I'm not sure if this is the right forum, but since it involves ECU data logs, I'd post it here.

I've searched the internet and the forum and have yet to find a method for calculating "road" torque based upon acceleration times and how to adjust for drag and rolling resistance. I figure that when I bought the Haltech, I sort of got a dyno as well since all of the data is right there in the data log (except for vehicle weight & drag), I just have to do the calculations.

Does anyone know how to do this?

 

These two sites have some car math calculators which may help:
http://www.prestage.com/carmath/
http://www.timmcamis.com/calculators.html

The most accurate way to determine road torque is to measure it on a dynamometer. This is not very expensive if you have a large group use the dyno for the day.

An accelerometer is also a good way to measure your car's performance when you are not at the dyno or drag strip. My friends and I use the Tesla G-Tech Pro, but I'm sure that other brands of accelerometers work just as well.
http://www.gtechpro.com/products.html

 

This is a great question and there must be an appropriate calculation to get this estimate. The g-tech, and Pocket Dyno accelerometers calculate HP as follows:

HP=G*A*K1*(K2*W)

where
G=g force acceleration for every sample
A=time to 60 mph
K1=conversion factor for 0-60 times to 1/4 mile ET time
K2=constant based on weight

(they determine 60 mph times also from g force acceleration time)


We should be able to make a similar calculation based on 0-60 times according to the speedometer parameter on the datalog. We have everything except for:
1. the constant used to factor in the weight
2. the constant used to estimate 1/4 mile ET from 0-60 time

Since the datalogit logs everything versus time from log start, it will be a piece of cake to figure 0-60 times even if you don't start accelerating until 15 seconds into the log. (simply deduct the 15 seconds[or whatever] from the time log at the instant 60 mph is reached. (Don't forget that you will need to verify your speedometer. You can do that by running your car through a reference mile at exactly 60 mph while starting and stopping a stop watch. If you time exactly 60 seconds through the mile, you won't need a correction factor. If you are off, calculate your actual miles per hour and adjust your speedometer reference figures accordingly by dividing 3600 [the number of seconds it takes to travel 60 miles at 60 mph] by the number of seconds it takes to run the one mile and take that result and add it to or subtract it from the 60 mph as reported by Datalogit.

e.g. If you did the mile in 59 seconds you divide 3600 by 59 and your actual speed is 61.02 mph while your logged speed will show only 60. To get a rough estimate of your actual 60 mph time, you take the datalogged 59 mph as the top part of the 0-60 run).

Anyone want to try to work out the rest of the math?
Hell, I am a lawyer, if I could do math I would have gone to med school

If we can work this out, we should be able to cross chart ANY other parameter and HP.

 

OK

Did a quick check and decided that the accelerometers do a couple of different calcs. One takes the 0-60 time and converts it to 1/4 mile trap speed. The other takes the 0-60 mph time and converts it to 1/4 mile ET.

For our purposes it may be better to find the estimate equation for 0-60 to 1/4 mile trap speed and then simply apply the HP estimate calculation which is:

HP = (((1/4 mile trap speed in MPH / 234)^3) * Weight)

Now it looks like the only thing we need is the the estimate equation for 0-60 to 1/4 mile trap speed and we will all have a free and "dependable" dyno estimater.

Remember that the final estimated HP will be off of actual dyno'd HP by some margin, but that margin will be constant across the numbers. For example the Pocket Dyno is figured to have a 10% lower HP estimate than a dyno. This is not too hard to understand when you consider that on the chassis dyno you are doing a 4th gear pull (approx 1:1 ratio) throughout the top range and when compared to a third gear pull you may show as much as a 5-7 HP increase for 4th.

 

This link doesn't provide the info we need, nor does the product work for our cars, but it's interesting nonetheless: http://www.nology.com/pdadynoscreens.htm

 

You guys need something like Data Log Lab (www.dataloglab.com) to do all the hard work for you!

I'm currently extending it to load other ECU data log formats, including the output from FC-DataLogIt if there's enough interest:

https://www.rx7club.com/forum/showth...hreadid=187672

All help appreciated!

Thanks,

Glenn
Data Log Lab Support
www.dataloglab.com