Anyone know the formula (or smart enough to make a website to do this) such that: Given a specific HP, the gear ratios, and HP (or torque), that given NO wheel slip, who is "quicker" in the 1/4 mile? That way, there is no questions (I suppose its power->weight)... but it would be kinda nifty to see.

That way, we can say X is quicker than Y given the perfect conditions and perfect driver... thus leaving the rest to human error and traction.

-- Aaron

 

Why do you want to take the fun out of racing? You may want to go out Saturday night with your calculator in your pocket, but I'd rather put my car's reputation on the line and race anyone who wants to.

Wesmaster

 

yea, that really isn't fun.

Also, what if a car's RWD, FWD or AWD?

Take the risk and race other cars. That's what I think is fun.

My friend in his B16 with I/E/H thinks he can beat my friend's '95 NSX with H/E.


I think the NSX will SMOKE the b16 but my friend thinks his b16 will smoke the NSX.


B16 I/E/H - 14.6 at Carlsbad raceway
NSX E/H - Never timed, should be able to do mid-high 13s with good driver.

Who knows what the outcome will be.

 

well, i'm no expert in this field but i do remember R&T's Technical Correspondence column addressing a similar question recently. it was for estimating post-mod power increases from 1/4 mile times or speeds, but maybe you can express the formula differently to go the other way.

ok here it is, from the September 2001 issue:

[begin quote]
If you know the vehicle weight and either its mph or elapsed time in the standing-start quarter mile, you can calculate to within 5 percent or so of an engine's horsepower. If you know the elapsed time, figure horsepower thusly:

HP = weight/(ET/5.825)^3

If you know the mph, figure horsepower as shown below:

HP = (mph/234)^3 x weight

[end quote] (any errors are my own)

So, i would imagine you can rearrange to get the equation from quarter mile time from horsepower and weight, which ought to be:

ET = 5.825 x (weight/HP)^(1/3)

R&T wrung out a 14.1 on the last S2000 they tested, and I would assume that is a fair number to check against. So for the S2000 and its 2800 lbs (incl. driver) and 240 hp, using the formula we would get a 1/4 mile time of 13.21... a little faster than real life it seems. Using the +/- 5% HP error value would give us a range of times from 13.00 to 13.44. I am sure many people have gotten times in or below this range, but it probably has a lot to do with how willing you are to break the car with an 8k clutch drop.

If you're curious, the HP number you'd need to input to get the 14.1 time is almost exactly 200. Perhaps the unorthodox power curve created by the VTEC is responsible for the anomaly. We're all familiar with the Cringer/Battlecat nature of our straight-line performance, and the relative ease with which one can bog at launch. They imply traction issues are relatively insignificant in this equation, probably because a 1/4 mile is long enough to make launch characteristics the least suspect variable in a purely theoretical formula.

Anyway I would say that the equation is a fair estimate to within a few tenths either way. For non-modded cars, just consult your favorite car mag and argue away. For modded ones, I guess the formula can be helpful, but to give it any validity you have to have accurate estimates of crank HP and vehicle weight for both cars, which in itself it no mean feat.

IMO, if there is a big enough difference in the two cars to make the equation show significant differences, it's probably already obvious who's faster without resorting to math. And when it's really close, a tenth here or there is more than made up for by driver skill or track conditions. After all, do you really want to be the guy whose car "theoretically" goes faster but can't put his money where his calculator is, or do you want to be the guy whose car is supposed to be slower but in the real world wins anyway?

 

[QUOTE]Originally posted by Wesmaster
[B]Why do you want to take the fun out of racing?

 

Just to get rid of the "Who would win if it was an X versus Y" car... I don't care about FWD, RWD, AWD... doesn't matter. Mearly on the perfect launch, with the perfect driver, and perfect traction... who would be faster. That way, regardless of all the HP and wheel conditions, we would know "WHO" is has the fastest car... THEN, and only then we know who is the better DRIVER... After all, isn't that what its all about?

-- Aaron

 

Hmm... 3000 lbs (2800 + 200 lbs driver) (aprox).... to the power of .333333 times 5.825 is a 13.5... pretty damn accurate if you ask me.

-- Aaron

 

Very true. I was using the FAQ figure of 2650 lbs and a 150 lb driver for my 2800 value, but maybe 3000 is more appropriate. It's interesting to note that a 300 lb swing can make a 0.5 second difference, and a 100 lb swing can make a 0.15 sec difference... time to lose that beer gut fellas!

Also, with a car with as little low- and mid-range torque as the S2000 (i.e. most imports), screaming bejesus launches are necessary for good times... as an amateur racer I would prefer to sacrifice 0.25s to save my diff and clutch, and just ignore the bragging of the guy who beats me by .05 but has to get a new clutch every 15k miles.

 

You guys are way off. 'This' equation is way too simplistic to give you a number of any meaning. Acceleration is a lot more then a product of peak-power and weight .... a lot more. To start of, the 'power' figure that you should be using is 'power at the wheels' and not at the crank. Also you need to account for the gearing and tyre diameter. Still that is not enough - peak power is meaningless - look at it this way - when you accelerate a car then you move though a revrange. Even if you you can keep the S2000's engine between 6 and 9k revs, the engine delivers 'peak' power only when you're at 8.3k revs (not a bit more or less) .... how long do you stay at 8.3k revs? 0.01sec? Hardly long enough for it to have any meaning. The S2000 delivers between 167 and 240hp between 6 ad 9k revs. So what you'd need to use is the 'average' power delivered under acceleration .... you need to consult the actual car's power curve for that.

Look at it this way - do you think that S2000 with it's 240hp peak could take on another S2000 (hypothetical) that just happens to have 'only' 200hp but it has 200hp at all/any revs (ie. 200hp flat power curve)? It will not even be close - the 200hp S2000 will smoke the 'standard' S2000 so much it's not funny - the 200hp S2000 will be eating 911s for lunch.

Anyway, in order to 'approximate' the acceleration of the car you need to know the exact power curve (at the wheel), the weight, the gearing as well as the tyre diameter ... though even that will still be a loose aproximation of what will really happen.

Though, if you want something that will work things like this out (if you have all the required/mentioned data) then ask Sev as he has a utility called "car simutator" - you feed all this data into it and it will plot the given cars accelerating on the screen.

ps. 13.5secs for 1/4 mine is way too optimistic for the S2000 - better baseling is 14 secs flat and even that is incredibly hard to achieve. Only a few people here who have gone under 14secs.

 

um, duh. but if one really must make an estimate without averaging extensive track runs under various conditions, i challenge you (or anyone else) to come up with a better method that is anywhere near as accurate AND simple.

we ALL know that it's an incomplete model and nothing can ever take the place of real-world results, but really where does that argument ever go? because, you know, calculations that would account for gearing, tire diameter, and energy losses rely on Newtonian physics, which we all know doesn't truly reflect the behavior of particles at the quantum level.

i'm not trying to blow smoke, i'm merely trying to help this guy with his guessing by applying some information from a semi-reputable source, which by the way is about 10^3% more reputable than your condescending ass.

save the negativity for your home life pal. some of us are trying to engage in an interesting conversation.