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HP, Accel, Speed vs Weight

9K views 57 replies 29 participants last post by  sparksfly 
#1 ·
So I'm currently in my astrology class. We're currently learning gravity and physics as well.

To the juicy stuff!

My teacher is japanese and she's currently telling us how she use to race back then in tokyo. I've never paid full attention in a class before lol. Since we're learning about gravity, force, and acceleration, she was telling us how she made her RX-7 faster and lighter. Nowadays, we know that if we take out interior stuff like seats, plastics, and stereo it makes our cars lighters. She told us that "for every 5 pounds, you lose 1hp" She did a science experiment testing this and apparently she had the lightest and fastest car around.

I would post pics of her car, but can't take pic right now lol

short little story. don't know if it's actually true! thought you guys should know
 
#3 ·
#6 ·
Discipline and self-control are the keys to weight-loss and success in most things. Eat a salad and take walks...then watch the hp increase.
 
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#18 ·
Confusion abounds.
 
#20 ·
Not true,
Say, you have a 4000 lb. car that makes 400 hp. The power to weight ratio is 10 lbs per hp. Got it?

Say you can reduce the weight of the car by 500 lbs. Now your power to weight ratio is 8.75 lbs per hp.

If you kept the car at 4000 lbs, to get the same power to weight ratio, the engine would have to make 457 hp. (Divide the weight by the new pwr/wt ratio.

Using the above example, reducing the weight by 100 lbs, would be equivalent to adding 10 hp. (That figure is not constant and will vary according to the power to weight ratio.)

-In an SI it is about 14.5 lbs for 1 hp, add 30lbs of tires and rims loose 2hp, get your ass to the gym and loose 30lbs it's like gaining 2 hp. The big difference comes when you have a 1000 hp and acar that weighs 3000 lbs, that 1hp for every 3 lbs
 
#39 · (Edited)
Disagree with Mrs Professor statement. Being logic, power is force x velocity. The HP output should be about the same no matter the weight. But because you need more force to move the car when weight is added, the result is less velocity and/or acceleration.

The quote above is Very true, When I stated about the 4000 lb car and 500 lb reduction. To all that read here, it was an example of power to weight ratio so you could understand. Any hp gains through weight loose are like thrust. no matter how much weight you loose, the car will still dyno the same, it about getting the car moving
 
#44 ·
I was wondering how HP, Acceleration & Speed were affected by weight. So this is a physics question for all you physics people or top-notch mechanics / Motorheads. Lets throw all other variables out the window or now.

How much weight needs to be added to our Si's to negatively affect 1HP, 2, 3, etc...?

What are the specifics on how acceleration (0-60) & top speed is affected by weight added to our Si's?
For example, added cosmetic mods, subwoofers, passengers, stuff in the trunk, etc...

(If you could include the formula's or the formula used to figure this out, that would be a plus.)
 
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