Which gear for dyno

[efurlong]

Just completed my first oil change, and now have around 1100 miles on my GT. MPE racing in Whitman, Massachusetts is having a dyno day - car show on April 15th. I am going to dyno the GT, but which gear is one to one? Is there a true one to one in our cars? Thank you in advance.

 

[Mod Friendly]

6 speed tranny best gear would be 4th gear, just from previous experience in dynos in the past.

 

[barondw]

I have used 3rd and 4th with no significnt difference.

Some dynos are not rated to 200 mph. Find out the limit and that will determine which gear you can use.

Dave

 

[KenBMD]

4th would be best. 3rd would make for a pretty short dyno pull.


Ken

 

[SLF360]

4th. Over and out.

 

[Specracer]

You in SE MA?

 

[efurlong]

thanks

Thanks for the quick response. I am located in West Bridgewater, Massachusetts.

 

[barondw]

4th would be best. 3rd would make for a pretty short dyno pull.


Ken

Time isn't important its what the car does. Having done multiple runs in both 3rd and 4th there is no difference.

Dave

 

[barondw]

One thing I forgot to mention is the tach reads a bit low. Somewhere between 300-500 rpm. Thus the car can exceed redline on the dyno to reach max power. I never hit the rev limiter.

The last few rpms make a major difference in max power readings. If you stop to early you can lose 20-30 rwhp in the reading.

Again no difference between gearing.

Dave

 

[KenBMD]

Time isn't important its what the car does. Having done multiple runs in both 3rd and 4th there is no difference.

Dave

Time is absolutely important. Especially if you are tuning it. Too quick of a dyno pull doesn't give you proper data for stablized open loop fuel information, fuel pump duty cycle and many other critical data points. Considering that many of the GT owners out there are interested in doing a high speed run, this information because even more critical with these cars in particular.

Ken

 

[TrackDay]

I completely agree with Dave. Third or fourth gear should make no significant difference in HP or Torque measured on a DynoJet. I also agree with Dave that it is important to run the car close to red line to get the maximum HP figure.

That being said, those that plan to do some tuning might be asked to run in fourth gear but this all depends on the individual shop, how the individual shop is set up to pull data off the car / engine, etc. Some shops can pull all the data directly from the Ford EEC and pull independent data for comparison too. Pulling data directly from the Ford EEC gives the ability to see all kinds of things like air inlet temperatures, engine temperatures, etc. If you are asked to make multiple pulls in fourth gear, be sure check your rear tire pressures for safety sake prior to making these pulls. We all know a fourth gear pull to 165-170 mph is nothing to be casual about. As Dave said some DynoJet machines can run up to 200 mph, others can not! There are software and equipment differences between machines. Third gear pulls will run you up to about 140 and nothing trivial about that too.

If you choose a shop for tweaking the computer do some homework first. I myself have not (yet) made any changes to my GT computer but will perhaps in the near future. I’ve checked into the Ida Automotive shop a bit and it looks like an A#1 shop. Anyone with that many SEMA show cars and having this kind of historic background (with Ford and other major manufacturers) would get my vote. Now thinking those guys in the north east are real lucky to have a guy like Bob Ida in their area!

 

[TrackDay]

Follow up of what is significant:
That the dyno measurements are of a similar nature / format (and for our cars run to the same RPM).
For example most shops are using a DynoJet so I suggest that data posted here be provided as a WinPep7 (drf) file so each of us can see the entire data (not just an image bmp, tif, jpg, etc file).
Significant differences exist when running at different:
Ambient air temperature (largest relative effect)
Barometric pressure
Relative humidity (smallest effect).

WinPep7 drf files will show the ambient air temperature, barometric pressure and relative humidity.
Even more detail is contained within the DynoJet file such as air / fuel ratio, spark advance, etc. depending on how much data you are able to log and what latest DynoJet software you are using.

 

[Black2003Cobra]

There are a few more good reasons to run in 4th gear.

1) Power to accelerate a rotating mass (rear wheels, axles, gears, drive shaft, clutch, flywheel, etc) goes in direct proportion to angular acceleration, (i.e., P = Iαω). So the faster you accelerate, the higher the inertial losses in the driveline.

2) In 4th gear, the transmission’s input shaft and output shaft are directly coupled (1:1) so there’s less loss through extra gearing within the transmission.

3) There is less chance of tire slip in a higher gear due to the lower rear-wheel torque.

Other than that, (and assuming you stay under the speed limit), the dyno doesn't much care about the actual gear ratio. It backs that out by monitoring the rotational speed of the drum and the engine speed to give you the right torque numbers. I agree about having a longer pull from the tuning aspect.

I would also like to see the RUNFILEs for dyno runs you guys make! That would be awesome! I haven’t heard of a shop yet that wasn’t willing to give them to the customer. :cheers

 

[Fast Freddy]

4th gear on the GT is not 1:1........... its .94:1

 

[Black2003Cobra]

Really? Ok...my bad. I thought it was 1:1. Scratch that one then! Thanks for the info.