Muffler question

[Danno]

I have a '72 302, 2v with a stock single exhaust that needs rplm't.

I plan on going to a dual set up and using Flowmaster 40's like I had on my '66.

I am hoping to save a few $$ by buying the "H" pipe and mufflers online.

I "think" I need a 2 1/2" system, but what configuration of inlet and outlet connection is best on the mufflers, center offset or what?

 

[Mikes73]

I am pretty sure you want a center inlet and offset outlet on the mufflers.

 

[c9zx]

The information I have shows offset inlet, center outlet. If you want to use the factory hangers you'll need to buy or fabricate mounting points on the mufflers. The only source I know of for the mounting points is http://www.scottfullerreproductions.com/NewsandUpdates.html

Chuck

 

[jeff8877]

I used these guys for my 73 4V and couldn't be happier. Complete system out of the box and bolted up directly to stock hangers. Mufflers already come equipped with brackets to bolt on hangers.

http://www.precisionexhaust.com/

 

[Dave73]

You don't need a 2.5" system untill you're over 400 HP. The exhaust size is determined on HP not displacement.

Center in offset out is what I have under mine. 2.25" with true X pipe.

 

[Totalled]

Yeah, your car may be a good candidate for a stock style reproduction system. Just going single to dual will be a big improvement in performance and sound.

 

[luxstang]

If you go too big you risk drone frequencies without any gain in power, so I´d stay with something a little smaller.

2.5 is a bit much. Mine used to have a 2 inch one that was nice and quiet with the Edelbrock mufflers and the long tube headers (and the 351 Windsor). Now I have 2 1/4 inch system with the same mufflers and shorty headers and I have a very annoying increase in noise with some bad drone frequencies at several rpms without any noticeable increase in power whatsoever. I wish I could go back to a 2 inch again.

With a 302 you will definitely not need a 2.5 inch one. 2 inch will be sufficient.

 

[Don C]

+1, for a 302 2V a 2-inch dual exhaust is plenty.

 

[Dave73]

WOW that's awesome guys. I expected to catch grief on exhaust size.

Mine had a 2.5" with 40 series flow masters. 4" chrome trumpets on the ends as if it was a truck.

It was super loud. And a loss of low end power.

The exhaust flow must fill the pipes completely for the right velocity. Too big and there is turbulence at low rpms.

Think of your exhaust like it's a garden hose. Wide open end and the water just falls out. Pinch it off just 1/4 and it shoots out more rapidly and more GMP flows out. In exhaust terms that's a scavenging effect.

You could do 2.5 right off the headers to X or H pipe, and make the X or H pipe drop to 2.25 on the exits. Creating a tapered effect and that can scavenge. (helps pull exhaust away from the cylinders.) As it leaves the headers it is at it's hottest point and greatest expansion point. As it flows through the pipes it cools off and takes up less space. I been doing this for years and just recently saw it done on one of the car build shows. I forget which one.

Also.... if you want more quiet then make a true X pipe. Not 2 elbows with holes and welded in the middle (most pre made x pipes) If the X is made right the sound waves will cancel each other out until you reach higher rpm's. MIne is super quiet untill I stomp on it. Or you can make a V baffle and insert it in to the middle of the pipes. I did that on a Monte Carlo. Basically made my own resonator. Use a 2.5" section and make a V baffle and weld in to the middle. then put 2.25 reducers on each end. Viola! Resonator.

It seperates the sound waves and causes them to slam back together canceling out at low rpm's.

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[Kit Sullivan]

A stock '72 "F"-code 302 will run great with a 1&7/8" dual exhaust set-up, even if you switch to 4-barrel. The smaller-diameter head-pipe will give you a very noticeable increase in low-end torque. Most definitely no bigger than 2".

Oversizing the exhaust...one of the "rookiest" of all rookie mistakes.