[Formulajones]

Originally Posted by Quad

from Motor Trend Archives; Pure Stock Prep School Part 2- Pontiac Tech
Learn What Makes Them Really Run
Mark Weymouth writerDan Jensen photographer Aug 1, 2008

"ExhaustThe exhaust system is your last drivetrain issue to address. How important is the exhaust? Very! The Ram Air IV Judge in the lead shot of the last installment is a good example. The previous owner used it as a show car and we were going to use it as a race car. Its NOS exhaust system and factory-spec engine only allowed 13.90s at 105 mph. With a change to an X-type pipe system, the car went 13.13 at 111.8 mph.

To achieve the best results, you'll need to start with an all mandrel-bent 2.5-inch exhaust. Next, you need to decide whether to use an H-style pipe or an X-type pipe. Each has its own merit.

Most racers have adopted the X-type pipe system. It provides excellent scavenging in the low to upper midrange. At very high rpm, it's not as effective. Most PS cars run completely in the rpm range, where it does its best work. The one exception is the Ram Air IV, but even this motor, overall, is well served by the X-type, as it provides additional bottom end and midrange that the engine lacks on its own."

I can attest to that with my own testing I did that I mentioned earlier on my RAIII. While not as powerful as a IV I still found substantial gains over the repo factory Gardner exhaust where the car was stuck at 14.10's and teens and 99 mph. An h-pipe flowmaster transverse kit picked it up to 13.70's at 102 with no other changes. I later changed to a pypes transverse setup with x-pipe and gained another couple tenths and similar mph.
I've since tuned and tweaked some more to run a best 13.10 @ 106 uncorrected in a bone stock RAIII.
I contribute a big part of getting there in just the exhaust system alone.