10R80 Dyno 6th vs 7th Gear Pull

[Autopart101]

Anyone have any info on the difference between a 6th-7th gear Dyno pull? Is the difference a fixed number 10-20WHP, or a % of total HP?

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[sabtaj1]

7th gear n up have weakest clutch packs. Don’t think either of those gears are correct for dyno though.

 

[engineermike]

I spent months trying to determine the cause of a high rpm power rollover that shouldn’t have existed, dyno’ing in 7th. Then I learned that the coefficient of rolling resistance actually increases significantly at high speeds. 7th gear gets you up in the 170 Mph range iirc. I dynod in 6th and suddenly the power curve looked how it’s supposed to and it made more.

 

[engineermike]

Here’s an example of a 7th gear dyno. It peaked at only 5800 rpm. Of course, how drastic the effect depends also on the tire design. I’m sure some are better than others.

https://lmr.com/products/2020-e85-mustang-gt-lund-tune-dyno-results

 

[Beerdy]

I spent months trying to determine the cause of a high rpm power rollover that shouldn’t have existed, dyno’ing in 7th. Then I learned that the coefficient of rolling resistance actually increases significantly at high speeds. 7th gear gets you up in the 170 Mph range iirc. I dynod in 6th and suddenly the power curve looked how it’s supposed to and it made more.

Mine was dyno'd in 7th gear and carried out close to 7000 RPMs before they started seeing some knock and let out (93 without octane booster). What could be the difference here?

 

[Autopart101]

Just wonding if anyone has a 6 then 7th gear pull same day. Some shop dyno in 6th some in 7th. 7th is 1-1.

 

[ZXMustang]

The reason most shops dyno in 6th is more of a self serving reason. It’s because they don’t want to run their dynos that fast. 6th might be a tad different in power numbers but remember the Dyno is a tool to measure gains and losses. Not the actual power number. So being safer running it in 6th will yield lower top speeds and maybe not hurt the machinery or the car. There is a difference in power too since 7th is true 1:1.

 

[engineermike]

Mine was dyno'd in 7th gear and carried out close to 7000 RPMs before they started seeing some knock and let out (93 without octane booster). What could be the difference here?

The coefficient of rolling resistance’s speed effect is highly dependent on the tire design and how much damping it has inherent to it. Lower damping will cause less negative effect at high speeds.

 

[engineermike]

Just wonding if anyone has a 6 then 7th gear pull same day. Some shop dyno in 6th some in 7th. 7th is 1-1.

I have tests in 6th and 7th on the same dyno but they were 3 months apart.

This page has some good comparisons and you can see how some are affected more than others:

http://www.bishopsperformance.com/dynoinfo.htm

And to be clear, I’m not saying dyno’ing in lower gears will always show more power. The lower gears eat up more power accelerating the drivetrain and the higher speeds eat up power in rolling resistance. There is one gear somewhere in the middle that will show the highest numbers. I suspect it’s 6th.

 

[dukecrazy]

I've wondered about this since dyno time was done for my car. I had read somewhere about not being able to dyno in 7th (even though it's 1:1) paired with the 3.15 rear gear because it would be too high of a speed and also risk damage to the stock driveshaft. We dyno'd in 6th and the results always made me question how much of a difference there would be if I could dyno in 7th as well.

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