SoloRacer

I bought a 996TT back in December and have been enjoying it. The car has a stock exhaust but it is obvious that it has an ECU flash. There is also an EVOMS airbox. On the gauge I hit an indicated 1.1 to 1.2 bar at peak power output. The car really screams. I don't know who's flash it has but since it has the airbox I assumed it's the EVOMS one.

Then I saw a 996TT with a GT2 body and I bought it too. This one has a Agency Power exhaust and a dyno sheet for 422 RWHP that was from a tune at Rennen Motorsports. It was hitting only 0.8 bar at peak power. To me it didn't feel as alive as the other car.

Today a buddy and I did a couple of runs with both cars. They were pretty much dead even. The earlier car may have had a little more on the top end - but it was hard to tell as they were so close. This really surprised me as they didn't feel the same. Does it make sense that they are as quick considering the different mods and different boost levels?

Just wondering because this is making me scratch my head. Shouldn't the higher boost car be quicker?

Michael-Dallas

Not necessarily, turbo size and intercooling can make a big difference. Meaning, a larger turbo w/ less boost can produce as much power as a smaller turbo w/ more boost. The ECU maps could also be a factor, some maps are more aggressive on timing, a/f ratio, etc than others.

///Michael

Jean

Soloracer,

IMO the car hitting 1.2 bar has worse programming than the other one. It looks like it compensates for the poor programming by adding more boost to get to the power levels, typical amateurish tune. The reason you feel it more powerful with your butt dyno is because it goes from nothing to sudden peak torque, therefore the kick in the back makes you think it is fast. The other most likely has better area under the torque curve and builds power gradually.. This is both better for your engine, and better for traction and drivability.

If you have any GPS datalogger runs we can very precisely measure torque and power curves between both.

SoloRacer

I thought about the turbo's being different but from the looks of things they are the same. I am aware that boost pressure and air flow are two different things (think garden hose at 5 psi and culvert at 5 psi - not the same flow). I'm pretty sure the intercoolers are the same on both cars but can't say 100% for certain. I think the ECU maps or exhaust differences might be the reason but I thought that the way exhausts help on a turbo car is by letting you make more boost. And I didn't think that through tuning you could compensate for .4 bar of boost difference.

SoloRacer

I think you may be correct although I still am not 100% convinced. I have Dynolicious for the Ipod touch. I should give it a go and see what it says. Any comment on my post above? I always thought a more aggresive tune would give you maybe 10-15 more hp. Isn't 0.8 bar close to stock boost levels? Stock these cars probably only make 350 whp so to gain 70 whp over the factory level by tune alone without increasing boost didn't make sense to me. Wouldn't that imply that the lower boosted car is actually running too aggresive and is more at risk? (ie: more boost car is not running close to ragged edge while less boost car is pushing it to the limit at that boost level where one bad tank of fuel gets you a blown engine)

Jean

I agree with you, but only partially, at 0.8 Bar, the same engine with exhaust and different tune would have the same "peak" torque, but not HP necessarily.

By playing with the timing, and wastegastes settings, boost can come in earlier and have a broader torque curve even at the same 0.8 Bar maximum boost, peak torque would be the same, but torque overall will build in earlier. If the 0.8 Bar boosting engine has the rev limiter set at 7200 RPMs, a better exhaust, and more aggressive tuning than factory stock, it can deliver higher peak HP, provided turbos are not at their limit at those RPMs.

I dont know the IPOD dynolicious, but if it shows you the acceleration Gs across the entire run, you will most likely see higher Gs early on with your 0.8 Bar engine.

A good way to clearly prove the impact of good tuning, is by running both cars side by side in 6th gear at 50mph and step on the throttle all the way up to 75-80 mph, your 0.8 bar engine will be faster even with the same turbos.

Michael-Dallas

Perhaps one Turbo has a boost leak?

///Michael

Macster

If you really want a better picture of what's going on arrange to put both cars on a chassis dyno and post torque/HP plots for both.

I believe the plots will make it clearer why the two cars feel so different.

Sincerely,

Macster.

adam_

Just had to acknowledge this....

Hoosier_Daddy

+ 1000

SoloRacer

What can I say.....it's a mental illness

tvurt

K24/18g or K16/16g can make the same HP as K16's with far less boost. You cant tell the difference by looking at the outside of the turbo.

In fact one regular ran K16/16g for several years thinking he was running K24/18g, due to a mix-up in shipping at the manufacturer. . . . .

Jean

Just a small precision, all else being equal HP is proportional to the amount of air the engine absorbs. Two turbos at 1 Bar will produce the same amount of HP at the same RPM..except if the smaller turbo is beyond its efficiency level. The smaller turbo will get to that boost level faster so will give more hp earlier on, however the larger one can reach higher boost levels (within efficiency) therefore more HP.

Al Pettee

Except neither is air-cooled....