Exhaust backpressure question

[RedMisted]

I had the exhaust tailpipes removed from the catbacks on my ITR Mustang, in part to reduce weight. In their places now are "turndowns."

The exhaust tailpipes extended from the mufflers, which are located just ahead of the axle, to the very back of the car, snaking around the axle and panhard bar bracket. As such these are long pieces.

My question: What usually would be the change to the backpressure? Would it be anything significant? I hope I don't have to revisit a tuner to reset things.

Thanks for any replies.

[dj10]

I had the exhaust tailpipes removed from the catbacks on my ITR Mustang, in part to reduce weight. In their places now are "turndowns."

The exhaust tailpipes extended from the mufflers, which are located just ahead of the axle, to the very back of the car, snaking around the axle and panhard bar bracket. As such these are long pieces.

My question: What usually would be the change to the backpressure? Would it be anything significant? I hope I don't have to revisit a tuner to reset things.

Thanks for any replies.

Chris, when in doubt always ask your tuner. Don't just make noise, make HP & torque with the noise.:) If he saves you from making a 5 hp mistake, that's like him getting you 5 hp.

[jimbbski]

A general rule of thumb is the longer the pipe the better the torque. The shorter the pipes then less torque but more horsepower. This is of course measuring at the same rpm. AS said if you want the most you can get then you need to dyno it!

[RedMisted]

Thanks, guys, for the replies. I kinda figured something was up with this change because the car likes to go about 2mph faster down the back straight at Nelson. The cool temperatures there last weekend were conducive to good acceleration but the car ran a bit below par.
Since it's back to the tuner, I now have a great excuse to change to LT headers, remove the cats and run a single muffler. :)

[Ron Earp]

Hi Chris,

the majority of the back pressure in your system will be coming from those stock catalytic converters. What little back pressure changes (and resultant increase of airflow) you made in the system with the tailpipe removal will be easily compensated internally by the MAF and system V ECU.

Time to ditch that stuff and get a race exhaust system on that Mustang. You might want to do some calculations on required primary diameter and length. There are some stock long tubes that have a very close to ideal primary diameter and would really only require length changes and collector modification to get them close to the model ideal parameters.

Ron