2 1/4 vs 1 1/2 inch exhaust?

My '73 Mach-1 has a mild 351c (headers, mild cam, intake, 4v heads). As for exhaust it has 2 1/4" all the way back with magnaflow mufflers. At what point is it necessary to change to 2 1/2"? Also, at what point will an exhaust system be too big?

The way I understand it... for high end horsepower you want the exhaust to be as non-restricted as possible. But for low-end torque, some restriction is good

The way I understand it... for high end horsepower you want the exhaust to be as non-restricted as possible. But for low-end torque, some restriction is good

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+1. It sounds like your engine is set up for mild performance. You want to be quick from stop sign to stop sign. 2 1/4" is perfect for that. You need a little back pressure to help with low end torque. If you had a high performance, full race engine, you want larger exhaust (2 1/2-3") to allow the engine to flow easily at high RPMs. I would stick to the 2 1/4".

Ok.. thanks.

4v heads? 2.5 inch.

I understand I am not using the 4v heads to their full potential. But they were on the car when I got it (not originally a 4v car). My future plans are a 393 or 408 stroker. Nothing to crazy. Maybe a Cleveland version on my 393w in my '68. Any way, that won't be for some time...

i have 4v thats more wild then mild, i made a 3"exhaust that narrows into 2.5 after the X, no problems with low end torque whats so ever...

Interesting.. if the back half of your exhaust is 2.5", then does the whole system flow like a 2.5" system?

well yes ,..when the exhaust gas is hotter it needs more room, the gas expands, so when it cools, it needs less room.

that was the idea behind my exhaust,.. i have no backing by dynotime or anything..

its just my idea of the fact that hot gasses expand , and cooler gasses need less room.., but i think that if the whole system is in 2.5" it wouldn't matter much,.., but since my headers are in 3" , i thought this would be the best of both , and that big 3" X looks pretty cool..

It does look cool.. I want criticizing your setup. I was just wondering.

no worries!

;D

What size headers are you using?

Well, that's sort of on the table.. I currently have a set of old rusted long tubes that hang down way to low. They hit everything. I'm considering a set of shorties from Sanderson. Unfortunately I don't know their specs.