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Discussion Starter #1
I'm thinking of changing my exhaust form 2 1/2 to 3inch. Mostly to help cool down the big block. Your thoughts?? Car sounds awesome now wondering if it will be too loud with upgrade to 3inch
 

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3 in didn't do anything for my cooling.jetting up 2 points did cured the heating.
car is louder and more of a drone noise .
I actually lost power with 3 in.
 

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Engine masters did a test of 2.5" vs 3" on a 600 HP BBC. 3" made 13 more HP and 15 more ft-lbs at about the same RPM's.

3" was better from about 4K up on both torque and HP, below that it was nearly identical to 2.5"


Dyno sheet below, Red is 2.5", Black is 3" and blue is open header with 18" extensions.
 

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As a man who has done a lot of experiments in his life, I thought this test was quite flawed. Start off with a poorly designed exhaust system and hope what you do does better.

A little science applied to the exhaust system would go a long ways.
 

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As a man who has done a lot of experiments in his life, I thought this test was quite flawed. Start off with a poorly designed exhaust system and hope what you do does better.

A little science applied to the exhaust system would go a long ways.
Speaking of science, I came across this article a while back and thought that it might be of interest here.

http://www.pontiacstreetperformance.com/psp/exhaust.html

Gerry
 

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3" vs 2 1/2"

I have a 70 BB with 3' exhaust, didn't see any big change but they are a PIA to clear 275s, not much room between the leaf spring and tire. I would not do it again, just my 2 cents.
 

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I'm thinking of changing my exhaust form 2 1/2 to 3inch. Mostly to help cool down the big block. Your thoughts?? Car sounds awesome now wondering if it will be too loud with upgrade to 3inch
Save your money
No real gain
I’d go with 2.5” and use a cross over pipe and some magnaflow mufflers
I’ve got 3” on my 66 nova. It’s too loud on the street. I like my 2.5” set up better on my 67 nova.
 

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Big Pipes

I'm thinking of changing my exhaust form 2 1/2 to 3inch. Mostly to help cool down the big block. Your thoughts?? Car sounds awesome now wondering if it will be too loud with upgrade to 3inch
3 in for yuge CID or power adder motor. Tends to B boomy sound and probably not cure of hi eng temps. Proper size rad , 3000+ cfm rad fan, correct AFR ,timing and correct vac adv on hiway should correct heat issue if motor good.
 

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Discussion Starter #9
Thanks everyone for the feedback. Motor is perfect. Its 70 over never overheats just gets a little warm in traffic. Thinking of putting a electric fan in it. Again thanks for the input
 

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Thanks everyone for the feedback. Motor is perfect. Its 70 over never overheats just gets a little warm in traffic. Thinking of putting a electric fan in it. Again thanks for the input
An electric fan is a great idea. In my opinion, for all practical purposes a 2 1/2 inch exhaust for street driving is far more practical. For a possible 10+ hp/torque gain at higher rpm, a quiet 2 1/2 " system far outweighs the increased noise and drone of a 3".
 
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