I've seen this in a number of forums, but guessed this would be the appropiate one to pose this question. This is strictly a guesstimate right? Or can you seriously conclude someone's HP by their 1/4 times?

Here is the dilemna I see. I've seen people post, and perhaps they are not doing justice to this calculation, but I've seen posts where one will say his car makes xxxhp and xx.xx time in the qtr at xxx speed. So therefore, someone else at xxx+y speed makes more hp and someone with xxx-y speed makes less and anyone that goes xxx speed makes the same.

Some compare Z-28's to 300z's to McLaren to Mustang. But all have different wieghts. Granted they may be close in weight,(depending on your definition of close), but they are different.
If you were to go the extreme and compare a bike that does a 10 sec 1/4, does that mean it has more hp/tq than my Z28? Of course not.

The other extreme: take a theoretical car that can go 0-100 in 2 secs but 100-120 in 10 secs. Then a car that goes 0-100 in 10 secs but goes 100 to 500 in 2 secs? See my point? Power curves and Torque curves could be all over the spectrum.

Anyway before I stray too much, (too late), my question really is this. Is there some calculation that people use to determine hp/tq from 1/4 times? And if so, what justifies that calculation?

Nate.

 

Work is torque. HP is how quickly the work can be done.

A 300hp Camaro might go from 0-60 in 4 seconds
A 60hp VW Bettle will go from 0-60 in 20 seconds.

The lower HP engine takes longer to get up to speed because it doesn't work as fast.

Weight is the biggest factor.
My 500hp Camaro goes 0-60 in about 2 seconds.
A 500hp, 30,000 pound tractor trailer should take about 60 seconds.

Although they have the same HP, it takes a lot longer to move so much more weight. Massive amounts or torque and gear help but it still isn't as quick because of all the weight.

You can't really calculate torque from any 1/4 mile time because it's multiplied and changed so much going through a torque converter, tranny gears and diff gears. HP can be calculated from the 1/4 mile mph. The only true way to know an engines torque is on a dyno.

For more information on HP and torque read this:
http://www.hardtail.com/techtips/hpandtorque.html

 

Thank you. I prefer a systematic approach to problem solving, and with what you said and the information on that link, I feel better knowing that a dyno is the most practical solution to determining torque.

If power equals work over time, then more power is needed to do more work (move more weight) in the same amount of time. Hence why a 600 lbs bike w/ rider and a 3800 lbs car w/ rider can run the same 1/4 mile, yet the torque on the bike will be about 1/6th that of the car, and the HP about 1/4th.

 

Yes. That's why it's all about power to weight.

It takes a lot of HP to move a 3500 pound car into the 10's while a mild SBC could do it in a 1500 pound altered or dragster.

It's cheaper to go fast by removing weight than it is to make hp. NHRA records could be broken easily if there wasn't a minimum weight for many of the classes.