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Posted by c5chris, Jan 24, 2003
Newbie Forum - Beginner/newbie/general DSM modification questions. First mods, how to run 10's when you haven't run 12's yet, any tech question that doesn't fit in another tech forum.
I've hard of people adding upwards of 20 horsepower with 3 inch downpipe, test pipe, and 3 inch cat-back, i.e. 3 inch turboback exhaust.
Some will say they've seen more, so we'll let them add their .02 cents too.
Have fun Chris, I know my goal with my car was to go fast with class i.e. a Corvette, I hope you can do the same with your GSX.
Exhausts do help a lot on turbo cars.
what size was the catback and testpipe? 2.5" or 3"?
also with the boost controller what was the boost set at?
is that all the mods he had on his car or were there more , and if so, what were they?
Well, ya. Since no dsm's are rwd then ya thats impossible.
2.5" Testpipe, 3" A'PEXi N1 catback, boost was around 19psi.
No more power mods, just ACT Clutch.
Either NA or TC'd the gains of the exhuast depend on the other parts of the car.
Breathe in Breathe out. If it's having trouble breathing out because the exhaust is stock but the turbo was swapped and it was cammed or something. You will gain alot. If something is choking the intake side or you don't have enough fuel for the amount of air you can flow now you wont get much.
The only major point of restriction on a turbo car should be between the exhuast ports and the turbo. From the turbo gradually expand from the turbine exducer diameter to the diameter of exhaust that matches the power level you are looking to produce.
NA cars typically run best with equal length headers that have primary and collector tube sizes matched for the power band the intake and cams are setup for.
Free flowing exhausts are key to extract HP from turbo cars.
Well the great thing abt N/A mods is that sometimes the parts stack in HP, increasing 1 part is not enough, but increasing many parts make them all more HP since they are increasing free flowing airflow. so you will need downpipes, free flowing cats and such... Its never just an exhuast. its an "exhuast system" System being key word, you change 1 link little is done you change the whole then everything is done.
P.S. well they also have other functions too, like take intakes for example, they help spool ur turbo up faster but they also dont add that much HP... And i believe exhuasts are supposed to release backpressure?
Actually I plan on getting 3" press-bent turbo-back w/3" cat. Reason for 3" press-bent, so I can use the 3" cat with 3" inlet and outlet, opposed to only 2.5" inch inlet/outlet on cat. And it stays _approximately_ equal to 2.5" mandrel in terms of flow.
No other power mods huh? So he was running 19psi on the stock injectors, fuel pump, and wiring? Thats smart
Yep... his car happened to be one of those "super rich" from the factory cars, so he was fine.
Are you talking about with the stock catback? Can you try to explain boost creep in lamen terms, I'm not too knowledgable about all the exhaust flow and backpressure crap. I only know of the physical parts of the exhaust system.
Boost creep is rising boost due to not enough exhaust bypassing the housing. For example, you're set for 13 psi, and when you floor it, you get a quick rise to 13 or 14 psi. But then as rpm's climb, the boost creeps higher and higher: 14, 15, 16, 17, etc. Enlargening the wastegate hole is one cure for boost creep.
Spiking is when your wastegate hole is large enough, but your actuator can is taking too long to fill with compressed air, so you *temporarily* overshoot your boost level. Example: you're set for 13 psi, and when you floor it it quickly rises to 16 psi, but then gradually drops downward towards 13 psi again.
A common problem with modded engines is a combination of spiking AND boost creep. That's where you're set for 13 psi, and when you floor if it overshoots to 16 psi, *begins* to drop back down, but as the rpm's rise it goes up again!
Normal boost rise when set to 13 psi = shoots up to 14, then 13, 13, 13...
Spiking = shoots up to 16, then 15, 14, 13, 13, 13...
Boost creep = shoots up to 14, then 13, 13, 14, 15, 16, 17...
Spiking and boost creep = shoots up to 16, then 15, 14, 13, 14, 15, 16,17...
Set a manual boost control to 11 psi and floor it slowly in high gear. It should go to 11 psi and hold it pretty well. If it starts to slowly climb over 11 psi as the rpm's get high, that's "creeping". The boost creeps higher at high rpm's because there's too much exhaust flow for the wastegate hole to bypass.
Now go to 11 psi again, but tromp on it quickly! It will shoot to 13, or 14, or 15 psi, then drop down to 11 and stay there. That's "spiking".
Spiking is a quick flash of high boost that goes a little beyond your set boost point. If you are set for 11 psi, and you tromp on it quickly, this might happen: boost "spikes" to 14, quickly drops to 11, then slowly "creeps" back to 14 or more as the rpm's climb. Now you are seeing spiking followed by creeping!
With air filter and MBC @ 16psi I ran 14.6 @ 93.9 mph. Added 2.5" downpipe, hi-flow cat, and 2.5 cat back (mandrel bent) and ran 14.0 @ 100.6. Both runs were in similar cool Fall conditions. Haven't been able to repeat that run, usually trapping around 97-98 now (summer).
Don't know how much wheel horspower increase that is, but you can definitely feel it. Downpipe is a must.