raisantos

ok.. so our S(at least the MY07's) have a 0.0830 hp/lb (237hp/2855lbs)

my question is?

if i try to make a gain of lets say 20hp from bolt ons to make my P/W ratio be 0.090 hp/lbs,

and i can get the same P/W ratio (0.090hp/lbs) if i reduce the weight by 222 pounds and keep the stock HP,

will this two cars run identical laptimes(or close), or maybe in the quarter? or there's a lot more i have to take into consideration???

p.s. just a thought, i always hear that it's easier to make a car go faster by reducing weight than to make the motor more powerful, but from my example.. i feel like it's easier to make extra 20 hp than to strip my S 222lbs...

the smart ones please chime in, the smart ass ones, feel free to engage also..

Sabre

I'm no expert, but I would say that pure P/W would matter less than what you did to arrive at the numbers. The track you are running would matter. On the strip..a good launch is paramount so I would think less weight = less torque required to launch and since P/W = HP, it becomes more critical to look at exactly what you are gaining from the mods. 22Hp but say...5Lb/ft?

Basically:
Lighter weight = better cornering, more control
More power = better acceleration...to the limit of your gearing/drag.

Just a rough assumption on my part.

ace123

thats how you compute power to weight ratios. the 237 crank hp from your ap2 makes about ~210whp, and that's the hp figure you should use when comparing cars, as it's what is measured after tuning, and it's what your car actually puts to the ground.

but it sounds like youre asking what else makes a difference in performance besides power to weight ratios, right?

here are some things:
lower weight also means you have less mass/inertia to control/fight with when turning or stopping. for this reason, on a track, reducing weight to reach a target P/W ratio makes for a slightly faster car than adding horsepower to reach the same P/W ratio. for a straight drag (ie 1/4 mile) it makes little difference how you got the P/W ratio (in theory anyway).

area under the HP-RPM curve makes a difference--meaning your average horsepower over time. our car is very peaky, so going from 6k-8k RPM, say we go from (i dont know im making numbers up) 190whp to 210whp, our average is about 200whp, and that's what our effective acceleration will correlate to. so getting your peak hp to be across a broad range helps. thats why turbo hp >> supercharged hp on our cars.

gearing makes a huge difference, and high torque at high rpm (essentially horsepower instead of torque) lets you take full advantage of gearing. this is because gearing is a torque multiplier, which puts more or less force to the ground in the physics F=ma way. shorter gears (like 4.77 or 4.56 final drive ratios) will increase the multiplier but you run to the end faster, so you get more acceleration but you have to shift more. when you shift you cant accelerate so there's a point where it's no longer faster if you shorten gears. also, short gears cut your top end speed.

aero drag gets into it and such, but that seems off topic. but downforce allows your tires to hold higher G loads and handle better, therefore getting better lap times at a tight track, but due to the drag you'd get a slightly slower quarter mile time, especially if you have a high trap speed.

and for drag races, tire deformation and launch technique have a science behind them. it hasnt interested me enough yet to look into.

sorry if this is all stuff you knew 10 years ago; i hope its helpful.
and btw i like the 6 rules, especially the last one

smurf2k

this is an easy one to answer

in almost all circumstances*, less weight, while maintaining same ratio to power, is preferable

why?

because driving in a track involves NOT ONLY accelerating (power to move weight), but BRAKING and TURNING, both of which will benefit from lower weight



*the only exception is in pure drag racing, or otherwise high-speed contests, where more total power is needed to overcome increase in drag (that grows more rapidly)

vader1

I never like comparing power to weight at the crank. Different cars have different drivetrain loss. More power loss to the wheels in an AWD car for example.

I think whp is a better measure, but you need comparable dynos to figure that out. And preferably corrected sheets from same type of machine.

gomarlins3

As stating above, if you are going straight, more HP is great. If you have to turn, less weight is better. Combining both is even better.

Spec_Ops2087

Its usually calculated the other way, weight to power ratio because the numbers are usually easier to work with.

Instead of like .9019 or somerhing its 12.1

afwfjustin

I had 210 pounds taken out of my S before my FI install along with 4.77 gears and the car was VERY MUCH quicker than a stock S2000.

raisantos

so in theory...(if we are talking about the same car, in our case, S2k)

a stripped down S will outrun one with more power in a track, if their P/W or W/P ratio are the same???

Spec_Ops2087

Depends on the track (ie, low speed / high speed)