loss hp with 3in DP

[jonGST]

I installed an UPC (brand) Down Pipe (with cat removal) on my '96 GST. I did a dyno run before the dp was installed, and at 16.8psi it made 226.9whp. After the dp install and cat removal, we upped the boost to 19psi. The car dyno'd out with 217.3whp, and above 4000RPM was running so rich that the dyno could not get a proper reading on the air/fuel ratio. The dyno cut at 10.0 A/F Ratio, and above 4000 it was solid 10 to redline. Basically, I installed a Down Pipe and cat removal and lost 9whp. Any suggestions as to what the problem could be. Also we replaced the spark plugs with NGK and regapped all of them to 30. Thanks

 

[nine5raptor]

did you put the 02 sensor back in?

Did you reset the ecu? If so, give it some time to get the fuel trims back in line.

 

[jonGST]

yes we did both but how long does the battery have to be disconected for

 

[nine5raptor]

Mine seem to reset almost immediately. Give it several days of driving around town and then see if the power is back up.

Are you running 19psi on stock injectors?? bad, bad...Power is low due to knock and timing being pulled. Lower the boost and watch your power go back up. A/F is probably so rich due to the injectors going static. I don't see why you aren't fuel cutting.

 

[jonGST]

the only reason i went to 19psi is beacuse i lost power with the dp
but i will turn it down and give it a few days then see what happens
Thanks

 

[nine5raptor]

Anyone you know have a logger?

See if you can't log your timing and 02 voltage for us.

 

[jonGST]

i might be able to find someone tomorrow but it might take some work
i was thinking about buying one this might be the excuse i need

 

[yo2001]

DP might be hitting something , making the knock sensor picking up the false knock. I know my 3 inch DP hits the rear cross member. Just a thought

 

[yo2001]

DP might be hitting something , making the knock sensor picking up the false knock. I know my 3 inch DP hits the rear cross member. Just a thought

 

[kpt4321]

I've seen a LOT of cars pick up 10-30 horsepower from a cat removal and a downpipe, based on 1/4 mile times.

You messed something up when you did the install, I'm afraid.

Did the car throw a CE light for the rear O2 sensor?

 

[jonGST]

i drove my car today at 15psi and it was fine, the dp is hooked up fine and its not hitting anything, but i will know for sure on monday went it goes back on the dyno.

 

[jonGST]

and no ce light even did a diagnostics and there was nothing

 

[johnh]

did you put the ground strap back on the downpipe when you installed it? do you guys think this could be the problem? just my thoughts.

 

[kpt4321]

Originally posted by johnh
did you put the ground strap back on the downpipe when you installed it? do you guys think this could be the problem? just my thoughts.

Nope, that should not be the problem.

 

[pickens]

maybe its time to start tuning now that the motor is breathing alot better.