The Effect of Dynoing in Different Gears

Jordo! · 02-23-2011, 11:00 AM

Quote:

Originally Posted by Skeeterbop

Maybe I'm thinking the same thing that you guys are talking about here, but why not figure out which gears give you the most similar roll out between transmissions? Lets go hypothetical here. Lets pretend fifth gear in the mt gives you a roll out of 20 ft and 4th gear only gets you 15 ft. Then the AT gives you a roll out of 17 feet in fifth and 14 ft in fourth. It would be a much closer comparison if you used 5th gear in the MT and 4th in the AT in this scenario. Granted in order to figure out roll out you would have to know the circumference of the tire. Also if you change tire sizes it would require a recalculation. It would be awesome if you figure out a way to make this work.

Honestly though I look at dyno graphs to see what percentage they gained. The logic I apply is that if they gained 10% hp or 10% torque, then I should see something pretty close to 10% on my car regardless of what dyno or gear I use as long as I keep those two variables constant.

Well, up to 125ish MPH, both the 6 and 7 speeds are in 4th gear, so I think that makes them more comparable than 5th to 5th.

Your point on the tire size and roll out distance is well taken too, but so long as everyone uses the OEM diameters, the difference will be negligible. Also, even if they are using different sizes, the effect will be further minimized in 4rth than 5th given the closer startng points.

In terms of determining changes to an individual car, it doesn't matter so long as you use the same gear each time, but I've now seen a few dynos where baselines were taken in 5th and post-modification dynos were in 4th, which led to all sorts of confusion.

Also, I was trying to figure out why all the data I saw pointed to a baseline wtq on a dynojet of around 225 whereas some people claimed a higher baseline of about 240 -- the answer, it seems, is that it depends on the gear used on the dyno.

Someone also recently started a thread asking about typical baseline torque, so clearly it's not just me/us who find this issue somewhat important

At minimum, it means people need to indicate the gear they used at the dyno when posting numbers (which some members have been good enough to do) in order to interpret their results.

Skeeterbop · 02-24-2011, 10:48 AM

Quote:

Originally Posted by Jordo!

Well, up to 125ish MPH, both the 6 and 7 speeds are in 4th gear, so I think that makes them more comparable than 5th to 5th.

Your point on the tire size and roll out distance is well taken too, but so long as everyone uses the OEM diameters, the difference will be negligible. Also, even if they are using different sizes, the effect will be further minimized in 4rth than 5th given the closer startng points.

In terms of determining changes to an individual car, it doesn't matter so long as you use the same gear each time, but I've now seen a few dynos where baselines were taken in 5th and post-modification dynos were in 4th, which led to all sorts of confusion.

Also, I was trying to figure out why all the data I saw pointed to a baseline wtq on a dynojet of around 225 whereas some people claimed a higher baseline of about 240 -- the answer, it seems, is that it depends on the gear used on the dyno.

Someone also recently started a thread asking about typical baseline torque, so clearly it's not just me/us who find this issue somewhat important

At minimum, it means people need to indicate the gear they used at the dyno when posting numbers (which some members have been good enough to do) in order to interpret their results.

Yeah, I could see how doing before and after dynos would skewer the results and make for bad comparisons. I guess i just assumed people would be smart enough to use the same gear for before and after. But yeah, I think the easiest thing to do would be to just post which gear the car was dyno'd in. I do have one assumption I figure you would be able to clear up since you have a lot of info on this. I'm assuming that for any given tranny, that the dynos done in the lower gear are producing more torque due to transmission ratios correct? Maybe not a huge difference but still noticeable right?

Thread Tools
Show Printable Version Email this Page
Display Modes
Switch to Linear Mode Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
5th and 6th Gears Grind	nicole	Engine & Drivetrain	4	12-28-2010 09:41 AM
3.89% is in effect	dalparadise	Nissan 370Z Pricing / Ordering Discussions	3	01-10-2010 07:59 PM
Oil cooler and effect on volume	tbonesteak	Engine & Drivetrain	15	01-02-2010 04:41 PM
Tire Patched- any effect on performance?	davidyan	Wheels & Tires	32	12-06-2009 10:18 AM
5zigen Dynoing their white Nissan 370Z in Japan 12.10.08	AK370Z	Nissan 370Z Photos / Spyshots / Video / Media Gallery	29	12-17-2008 04:19 PM