I have them on my '69 ... they're also known as Dynomax Race Turbos. I have them behind a 408 roller stroker with Hooker Competition headers, 3 1/2" mandrel bent exhaust with an H pipe.
At idle, the car is very mellow, but sounds sweet. Under "normal" driving they are moderate loud. Give it some throttle, and heads turn a block away at the sound. 70sportsroof took a ride with me a couple days ago and he likened it to more of a NASCAR sound. They don't sound like all the Flowmasters out there. To me, they sound like pure '60's Muscle Car.
At freeway speeds, like the rest of the Dynomax mufflers, there is not the annoying Flowmaster drone, either.
I HIGHLY recommend these mufflers to anyone looking for a unique sound behind a performance build.
Ultra Flow and Race Turbos? I believe they are two different models of DynoMax mufflers. see: http://www.dynomax.com/mufflers.stm I think the race turbo model is superseded by the super turbo.
I had race turbos on the 70 when I lived in MI. Since my driveway was next to my neighbor's bedroom window, the exhaust echoed between our two houses and woke them up every A.M. I changed to Flowmaster 3 chambers to quiet down the exhaust for them.
JohnPro's 408 sounds great ahead of the Dynomax mufflers he has. It sounds a lot like an X pipe exhaust, although I think he is running an H pipe.
Negative. If you look at the link you provided, the Super Turbos are listed underneath the "Ultra Flow". The Super Turbo is what I have on my '66 and son's '69 and they are very different from the Ultra Flow. When I went to the exhaust shop, they couldn't understand what I was talking about when I would say "ultra flow". The exhaust shops know them as "race turbos".
The Ultra Flo's (yes, that's what they are called) are louder than the Super Turbos (yes, thats what they are called). The Ultra Flo's have a straight thru design, while the Super Turbo's do not. The difference between the 2 Ultra Flo's is the construction (welded/aluminized vs. SS non-welded). I have a welded Ultra Flo on my F150, and SS Super Turbo's (prototypes, not available in SS) on my Mach. Both sound awesome. Super Turbo's are probably the way to go. Oh yeah, I'm a designer for Tenneco (Dynomax).