Does anyone know anything about exhaust flow and back pressure. I'm going to swich from full length headers to shortie headers, and I was thinking about trying to offset the restriction I will be getting from the shorties with 2 1/2 inch exhaust all the way out the back instead of the 2 1/4 I have now. Does anyone know if this will work the what I think it will or will I do more harm than good by eliminating healpfull back pressure. Thanks
IMHO First off, let me say I believe you're going the wrong way, if performance is your goal. Full length headers will free up more horsepower in the mid to high rpm range than the shorties. If you wanna go to shorties, I'm sure there are PLENTY of people out there that'd readily swap you (for maximum h.p., long tube = better), if you haven't already been talked out of 'em. Re: Back pressure I'd only be concerned with this if you're running open headers. With your 'full exhaust', you'll have adequate back-pressure using either the 2-1/4" OR the 2-1/2". Going to the 2-1/2" exhaust = good (engine = airpump, more air in and out = more horsepower). Try "http://www.prestage.com/carmath/calc_headerlength.asp" to help better understand your situation. I don't claim to be an expert in this area, but I believe the link will be helpful (use different rpm's and tubing O.D.'s to get an idea of how the changes effect lengths.) Again, just MHO. 'Luck.
Shorties do not flow better than long tube headers. I definitely would scrap that plan. 2-1/2 inch exhaust on the other hand will give you enough backpressure and improve performance. Usually, the shorter the primary tube length the higher RPM range the powerband moves. But shorties are so short that they basically are just free-flowing manifolds. http://www.ssheaders.com
watch the long tube headers, I had a nice set on my 67 stang back in the day, and they have a bad habit of scraping on just about everything, they hang real low.
