Pypes Race Pro muffler replacement
 

Hi,

I have the Pypes SGF70 exhaust system with the Pypes Race Pro muffler on my 68 firebird. It is a straight through muffler (dual input/output with 1 input coming in top left, with top right exit, 1 input coming in bottom left with bottom right exit). Unfortunately, the Race pro muffler produces a resonance at idle RPM that is driving me crazy (higher RPM sounds good). I would like to replace it with a Dynomax or Magnaflow mufflers but the only ones I came across have a built in X-pipe inside the muffler. Can I use one of these with this setup? If not any recommendations on what I could use?

Magnaflow 11386
https://www.summitracing.com/parts/m...SmLM3dB6moHM1V

Dynomax 17553
https://www.summitracing.com/parts/w...HbhqauxXFQleJv

I'm not sure what the dimension differences are between the mufflers. There could be a bit of pipe fabrication needed to do that. As far as the mufflers having an X in them, that functionally won't really matter. It'll change the sound a bit compared to your Pypes race pro muffler.

What you might look into is adding resonators to the under-carriage piping.

Both the magnaflow and dynomax mufflers are a straight through packed muffler, just like the pypes race pro. The internal X design probably does a bit better job of reducing decibels at idle over the straight through design of the race pro muffler, but if it's a resonance issue you are experiencing, it's possible that all of the mufflers would cause the same issue.

Resonators, by design alter the tone of the exhaust note and are there to reduce buzz, raspiness and drone. If you like the way the current system sounds everywhere but idle, resonators are probably what I'd do over a muffler change.

The one issue with the sgf70 is pyoes cross flow muffler design doesn't follow the traditional cross flow design of the in and out configuration.
So that means the intermediate pipes and the tailpipes are all bent specifically to fit their muffler in and out configuration.

All other transverse mufflers have your more common configuration. Both inlets usually in The bottom and both outlets in the top.

With that said I'd suggest what jlmounce mentioned, adding a pair of resonators, and/or possibly using the factory hanger setup if you haven't already as some of the generic aftermarket exhaust hangers do tend to transmit more noise.

Headers with Pypes X-Over on 455. I had to change my Magna Flow to Borla (ProX pn 40352) for clearance. The Magnaflow had some resonance but tolerable. The Borla sounded great but a bit more resonance. I added the Vibrant Performance Resonator pn 1793 just behond the headers. Problem solved for my set-up.

76TA462- did you go with the 4" or 5" OD on those Vibrant resonators?

I ran through this with my 68 FB convertible.

2.5" X pipe kit had straight through mufflers - Drone was horrible
I changed to Dynomax ST - Still Drone

Unfortunately the muffler that fixed the issue, Dynomax doesn't make any more. I used the Dynomax VT muffler and they still work great for me.