Hello all,

Looking for recommendations on exhaust for my 71 442. I had planned to go with stock exhaust sizes which I believe are 2 1/4" head pipes with 2" tail pipes. I have read that BBO thrive on the back pressure. I already have a set of the OEM trumpets, but that's the only parts I have for the exhaust so far. Now I am second guessing this decision. The engine build is as follows:
1971 Olds 455
Stock heads
Pistons 30 over and 10.2:1 (Wiseco PTS537A3)
Erso Cam specs:
.542/528 lift
Duration @ 0.006" is 283/287
Duration @.050 is 229/234
LSA is 112

I have two questions:
1) How much more would the engine benefit from larger exhaust, performance wise?
2) I am looking for an aggressive sounding muffler but don't want the interior drone noise. I am thinking about using the flowmaster super 40 mufflers. Is this the right choice? Is anyone else using a set of these on their BBO, who could weigh in on interior noise?

 

John, you have a rather aggressive cam. Back pressure will prevent it from emptying cylinders and the overlap will allow reversion. Both these will decrease your power.

3" exhaust is more difficult to silence, you may find it too loud. 2 1/2" is a compromise between too much back pressure and too much noise.

 

I’d go 2- 1/2 inch with almost anything but flow master mufflers. Nothing wrong with flow master mufflers, but you said you don’t want drone.

I have Dynomax Ulfra flows on my 69. They have an aggressive sound, but are quiet enough to conversation in the car without yelling. Generally, the bigger the muffler, the quieter the sound.

 

So you're saying 2 1/2" for the head and tail pipes? Do they make the factory tips for that size?

 

Pypes makes 2 1/2 trumpets.
That cam isn’t very big for a 455 but 2 1/2 from the collector back should work just fine. I’d also consider an H pipe to smooth it a bit.
And Flowmaster 40 series wont be quiet. I’d use either a three chamber Delta 50, Dynomax long case Turbo mufflers or Magnaflows if you’re looking to keep the noise level and drone in check.

 

I run 2.5" mandrel bent pipes into Dynomax 17749 Super Turbo mufflers using W and Z manifolds.

This system has a nice rumble to it, noticeable but not excessive.

No drone at cruise, and it is the perfect muscle car sound,

 

I responded to a similar question recently but will repeat here. I have a '69 442 with modified 400G.
Downpipes: Pypes 409 stainless 2.5". Good quality. Work perfectly with either manifolds or short tubes (see below).
Full system: Flowmaster 'American Thunder' 409 stainless 2.5". Mandrel bent with an H-pipe. Fits great. No cutting and tucks up nice throughout the car.
Trumpets: Pypes 2.5" ('Pypes' is engraved on the top but you have to look pretty close to see it. These are polished stainless (good) and not chrome plated steel (junk).
Mufflers: Flowmaster 40 (came with the American Thunder kit). I like the sound. Not nearly as loud inside as you'd believe listening to what everybody says about them but, if you're looking for quiet, look somewhere else.
Manifolds: Was running the original W/Z manifolds but recently switched to Thornton's short tube headers. No noticeable performance benefit. Interior noise actually seemed to go down slightly after the swap. These are also stainless and very good quality.
With your set up I wouldn't even consider going less than 2.5". 409 stainless is a good compromise in material. Cheaper than 304 (not quite as good for corrosion) but much better than aluminized steel.
Hope this helps.

 

I have a 3" SS complete exhaust system for sale.
$750.00
Stainless Steel headers 1 3/4 tubes thick flanges 3" collectors ( Mondello ) No dents.
3" 304 SS Flow master 40 series H- Pipe system.
Cut and welded for a 69 cutlass.
Ball connectors at headers and after H pipe to muffler /tail pipe for quick disconnect
(2 headers, 1 H-pipe, 2 mufflers and tail pipes)
Like new

 

I went with American Racing headers, x-pipe, Hooker aero chamber mufflers, 3”
mandrel bent pipe all the way out the back. It sounds pretty good. Not super loud but not quiet either. I had 40 series Flowmasters before, I like the aero chambers better.

 

No engine "thrives on backpressure".

 

Maybe thrive was not the correct word to use, but at least benefits. I really have no idea how all the modifications effect performance, but I do try to read up as much as I can. I really appreciate all the help you all are giving me. Thanks everyone!
Just out of curiosity, can anyone ID these mufflers? They are on my other 71 442. The one I am second and fourth owner of. The third owner put these on while he had it. Originally I put the Walker muffler for OAI 442s on it and really liked the sound of those, but I've been unable to find the part number for those to even start looking for them again. The mufflers in the pictures are approximately 14" long, sorry didn't have a tape measure handy. Thanks again for all the help!

 

No engine in the world wants more backpressure as opposed to less. That's an old wives tale that refuses to die, like HV oil pumps sucking the pan dry or headers won't fit Supremes. It the engine wanted backpressure, racers would make more power with mufflers than without. Guess what?

 

Thanks for clarifying Joe. When you put it in those terms it makes perfect sense.