Write-up: How to determine approx. HP gains from removing weight!

[Taiden]

Originally posted by fokuzx3
did i do something wrong?


The Corral - Horsepower Estimator

Your trapspeed was 90 miles per hour
and your vehicle weight was 2798 pounds.

You are making 223203 hp.

That's funny.

[SVTkonig]

rotational mass of the wheels only matters for the front two wheels. the rear wheels are considered sprung mass because they're just along for the ride so to speak. sprung mass is silly for the quarter mile unless you're talking hundreths of a second.

[Taiden]

Originally posted by SVTkonig
rotational mass of the wheels only matters for the front two wheels. the rear wheels are considered sprung mass because they're just along for the ride so to speak. sprung mass is silly for the quarter mile unless you're talking hundreths of a second.

Hmm. The front wheels and the rear wheels are technically connected through the road surface, so I would say rear wheels are considered unsprung mass unless this has already been established elsewhere.

Ideas?

[Carrera26]

Considering straight-line acceleration you are still working with the rotational inertia of the rear wheels, even though they are not powered. It would be like dragging a large hoop. The heavier one would still be harder to get moving and accelerate with than a lighter one of the same dimension.

It makes MUCH less difference on the undriven wheels than on the driven wheels in this scenario, but it still applies full force for braking and handling situations.

Also, the test vehicle that yielded the ratio was a 2wd vehicle, so the 3:1 ratio still applies regardless.

[xFOCIx]

To call it "hp gain equivalent" is incorrect scientifically and in real life overall performance.

The specific weight is decreased as a function of Δm where power is a constant.
ΔV/Δt is all about specific power, but not so for top speed. Weight is a factor because rolling resistance is a constant x load, but when it comes to top speed, rolling resistance is a distant second to air drag, so reduction in weight to yield specific power comparable to increasing 25hp will not get you the top speed of 25 real hp gain.

[xFOCIx]

Originally posted by SVTkonig
rotational mass of the wheels only matters for the front two wheels. the rear wheels are considered sprung mass because they're just along for the ride so to speak. sprung mass is silly for the quarter mile unless you're talking hundreths of a second.

You're wrong. Anything that must be spun up is a rotation mass(flywheel, brake rotors, transmission parts etc). The way mass is distributed matters as well, because it affects rotational momentum.

[xFOCIx]

Originally posted by Carrera26
I've heard that you can make 223203 BHP with this chip you can get off of Ebay...

hp applies to braking too. Horsepower is basically drag + change in kinetic energy over time.

When you crash into a tree, an instantaneous rate of acceleration of -490m/s^2 is possible for a very short amount of time and the "peak" hp can easily be 10,000 hp ;)

[Taiden]

Originally posted by itsme
To call it "hp gain equivalent" is incorrect scientifically and in real life overall performance.

The specific weight is decreased as a function of Δm where power is a constant.
ΔV/Δt is all about specific power, but not so for top speed. Weight is a factor because rolling resistance is a constant x load, but when it comes to top speed, rolling resistance is a distant second to air drag, so reduction in weight to yield specific power comparable to increasing 25hp will not get you the top speed of 25 real hp gain.

I'm going to say that this isn't applicable, because top speed isn't concerned, only top acceleration. Top speed is mostly effected by an unflashed ECU, so I don't understand why it would be discussed in the first place.

[Karniv04]

Unrotational sprung weight mass equivalent to the ratio of 312:42139 is applicable to the gains of non horsepower drivetrain increase. Now when you take a look at the acceleration equation of 12^mn-bc/3 you can see the results between the differential locations of non powered flywheel. Who knows what capable?

[Carrera26]

All weight loss gets progressively less important as speed increases though. The increase of performance is directly related to the rate of acceleration. So in 1st gear, say, the improvement is going to be the most prevalent, because the rate of acceleration is the highest. It will drop seriously in each higher gear.

Like with a flywheel, accelerating it from 1000 to 7000 rpm in 3 seconds in 1st gear is going to show much more effect than the acceleration from 5000 to 7000 RPM in 4 seconds in 2nd gear.