Hey guys, I posted this on the exhaust board, but think you all should check it out also...according to this chart off of the Dynomax homepage a single 3in pipe is capable of supporting over 500hp...I actually called dynomax and asked them if it was accurate and they said yes. What do you all think?

Yep, sort of…. Those numbers are based on a study that David Vizard did a few years ago. He figured that at some point most tracks will set noise standards and wanted to know how much flow you would need not to loose any performance. He found that above 2.2cfm/hp there was only a negligible restriction that was almost statistically insignificant. You couldn’t measure any change above 2.4cfm/hp.

He also found that the required flow drops as you go further back in the exhaust because the gasses cool and take up less volume, so the further back you mount the muffler the smaller it could be. The muffler only has to be that big if it is mounted right after the collector, and that you could make an exhaust that has sufficient flow behave exactly like open collectors if you build a ‘pressure wave terminator box’ (basically an expansion chamber) and mounted it at the end of the collectors and ran whatever exhaust out you wanted. This is somewhat the idea behind some of the funky designs coming out now by Magnaflow and a few others. You’ll see long, 3.5” collectors, a 3” x-pipe with 2.5” outlets and mufflers and then 2.25” tailpipes on a QUIET 600hp car… I did something like that on my truck a while back, the Y comes together into a 3”, and ends with a 2.25” tailpipe.

this is an extremely interesting concept and really does make sense...so this actually works? I may be getting rid of my duals and making my own 3in y pipe, run the two 3in into an Expansion chamber (basically I think I would use a 4in, to 3in adapter,about where the cat used to be, oval it slightly so it would be about 3inx5in, make sure to make it as hollow as possible inside by cutting as much of the 3in back as I could, and run that into single 3in over the axle and into the Dynomax single 3in dual 3in out crossflow muffler, it flows over 1100 CFM).

The guys at mufflex told me they have a guy running the 4" with the offroad 3" Y pipe making just over 700 RWHP. I dont expect much over 500 with my 91 project.

IROCFAST, if by 'expansion chamber' you mean a pressure wave terminator box, you should probably be aware of 2 things. First, the reason Vizard was playing with it is that he feels that most of the scavenging/HP increase available in an exaust system is in getting the collector length tuned and that playing with primaries is a wast of time. He was attempting to specifically tune the collectors with the terminator box. In your setup you'd have grossly different collector lengths, both of which would probably be too long for any usefull tuning. Second, he found that to be effective he needed 2 chambers roughly 8x the effective volume of a cylinder or greater (kinda big to fit under an f-body)

Great information Crossfire...thanks