95Juan

I'm somewhat.......confused, let's say- as to how HP and TQ relate to each other. i understand dyno sheets, and that usually TQ is made at a lower rpm than HP. etc, etc. but i've often wondered-

what's more important in going "fast"?

in straight-line performance what's more important? HP or TQ?

let's say you line up 2 cars against each other, one has 250rwhp and 300ft-lbs of tq. and the other has those numbers inverted- 300rwhp and 250 ft-lbs.

which is (theoretically) faster, assuming both have the same weight, gears, and drivetrain loss?

when the disparity gets bigger, say, 200rwhp and 300ft-bs vs 300rwhp and 200ft-lbs, i know that hp will probably win...probably.

but overall, my question is- how do HP and TQ relate to each other in terms of moving your vehicle at a high rate of speed?


not really important, just something that gnaws at my brain every now and then.

toddk911

Tq wins races, hp sells cars.

Tq is force, hp is power.

Tq gets the car moving, hp keeps it moving.

95Juan

now see, i always thought in that old "musclecar mantra" of "Torque moves mass" which i guess is true- but i'm talking theoretically- 300/200 vs 200/300. who wins? i dont think that say (for the pure sake of example) that in a race between--- an RX7 with 300/220 in hp/tq, and a 951 with 220/300 in hp/tq (or around those numbers), that the 951 would necessarily win.

Of course- taking into assumption that both cars could launch equally, and made those numbers at the wheels. such as- maybe a roll-on situation.

just taking 2 cars, one that typically makes more TQ than HP (951) and one that usually makes more HP than TQ (rx7)

toddk911

Horsepower is tqx rpm, so in the case above, the 951 would make the same power if it could rev as high as the Rx7

Same with Ferrar that make 400+ hp, but only 275-300tq. They simply rev very high.

95Juan

?



if a 951 makes those numbers at say- 5300rpm for hp and 3500rpm for tq, and the rx7 makes it's numbers at say- 7000 rpm and........whenver boost hits, say- also 3500 rpm for hp/tq respectively- then if the 951 could rev to 7000 it would make, or better the numbers from the other car?

so if the 951 could rev to 9k rpm, but made peak power at 7k like the rx7, it would make....more hp than the rx7?


how would that work, seeing as if the car made peak hp at 5300 rpm, just adding 2k rpm to that powerband....wouldnt that just make it lose more power as it gained rpm, because it follows the curve that it was going along in the first place? or would the "curve" change to reflect different mid-points, high-points, since "high rpm" would be mid-range now on that motor.


......did any of that make sense?

JustinL

If you assume identical gearing, revving high is important because it lets you stay in a certain gear longer before you have to shift and cut your actual force to the road down. So your example of cars with inverted tq and hp, the car with high tq would get out to an early lead, but would have to shift sooner, and as soon as he did he loses his advantage and the high hp car continues to accelerate to his redline and would win the race.

If you regeared the cars to hit the same top speed in each gear, i.e., 60mph @ redline one car at 6200, and the other at 9000. You would have to give lower gearing to the higher revving car, thereby increasing the torque to the rear wheels and it would win again.

If you are going to take it to the redline, then power is what you want to take advantage of gearing.

95Juan

that's a good thing to take into account.

so if the car that redlined at 6200 rpm got some drivetrain changes and could rev to 8000 rpm, the curve would shift, right?

hosrom_951

Almost impossible to say that one car would win, unless they are BOTH exactly the same (gears, diff's, tires, wheels, weight, fuel etc).

95Juan

taking out what i had said about rx7 and 951 (~9000 redline and 6200 redline), if both cars were exactly the same. gearing, diff. same size tires, and same quality, same weight. 91 octane, etc.


200rwhp/300rwtq vs 300rwhp/200rwtq in say, 2 2500-lb cars that are the same minus mods.

this is theoretical, dammit!

hosrom_951

Just pushing you're buttons

streckfu's

HP is determined by torque applied over time.
HP=(TQ*RPM)/5252

toddk911

Assuming that info, I would say the distance of the race would be the factor.

0-60 higher tq would win

1/4 probably higher hp would win.

I would research 0-60 and 1/4 times and see which cars are hgiher. cars with more tq or more hp.

In a track situation, once again depends on distance and layout. Short track, short straights, then tq car probably. Longer track, long straights, hp car.

Of course assuming everything else was the same.

JustinL

If you are racing to a point where you have to shift, then power will win. If you don't let the high revving car get to it's high revs (high power) then it will lose.

So todd, unless the race is shorter than the peak power of the high revving high power car, the torquey car has a disadvantage.

95Juan

so does that mean that gearing and more rpm can make power?

streckfu's

Too many factors for a concrete answer but if your TQ remained constant accross your RPM range, increasing the RPMs will result in more HP.

Gearing is a completely different subject as it is a mechanism of transfering the engine's work to the wheels and has no impact on what the engine can do.