I race bikes and the rule of thumb is 7 lbs is equivalent to 1 hp.

 

OK - this is simple math and varies per vehicle. For example, if your car weighs 3000 pounds and makes 300 hp, then it's 10 pounds per hp. The power to weight ratio is 1:10. Now, add 40 hp. Power to weight is 1:8.82. To get the same power to wight, through weight reduction, you would need to drop 353 pounds. It's easy to play with the math - just simple division and multiplication. In this case, each of the pounds lost is worth 0.1133 hp, so 100 pounds would be worth 11.33hp.

Also - you don't only get the power to weight benefit, you may also use less gas, less brakes, less tires, etc.

Make sense?

Now - to complicate things, some say that every pound of unsprung weight is worth 4 pounds of 'regular' weight. This is pure speculation/witchcraft/personal_opinion, but it's related to not only dropping the weight itself, but becoming more agile in corners, etc. I don't think there's much math/science to this one, but I could be wrong.

 

btw - if you use rwhp in the first calc, then you get rwhp throughout. Same for hp at the crank.

 

also - to give you an idea on how it varies per car, my 944 weighed about 2900 pounds and makes about 140 hp at the wheels. I'm putting it on a diet and hope to get down to about 2550 pounds.

That's a similar drop to the one in the example above, which equated to 40hp.

In the 944, I'd be going from a hp:weight ratio of 20.7 to one of 18.2. If I wanted to get to that power to weight by adding hp, I'd only need to add 19hp. One hp only gets me 0.055 hp, and 100 pounds only gets me 5.5hp (at the wheels).

Obviously, it would be different on a race bike, etc.

 

Obviously a true racer. Been there done that, but not with a Porsche. Love the Pics, would like to see a pic with the seat in place.

 

Guys

Thanks for the kind words... Gomez is taking the appropriate steps to have a safe and reliable track car..

Yes he could have purchased Cup car but that was not the point of this exercise, he owned this car and wanted to something that was easy to run at the track and did not require a full team to maintain..


We wanted to do a cost effective build that maximize the return on investment and he has done so by enjoying the car along the way while he has improved his driving skills at the track. He gets better , the car gets faster.
Way to many guys jump into cup cars and cant manage to get out of there own way... I am of the old school racing mentality, improve your skills before you improve your car.. Way to many people get caught up in the fluff and they end up with cars that are way to fast for there abilities.



It will be a great car to run in the POC GT/S Class, Time trials, etc and frankly he is not caught up in building it for one specific class. He wants to enjoy what he has in different series as well as track days throughout the year. This gives him an opportunity to build a car that he likes and wants..



When the time comes for a cup car.... We all know it will ... We have him covered for that too

 

I have a ton of pics here of the car.

 

On the contrary, i believe it's all about physics laws.

But i also think the unsprung weight thing got overestimated over time for marketing reasons. I'm sure serious scientific studies could demonstrate that 10lbs of unsprung weight per corner does NOT equal to, let's say, 40whp...

 

I think the REAL lightweight fun starts below 2000 pounds. And that is only possible with early 911's, Lotuses, Miata, etc...

Just try a Lotus Elise/Exige, you'll see it's another world. The braking feeling (weight transfer) is actually weird at first when you're used to drive 3000-4000lbs vehicles..

 

btw, congrats Gomez for this awesome project. Pretty extreme but very interesting for sure!

 

I should have been more clear. I was speaking of quantifying the benefit of reducing unsprung weight. Calculating the approx benefit of weight in general is simple and easy, as I showed above. After that, it get's pretty difficult to QUANTIFY. How about this:

- Reducing weight is great
- It is better to reduce unsprung weight (like wheels, rotors) vs general weight (carpet), but how much better is it? That is a tough one.
- It is better to reduce weight up high (sunroof, carbon roof) than weight down low (carpet). Also, if you need to add ballast, it is much better to add it down low than up high (bolt some weights to the floor). Also, it's a good idea to reduce weight all around your car to get under your class weight, then bolt the weights to the floor (moving the weight lower). Having weight lower is better, but how much better? How to quantify? That is a tough one.

Sure, I bet there's some physics involved, and someone could calculate that - but it would be very difficult, I'd imagine, and difficult to come up with a somewhat accurate 'rule of thumb'. Some say unsprung weight is 4x better to remove than 'sprung' weight. Who knows??? If you can figure it out with physics, science, math, etc, I'll send you a dollar!

 

I believe the unsprung weight theories come from the fact that you are not only decreasing the weight but also the amount of mass the engine is responsible for moving in order to get the car to move. For example, if you installed lightweight wheels that save 5lbs per corner and lightweight brakes that also save 5lbs per corner then you are not only reducing the total weight of the car by 40lbs, you are also reducing the rotational mass the engine must move in order to accelerate. Or effectively you have created a more efficient drivetrain and more HP is getting to the road.

Jason

 

Slowly but surely the cage is coming to life......

 

That is looking good Gomez!

 

Very cool car... but why is it that my gut feels like I just viewed a cadaver on the autopsy table??