WNeal

3 weeks into gutting the car to build a cage and some other mods, the total net weight loss will be about 400 pounds. We figure it to be about 2900 #s when we are finished. Stock 400 HP now.

Any ideas on what the "equivalent" HP gain might be for something like this.

My Arch Rivals all have more HP than me and I wanted to get an idea if this will now allow me to smoke their Dominating, Trashy, Pumpkin assses

Thanks for your input

AU N EGL

Drag racers say 100 lbs reduced is ~ .1 or 1/10 sec again ~ 10 hp gain/ 100 lbs reduced.

also it depends on where the wt is. Light wheels have the most gain as rotating mass or unsprong wt . Each 1 lb remove from the wheel ( unsprong wt) ~ 6.5 lbs removed from the car itself or sprong wt.

sgsvette

Bill,
you will notice the biggest gain will be under braking and cornering. Yes you will also gain some straight-line speed but your lap times will come down from handling. Tires and pads will wear less, so in a long run your car will be more consistent.
Remember what you learned at the school: smooth is fast!
Go get em!

robvuk

I would figure it as follows:
3300 lbs divided by 400 hp is 8.25 lbs /hp.
2900 lbs divided by 400 hp is 7.25 lbs /hp.

If your new ratio is 7.25, the equivalent, if the car was still 3300 lbs. would be:

3300 lbs divided by 7.25 lbs/hp would be 455 hp.

Now that's your straight line acceleration. As mentioned elsewhere, you pick up your handling benefits as well.

WNeal

Thanks Henry, Tom,

It will be interesting to get it back on the track to see the difference.
29 pounds of it is in the clutch so losing some rotating mass there.
I am sure we will corner weight the car again to get it back where it needs to be.
Should have some final pics this week.
Joe has done a very meticulous and fine job on the cage.

davidfarmer

robvuk is dead on, power-to-weight ratio is simple division. On a Vette, each 10 lbs is about 1hp until you start reaching the extreme weight reduction/power increase levels. 400lbs probably won't make your car feel extremely different, but your laps times should show some significant improvements.

Z06Norway

10 pounds might be 1 hp, but that has to be weight shed off the car ?
IF you take off 10 pounds rotating mass, wheels, tires, brake rotors etc. it makes a HUGE difference, like 5 times more than actual weight savings.
i got my Z06 down to 3040 full tank, alot from lighter wheels , tires and brake rotors.
It felt like a totally different car.
more HP, better coil overs helped a bit too

Carbon Fibre 18x13 wheels are 17 pounds, i think stock wheels are 30 pounds? anyone know.
ccwheels Corsair C10 was 25 pounds

Stock vs. modified with Dymag, Brembo and Hoosiers is:
Wheels 17 pounds vs. 30 = 12+ pounds pr. corner
Tires 27 pounds vs. 36 = 9 pounds pr. corner
Rotors 17 pounds vs. 25= 8 pounds pr. corner

29 pounds removed of unsprung weight, guess that will give a good feeling....

Should feel like loosing 500+ pounds OFF the body of the car....?

I get to keep AC, radio, carpet, what a great car Z06 is


regards
Rune

gonzalezfj

Rob, your analysis is correct for dead (static) weight in the car. However, in the case of rotational mass, you get the benefits of losing the dead weight but also you don't have to accelerate and decelerate the lost weight.

How much benefit depends on the rotational inertia of the lost weight. For example, weight loss in the tires is a lot more significant in performance gain than weight loss in the rotors. This is because the tire weight is at a longer radius than the rotor weight. This can be accurately calculated. See any mechanical engineering manual.

Frank Gonzalez

AU N EGL

Carbon fiber rims are a no no on US road course. So that does not count.

and Frank and Rune are correct. Loosing that rotating wt is vital.

a year or so ago a friend and I did the calculations ( ok well he did) the difference between a 19" rim and the 18" Plus my 51 lb rear street wheel and my 39 lb rear track wheel.

Quite a difference.

Just like some one who has some good CCW Classics and some knock off ZO6 repo wheels. You feel that difference right away

robvuk

That is well understood. It also makes a difference on how far out from the center that the mass is located from the center of rotation. I was responding to his simplified request for equivalence before he specified that he pulled out rotational weight as well, in regards to HP. Obviously he has much more than the additional equivalent of 55hp working for him and I did point out that it was strictly his straight line advantage at a minimum.

I also wanted to make light of the fact that a simple 10lbs/1hp ratio is not accurate but my simple arithmetic method will demonstrate. If your car is 10,000 lbs and 1000 hp obviously, taking 10 lbs off of it will not add the equivalent of 1 hp. Just as taking the same 10 lbs off of a go-kart would make a huge difference. It's more dependent on the percentages of weight vs the percentages of hp.

jwt1603

I went from knock off ZR 1 wheels to Speedline Z06 wheels to CCWs. There was a definite improvement in the steering response.

As Wneal did, I also got the net weight down by about 400 lbs after removing everything and then adding the cage back in. I forgot about the wheel weight difference so that's a few more lbs of unsprung weight.

Great thread.

WNeal

Some great info
I will report back once I get it on the track.

Should be 5-2-09 at Bluegrass Motorsports Club

Webz

450HP!!!!

I might need to skip a meal or two and maybe I could pick me up some of those weight reduction HP's ............ Nah ....... what was I thinking.

linutux

For your viewing pleasure...



This graph shows the relative effects on the power to weight ratio when adding horsepower or reducing weight; or even better... BOTH!

Notice that:
1. Adding HP results in linear increases in power to weight.
2. Decreasing weight gives modestly exponential increase.
3. Combining both shifts the slope of the exponential return up, the "right way"

Hope this helps. I'm just an amateur bench racer, not a pro.

WNeal

AND,
I only had one Coke today so that should be good for another 25.

Want to give up now mister????

WNeal

Very interesting,
Thanks

rustyguns

Independent1

Weight affects all aspects of performance - braking, cornering, and acceleration. More HP only affects acceleration.

Also, where the weight comes off and the type of weight (rotating versus static) is important. The further the weight is from the center of gravity and the higher it is, the greater the benefit from reducing the weight.

Reducing rotating mass (brake rotors, flywheel, rims and tires, etc.) is also has a greater effect than removing static weight since that mass has to be accelerated or slowed down, which takes a lot of energy.

Even if they have more HP, if you have less weight, all else being equal you may find you are faster!

drivinhard

On a road course you'll only see a hp improvement from point A to point B when the engine is at 100% duty cycle. When you get down to it, the % of the lap run at full throttle is pretty small (obviously varies from track to track).

Less weight is an advantage for the car at virtually any point on the track.

9 times out of 10, you can have more fun in a lower hp/lighter car to. A heavier/high hp car can be frustrating at times.

BTW here's the best of both worlds sitting in the shop, I am building this now for (with) a friend. 475 hp cam'd LS6 miata



hp/weight is roughly the same as the current 638 hp ZR1. Finished weight of the car should be ~2450 lb. should be a fun occasional track day car.

BrianCunningham

What sized tire though?

and what the weight ratio f/r??