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Uncorking the Pypes… I have the Pypes downpipes which have a 2” neck that attaches to 2.5” pipe for the rest of the exhaust. it was fine with the stock manifolds, but I put the Thornton headers on which actually have a 2.5” outlet. the Pypes were now a cork going 2.5” into 2” then back to 2.5”. Brought them to my local exhaust specialist and had him remove the corks and add a new full 2.5” connector and also added O2 bungs for future tuning of the carb.
I have a second set of these that I will swap ends on also, if I get them done in time I will send them to Jerry so maybe he could dyno test his original Pypes against a full 2.5” with the manifolds and shorty headers. I gotta believe squeezing down to 2” killed some power.
Going 2.5" to 2" to 2.5" may hurt HP numbers, but it will be undetectable with a butt-dyno.
haha..totally. It has run fantastic as is, I am about to tune the carb and with the ported heads wanted to make sure the flow is all open before the carb tune. I bought a PE wideband O2 so I’m exited to try it out.
That looks great. Ram Air Restorations used to have a really nice 2.5" down pipes, unfortunately don't make them anymore. It would be nice if Thornton offered down pipes in 2.5" to go with their headers and larger outlet manifolds. Either way, fixed.
Last edited by olds 307 and 403; Feb 17, 2026 at 02:24 PM.
I ran into the same issues years ago with Thornton shorty headers and Pypes down pipes. I got frustrated with Pypes poor response to my questions and put everything in the boxes and stayed with my long tube headers.
I must say, the Thornton shorties are good looking pieces.
I ran this combination on my 400G for about 5 years. The Thornton description of the short tube big block headers states a 3" collector but the flange and ball shaped pipe mating face is designed for a 2.25 or 2.50" downpipe. This is due to the fact that the original factory exhaust was not 2.50". I never saw that neck on the Pypes downpipes as a performance harming restriction. Glad you're happy with your mods.
