What is a good ft.lbs. per cubic inch?

[CamKing]

Who cares how much max torque?

Torque doesn't mean anything without the RPM, gear ratio, and tire size.

An engine coming off the corner with 500ft/lbs at 4,000rpm, will get it's arse handed to it, by an engine coming off the corner with 475ft/lbs at 4,500rpm.

[Belgian1979]

Strange, I always hear people advocate the cu inch rule.

[plovett]

Who cares how much max torque?

Torque doesn't mean anything without the RPM, gear ratio, and tire size.

An engine coming off the corner with 500ft/lbs at 4,000rpm, will get it's arse handed to it, by an engine coming off the corner with 475ft/lbs at 4,500rpm.

Thank you for saying that. I've been saying basically the same thing for years and people act like I'm talking a foreign language.

paulie

[John Wallace]

500ft/lbs at 4,000rpm = 380 HP

475ft/lbs at 4,500rpm = 406 HP

I'd take the more HP also.

[MadBill]

AAAGGG! For the love of Mike lets not restart the Horsepower Vs. Torque War!

[Brian P]

What kind of BMEP numbers do you get for forced induction?
Most NA Formula one engines are in the 15+ range but at a very high rpm.

Forced induction changes everything.

More-or-less, the torque will be in proportion to the intake manifold absolute pressure corrected (inversely) for the intake manifold absolute temperature BUT the loss due to operating whatever is creating the forced induction has to be accounted for. In the case of a supercharger, that is a direct loss of the mechanical power that it takes to run it. In the case of a turbocharger, it's a loss caused by the higher exhaust back pressure and the loss of the ability to do any pulse tuning.

The pressure waves and velocities etc all work the same in forced induction as they do at atmospheric pressure, they're just scaled up by the higher density. If there is no intercooling then the higher temperature raises the speed of sound (pressure waves).

The complication, of course, is whatever has to be done to combat detonation (if spark ignition) or peak cylinder pressure limits (for diesels).

A plain ordinary production 2015 VW Golf TDI (turbodiesel) makes 250 N.m from 2 litre displacement; that is 15.7 bar BMEP ... and that's for an ordinary model, there is a higher-tuned (sequential turbo) model that makes 500 N.m for 31.4 bar BMEP ... http://www.autoevolution.com/news/volks ... 88759.html

[BAracer]

To keep the records straight, the ~1.64ft.lb. per cu.in. is with a 14:1 Methanol fueled engine, not one that runs on 110 octane gas. The highest torque per cubic inch on gas we've done is somewhere around 1.43ft.lbs roughly. Not super advanced.

Mike,

We generally run on the same principal of "torque at the tire" which seems fairly accurate. Multiplying the torque by the gear ratio seems a lot more realistic. But how do you compare engines that run in the same rpm range without some sort of benchmark?

[iadr]

500ft/lbs at 4,000rpm = 380 HP

475ft/lbs at 4,500rpm = 406 HP

I'd take the more HP also.

No.
Because of gearing- 4500/4000=1.125
Because you can run 1.125 extra gear x the 475 ft-lbs= 534.4 lb-ft at the tire. No other reason.

[nitro2]

The great HP vs. TQ debate, the sequel, is looming. Just put a couple more coals on the fire and it'll take off for 120 pages.

[iadr]

No debate- those who want to work with derivatives: Hp & rate of change of velocity can fool themselves if they so wish (do the math, the time elements cancel out).
The correct way is sticking with basic units.

[mk e]

No debate- those who want to work with derivatives: Hp & rate of change of velocity can fool themselves if they so wish (do the math, the time elements cancel out).
The correct way is sticking with basic units.

Yes, basic units but at the wheel not the crank

torque tells you how much force you have available
HP tells you what you can do with it.

They both matter just for different reasons.

[MadBill]

Aaaand, away we go! -Jackie Gleason

[CamKing]

But how do you compare engines that run in the same rpm range without some sort of benchmark?

If they run the same gear, same tire size, and same RPM, then you can look at the torque numbers, but if I'm building the engine, unless there's a gear rule, or rev-limiter, I'm not going to be turning the same RPM. I will give up max torque to increase HP and RPM, and I'll be faster.

There's no debate. If you look at the evolution of any top form of racing engine that didn't have something limiting the RPM, over the years, the engine would lose max torque, gain HP and RPM, and run faster.

[mk e]

Aaaand, away we go! -Jackie Gleason

Sorry......my bad....I thought it was a trivial question

[MadBill]

No apology needed Mark. You would have had to search deep in the archives to stumble across it. At the risk of having hostilities renewed, here's the link: viewtopic.php?f=15&t=29115&hilit=HP+Vs+Torque