X-cellerat -tour formulae ( that doesn't work) from Blighty

xctasy

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Hey, get a load of this book I got a while back.

V276.jpg


It's a little expensive for the US, about 30 ping I'd say. But the team that sell it have some ace books http://www.veloce.co.uk/cgi-bin/veloceco/V276.html?mv_pc=113


Any way its written by dudes with letters after there name, and 99 % of it is just awesome. However, I'm gonna talk about the 1% that
isn't.... just to be a kill-joy :roll:

Any way, on Page 99 theres a formulae that StrangeRanger and I discussed. He claimed it didn't work. After doing the sums, I can confirm it. It's just taken 6 months for me to get around to doing it.... :stick:

The formuale for 0-60 mph in seconds is 2*W, all over T, raised by ^0.6 (the 0.6 th power). W = WEIGHT, T= lb-ft maximum.

Eg1: 69 Mustang 250 with 155 hp gross (133 net) and 235 lb-ft gross (205 lb-ft) in a 3200 pound car including its rider.


The answer is 2*3200/205 all rasie to the 0.6 th power, which is 7.88 seconds. Now anyone with a 250 Stang knows they had troble breaking 10 seconds for the 0-60, and 17 seconds for the quarter, so this is a bif over estimation.

Eg 2: 1970 2liter Pinto with virtually no emission gear and 112 lb-ft of torque in a car about 2550 pounds with its rider on board. Do the sums, you get 45.536^0.6, which is 9.89seconds. Still a bit quick for a car that never did better than 13 seconds. Over estimation again.

Eg 3: My Falcon does 260 lb-ft at the chassis dyno, allowing for 33% drive line loss. In a 3650 pound vehcile loaded up. The figures are showing a best 0-60 mph time of 2*3650/260, or 28.08, to the ^0.6 = 7.40 seconds. The best I've ever done is broken 9 seconds for the 0-60 mph, and a flat 16 for the standing quarter. Over esitmating again. What gives?

Eg 4: The new 2003 XR6 Turbo twin cam 4 liter Falcon weighs in a 3950 pounds with a driver. There is abour 321 hp net, and 332 lb-ft. Doing the sums, 2*3950/332 = 23.795, which to the ^0.6, is 6.70secs. But it does 6 seconds flat 0-60 mph with two passengers. Ok, Ford has fudged the torque rating a little, it may be higher, but the formulae is clearly pessimestic here.

Oh golly.

I've done some net impulse calculations, and they don't line up with the formulae from How to Build, Modify&Power Tune Cylinder Heads.

It's a turkey!

My advice? Buy the Ford Six Performance book instead
:)




I just spent 30 minutes doing some editing. I keep gettin moofed...trans pacific cable has falied ping test :cry:

Changed the spelling form dosnt to doesn't. Ahhhh. Much better!!!!!
 
Using any formula to calculate acceleration has to use RWHP, not net at the flywheel. In your first example, reduce the actual HP to about 75 or 80 at the rear wheels and you'll find a truer number for both the 0-60 and the 1/4 mile.
 
That's it! Torque is irrelevent. Rear wheel power is the measure of how quickly work can be done. Work is a force times a distance (torque).

Sure, you got to have torque to make power, but even if you have only, say, 100 lb-ft at the flywheel, there is often ten times that after the trans and diff has multiplied it at the bags, and if you had 130 rwhp, that is what governs the acceleration, not 1000lb-ft of startline twist. I don't think its irrelevent for 60 foot times, but where not talking about that!
 
Two examples from my stable:

My Mustang: 3200 bs w/ driver, 330 ft-lbs on the chassis dyno. The equation gives a 0-60 of 5.92. Only if I stop to eat a sandwich on the way. :D

My truck: 230 ft-lbs at flexplate, figure 195 at the wheels and 4400 lbs works out to 9.83. Actual is 11.6 :cry:

It seems to fall apart with very good and very bad combinations. Maybe it works for a Taurus with the standard Vulcan engine. Who cares.
 
I just cannot understand what all this stuff about torque and HP is all about. I wish that they would just use one rating and be done with it.
How can torque not make a difference over quarter mile is torque power or at least sort of. I just dont get it.
Only thing I know is if you lighten a flywheel it will usually cause the vehicle to accelerate faster but the down side is it will cause it to be unable to hold its rpm as well on a hill.
But if this is true it seems the "torque"? (heavier flywheel) actually slows the car down over the quarter mile. Doesnt make much sence to me?
 
The article Whittey posted is great. :D
I like to explain it in terms of guys carrying buckets of water. Two little guys carrying 1 gallon buckets can carry as much water as two big guys carrying 5 gallon buckets, they would have to run five times as fast. The bucket is the torque. The torque times the speed gives you the work (HP). That's why little rice engines blow up. :twisted:
 
Great simplicity. I finally understand.
I reckon the two big de-stressed guys are less likely to do an injury than those two little ones. All that running around has got its hazards.
Oh and the big guys would win a tug of war with a rope. If it were a human contest this would be the true measure of "Power". The other is termed fitness. Interesting that both can achieve the same result.
But watch out out if the big guy learns to move too?

Thanks for the reply.
 
(saint) BIGREDRASA
I like to explain it in terms of guys carrying buckets of water. Two little guys carrying 1 gallon buckets can carry as much water as two big guys carrying 5 gallon buckets, they would have to run five times as fast. The bucket is the torque. The torque times the speed gives you the work (HP). That's why little rice engines blow up.

This needs to be cannonized in a book called the Authorised Version of Pro Six, Anti-Ricer Knowledge!

:thumbup: Nice one!
 
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