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Old 12-26-2012, 05:48 AM
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383HT exhaust recommendatations

I built a clone to the GM 383HT. I am at the point of putting together the exhaust system. The engine is in my 1949 F-1 truck. It sits in front of a 700R4 and 9 inch ford running 3.70 gears. The way that I will use the truck has not changed i.e. low to mid range torque to tow up to a 5000 lb. trailer and I do want to stay with the 2" GM angled back rams horn manifolds for reasons of fit (around my Jag IFS) and $ (I own them). I had a lot of help on the forum in the past and want to stay with my OEM curved down rams horn exhaust manifolds (2 inch diameter). The question is, is there any advantage in trying to run the dual exhaust any larger than 2 " diameter pipe? Given the donut design of the 2" angled rams horn manifolds, the only way would be to transition up to larger pipe greater than 2 " would be an expander in the pipe downstream of the 2 " restriction at the exit from the manifold. It does not make sense to me but I would appreciate the thoughts of others on the forum. What do you think?
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Old 12-26-2012, 07:49 AM
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383HT exhaust recommendation

Check out this website for the size of pipe to use based on CID. Magnaflow Technology
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Old 12-26-2012, 04:41 PM
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2 inch Dual exhuast should flow well enough to support your engine. Usally its the pipes that go over the rear axel that produce the highest restrictions in stock systems. A larger pipe in the restricted areas is best if its a straight shot 2inch is fine.

Mandral bent pipe will help make the 2 inch work better. Also 2 1/2 right after the collector will help with more flow. But under 5000 rpm 2inch should provide plenty of punch. Larger full legth headers and 2 1/2 will be worth about 15-25 hp. So its not alot to give up even if its not flowing its best.

A badly setup system could cost you a few ponies more than it should. So be sure to get a nice welded up system. Alot of muffler shops will weld something up they bend for little moeny on older trucks. Some will also try to make a lot of money. Best to shop around or buy a flowmaster or other universal kit.
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Old 12-26-2012, 06:38 PM
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If it were mine and I absolutely had to use cast manifolds, I'd make some type of step-up adapter from 2" to at least 2-1/2" as near the manifolds as possible(even if it just were welding larger pipes onto smaller pipes, say welding 2-1/4" dia. two inches long onto 2"pipe connected to manifold, then welding 2-1/2" pipe onto the 2-1/4" "adapters" kind of like stepped headers).
Then you could use 2-1/2" exhausts/mufflers for more flow. Even if the exhaust is coming out of the restricked manifolds small dia. opening, it will still expand enough to make use of the larger exhaust/mufflers for more power/torque and reduce backpressure IMO.
Someone probably makes an adapter for this already, and have for many years, expanded pipe or whatever, but I don't know the details. Google it.
Overlook the spelling.
FWIW
ssmonty
PS I know you said in another post that you had tried different types of headers. Did you ever try Tri-Y's instead of 4 into 1 types? These Thorleys have a 2-1/2" collector.
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Old 12-27-2012, 11:24 PM
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For towing a trailor ,the 4 tube headers probably hurt more then they help ,i think you need cast iron like sanderson or factory 2-1/5 mid sixtys corvette , as for exaust pipes ,you can run 2 " since exaust Cools and reduces in volume as it exits ,if you notice medium and heavy duty trucks ,larger at front than rear to keep torque high at lower rpm ,also heat wrap on front pipes like D E I or similar will help.
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Old 12-28-2012, 02:32 AM
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I'd make a template out of paper or posterboard of the head ports and bolt holes, then check the rams with the template and see how much different the ports line up..
not knowing what heads you're use'n.. but if those ram horns are from a g.m. truck.. the ports on the old engines and the exhaust ports on newer heads are not the same.. and iff a tad off, open up the horns.. I'd go to 2.25 pipe as soon as you can off the horns..
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Old 12-29-2012, 03:20 AM
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Thanks all for your help. I have pieces in transit to build a 2 1/2 inch 304 stainless system. I found a transition piece that will step up from the 2" curved rams horn right at the exit from the manifold to 2 1/2". Lots of Tig welding ahead of me!
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