# Determine Torque Data Without Dynamometer

Hi, this is my first post here. I have come across this site many times when looking for help and have found the most helpful information here. Thanks!

I am creating a spreadsheet that you can input your vehicles Cylinders, Piston Diameter, Stroke, Displacement, HP, Torque, Size, Weight, Tires, etc.. all used together to help find your vehicles optimal performance for racing. I have found many issues that I am working with. Mainly right now is to determine a torque curve without the access to a dynamometer due to not having access to the actual vehicles in question. There has got to be a way to calculate torque data without dyno tuning. If anyone is interested in helping I can include you in the online spreadsheet.

## Answers and Replies

Doug Huffman
Gold Member
If there was a hypothetical model that produced useful data then why build the machine?

SteamKing
Staff Emeritus
Homework Helper
I agree with Doug. Due to the number of variables involved, there is no simple formula or procedure which can predict the torque curve of a given engine. The performance curves built into electonic engine controls are derived from extensive testing of actual engines.

What if all variables (which are?) were calculable. Would it be possible to establish a probable curve reading if one knew the hp@rpm and the torque@rpm, speed, time.

Last edited:
SteamKing
Staff Emeritus
Homework Helper
What if all variables (which are?) were calculable. Would it be possible to establish a probable curve reading if one knew the hp@rpm and the torque@rpm, speed, time.

Obviously, if you know HP @ RPM for multiple points, you can calculate the torque required to produce this power:

HP = TORQUE * RPM / 5252, where torque is measured in lb-ft.

There are many variables which contribute to the output of the engine and which influence one another. There are some which cannot be measured reliably under any circumstance.

Just off the top of my head, you would need to know the heating value of the fuel, the compression ratio, the volumetric efficiency of the intake system, the back pressure of the exhaust system, internal friction of the moving parts of the engine, etc., etc., etc. It's much easier to build and test an actual engine than to try to measure all the variables and calculate the output. Even if you had a supercomputer available, your engine output model would still miss something, because even today, there are still some physical phenomena which must be modeled rather than calculated.

Is what you are aiming for a sort of hybrid of this and this?

OMG YES that is what I'm looking for EXACTLY. I would to be able to this also.

Well, better knuckle down and get started then. Those two were not light work!

It can't (at the moment) develop a full torque curve from idle to rev line, because that would require some form of engine map for the ignition and fuelling at each rpm interval, but you could probably write a version to figure out a basic curve, (i.e. you'll be able to figure out the maximum sustainable RPM, the maximum realistic torque figure etc) and then use that to drive the acceleration model.

I thought about doing it but realised it would be far too complex to actually use so decided not too. I may do it to satisfy my own personal curiosity at some point though...

Honestly, I do not think either of those are as good, but then I am biased.

jack action
Gold Member
Honestly, I do not think either of those are as good, but then I am biased.

That is because the goals are different. The simulators from HPWizard are meant to be used to determine what you need before you know what you have. The question it answers is: What do I need to accomplish a certain level of performance? Who knows the gear ratios of the transmission, the tire size or even the aerodynamics characteristics before you even know what transmission, tires or body shape you will use? Who knows the rpm limit, the compression ratio or even the rod length before you know which engine you will use? What if it is an electric motor? Once you have set up the basics that gives realistic results, then you can go into deeper analysis, like BAD propose. The question BAD answers is: What performance can I get with a known vehicle?

Even then, note how close results are with both simulators using the same vehicle, the only difference being less inputs required by HPWizard. HPWizard also takes care of downforce in the acceleration simulator, which BAD doesn't. That makes the results very inaccurate when it comes to vehicle like top fuel dragsters.

But then I am biased.

You are absolutely correct there, well explained.

I wonder what the boys at Ford do when designing an engine. I think they must have sort of a sixth sense from all their years of real world testing. They also have to consider marketability , durability and a lot of other factors. I think that's why you see engines like the 300 six on the market for so long.
A friend of mine is a factory trained Mercedes mechanic , he said that our fuel energy content has gone down considerably over the last 40 years. That would make a huge difference in any calculations.