bl85c

iTrader: (2)

I think Mark already has plans for this, but I need help coming up with a torque equation for tunerpro. There's loads of math I can dig up, I just can't put it together. My patience for this sort of thing has waned over the years. What I need is a formula that describes torque from current speed using vehicle weight as a constant.

bl85c

iTrader: (2)

Ok, I have the formula I need for horsepower and from that torq is easy. Main issue is finding a way to get multiple speed samples using tunerpro. The formula is-

.5 * W / 32 * (5280 / 3600)^2 * (A^2 - B^2) / T / 550

Where W is vehicle weight, A is current speed, B is initial speed and T is time between samples. Look valid?

By setting B to 0 and T to your 1/4 mile time (or whatever time you like) you can get a quickie power esimate at the end of a run without needing to come up with a way to get a lagged speed sample.

bl85c

iTrader: (2)

Atleast that's how it should work out. Can't get this formula to work out... need some more info.

89_RS

Theres an equation in David Vizards book "How to build SBCs on a budget", while it doesn't use vehicle speed, it does use engine revolutions. So if you know you HP curve, then computing tq should be easy

HP=(Tq*RPM)/5252

So for Tq it would be:

(HP*5252)/RPM=Tq

Hope this helps.

bl85c

iTrader: (2)

Yea, that's what I need for torque from horespower. Just need to wrap my head around the horsepower from acceleration equation. More stuff...

Energy = 0.5 * mass * velocity squared
Power = Energy / time

So it's pretty easy to understand most of the equation, but I don't see what the value 32 is supposed to represent. (5280/3600) reduces mph to feet per second, (A^2-B^2)/T converts speed to change in velocity over time and 550 is the constant for horsepower (550 ft/lbs per second).

bl85c

iTrader: (2)

Hmm. Maybe this looks more accurate?

.5 * W / 32 * ((5280 / 3600)^2 * (A^2 - B^2) / T) / 550

RBob

iTrader: (1)

The 32.1 is the conversion of mass from gravity. Without gravity there is no mass. Note that you also need to take into account the vehicle Cd and frontal area. It is also easier to do some of the math in metric, such as newtons, and slugs.

Google for the Physics of Racing series. Chapter 6 is what you want.

RBob.

bl85c

iTrader: (2)

Thanks, that's a big help. Ok, so I've broken down the formulas in that artice so it's useable for any vehicle. So to calcualte how much power your car expends at a certain speed (regardless of powertrain and weight) you use...

(R) Air resistance multiplier = .5 * C * A * .0801 * 2.1511 / 32.1

(E) Hp expended to overcome air resistance = R * 22 / 8250 * V^3

Where C is coefficient of drag, A is frontal area and V is velocity.

Then you simply add the results from these equations to the result from the previous equation like so...

.5 * W / 32.1 * 2.1511 * (A^2 - B^2) / T / 550 + E

And you should have a decent estimate on your power output. Still need to verify this formula and come up with altitude and temp compensation but I'm tired and need to get to bed.

bl85c

iTrader: (2)

Dud. Still comes up low by about 21%. What else is missing from this equation to make it work?

bl85c

iTrader: (2)

Screw it, here's the final equations. This would obviously be a huge single equation to put in tunerpro so I left them separate. It's interesting to see how much power you're wasting at speed anyway. This gives you an estimate of your wheel horsepower. For an estimate of flywheel horsepower multiply by 1.17. If you choose to have a torque esimate as well you need to use the 1.17 multiplier for flywheel estimation only since torq measured at the wheels changes with what gear you're in.

(E) Hp expended to overcome air resistance = R * 22 / 8250 * V^3
Where C is coefficient of drag, A is frontal area and V is velocity.

(H) Horsepower = .5 * W / 32.1 * 2.1511 * (A^2 - B^2) / T / 550 + E * 1.22
Where W is vehicle weight, A is current speed, B is initial speed, T is time between A & B

Torque = H * 5252 / RPM

.0219 is the correct multipier for R for your typical 3rd gen. Now how to set up a lagged speed sample...

bl85c

iTrader: (2)

Problem with using the formula as mentioned in post #2 is that it's only accurate at the sec you set it to. I'm not finding an easy way to set up a delayed speed sample either. Ideas?

RBob

iTrader: (1)

Best bet is to dump the log file into Excel. Then do the math with the results as another column. Can then do stuff like graph torque and/or HP vs. RPM and/or MPH. This way it also becomes useful for WOT SA tuning.

RBob.