2.5" outlet header/manifold - Chevelle Tech
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  • 1 Post By spoffie1962
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post #1 of 3 (permalink) Old Sep 24th, 19, 3:16 PM Thread Starter
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Location: South Eastern PA
Posts: 78
2.5" outlet header/manifold

Please let me know your thoughts on this and if this is something you'd consider:

If any of you are familiar with Troy Thornton, owner of Thornton Restorations in Quakertown PA, you know he is THE top Oldsmobile restoration shop in the country. His restorations and restoration parts are second to none. Several years ago he saw a need for the Olds 350 owners to have a freer flowing exhaust manifold, so he developed the '350 Junior' manifold. It's a like-for-like manifold only with a 2-1/4 outlet (vs.2") and larger ports. Basically a W-30 manifold designed to fit a 350. He then designed a header that fits the factory manifold dimensions, so to can hook your factory downpipes straight to the header. Admittedly not a tuned header, but better than a shorty since you don't have to have a custom downpipe made to hook to the rest of your system.

Which leads me to my point...he is in development of a similar header for the A,F,& X body SBC. They have been sent out for production (haven't been delivered yet though) and look very, very nice. They have a true 2-1/2" outlet and like the Olds, exits in the same location as a stock 2" manifold. What you would do is use a Big Block downpipe such as Pypes DGU20S, hook it up to Pypes/Flowmaster/MagnsFlow system and you have a true 2-1/2" exhaust without the hassle of long tube headers.

Which leads me to my NEXT point..I asked him if he would be willing to make a 2-1/2" cast iron log manifold for the SBC, like the Olds 350 Junior. He looked at me and said "That's a very interesting question, do you think there's a market for it?". So I'm asking everyone out there- "Is there a market for something like that?". His concerns, and rightfully so, are that these things need to be produced in larger quantities to be competitively priced, and larger quantities mean larger quantities of cash to put up front to start production. It would be a lot of expensive cast iron sitting on his shelf if they don't sell.

So, if you were in the market, would you consider a 2.5" Cast Iron Log Manifold or a Header that is dimensionally the same as a manifold? Is there a market for both? BTW, the header was worth 11 HP over the 350 JR manifold on a hot 350 Olds.
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post #2 of 3 (permalink) Old Sep 25th, 19, 7:24 PM
Dave Varney
Join Date: Apr 2015
Location: Ottawa,IL
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Re: 2.5" outlet header/manifold

I have a strong interest in either set up for my 1966 SBC.
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post #3 of 3 (permalink) Old Nov 4th, 19, 6:05 PM Thread Starter
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Re: 2.5" outlet header/manifold

DV327- These were just test fitted on a '70 Malibu 350 with A/C & P/S and they fit very nice. Used a Big Block downpipe to hook up to the rest of the 2.5" system. They will be available soon at https://classicmusclecarexhaust.com/
Probably in the mid $300 range.
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