Last post on Oct 24, 2006 at 3:56 PM
You are in the Speed Shop Tuning and Modification
What is this discussion about?
Dodge Viper, Porsche Carrera GT, Chevrolet Corvette, Ford Mustang SVT Cobra, Performance Mods
#1 of 22 Horsepower to Weight Ratio
Jan 15, 2006 (9:15 am)
With so many people reluctant to buy a vehicle that uses more gas than the next guy, but is afraid of ending up with a slug that may get rear ended entering a 55+ MPH highway we need a standard. I would like to suggest 10:1 ratio of weight in pounds to horsepower. Easy to figure out. If your car weighs 3200 pounds you should have 320 horsepower. The mustang GT almost hits it and the GTO exceeds it, but as we all know GTs are overpriced and the GTO is a major gas hog (gas guzzler tax). The solution is to build lighter cars. A 150 HP engine would save gas and still have enough power to climb a hill with the A/C on if the car it pushes weighs 1500 pounds. How? Plastics and carbon fibre, tubular frames and air bags. Are they safe? You bet. That's how race cars are built. When buying your next vehicle look at the HP to weight ratio. If you come up with 16:1 you can count on it being a real dud. 9:1 and you can not only keep up in traffic, you'll be just plain fast. Ideas?
#2 of 22 Re: Horsepower to Weight Ratio [mako1a]
by Stever@Edmunds HOST
Jan 15, 2006 (9:37 am)
Makes sense but it's cheaper to build heavier cars. Cheaper to repair sheet metal than carbon fibre too.
So perhaps the early adopters are more likely to be performance cars and even then you may have more emphasis on lightweight wheels and unsprung weight, aluminum blocks etc. Expensive items but maybe not as expensive to fabricate as exotic body and frame parts?
It'd be fun to post some other hp to weight ratios. As near as I can figure, the Smart comes in around 10:1 for its 50 bhp powertrain.
#3 of 22 Re: Horsepower to Weight Ratio [mako1a]
by MrShift@Edmunds HOST
Jan 15, 2006 (11:48 am)
Power to weight isn't the only indicator for performance. You have to include gearing. One of my cars is only 15:1 weight to power but it's not a slug because of gearing...sure at 80 mph+ you pay the price for low gearing but in the city or on-ramps it's more than adequate.
Also weight affects handling, braking, etc. so while you may be very "fast" at 10:1, you may also have to work very hard on anything but a straight road. (e.g. Viper).
#4 of 22 Re: Horsepower to Weight Ratio [Mr_Shiftright]
by Stever@Edmunds HOST
Jan 15, 2006 (12:29 pm)
What you call low gearing I've always thought of as torque - something tells me they aren't equivalent.
What other factors do you have to look at? Coefficient of drag? How the weight is distributed or the front/rear bias?
#5 of 22 Re: Horsepower to Weight Ratio [steve_]
Jan 31, 2006 (2:18 pm)
The way I think about it is that gearing multiplies torque at the wheels, and low gearing means greater multiplication.
Take a hypothetical 9000rpm engine with a flat torque curve of 100 ft-lbs. And another engine, 6000rpm redline with 150 ft-lbs of flat torque curve.
If you gear both of them so that the top of second gear is the same speed (usually 62mph), the high-revving one will have its torque multiplied 1.5 times more than the other one. So the wheels on both cars will experience the same torque per rev, thanks to the gearing.
But the high-revver will output more revs before they get to 60mph, so it'll actually reach 60mph faster. It's not totally intuitive to me... I might be wrong, so correct me if you see a mistake in there.
#6 of 22 Re: Horsepower to Weight Ratio [carlisimo]
by Stever@Edmunds HOST
Jan 31, 2006 (2:37 pm)
lol, I'm not going to see any mistakes there.
This reminds me of those word problems I couldn't do in school - if one guy leaves NYC driving a 9000 rpm engine and another guy leaves LA driving a 6000 redline engine, who will reach the steak house in Kansas City first?
I'll have to rely on a seat of the pants guess when the equations start flying.
Feb 01, 2006 (12:36 pm)
Actually, your hypothetical case should yield identical 0-60 times. What really matters is force at the drive wheels, which is torque times the radius of the drive wheels. Velocity equals acceleration times time and acceleration equals force divided by mass. So two cars with identical mass and identical force applied will reach identical speeds for any given amount of time.
Of course the case is so hypothetical as to be nearly meaningless in real world applicability.
#8 of 22 Re: Horsepower to Weight Ratio [mako1a]
Mar 18, 2006 (9:04 am)
Some high end picks.
Horsepower to Weight Ratios
Model weight HP lbs/hp price
1999 Dodge Viper 3,380 450 7.51 $80,000
2001 Corvette Z06 3,115 385 8.09 $48,055
2000 Porsche Turbo 3,400 415 8.19 $118,000
2000 Ferrari 360 Modena 3,241 395 8.21 $179,000
1999 Porsche GT3 2,975 360 8.26 N/A
1995 Corvette ZR-1 3,535 405 8.73 $65,000
1999 Corvette C5 Coupe 3,250 345 9.42 $37,171
2000 Porsche Boxster S 2,855 250 11.4 $54,303
2000 Audi TT 2,655 225 11.8 $36,000
2000 BMW M Roadster 2,899 240 12.1 $43,743
#9 of 22 Re: Horsepower to Weight Ratio
Mar 19, 2006 (3:59 pm)
If 2 cars make the same torque, one at 4500, the other at 9000, all else being equal, which one will get to Kansas City first ...?
Mar 21, 2006 (12:39 pm)
The one without the navigation system. Nobody goes to Kansas City on purpose.