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3" or 3.5" or?

Mally69

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Okay, 69 bee total restoration happening here. Let me explain my ideas and ill hopefully snag one of the other guys running a big hammer that can give me a bit of advise. So im running a 505 indy headed EZ-1 295s. 11:1 COMP Fairly large flat tappet cam everything was spec'd out by porter racing heads, cam heads being ported etc... Ill assume im 675 700 hp range. Im running a dana 60 BUT no fuel tank. Ill have a fuel cell mounted in the trunk. My issue is the exhaust size. Ive always used 3inch. But this time im kicking around 3.5 due to power level. id assume but not sure if 3 inch is big enough or if it would be a bit restrictive, or if 3.5" is over kill. Not concerned about price. It is what it is.


Origional plan was since my collector is 3.5 inch i was going to run a granatelli 3.5" elec cutout then from that down to a 3" X-PIPE and run 3" all the way out.



2nd idea was stay with 3.5 the whole way through a 3.5 " Xpipe 3.5 out the tail end.


3rd was to stay 3.5" from Collector thro the cutout 3.5" Xpipe, then possibly step down to 3" out the rear.

Mufflers are chosen i plan on running the round dynomax ultraflows whatever size i decide on pipes. Id love to hear some 3.5 inch exhausts if anyone has vids. Anyone think for 700ish HP the 3.5 is over kill???? I think it would have a nice sound.
 
Last edited:
No video, but.....
I have run 3.5 pipe with a LOT less motor than you have. I have 3.5 on my 440 powered 62 back to the bumper, made with straights and mandrel bends. I'm using giant Flowmaster big block mufflers, and I love the sound. (The system was built for the nitrous 522 that's in progress)
I also ran 3.5s on my n/a small block car, made with leftover pipe, homemade flanges, and cheap hooker aeros. ( the aeros were 1/2 the price of the flowmasters. Still are). It couldn't have been too bad a choice, the car ran 6.30 eighths, thru the mufflers.
Just be aware, 3.5 is heavy (my 62s' setup, header back, is over a hundred pounds), and straight thru 3.5s will be LOUD.
Both cars are probably around 500hp.
 
Something of interest is the roadkill engine masters series, they did some tests on 2 and 1/2 and 3 in.
 
No video, but.....
I have run 3.5 pipe with a LOT less motor than you have. I have 3.5 on my 440 powered 62 back to the bumper, made with straights and mandrel bends. I'm using giant Flowmaster big block mufflers, and I love the sound. (The system was built for the nitrous 522 that's in progress)
I also ran 3.5s on my n/a small block car, made with leftover pipe, homemade flanges, and cheap hooker aeros. ( the aeros were 1/2 the price of the flowmasters. Still are). It couldn't have been too bad a choice, the car ran 6.30 eighths, thru the mufflers.
Just be aware, 3.5 is heavy (my 62s' setup, header back, is over a hundred pounds), and straight thru 3.5s will be LOUD.
Both cars are probably around 500hp.
Did you happen to lose any bottom end torque like a few ppl said on other forums? Also i didn't give the weight much of a thought, i figured it be a bit heavier but wasnt sure how much.
 
With a good stout converter and gear, you can't notice any loss of low end torque. The 62 has a 4500 converter, the small block car has a 5500.
Iron head pump gas 440 goes 122 with 3.91s, small block car had 5.14s, runs better with 4.57s now.
 
With a good stout converter and gear, you can't notice any loss of low end torque. The 62 has a 4500 converter, the small block car has a 5500.
833 hemi box. 4.10 gears . 295/65 rear tire
 
The big question is how quiet vs. how much weight to add. 3 1/2" bullets with no pipes. Or complete heavy system with an X pipe.
Doug
 
Well, they way I looked at it when I built my car is I've calibrated a ton of LS 4th gen F-body's at well over 400rwhp on the original single 2.75 exhaust.

Many more at 450rwhp and 3" single exhaust.

My headers are 3.5 collector. The mufflers I wanted to use come no bigger than 3" so I ran 3.5 from the headers to the crossover and 3" from there. Just under 600rwhp.

Made a few changes and expect to be in the 620rwhp range.


Exhaust doesn't like to change directions. I built my exhaust with very large radius bends.

I think doing it that way can support a ton of power, vs tight radius 3.5 which would also weigh much more.
 
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