[Vettezuki]

Originally Posted by enkeivette

. . .
???
. . .

Que? Are you wondering how I came up with 485 -> 557 HP?

[enkeivette]

Yes indeedio.

[Vettezuki]

Originally Posted by enkeivette

Yes indeedio.

The following is my current (and hopefully sufficiently accurate) understanding:

Torque is a force that tends to rotate.

Work = Force x Distance

Horsepower is a unit for measuring the rate of doing work.

1 HP = 33,000 foot pounds per minute. (There's an interesting history to this number. Look up horsepower on "How Stuff Works".)

Therefore we derive HP thusly.

HP = Torque (in ft/lbs) x RPM (how many "times" the force is applied in a minute) / 5252 (a constant - don't remember how it was derived).

Assuming peak torque of 425 ft/lbs is sustained at 6,000rpm:

HP = 425 X 6,000 / 5252
HP = 485

Since we're measuring torque at the wheels, that's HP at the wheels.

Factoring back in driveline loss at conservatively 15%
485 x 1.15 = 557

A dynometer measure torque at rpm and plots the hp curve.

[Vettezuki]

BTW, what was your peak torque? Here's your algebra homework. If you were making 432WHP at 4,750 RPM, what was your WTQ? Hint, it was higher than 425 . . . If you were making 432WHP at 4,750, then the scenario above would be much higher.

[enkeivette]

So if an IRS car with a manual trans loses 15%, how much does a solid axle car with a manual trans lose?

[Vettezuki]

Originally Posted by enkeivette

So if an IRS car with a manual trans loses 15%, how much does a solid axle car with a manual trans lose?

I may be corrected, but I don't believe an IRS looses any more power. Driveline loss is power consumed by friction and moving the driveline itself. In this sense, there isn't much difference between a solid axle and IRS (to my knowledge), though there might be some I suppose. The big deal for an IRS vs. Solid axle is traction in straight line. (Not to mention basic strength.) In other words, and Sean can clarify, I don't think the dyno numbers for the solid axle F-Body were any different than the IRS Y body with the same LS1.

[SeanPlunk]

Sorry Ben, actually not true. IRS cars are generally thought to eat slightly more HP. There is a famous magazine article where an LS1 Fbody does in fact out dyno an LS1 Vette.

[enkeivette]

Think about spinning 6 u-joints as opposed to just the 2. Not to mention, a halfshaft (or an axle) is rarely parallel with the ground. They typically angle down (or in my case up) which also causes some more resistance. Not to mention, the added weight of a halfshaft, yokes and u-joints as opposed to a simple slip in axle.

I'm positive that our IRS would eat more power than a C5/C6 IRS.

I've always been told that a solid axle stick shift car loses 15% to the rear wheels. While an auto can lose 20-25% to the wheels. So, it makes sense to me that an IRS stick shift car would lose between 15 and 20.

[Vettezuki]

Originally Posted by SeanPlunk

Sorry Ben, actually not true. IRS cars are generally thought to eat slightly more HP. There is a famous magazine article where an LS1 Fbody does in fact out dyno an LS1 Vette.

It's cool yo, I didn't know. I can imagine a slight loss because of the gemoetry and connections, but how big are we talking? What's the physics behind it?

[Vettezuki]

Originally Posted by enkeivette

Think about spinning 6 u-joints as opposed to just the 2. Not to mention, a halfshaft (or an axle) is rarely parallel with the ground. They typically angle down (or in my case up) which also causes some more resistance. Not to mention, the added weight of a halfshaft, yokes and u-joints as opposed to a simple slip in axle. .

Yeah, I guess it adds up. I know my motor (with headers, a Y body airbox, and more aggressive tune, but NOT an LS6 intake) was dynoing at 432 in the Vette it came out of. I guess this could account for some of the difference. With my fairly conservative tune, stock manifolds, and hotter air intake, the best I've gotten was 391; that's quite a difference.