I originally installed the full Flowmaster American Thunder kit on my 69 Z/28. That's the 2.5" inch mandrel bent kit with 40 series delta flow mufflers. I am connecting the system into Thorley tri-y headers. Motor is a nicely built 383.

I was pretty happy with the system, install was a breeze. The sound was good, but a little too loud for my taste. People could hear me coming from quite a ways away. There was some interior resonance too. So with Dynomax offering a $20 rebate on mufflers, I decided to pull the trigger and get some welded UltraFlo's. I got them on today, and there is a noticeable difference. In the car it is much quieter. Even with the windows down I can talk to a passenger in a normal voice. At idle, it's pretty quiet unless you are standing directly behind the car. At wide open, though, they are just as loud as the Flowmasters. I can't judge any power difference, seems about the same.

I bought part# 17219, the fit was exactly the same. Well, that's enough rambling from me. Overall I am very pleased with the switch. I didn't hate the Flowmaster sound, but I have to say I like the Dynomax's much better. Just my $.02.

-Marc

I can understand what you're saying about the flowmaster, the problem with the american thunder kit is that it comes with the 40 series muffler and they're a bit too loud at least for my taste as well. Skipped buying the american thunder kit just because of them coming with the 40 series. Instead, I bought some 50 series 2.5" flowmasters and had a local muffler shop fix me up. I absolutely love the sound. It has a deep "big block" sound to it, yet still has the sweet flowmaster tone to it and wide open throttle, certainly lets folks know your coming. At normal cruising speed, it still is fairly quiet in the car. The only problem with the 50 series is that it's a bit longer than the 40 series and the muffler shop had to install them at an angle.

I'm glad your happy with the dynomax mufflers, I haven't heard what those sound like but will keep my eyes open to find someone with a set. One downside to the flowmasters is it seems like everyone has them, so going with something a bit different with a good sound to it sounds okay with me...

lakemg - you can hear them at my site here: http://www.1970chevelle.net/muffler.mov

I absolutley love them plus I gained over .3 at the track compared to the flowmaster 40's I had. I love the Ultraflows!

Lee

------------------
My WIFES'S 1967 ZZ502 Camaro 11.11@122
<A HREF="http://www.1967camaro.net" TARGET=_blank>http://www.1967camaro.net
</A>
ZZ502 Chevelle 12.26@115
http://www.1970chevelle.net
13 Second Yukon 4x4
<A HREF="http://www.blown4x4.com" TARGET=_blank>http://www.blown4x4.com
</A>