I got a g35 coupe/manual with a ATI procharger.Running on stock injectors . I had no other mods done and ran 350whp and 299tq at 8 psi.
I just installed stillen dual exhaust/ race pipes/ and headers,. After the install i ran again and loss 20hp and 10tq. What did I do wrong and what can I do to fix it? I feel like I wasted my money with the extra mods

 

i also loss 1.5psi but procharger told me that was expected but I should have still gained HP

 

you need a tune.....

 

has this happen to anyone else on the forum?

 

Please post before and after dyno charts. Thanks.

 

Get a tune.

 

you lost power because:

a. you lost psi.
b. the exhaust its too big for your application and you lost back pressure.
c. you have bought a bunch of "cool mods" and no fuel mods, chances are you are running lean and possibly "♪♫knock knock knocking on heavens dooooor...♫1♪.
d. you dont do your homework before picking your mods.
e. you are a noob without a tune.
f. all of the above.


urwelcombye.

 

thank's dic

 

did you get your car tunned to the exhaust headers and test pipes?, if not then thats why you lost power...everytime put bolt-ones you have to make sure you get it tunned to those parts

 

you can call him a dick if you want but he gave you legitimate info..

 

x10000

 

I disagree with most things you said. There's actually 'almost' no such thing as a 'too big of an exhaust' on an FI engine. I say almost because supercharging is a bit different and having a well matched exhaust is key to have proper flow before you're in positive pressure. Once you start running positive pressure in the intake, having a huge exhaust does not hurt at all. Backpressure is never a good thing. This is a myth that has been around for very long time. You do not need backpressure.....EVER. Exhaust is all about flow, not adding restriction.

THe OP does need a tune ofcourse. He most likely lost HP because he swapped out his stock exhaust, which retains heat extremely well, and put on a SS exhaust system that does not hold heat very well. I think he lost HP due to the loss in peak boost and because his exhaust flows worse than before. His headers may also not be as good as he thinks. Everybody loves to swap in SS exhaust components but it ends up usually hurting more or not helping much for a pretty hefty price.

To the OP, get your fueling on order. Check your logs and make sure you're not maxing out your injectors which you probably are. If your fueling is wacked, you're playing with fire and you're on borrowed time. Going boom on an FI engine is very easy if you induce enough detonation.

 

Super chargers do not create additional back pressure like a turbo does, so it's not AS important to have a huge exhaust with an SC. You have to consider your breathing mods for SC much like for NA because the reactions to the mods are going to be very similar. If you open up the exhaust, you will loose low end power, but pick it up at the top end.

Additionally, you will show less boost being made with better breathing, yet you'll make much more HP/TQ with a good tune.

There'sa MASSIVE difference between turbo and SC in how they work and how additional bolt on's affect them.

 

I agree here.

From my mustang days (03 cobra), the exhaust didn't ultimately change the power (to a point, you run a straw size exhaust you are going to loose power obviously)....but most often, the smaller diameter exhaust made the tq sooner, larger diameter exhaust made the tq later. As much as a 1000rpm difference when still on the eaton blower.

just fyi

And oh like everyone said, tune tune tune, how big are the stock inj too?

 

stock injectors are around 290cc

 

you prolly need to upgrade your injectors to 450cc or so and get a tune. what is your A/F reading on WOT? Not sure if the header will do anything.

 

wow, I'm surprised it made 350rwhp on inj that size

 

i disagree with you being alive... i guess we r even

 

You can listen to all these people talk all day long but, unless you had a SC or Turbo put on your car. You always have to get a Car tunned to your parts that uve installed exhaust isnt so much but doing stuff where it really effects your car. Injectors, test pipes U-Tec Cold Air Intake and some other stuff. I had a JWT pop charger on my 2005 Track Z with Magnaflow exhaust yea i said Magnaflow. I took it to DynoComp and had them install the PB U-tec and ran 327.6max hp to the crank for a week. I started Loosing HP becuase i didnt have an Cold Air Intake and test pipes. I got a Nismo Cold Air and Megan Racing pipes left the Magnaflow on and im still to this day running 344.7 HP tunned to the bolt ones. Who ever said what exhaust you have on really doesnt matter unless your a V8 or V10

 

because i didnt have a cold air intake? its already been proven on this board time and time again that most of the time CAI's yield losses on most N/A applications. and whens the last time a dyno took crank hp numbers? for you to say that exhaust size matters is ridiculous. on a turbo car it plays a HUGE difference. ive heard of a turboxs utec but never a PB u-tec? your 4 post history speaks volumes of your actual knowledge.

now on to the op's problem. now back pressure isnt an issue with the vortech system. if it were a stillen that yes it would be a problem as most stillen cars with exhaust mods end up loosing alot of power. so what do i think. i think your motor is dead already. running your car on stock injectors and on boost is a deadly combination. i also doubt that you had any gauges. if you look in the FAQ section theres a write up about injectors. at base fuel pressure your injectors flow approx 1whp for 1cc of injector you also have to take into account that the engine requires a little more fuel to run the supercharger because it robs power from the engine to run it. so your car must have been running lean for quite some time and slowly destroying itself. i think its only apparent now that the car has been put on a dyno that your finding out that there is a large problem.