Looking for source of HP vs weight (mass)

[Kurt B]

And the specifics again. In general, for every k kgs of mass to be added, one must add h horsepower to compensate for the added mass and achieve (roughly) the same performance (to a certain point).

What were those numbers and where did so-and-so get them?
Also, there are upper and lower bounds for this.
Does anyone have a dataset for performance we could find a good fit through using polynomial approximation? I'm sure it's not linear.

The dataset would be KG (X) and HP (Y) where 'equivalent' performance (acceleration is what I want mainly) is achieved.



It'd be nice if were could find a good curve fit for it--for any torquie type engines like ours

[Jack Olsen]

It's only meaningful in a straight line race.

On a track, a 40hp shifter kart will beat a 911 Turbo or Vette or Viper, no matter what mods are made to the cars. Light weight reaches a point of absolute good at about 400 pounds.

[Natchamp]

Good point Jack, you just brought back many a fine memory of my racing days.

[emcon5]

Originally posted by JackOlsen
It's only meaningful in a straight line race.

On a track, a 40hp shifter kart will beat a 911 Turbo or Vette or Viper

Anyone see the current Grassroots Motorsports?

That is pretty much the cover story.

Tom

[boyo]

Horsepower isn't the best measure of acceleration, torque is. Torque and horsepower are non-linearly related, but there is a relationship. Still - many folks document their performance in terms of weight/HP.

Both HP and torque are non-linear as well, HP is usually quoted as peak HP. Torque usually isn't quoted because nobody knows what it means and the units are different for der Amerikaners and der Europeans. It's a good measurement of acceleration, but varies depending on the RPMs. You also have to factor in gearing, where the optimal balance between torque over the range of RPMs and gear ratios would produce optimal acceleration.


But anyway! I think the quick answer to the question is: focus on the ratio between HP and weight. If a 2000lb car desires a weight/HP ratio of 10:1, that's 200HP.

If you car weighed 2100lbs and had 180HP, you'd need to add 30HP or drop 300lbs to achieve the same 10:1 ratio.

Ideally you want to do both weight reduction and HP increase. Add a 200lb driver to a 2000lb car with a 200HP engine, and your 10:1 weight/HP ratio goes to 11:1.

-Boyo

[JJH911]

If you are looking for comparisons on Power to Weight Ratios look in the Back of the PCA CLUB RACING RULES.
available on the PCA Website.

This will list the Power to Weight Ratios that each Group runs with.
Example:

87 Carrera Weight=2756 HP=214 Gives a Ratio of 12.88

would run in Class F With the following other cars.

All Boxster W=2822 HP=201 R=14.04
72-73 911s W=2365 HP=190 R=12.45
All 944 Turbo W=2899 HP=217 R=13.36
All C2,C4 C2 R= 12.27 C4 R=12.94

For others in this class and other Classes look at the PCA Club Rules for Racing and find out how your ratio matchs up.

Just a quick tip!
John

[RarlyL8]

Let's see, 2500lb lightweight SC with a 350 HP modified 930 engine..............
7.14 lb/HP
with a 5spd geared to 140MPH @ 6500RPM.........
That aught to do it.

[Yargk]

7.14 lb/hp, not bad at all.

2800lb 930 (glass bumpers and rear wing, no A/C, sport seats, no sound pad, etc.) / 600hp twin turbo 3.6....

4.7 lb/hp

Waiting is such sweet agony.

[JJH911]

High Horsepower and a light weight car is great but if you are racing under the PCA Club Rules this Avenue of Changing your car will bump you up into Super Classes GT-1 through GT-6 and GTP-1 Through GTP-6 rather than Stock or Prepared Stock Class.

So in racing your Porsche the Higher Classes becomes a question of putting 100k into a car that you can't drive on the road.

If you have the money go for it!
or if you think your good a driver prove it in the Stock or Prepared stock Class first.
Not in the I have more power because I have more money Classes.

Just you humble feeling from a poor prepared stock class racer!

[89911]

Hey, that was my brother that post that! Hey John, why don't you throw up a pic of your tub so they can see the "before" picture. I'm hoping the "after" picture will happen soon!

[Jack Olsen]

Here's the kart thing, illustrated (you need Quicktime):

lawsonwillow.mov

[RarlyL8]

Keith - those are motorcyle numbers. You better get a rollcage, I can't imagine how fast things are going to happen.

How's the motor coming? Is IAuto doing the work? ETA? You putting it in? Details man!

Jack - I had the horrifying experience of driving a friends 125cc shifter cart a few years ago. I honestly have never been so scared in my life! He coached me as to what grears and speeds to enter corners, and I quite frankly could not do it. I didn't have the nerve. Those things are so much quicker than anything on wheels it is hard to describe. For a year or so this guy held the track record at Putnam Park in his 250cc cart. Mind you INDY cars and 962s commonly use this track. That is FAST.