hinchcliffe

Anybody know the HP differences between the two? Is the X-pipe really that much better? Is it worth the extra $$$$.

Jeff F

Yes, there is a benefit to the "X-theory" behind design. Test pipes get rid of the weight and slight horsepower negative related to backpressure that cat-converters cause--even the best ones. "H-pipes, or "crossover" pipes were the next evolution. They balance both sides of V-type cylinder banks, improving noise, improving capacity, and allows the rear of the exhaust system to work together to improve the performance of both banks, and the total package as a result.

"X-pipes" are the latest evollution of the "H-pipe." They have all of the advantages of the other two, plus more. They assist in exhaust scavenging, which means that the negative pressure of one bank of cylinders after the exhaust passes on one side, helps "vacuum" the next pulse on the other side. You gain power and efficiency as a result.

I have used "H-pipes" on my old Pontiac race cars (years ago), and new Ott "X" on the S4. Great results. If I could not buy another Ott X today, I would buy a Dr. Gas (do a search, or check their website, it was posted here somewhere recently) X-crossover, and have it welded in by a muffler shop for "racing use only."

I spent a lot of time looking into exhaust for V-type racing motors, so I think I know some of this stuff as a result. Good luck!

Jeff

'87 S4 Some extra stuff
'86 951 2.8 Lots of extra stuff
'92 968 Cab. Mostly stock and staying that way

Mattman928

Do you think a 928GT would still pass emissions with the X-Pipe installed?

Intrinsicate

I have the test-pipes installed, and my car sailed through the emissions testing. Of course, it would fail the visual inspection, but nobody ever seems to look!