Quote:
Originally Posted by RedSol
No, Horsepower does not equal less weight. A 3000 lbs car with a 14lb/HP ratio will never equal a 2000lb car with 14lb/HP. Unless both engines develope max HP at 700 RPM the lighter car will completely out accelerate the other. Not to consider breaking and handling.......
Braking is more related to tire traction than weight. That's how a Corvette, a Solstice, an S2000, a Miata, and a Lotus Elise can range from 110 - 119 feet (basically close to measurement error in a stopping distance test). There's more of a correlation of braking distance (lower) with max lat (higher). And the best braking of the bunch I mentioned is the PIG of the group - the corvette.
Handling? Well, that's partly objective, and partly subjective. One would be hard pressed to say that the Corvette is a schmuck next to the elise. Others would argue they are not in the same class... Bottom line, a Vette will beat an Elise at Grattan by quite a bit (seconds). If that's not a decent measure of handling...
Now: if you are thinking that weight:power ratio is somehow different for different weights, then why are the formulas for the relatively accurate calculators for 1/4 mile and 0-60 based primarily on weight and power?
The quickie answer is that, for most cases, weight:power ratio is MORE important than either power or weight individually. In fact, that ratio is really the important thing - the primary factor in acceleration performance.
A 2000 lb/190 hp (10.5 lbs/hp) IS darned near equivalent performance to a 3000-3200ish lb/286 hp (10.5 - 11.5 lb/hp) car.
Lotus Elise: 1/4 mile 13.3@103
Mitsubishi Lancer Evolution IX MR: 13.5@106
D'oh!
Why didn't I use the Corvette? Because it's 32-3300 ish and 400 hp (8.25 lbs/hp) and SHOULD perform better...
... let's see, YUP. Corvette: 12.8@144.5
Source: R&T
So, if we concentrate on the important stuff, this weight:power ratio... which is easiest and which affects the ratio more?
Say we have a car, it weighs 2900 lbs, and has 177 hp. That's 16.4 lbs/hp.
Say we wanted to get down to 15.25 lbs/hp - that would be fun, huh?
We could, say, leave the engine alone, spend $20,000 on carbon fibre body panels (everyone's fantasy, right?), and ditch 200 lbs, to 2700 lbs.
Ta DA! 2700/177 is 15.25 lbs/hp. BUT, that's an awful lot of money. We only had to change the weight by 7%, but jeez, as the commercials say, "dere's gotta be a bettah way! <smack forehead>".
OR, we could do some exhaust work, some intake work, maybe some other stuff to get the horsepower to around 192 hp. That's ONLY a 15 hp jump - maybe it could be done for <$1000? Anyone think they can figure out how to squeeze another 15 hp out of the current Ecotech for that much? Same roughly 7%-8% change, but much easier to obtain.
Ta DA! 2900/192 is about 15.1 lbs/hp.
BOTH of these cars, the 2900 lb one and the 2700 lb one are equal improvements in performance. They will measure VERY close in 1/4 times. In fact, with a bit more money, maybe you could squeeze 20 hp out - BLOWING AWAY the hard-earned weight savings benefit.
That's why it's easier to get as much horsepower as you can. If you want a car with 11.15 lbs/hp, and you have a 2900 lb car, then you need 260 hp to get there.
But what if you are stuck with a 177 hp engine? The only way to get there is to reduce your weight by
926 lbs to a svelte 1973 lbs!!!
Which is more acceptable? Easier to achieve? Biggest bang for the buck?
There's no substitute for displacement. (before the comments - F/I is a work-around way to increase "apparent" displacement, so it's approaching the same idea a different route - the statement SHOULD be there's no substitute for more fuel and air burned!).
Ahhh Yes. But the best of both worlds. More Pow