It's not just about pure flow rates, but also about exhaust turbulence. Flowmasters are basically the worst type of performance mufflers as far as exhaust turbulence goes. Compare the internal design of my Hushpower II's (basically two perforated cones) or a set of Magnaflows or Dynomaxes (straight-through perforated tube with fiberglass packing) to the design of a chambered Flowmaster.

No, you're probably not going to notice a difference (especially if you have stock 289/302 exhaust ports), but I'd like to think every bit helps.

 

I don't see how Flowmaster creates turbulence from the diagrams I have seen of them. To me the perforated baffles seems to me like it is going to create much more turbulence that the traingle baffle in the Flowmaster. Doesn't Flowmaster make Hushpower II?

 

It all sounds great, you guys, but keep in mind I am asking about mufflers for a 1967 mustang coupe with dual exhaust!!!

 

You never said how loud you wanted it to be? Are you looking for mild V8 sound or loud etc?

 

Yes, Flowmaster owns Hushpower, but they're an entire different division than the normal Flowmaster muffler line. Hushpowers were computer designed using some really complicated thermo and fluid dynamic concepts that decrease unwanted sound (especially any droning) and increase exhaust flow rates. Some of the race mufflers actually flow better than straight pipe.

Go here for more details.

Standard chambered Flowmasters were designed purely for sound. They flow terrible. If you run exhaust gas into a wall, it's going to back up. It'll go around eventually, but it creates all sorts of turbulence in the exhaust stream.

 

What do you guys think of the JBA side exhaust kit?

We are getting close to ordering a new exhaust and im split between spintech and JBA.

 

TX65coupe--

Would like something loud but it concerns me that there is "droning" inside some of the items discussed. What do you think about the hushpower and what do you think about the flowmaster super 40.

Some guys think that the flowmaster does not present itself well and does nothing to upgrade the power/in relation to the Doug Thorley headers I will have in it.

I hesitate just because I want to do this right and put in the correct thing once.

 

check the manufacturers website they typically have sound/video clips of the exhaust system. I've got the FLowmaster Super 44's and they can definately drone @ cruising rpms. I still love them tho. I dont cruise much so it doesnt affect me, plus im 18 so i can hear it all. I love the aggressive tone to the flowmasters but if you're looking for a system thats still respectable in both tone and quality I would say go with magnaflows. Just my .02

 

Wow i was in the same situation myself, haha FM 40s for me.

 

The Hushpowers are expensive. Keep that in mind if you're considering them. I absolutely love mine, but they're pricey.

My setup (331 stroker, full length headers, 2-1/4" pipe, H-pipe, 2-1/2" Hushpower II's, full tail pipes) resonates very slightly inside the cab at about 2k rpm under load. I don't really spend any time at that rpm, so it doesn't bother me. With better sound insulation, it wouldn't be there at all. As is, it's still a lot better than most cars I've been in with 40-series mufflers. And side by side with any chambered muffler, I'd choose the Hushpowers any day. More even tone, less raspiness, and an absolutely wicked sound at WOT all the way to 6k+.

Poke around on youtube and find recordings of classic mustangs with different mufflers. I'm sure you'll find something you like.