Exhaust size
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Junior User
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Exhaust size
I have a 360 with hedman headers and a pre 72' timing set.My question is exhaust size. The headers come out too 3inch. I looked at 36" cherry bombs that bolt directly to the header, 3inch in, 3inch out. Is there a problem with not necking down the exhaust size. Ive read a few things on here about back pressure.
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From: Douglas, Georgia
I've got a set of 1.75 primary, 3 inch collector headers on my 390 truck engine.
I neck down to 2.25 for each leg of the dual exhaust. Thats the smallest I'd go, but for an engine that doesn't go over 4000rpms I don't see going any bigger.
I neck down to 2.25 for each leg of the dual exhaust. Thats the smallest I'd go, but for an engine that doesn't go over 4000rpms I don't see going any bigger.
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Junior User
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its not a question of necessary. The collecters are three inch and the mufflers bolt right on and end in three inch. They are long enogh to get out from underneath the cab as well. Its a low cost solution. What i was wanting to know is will the three inch cause any problems?
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From: Douglas, Georgia
yeah, people always talk about backpressure. 
Just retune/rejet whatever according to however you have everything setup.
I've got about the same headers going to a 24inch piece of 2.25 pipe and a 12inch glasspack.
I don't think it's that loud. (of course I worked on Detroits for a good while). I wouldn't advise stomping the skinny pedal around the local cops.
Just retune/rejet whatever according to however you have everything setup.
I've got about the same headers going to a 24inch piece of 2.25 pipe and a 12inch glasspack.
I don't think it's that loud. (of course I worked on Detroits for a good while). I wouldn't advise stomping the skinny pedal around the local cops.
Hotshot
Joined: Jul 2005
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From: Middle Tn.
Stock 428 cj's came with dual 2 1/4's. I've run 2 1/2's and went back to the 2 1/4's when I restored the car. I wanted the factory cross over and quad tips. Unless you're doing 1/4 mile time slips you won't know the diff. except in your wallet and under car clearance. If it's in a truck the clearance is a non-issue.
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Elder User
Joined: Mar 2004
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From: Klamath Falls OR
2 1/2" would be perfect in my book. I ran a 360 (small cam and intake) with 2 1/2" and did just fine. I wouldn't go any bigger then that! And in the future you decide to change out for bigger CI, the exhaust is taken care of. JMHO
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Junior User
Joined: May 2010
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thanks everyone. Exhaust a little further from the cab is looking good. A final tune later on will be done to compliment whatever setup I do go with. Right now for moving around the driveway and wrenching purposes its the open headers for the neighbors pleasure. (truck doesnt have the trans or front axle in so no rush haha) Perhaps a couple flowmasters or something will be the way to go. Im like most guys I like the noise but only to a certain degree, I still have to sit in and drive the damn thing.
Fleet Mechanic
Joined: Jun 2007
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From: Ohio
I have headers on my 390 with 3" collectors also and have 2.5" pipes running off of both of them. They are about 2.25" at the bend so it's a bit of both 2.5" and 2.25". What truck do you have because if it's an f100/f150 like mine you'll have the crossmember in the way...
Hotshot
Joined: Jul 2005
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From: Middle Tn.
I have headers on my 390 with 3" collectors also and have 2.5" pipes running off of both of them. They are about 2.25" at the bend so it's a bit of both 2.5" and 2.25". What truck do you have because if it's an f100/f150 like mine you'll have the crossmember in the way...
yep lol
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