1999Cobra to 2003 Cobra

Rickyll7 said:

good point to the both of you.
however, when you spin the tires, it is because of your peak torque! a kb and a centri blower will have very similar peak torques. the kb just maintains it at lower rpms.
that said, imagine a kb with "x" peak torque and a centri with the same peak torque, both with approximately the same peak hp. (very possible)
if you assume that the peak torque measured isnt enough to spin the tires on either car,(both exact same cars except blower)

the kb will win. hands down, also assume same driver... etc, etc...

edit:
(it is possible for both cars to have the same peak torque and hp, not that they always do! that would be a completely different story and defeats the purpose of comparing the two for the sake of low end torque."

Click to expand...

Actually, I think you're confusing the issue a bit. Peak Torque isn't what spins the tires. It’s the power under the curve that breaks the hides loose. Your Peak Torque/Horsepower is the highest figure made across the board, which in most cases comes in between 4,000-6000RPM depending on the set up. Not matter what you drive, peak figures don't come on until later on down the line. As much air as Positive Displacement supercharger moves in a single revolution, even it needs to ramp up some first in order to sufficiently pressurize the motor. Peek boost levels on the other hand come on nearly instantaneously with a PD blower, which is why the Kenne Bell comes on that much under the curve and why your able to feel it down low.

That being said, you could always change the pulley ratio (smaller blower pulley) of the Centrifugal in order to increase maximum blower RPM. A byproduct of this is that airflow levels at all RPM come on that much sooner all the way through until redline (to an extent), at which point the excess could be bled off with some sort of secondary waste gate system (like hotmustang331 stated) in order to keep cylinder pressures manageable. Good idea in theory, but you’ll eventually run the blower out of it’s efficiency range (which again creates unwanted heat), causing horsepower loss (again as previously stated). Not to mention problems with excessive belt slippage.

The same principal holds true of the Positive Displacement blower. The main drawback with them though, is that they’re even more susceptible to heat than the Centrifugals. Run them too far over, or under their peak efficiency level and they succumb to elevated ACT’s. When ACT's go up, timing is pulled and fuel is added to keep things manageable, but cut power making capability in the process. That's why as fat as the torque curve is, horsepower curves tend to mellow out on the top end with Positive Displacement blower in comparison to a Centrifugal when the temperature starts to rise. Each blower is simply just designed to perform differently and move different amounts of air at different RPM.

Regardless what the dyno sheet states, I've seen results of Positive Displacement blown cars get whipped at the track by Centrifugal Cars making much less torque under the curve because either the driver of the Positive Displacement blown car was unable to put the power to the pavement, or the Centrifugal cars horsepower levels continued to climb more aggressively up top and was able to run them down. I've also seen Centrifugal blown cars that made more peak horsepower get beat by Positive Displacement cars because the PD blown car got out first and they weren't able to close the gap between the two before running out of track.

There’s really no definitive winner between the two as far as the horsepower or quarter mile performance goes (regardless of what some may think or try to promote). You’ve really just got to your system based on cost, driving style, ease of installation and “bling” factor.