reduce the rate of increase.

Its a problem of diminshing return.

138flywheel *.08 = 149hp * .08 = 160hp * .08 = 172hp *.08 = 186hp *.08 = 201hp * .08 = 217hp * .08 = 235flywheel at 7psi or 206whp.

 

@boardernr and edjee: That is true, because a larger turbo will offer boost in higher rpm, and thus bigger power. But for a given engine and boost, torque numbers will only vary slightly between different turbos.

@turbo_jimbo: true this is theory over a very complex environment, but what I ask is i believe truly fundamental and there should be a good answer (that I search for). Usually reality is below theoretical expectations due to all things not being 100% efficient. But being above the theoretically expected, well that is a big question for me!

@WTS: Thanks for the info! 8% per psi is close to what I would expect (~6%) I guess that the more free flowing exhaust and other modding accompanying a turbo modifications would account for the rest.

What finally made me start this topic was the Hass turbo kit offering 236whp at 5,3psi.
I find it hard to explain how an engine given 14,7psi of air will offer 138 flywheel hp, but increasing that to 20psi will increase output to ~260 flywheel hp...that is almost a double figure :?:

 

it has a lot to do with ve too. look at the s2000's head design. nearly impossible to improve on, so with boost it actually makes waay more power than the theoretical numbers. its ve is something like 98% whats the 1zz 87%???

 

I meant to add that my 8% crank guestimates are based on the dyno results of a GT28R on an otherwise stock 1ZZ.

Originally posted by nickolas
What finally made me start this topic was the Hass turbo kit offering 236whp at 5,3psi.

IIRC, that was at least a GT28RS in who knows what wheel trim?
<div class='quotetop'>QUOTE </div>

I find it hard to explain how an engine given 14,7psi of air will offer 138 flywheel hp, but increasing that to 20psi will increase output to ~260 flywheel hp...[/b]

Its 20psi gauge but wouldnt it be more like its 34.7psi to the engine? Unless its running in a vacuum!

Assuming 12% parasitic losses a GT28R will make 260crank at ~10psig @80* ambient but maybe only 275 @ 12 @ 100*F. At this level each additional lb of boost is making only 3-4% more power.

 

thats more or less a problem with the turbo itself though. he didnt mean 20 psi of boost, 20 psi of atmosphere. :wink:

 

Originally posted by turbo_jimbo
thats more or less a problem with the turbo itself though. he didnt mean 20 psi of boost, 20 psi of atmosphere. :wink:

dUH! 5.3psi!
God! Im getting Oooolllllddddd!

 

its alright, you get an e for effort!

 

Originally posted by turbo_jimbo
it has a lot to do with ve too. look at the s2000's head design. nearly impossible to improve on, so with boost it actually makes waay more power than the theoretical numbers. its ve is something like 98% whats the 1zz 87%???

I don't understand the bold... theoretical numbers are based on the stock hp figures that also benefit from the good VE (otherwise the S2000 wouldn't make 120hp/litre). But even if a turbo application includes VE enchancing mods, going from 87% to 98% still does not fully explain the big hp figures...

That is forcing 30% more air into the engine, making 80% more power :roll:

 

Originally posted by nickolas
What finally made me start this topic was the Hass turbo kit offering 236whp at 5,3psi.
I find it hard to explain how an engine given 14,7psi of air will offer 138 flywheel hp, but increasing that to 20psi will increase output to ~260 flywheel hp...that is almost a double figure :?:

The turbo is the number one factor here and tuning the second as the differing numbers between the kits was soley swapping turbos, all are generaly identical.

The run in question above used a GT2871 turbo and a Power FC for tuning. It's not an indication of what every kit will produce but what one CAN acheive at said boost level with proper tuning.

What you can expect from a GT28R in conservative tune and 5.3 psi is about 200-210whp.

The turbo used has a much larger turbine side using the NS111 turbine wheel and .86 a/r housing. That directly increases the VE and BSFC of the engine with all things being equal and that correlates to more power at the same boost level.

Example: Using a Nissan SR20DE we made 336whp at 20psi of boost using a T3/T4 turbo that spec'd out the following

Turbine side was a Stage-III 76 trim tubine wheel in a .63 a/r housing and a 46trim To4E compressor wheel in a .52 a/r housing.

Just by swapping the turbine side to a .82 a/r housing on the same day on the same dyno with the same boost and the same tune the car came back with 392whp. A 56hp gain from free'd up exhaust flow which increased the VE/BSFC.

I bet you'd really scratch your head as to how we made 285whp at 8.5psi on a 1.8 2Z. :mrgreen:

It's Saturday morning, and my oatmeal is getting cold so I'll have to revisit this another time if that's not enough information for you.