1970 Firebird Exhaust Mufflers - What have you used?
 

Just finishing up the restoration of my 1970 Formula 400 automatic and need to decide on the exhaust mufflers. I decided to forego the transverse muffler and go with mufflers under the back seat, where space is limited. 400 engine has been stoked to 461 ci with stock intake manifold, original #13 heads (worked over), and repo RA exhaust manifolds (2.5" outlet).

Looking at a 2.5 exhaust pipe, H-pipe crossover, and will run all the way to back with repo ss tailpipes. Looking at a "flow through", street muffler design, louder than stock, but not ratty or obnoxious (this is of course subjective; everyone hears different). I'd rather error on a too quiet muffler than one that is too loud.

Muffler shop says longest muffler length that can be set is 16', maybe 17". Because the car sits low, looking for minimum muffler height.

Best fit so far looks like Spintech Sportsman, Dynomax Super Turbos, and Borla Pro XS. Also considering Different Trends, but there's not much info or sound bites on them.

I'd appreciate any input or experiences anyone might have on these mufflers or others.

Thanks

you will get all kinds of opinions on this. best to do a search as this subject has been covered numerous times. just browse through this exhaust section, there a couple recent threads on it.

my 72 firebird has a pypes 3" system that fits great & i used their race pro straight through mufflers for max flow. they are not "loud" by any means but some dont like them, others love them. so as you said, its all subjective to what one person likes vs the next.

race pros are about 1/4-21/2 thinner than dynomax ultraflos so they will tuck up a little better but are very similar designs. the superturbos will be very quiet at idle & cruise but they dont flow as good as a true straight through muffler. many other brands sound good as well but most cost a lot more than the race pros at $60ea.

search here for opinions & some vid clips, i posted a short low rpm burnout of mine, or search youtube for all kinds of muffler vids.

As much as the installation was a nitemare, and the splitter tailpipes are an absolute joke, I actually DO recommend the Pypes 2.5" transverse system from an appearance and sound perspective. I would look into them. There will be no ugly mufflers hanging down, and the sound is good.

I've done both, turbo mufflers under the back seat with full tailpipes and it droned like crazy on the highway, not at all pleasant to drive.

I also used a transverse muffler from a 87 buick turbo regal that other than being too narrow and needing some pipe extensions to mate to the Pontiac tailpipes with extension pipes, fit quite well and sounded good behind a modified 455 with headers. I made both systems out of 2 1/4 inch pipe and didn't feel it needed to be any larger, car ran really well, sounded good. I never worried about dragging mufflers over speed bumps either.

If I had to do it again, I'd go for the transverse muffler, same as 77 Canamman said.

I had mufflers where you're putting them, eventually, they were hit enought times to warrant replacing;
The sutup I liked the most was a 2-1/4" system with a custom 'X' pipe, and a Dynomax muffler (can't recall the number, iirc it was the one intended for the Buick GN/GNX);
It sounded magnificent.

I think it's more important to pay attention to the pipe size, and how the bends are made, than what many people lead on.
I chose 2-1/4", because I understood that to be original for my car;
I cannot recall what my car had before that.
The shop I went to did not have a mandrel bender, but the owner did the work, and took his time doing smooth bends, as opposed to the easier wrinkle bends - some bends took several tries to get it right (I watched).
I intended to do the crossflow muffler in a stock location, because I HATED the "wrong" location mufflers - they weren't super tiny, but they would often hit the ground.

I'd go for the much more refined transverse system that will not drone , relatively speaking, will sound good, not hang low, and it will the engine put out the power.
Tom Hand

Waldron transverse higher flow is what I bought for the '72 T/A.

Meant to write "it will let the engine put out power".
Tom Hand

1970 Firebird Exhaust Mufflers - What have you used?
 

78w72 - did you have any issues with droning in your Race Pro Pypes set up?

Pypes also makes a crossover muffler using Race Pro internals, but with what looks like only one additional exhaust flow turn (the more turns the more flow resistance) up to the cross-ways muffler than what you'd assume in a straight individual dual set up.

Thanks to all comments so far; as you know it is a learning process in getting to your vision of the finished car, but it will not be perfect.

not too bad at all for what the exhaust is... but just like muffler opinions, drone levels are different to each person & car. i have the 3" pypes system with an X pipe & full tailpipes, running big round port headers with 2" primary tubes & 3.5" collectors, so that really just makes the whole set up louder than a smaller set up would be with the same mufflers.

it has a slight drone at about ~50mph & 2100-2200rpm that goes away quick by 55-60mph & 2300-2400rpm. but it's not one of the resonating through your ears type of drones where you can't have a normal conversation or hear the radio at normal volumes, to me thats real drone. ive heard what are supposed to be quieter mufflers like turbos have bad very bad drone in lower power cars. my dad used to own a 70 maverick brabber with a little 302, it had headers & probably thrush type or some other cheap mufflers & it would drone so bad at idle or low rpms it would make a oscillating, reverberating sound that made your ears feel weird!

my car is actually very quiet for the system & 500+hp at idle, & normal cruising or city driving, but when you step on it it really comes alive. i like the race pros a lot & for the price they really cant be beat for full flow performance, there are many other mufflers that will sound better, if sound is the main concern.

I run the Pypes setup on my Formula with the transverse race pro muffler. No drone, sound level isn't bad at cruise but it does make a little noise at full throttle, again nothing overly terrible.

https://youtu.be/er1z7PpqsnY

Plenty of pure stock class cars running well into the 12's and even 11's with this system, and if I remember right, the FAST class has a couple in the 10's with this system. So it has ability to support some HP.

I've actually had 3 different transverse systems on this car over the years. Pypes has by far been my favorite and best fitting.

If you want to look into something cheaper, quieter, and you want an "H" cross over rather than the "X", I'd go straight for the Dynomax transverse system part number 89021

1970 Firebird Exhaust Mufflers - What have you used?
 

Based on the comments, I am opening up to a transverse muffler, especially if the muffler's exhaust flow benefits the upgrade work put into the engine. I am also looking at lowering the car later 2-3 inches.

In addition to the Pypes MVR100 SS unit, Dynomax has Ultra-flow Welded X cross-flow muffler, where the inlets and outlet locations more match the original transverse muffler. It's hard to tell in the sound bites, but it seems quieter than the Pypes with a low throaty rumble.

Anyone know how the Dynomax Welded X cross-flow muffler flows or have any experience with it?

Yes I have used it. It's designed to put in place of the stockish Dynomax muffler for the system I gave a part number for in a previous post. That Dynomax system (89021) uses the stock style inlet and outlet pipe design.

Which is why the X crossflow Dynomax muffler will not work on a Pypes system, since Pypes changed the in and out locations in their design.

The X crossflow muffler is a bit louder and deeper sounding than the Dynomax muffler the 89021 system comes with.

I have the Pypes 2.5 " X pipe set-up with the Race Pro muffler on two of my cars and totally love it. Great stockish sound with a bit more nasty.
Keep in mind there are some older youtube videos featuring the sound of the older Race Pro design. I'm not sure exactly when the Race Pro was redesigned - maybe 6-7 years ago however the sound of the current version is greatly improved over the previous version.

The video I linked to in post #11 is the Pypes transverse with the racepro designed muffler. I put that system on a couple years ago.

Actually just put another one on another 2nd gen that I restored just a few months ago here..... They have a nice bark to them outside the car, but inside the car they are pretty darn quiet, and no drone.

https://youtu.be/AOqwz3QlO5k

https://youtu.be/Iesvy0R3isA