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Discussion Starter · #1 ·
Ok this is not on a drag car its my daily driver that was completely stock a little while ago. It is a Direct Injected 4.4L TTV8 and when I first took it to get dyno'd it made 385whp and 439ft-lbs. Then I installed catless downpipes and re dyno'd and peak hp increased to 387whp(which is within the margin of error) but torque decreased to 415. Thats no where near the worst part, in the midrange I dropped 97ft-lbs and 56whp.

What could be up? The car runs strong and is pretty new. I could understand maybe the drop in backpressure would cause the torque drop off but I've never seen such a massive drop. Another thing is the engine is pretty complicated and I think maybe the tune is all messed up for some reason. Anyways I took it to the strip yesterday and it ran 13.2 which isn't bad for a sedan that weigh's 4550. Here's the dyno:

 

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Computer thinking something.is wrong and pulling back the tuneup???
 

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Discussion Starter · #4 ·
Well the check engine light is on but I've got a reader plugged into the obd2 port and timing seems normal but for some reason the car always reads 2.6lbs max boost regardless of the actual max number. As in another guy who has a tune and is running 15psi max still only sees 2.6lbs when he checks the obd2 info. Because of that I don't know if the computer is pulling boost in response to what it thinks is a problem. Also the car smells like it's running pretty rich but I'm not sure if that's just the catless smell or if the tune is running richer to try and reduce egt's and emissions in response to the cat codes. I'm gonna try and put some non foulest on the secondary O2's and see if clearing that code gives a better performance.

Still assuming the lack of tuning or check engine light being an issue there no mechanical reason why removing the cats that where right up on the turbine housing wouldn't be beneficial right? I'm hoping once the tune is in place I will see a benefit from them and be able to turn boost past the stock 9lbs.
 

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Chupa Cabra
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I've always heard that having the least restrictive path for the exhaust gas to escape post turbine is what you want and that it can't be too big after the turbo, now I'm sure there is a point that too big is going to be bad for a smaller t3 or t4 turbine housing, but still...I can't see it hurting performance mechanically, it's got to be in the tune.
 
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