How do I find Peak Torque RPM ?

[hat_man]

Hello everyone.

I'm looking to see if there is a formula to find the RPM range where peak torque is at for a given engine. This doesn't really apply to my Ranger, but I'm putting together a "cheat sheet" of modding formulas for another (not so eco) project. Does such a formula even exist, or am I over thinking things again?

[freebeard]

There must be a formula, since the specification is published by manufacturers and third parties. Unless they all have dynamometers.

duckduckgo.com/?q=find+peak+torque+for+internal+combustion+engine &ia=web

[cRiPpLe_rOoStEr]

Never heard of such a formula, plus it may not take into account other factors such as cam profiling, ignition timing, size and shape of intake and exhaust headers, or even how some engines are electronically limited to a lower torque in order to not grenade a transmission...

[Piotrsko]

In one of my reference books from the 1960's there is a graph that indicated peak torque occured around 2/3 of maximum hp in terms of rpm. But that was for rather inefficient large displacement low revving carburated gasoline engines and has probably been superseded in the succeeding 60 years.

In my other cars that still have their owners manual, sometimes the manufacturer specify where peak is in the specification section

[freebeard]

Quoth DDG:

https://www.enginelabs.com › news › ...ctive-pressure
The Great Equalizer: Understanding Brake Mean Effective Pressure
Quite simply, through Brake Mean Effective Pressure (BMEP). Simply put, Mean Effective Pressure is a calculation of the average engine cylinder pressure throughout the combustion cycle. Adding "brake" in front of it simply means the number was calculated from a torque value measured on an engine dyno.

[aerohead]

1) GOOGLE search the vehicle of interest.
2) Find CAR and DRIVER's / ROAD & TRACK's specifications.
3) Read the peak torque rpm directly from the specifications.
Fini!

[ennored]

Originally Posted by freebeard

Unless they all have dynamometers.

This. Lots of them.

[Ecky]

No formula. Too many factors.

Honda's older engines often had two torque peaks. The cam is the largest way to shift torque around, and Hondas generally have two (or more) different cam profiles. As you increase the cam's lift and duration (larger lobe size), you shift the torque peak up in RPM (reducing torque at low RPM). VTEC exists specifically so that engines can have a cam that feeds enough air at 7000rpm+, while also not gutting the engine in the range people actually drive in.

Some other factors that move peak torque around:
-Cam lobe phasing
-Intake runner length
-Intake runner width
-Intake diameter
-Header length
-Header width
-Header pattern (e.g. 4-2-1 or 4-1)
-Intake and exhaust valve size
-Engine stroke ratio
-Engine rod ratio
-Compression ratio
-OTTO vs Atkinson vs Miller cycle

[E.Roy]

It's called a dyno. 1 test is worth more than a 1,000 expert opinions

[cRiPpLe_rOoStEr]

Originally Posted by Piotrsko

In one of my reference books from the 1960's there is a graph that indicated peak torque occured around 2/3 of maximum hp in terms of rpm.

Variable valve timing, and more recently variable-geometry turbochargers, are changing the game.

But that was for rather inefficient large displacement low revving carburated gasoline engines and has probably been superseded in the succeeding 60 years.

Reminds me of the first 16-valve 1.0L engines of late-'90s in Brazilian "popular" cars, which had peak torque way closer to peak power RPM compared to their 8-valve counterparts.