Hi, I'm gathering parts for my project and have ordered a pair of the eBay gt45. I have a set of headers I built for one of my other cars they are 1 7/8" primary and 3.5" collectors. I planned on cutting off the flanges, flipping them and shortening, but I'm wondering if the 3.5" collectors are going to be to big?
The engine is a very mild 454 in my 56 chev gasser project, more street than strip at this stage.
thanks
Jason

 

i would use that area to transition to the t4 flange

 

Yes way too big for a mild boosted 454. 2.5" is PLENTY.

Note the 2.5" collector on this 2800HP 482 Pontiac.

http://www.hotrod.com/cars/featured/hppp-1103-1963-pontiac-lemans/

 

Thanks for the replies, I had a quick look at the attached article. His car runs 2" primaries with only a 2.5" collector, so I'm guessing that would be a merge style collector. Just seemed like a lot of diameter to reduce down into 2.5", obviously it works though.
Thanks
Jason

 

Your exhaust ports are around 2 inches by themselves. Dont think I would worry too much about 3.5, but Im no pro. Would guess if anything you might introduce a little lag to instant spooling. 2 inch exhaust ports to only a 2.5 inch pipe seems like quite a reduction. Your turbine A/R comes into play also.

 

Quillen used 2" primaries to match his exh ports. 3.5" will slow the velocity down to a crawl if you run it for any length and actually hurt performance. Pointless to do IMO.The OP could EASILY run 2.5 collectors and 2.5" post collector with zero issues and improve performance over the 3.5".

 

I think we need more info... I agree if he's going to continue with piping off the end of the collector it should be smaller, but if he's just cutting the collector short, and adding a flange, or adding a cone reducer, and installing a v-band, I personally wouldn't cut the collector off if the only reason is to make it a 2.5"

 

Thanks guys, it's not a problem if I can't use them. I asked the question after using the search option and not seeing anyone using a collector that big.
The engine is basic 454, 049 stock heads, rv style cam, big single plane, and I'll do blow through 750 Holley.
I'll use this engine to play with first then build something more suited.
Thanks
Jason

 

For what its worth, Im basically using 4 inch collectors in my mild big block build. (Its in the build section, and probably about the same engine) I used to get some decent pressure out of the exhaust all the way back at the rear end, the thing left craters if I parked on dirt. So for a mild build I didnt figure a little extra volume in my pre-turbine hotside would make or break the power. Especially being just a mild build getting my feet wet, compared to maximum effort.

Forcefed and Mnlx know their stuff.

 

Thanks Dru, I did have a look at your build and thought the headers looked nice, but the wouldn't fit for me. I had some long tube headers I'd built for my bbc model a and thought I could just cut and shorten them but sounds like I'd be better to make another set for my 56.
Jason

 

u know what the set of headers sizes where before current ones?

 

Sure don't. Was just quoting info I read in his article and on Butlers website.