Does anyone have some practical information on a proper header size and exhaust system for a stock 1969 L78 with M20 and 3.73 axle for good performance up to 6000 RPM? I want a low restriction exhaust with a minimum of interior resonance. Suggestions? Equal length? True dual? Any transverse mufflers worth considering?
I would appreciate responses based on real information and/or experiences, not magazine article advertising.
Thank you very much.
Bob Telep

Starting this off is all here..............

I figure a lot of the guys will agree that a set of 1.75" to 1.875" four tube, long headers THAT FIT are fine for applications up to a 496 STREET motor!

Certainly 1.75" are FINE on a 396/402 motor, imho..

Bigger ones have their places if the engine combination needs them??

But I think think that bigger ones do give up lower and midrange torque at the expense of higher rpm hp sorta deal...

pdq67

PS., I put cheap 1.75" four tube, long Heddmans on my 496 b/c I built it for max. midrange grunt up to 5500 rpm is all.

My buddys 67 w/396 specs real close to L78 with 4spd and 3:73 gears runs mighty strong with Hookers comp series 2" tubes 3.5 collectors. And so does his brothers 69 chevelle with a bit bigger cam and automatic and 3:73's, and this motor sees 7k regularly and pulls from start to finish.
I installed the same on my 71 with 468bb and 373's and auto and couldn't be happier. The smaller tube headers will work fine for mid grunt but I've noticed a difference and I think with the lighter camaro body it won't really make a difference. So go 2's

RandyB..

I agree with smaller is better on the street. If your going to muffle it you are only hurting engine operation below 4000 RPM with big tubes, which less face it, is were the engine spends most of it's time. Long tube equal length competition headers don't come with collector flanges to hook up exhaust for a reason.

That being said, to minimize interior noise put money into insulation and isolating the exhaust hangers. With tail pipes out the rear you won't hear much inside so I would go with the most free flowing and include an X pipe as close to the end of the collector as is practical (Remember the trans has to come out, and the engine has to be able to move. I say this because many muffler shops will weld up whatever you ask them to do, and charge you again to fix it right when you come back.)

Muffler brand loyalty is a matter of personal preference. I suggest you hang out at a couple of car shows and ask the owners of cars you like, what they have installed. Otherwise there is nothing better than a pair of 3" Flowmaster Delta 50s for a BBC.


Larger Dave

Rodney Davis of Headerdesign.com thinks you should have 1-5/8" x 36" primaries, 2-1/2" x 14" collectors.

Pipemax Pro figures:

1-3/4" x 42" primaries with a 3" x 22" collector

Jack Burns would probably recommend the smaller ones.

Ed Henniman would probably figure that a 2" primary tube was a 2 tube size error.

Wow! This is my first post and I didn't expect such good responses so quickly. Thank you all for taking the time to share your experiences. I will start with the 1 3/4 tube size, and move up as necessary if I make any engine mods.

I'd measure your exhaust port and size your headers accordingly.

1 3/4" for sure. 396 need all the help they can get w/torque. I have 2" and as a result (one of the reasons) my bottom end is soft. Heck, most 454 guys suggest 1 3/4".