RomRaider

Not actually trying to get banned, but I do know the risks.

If you're interested, festivities begin at post 47:
http://forums.nasioc.com/forums/showthr ... ?t=1580831

I have an honest question and I'm trying to get a straight answer, if anyone here can help me understand what Clark is saying, I'd really appreciate it (in this thread, or in that thread). He's said something that just doesn't make sense to me, and I know he's not an idiot, so I'm trying to figure this stuff out.

Fundamentally:
How much air does a 2.0L motor move at 450whp?
How much air does a 2.5L motor move at 450whp?
Is it the same amount?

Yes it is!

I will try and help.

If they are equally efficient, yes. I'd think it should be close.

But that's not the disagreement. Temperature may vary. Not all exhaust gas passes through the turbine. There is a wastegate that passes some of the gas.

It takes different amounts of boost to reach a certain horsepower. It takes more or less energy to compress the gas with different size motors running different boost to reach the same airflow.

The motors may have different flow properties at different backpressure, manifold pressure, and RPM.

I don't think you can state a turbine size (whether A/R or otherwise) purely based on power level on different motors. I don't think it is quite that simple.

I think it would depend on the BSAC.

that's absolutely true, but not good enough explanation. So, if we like term BSAC: why, in general, brake specific air consumption, would differ on 2.0 and 2.5 ?

Clark seems to be saying that the .63 housing moves enough air for the 2.0L, but not enough for the 2.5L, when both are making 450whp.

So it seems to me that this question is the same as:

Why is a 2.0L engine so much more efficient than a 2.5L when both are making 45whp?

(highlights added because people in the other thread seemed to lose sight of that aspect of the question)

I think the answer is that the efficiencies aren't much different, but if they are, the 2.0L is probably a little LESS efficient then the 2.5. Clark has a s*** of tuning experience so I'm not so much trying to prove him wrong as trying to learn WTF is behind this counter-intuitive situation.

The rotating assembly of a 2.0L is 6% more efficient than the 2.5L due to the shorter stroke and less reciporicating weight. Proportinoally the valves, heads, intake manifold, and exhaust manifolds are larger on a 2.0L than a 2.5 which also makes it more efficient. 99% of the time the 2.0 will make more hp/liter than a 2.5. Think about it...

I understand that, but I don't necessarily have a problem with that. I can't say it is true for sure either, but it doesn't raise any huge BS flag in my head.

Not all air that goes into the engine passes through the turbine! It only needs to flow enough to push the compressor side hard enough to flow 450whp worth of air. The rest goes through the wastegate. It does not take all of the exhaust to compressor the next round of charge air once you've reached target boost.

It is at least plausible that two different size motors may use more or less turbine airflow to flow the same amount of air on the compressor side. You need power from the turbine, not necessarily a given amount of airflow. If you look at the turbine flow charts you'll see they only flow about half the compressor side. The compressor for the GT3076R is 52lbs/min while the .82 T3 turbine is only about 20-something lbs/min. The rest is going out the wastegate.

If you poke around in PPB forum on NASIOC you can see the GT30 2.5L motors with .63 hotsides choke up top on power. So at least if you can't believe the explanations given, you can look at end results. It's several different tuners, and even different rotated kits that seem to exhibit this behavior.

With my school and experience that 1lbs/min of air can make 9 to 10 bhp. Keep in mind that afr, air temp and air pressure will play a role in the amount of hp. I would say that they flow the same amount of air and only afr, air temp and air pressure will be different but the amount of air flow will be the same to make 450hp. Dont flame me if I am wrong. Only taking a guess at the answer.

I've looked at loads of dyno charts in PPB and not seen an issue with .63 housings that was outside of the "noise" of different dynos and conditions and so on. I'm not saying it's not there, just that I'm still looking for evidence.

I might be that I've been mostly paying attention to straight-pump results, and the choke point simply outside of the range that's attainable without meth or race gas. If it's really 450whp, as Clark says, that would explain it.

Clark has said more than once that 2.5s make more power across the rpm range with .82 housings than with .63s, and that's something else that I'm trying to grok. Better midrange with a larger A/R just doesn't line up with everything else.

Valves are the same size on the 2.5L STI heads as on the 2.0L, but I dunno if the convo is between a 2.5 WRX and a 2.0 WRX (the 2.0 has USDM sized STI valves, the 2.5 EJ255 has smaller valves). The 2.0L JSpec cars have the best heads though.

http://www.ferrea.com/general-results.p ... ry_id=6078