[Formulajones]

Can you explain that test a little more Lee? From the description it appears that you also increased the front head pipe size to 3 inch when you swapped to the race pro muffler?

I have only one car here left that I have flowmaster mufflers on. I run the Super 40's on my chevelle, don't even think they are made anymore.

Yes they are loud, it does sound good, some drone, but I don't drive the car regularly, I only bring it out when I'm in the mood for noise. The car goes mid 11's at 118 mph with them through a complete 3" system with tails. So they either aren't as bad as portrayed or I'm leaving a bunch of power on the table, lol.

Most of our cars here I prefer things a little quieter though, and at some point I may swap out the 40's for a pair of Dynomax ultra flows, not looking for a performance gain, just may want to tame the noise down a bit.

[Lee]

Originally Posted by Formulajones

Can you explain that test a little more Lee? From the description it appears that you also increased the front head pipe size to 3 inch when you swapped to the race pro muffler?

I have only one car here left that I have flowmaster mufflers on. I run the Super 40's on my chevelle, don't even think they are made anymore.

Yes they are loud, it does sound good, some drone, but I don't drive the car regularly, I only bring it out when I'm in the mood for noise. The car goes mid 11's at 118 mph with them through a complete 3" system with tails. So they either aren't as bad as portrayed or I'm leaving a bunch of power on the table, lol.

Most of our cars here I prefer things a little quieter though, and at some point I may swap out the 40's for a pair of Dynomax ultra flows, not looking for a performance gain, just may want to tame the noise down a bit.

The previous exhaust on that car had reducers necking the pipe to 2.5" going into 2.5" FM's. I replaced the mufflers and headpipes, going 3" through there. Tailpipes remained the same. No other changes at the test. I later retuned the carb and gained more power.

That same car had felt "flat" at upper RPM as well. It had been to the track, and would leave HARD. It would take other cars off the line, but by half track would fall behind, running bottom 13's around 102mph. It wasn't until I put it on the chassis dyno that I suspected the mufflers. I suspect the mufflers had baffles that had rusted/moved with age, even though they still sounded the same.

My '67 Firebird ran a best of 11.38 at around 118.7mph with 3" FM's. I replaced them with Goerlich large case mufflers. Car was MUCH quieter. Back at the track it ran 11.27 at nearly 120mph, no other changes. Sold the car a few weeks later.

On my current low-compression, low-rpm 455 in a '73 T/A-clone project, I previously documented the exhaust changes and performance gains. Although head and tail pipes were changed in it, so not as clear cut on where to assign the gains - although I'm rather confident the gains were mainly in replacing the FM's with Borlas.