Horsepower to Weight Ratio

mako1a

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?

stever

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.

Steve, Host

Mr_Shiftright

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).

stever

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?

Steve, Host

carlisimo

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.

stever

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.

Steve, Host

fredmcmurray

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.

gary045

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

hystricidae

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 ...?

fredmcmurray

The one without the navigation system. Nobody goes to Kansas City on purpose.

stever

Steaks, BBQ and some weird concrete history if you like graft. Nice fountains at the ballpark too.

Steve, Host

hystricidae

lol ... kind of like Levenworth

subygt

2007 DP1 V8 850/375HP 2.2 pounds per HP $125,000

www.dpcars.net

Made in the U.S.A :Portland Oregon.

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

wideglide

It's also not street legal, and there are plans to attempt to make it so. If they did, it would undoubtedly weigh a lot more, anyway (bumpers, airbags side impact protection beams, etc.).

subygt

I didn't see that as a criteria for being in the discussion. As far as street legal goes, you can register and get plates for almost any car you can drive in almost any state. You can get parade plates or special purpose plates...... thats what most people do they when import cars or build kit cars "IE: super seven", All you have to do is add a VIN to it, issued from the state you live in a , get a ins company and a license plate..... bang, now its street legal.

Just takes some doing by the person purchasing the car, its not for everyone, but people who have the will to drive something very different can find legal ways to do it... they also assume all the risks associated with it and most do, thats why it is possible but difficult.

I personally know people who have built kits and imported cars with a much lower build quality that the DP1 that have had zero problems getting the car thru the local DMV.

It all depends on how bad someone wants to do it. I see no problem with it as long as people know what they are doing....

stever

Bill Gates' 1988 Porsche 959 was impounded for ten years before he finally got it licensed for street use. :shades:

Forbes

subygt

That car was impounded because it was a widely mass produced car that they refused to crash test, so the U.S. decided to make an example of them and hold up a very high profile customer and car manufacturer.

Many a Lotus elise made it into the U.S. with not a second look by DMV. Along with another 20 or so specialty cars.... IE: Ariel Atom, Seven, Westfield, Different TVR's... Etc,

stever

I heard that fewer than 200 "street legal" 959s were made. The Ariel Atom looks like it may be a bigger hoot to drive, and for a lot less dough too. I thought the Top Gear review of it was hilarious.

No matter, my vision and reflexes wouldn't do any of these supercars justice. :sick:

starrow68

Low wt/HP cars are not just a hoot on the street. I see many trailered into HPDE track events that don't have plates and not all of them are driven at the limits, for that matter neither are the street legal ones. Last weekend I got to watch a 70-72? Pantera with a 351 Cleveland engine, best sounding machine I've heard lately, go around Buttonwillow Raceway. It was formerly a race car owned by Bob Woodhouse, still in World Challenge, and had been updated after sitting for over a decade. Probably 450+ HP for a package that should have been under 3000 lbs. The guy was very conservative on track, not a replaceable car.
Randy

jimveta

Steve, torque really is just torque and is the same once it gets to the wheels whether it comes from the engine or tranny. Non-inertial chassis dynos (those that apply a constant/braking load and can hold a car at a particular RPM) can show *REAL* torque output at the wheels. When you choose that option, you'll see high revving I4 cars making something like 250hp and 800 lb-ft.

Now if you're wondering then how does that work out with the equation of HP = Tq * RPM / 5252, you have to measure the RPM where you measure the torque. So the HP works out because RPM is not the engine rpm, but rather the wheels (or equivalently dyno rollers).

I think a good way to think of torque is the ability gain HP faster.

jimveta

While I agree that having higher hp / weight ratio is more ideal.. I think one has to also consider that hp / weight is not static, meaning that when most quote hp/weight, they are really stating the *peak* hp/weight ratio.

As an extreme example, try putting an F1 engine in a Hummer.. yes, the (peak) hp/weight fiqure will improve a great deal, but I bet it'll actually be slower in most cases! We can talk about the subject of torque, but we can omit the term "torque" entirely to simplify things and simply speak of HP, but now include RPMs.

So to truely determine the potential performance from hp/weight figures, we need to also consider hp/weight across all RPMs. But if we were to settle on "single" figure that's indicative of such across the board performance, perhaps *average* HP / weight would be it. Popular Hotrodding magazine for exmaple, scores participants' engines based on average HP in their annual EngineMasters contest.

Going back to the F1 example, it reminds me of a Motortrend article I read a few years ago where the author had his first experience driving an Forumla car. He stated that it was like learning how to drive a manual tranny all over again.. because clutching in at 4000+ rpms, still stalls the car!! Although I guess that's to be expected because that was close to where his car idled. I've read of more recent cars idling even higher..

Another example is Edmunds' own review of the Subie WRX wagon with automatic tranny: http://www.edmunds.com/insideline/do/Drives/Followup/articleId=48462
Accelerating right off idle resulted in 0-60 of 8.7 seconds. Brake launching at 3000 rpms, spooling the turbos up results in a 0-60 of 6.7 seconds. I should say though that the performance of turbocharged cars are even harder to model because not only does HP vary by RPM, but there is a transient effect varying HP at the same point of waiting for the turbos to spool up, if not already.

Another in similar vien was a C&D comparison of various cars. The S2000 faired significantly worse doing 5-60 (high 8's) than 0-60 (slipping the clutch in at nearly 5000 rpm; 6.1 if I recall). And again, I think we can predict or model these outcomes if we look at power delivery instead of only peak output.

brianapal

1995 Corvette
1999 Corvette
2001 Corvette
I am missing something here Subygt?????????

You compare these cars to a 2007.

It is 2006 and they are selling 2007 Corvettes!

I agree that the weight to horsepower ratio does mean something but why are you talking about ancient history??? But your comparisons are meaningless. Why don't you compare a 2007 Porsche to a 1958 Corvette? That would be a real valid comparison wouldn't it!

The 2007 Corvette coupes and convertibles and the 2007 ZO6 are all street legal cars that are great sports cars!

It is pretty obvious that you don't own any of the 3!