I just read an interesting article at Autoblog.com(
In the Autoblog Garage: 2008 Ford Shelby GT500 Mustang - Autoblog ) comparing the Mustang Bullit to the Mustang GT500. Some interesting insights. The GT500 is quite a bit heavier (3900 lbs) than the Bullit and has about 185 more horse (4.6 Bullit vs 5.4 blown V8). In the 1/4 mile it's just about a second faster, BUT on the 'street' the difference is NOT substantial. The GT500 is traction limited, something Cobra owners know about all to well. If you can't hook up, your wasting your time and your money. Extra power translates into a higher trap speed and lower ET IF you run a measured 1/4. Hole shot or stop light to stop light? No difference to speak of.
Small block 302's would almost always get the 'hole shot' on me at the strip. That would give them 'hope' just before I blew their doors off.
I was astonished when I rebuilt my motor and gave up an estimated 150 horse. You can MEASURE the difference in accelleration and trap speed at the race track, but on the street? I can barely tell the difference at all! Before: 11.90 with open headers, after 11.99 WITH the side pipes on! I never got a chance to run open pipes at the strip with the new motor before they closed it down. I bet I would have been right back in the low 11.9X range.
MPG doubled, streetability vastly improved, I'm a happy camper.
Was 667 flywheel horse on the dyno. Now, I GUESS around 500 horse, which seems to be just about optimum for a set of Goodyear Bill Board tires, which still spin. Slicks would no doubt make a big difference.
Who needs a dyno?