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2 G or not 2 G, there's no question!
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Randy, wouldn't that be rahp (rear axel horse power) since you didn't have your wheels on when you dynoed?

 

you're right Neff...that's why I mentioned in an earlier thread that the #'s were a little dif cuz it was taken at the axle...probably more like 365 with my 19's

2 G or not 2 G, there's no question!
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Wheels make no difference on dyno numbers. Just takes you longer to spin them up to speed. I dyno'd with the stock whel and the 19's and theres no difference in HP, just how long it takes to spin up to 60-80, whatever your trying to get to, basically your 1/4 run slows down, but your putting down the same Hp.

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Inertia my friend... increasing rotational mass ALWAYS decreases horsepower. There is no way around it. That's why they've invented Carbon Fiber Drive Shafts, Magnesium wheels, etc... for racing applications.

 

I think what Jim is saying is that lighter components don't add HP, they just increase the amout of time it takes to do the same amount of work. Meaning acceleration of components slows when they are heavier, but they will still arrive at the same speed eventually. As I type this I have to think that there's got to be some affect but I understand what Jim's saying.

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Jim, I don't believe you are right, but Clint will have to tell you why...something about center of inertia(sp?) or something.

2 G or not 2 G, there's no question!
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Well my dyno numbers prove my point.


Stillen Stage 2 Supercharger, Stillen Front Bumper, Stillen Carbon Fiber Hood, Injen SES Cat-back Exhaust, Injen Cold Air Intake, 19" Axis Hiro Anthracite, Clear Corners

 

G35spot certainly has the right idea. The amount of horse power at the engine remains the same regardless of what wheel/tire's used. The wheel/tire mass (and the entire drivetrain for this matter) will effectively rob power as seen by the tire to the ground (what really matters), however.

With that said, it all gets right down to how fast you ramp up to the redline. On a DynoJet in 5th gear, the ramp up time is relatively slow, so the wheel mass moment of inertia doesn't account for a very significant difference in the equation. If one were to dyno in 1st gear, where ramp up time is very short, the wheels mass will have taken a larger effect.

The beauty of a Dyna Pack Dynamometer is the omission of the wheel/tire vairable from the equation completely. That's one less thing to have to worry about, especially when it's one that very tricky to deal with.

With respect to the Dynapack numbers posted by Randy, it is effectively the output at the rear axle not flywheel. The DynaPack software is poorly worded. It has provision for the actual torque and power extered to the hydraulic brakes (measuring device). It than converts the values by multiplying the overall gear ratio and calls it the 'Flywheel' output, when in fact it is not accounting for driveline loss. A small technicality, but a very annoying one. Instead, focus on what his before and after numbers are. That different between the two numbers shown is where the meat is at and is not subject to accuracy issues (relatively speaking).

I hope that helps.


Clint (THX723)