Exhaust system?

[Jesse83]

So I have a 350 out of a 85 bored 30 over with 196 heads and I was thinking about running a 3 inch exhaust on it but I had a couple people tell me that was to big so I was wanting some extra advice ( I have a few other things on it so it's running about 380-395 hp)

 

[Honky Kong jr]

I say 2.5" maximum.

 

[SkinnyG]

Single 3" or dual 2.25 - 2.5"

 

[1987 GMC Jimmy]

I think a lot of the naysayers have to do with believers in necessary exhaust back pressure. I don't know if I'd feel comfortable with exhaust that big, but I honestly don't know how much it'd hurt you if any. If it were me, I'd just put 2.5" and call it good not because I subscribe to exhaust conventions but because I know it works.

 

[Jesse83]

Alright thanks guys I think I'm gonna go with dual 2.5 exhausts

 

[87silveradok20]

I have dual 3" on a stock 350 and I don't notice any loss in power


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[spanky55amg]

I do not have any experience with older carbed engines. All of my knowledge is newer FI stuff, specifically LSx.

The difference between 2.5 2.75 and 3 was more hp/torque as you went bigger. Now, when you go 3.5 is when you started not seeing gains.
You dont need back pressure unless you are running a turbo.

You're only looking at price and sound difference. (I assume you are running headers also, if not, then you dont need 3 inch.)

 

[SkinnyG]

Engine Masters (YouTube Motor Trend Channel) did a test on 2.5" vs. 3" exhaust

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[hirschdalechevy]

Great video , thanks skinnyg

 

[4WDKC]

So I have a 350 out of a 85 bored 30 over with 196 heads and I was thinking about running a 3 inch exhaust on it but I had a couple people tell me that was to big so I was wanting some extra advice ( I have a few other things on it so it's running about 380-395 hp)

What do you have done to make it almost 400 HP?

 

[Jesse83]

It was actually my dads and he gave it to me and told me a some of the stuff him and my grandpa had done to it but other than what I had said on here I know he put a rv cam in it the crank and rods resized and that's about all I remember off the top of my head but my dad and grandpa had about 1700 or 2000 dollars in the engine

 

[MikeB]

I kind of doubt 3" instead of 2.5" will make much difference behind a 350 at anything but WOT at high RPMs.

The main restriction behind the headers is the ID of the mufflers' internal pipes. The least restriction is achieved with a straight-though design with same (or larger) internal pipe ID as the exhaust pipes. Just because you buy a 2.5" muffler, that doesn't necessarily mean the case and internals are any different than a 2" muffler. For example I have a pair of 2.25" mufflers that neck down to 1.75" internally! Of course I'm not using them behind my 350, but they might work OK with a 265!

Another note: Use mandrel bends if possible. Crush bends used by muffler shops will effectively turn a 2.5" pipe into a 2.0-2.25" pipe.

 

[MikeB]

It was actually my dads and he gave it to me and told me a some of the stuff him and my grandpa had done to it but other than what I had said on here I know he put a rv cam in it the crank and rods resized and that's about all I remember off the top of my head but my dad and grandpa had about 1700 or 2000 dollars in the engine

Sounds more like 300 hp, just FYI.

 

[Jesse83]

Ah alright thanks