How much power do you lose dynoing in non 1:1 gear?

[Meatball]

I’ve heard from some sources that the 1 to 1 gear will show the best power and from others that the torque will be highest 1 to 1 but the power curve will converge at the top end. Anybody run the direct gear and another gear back-to-back? I ran in 5th (=direct on 15-17 mt82) and the torque was so much higher than 4th but I stopped at a lower rpm for mph concerns.

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[Patriot Six]

On my A10, I was down 15 hp/tq in 6th gear vs 7th (1:1).

 

[Meatball]

On my A10, I was down 15 hp/tq in 6th gear vs 7th (1:1).

Thanks. That’s right in line with a MotoIQ article where someone from PBD mentioned a 10-15whp loss in 4th vs 5th (mt82). Someone at Whipple mentioned a while ago on this forum that the pk tq is higher in the direct gear but the hp curves converge at high rpm, in their experience. I just want to figure a “correction factor” for my 4th gear pull to 7500.

 

[Jbcain]

Bump the load up the same % difference to mimic.

 

[Meatball]

Bump the load up the same % difference to mimic.

It’s interesting because the article said 10-15whp rather than a % drop. It makes more sense if its proportional but he got the same number supercharged as the Motoiq article got NA on a m6. Many other factors here probably (ratio of gears considered, diff ratio, a vs m, etc) so it could be coincidence.

 

[Burkey]

I’ve heard from some sources that the 1 to 1 gear will show the best power and from others that the torque will be highest 1 to 1 but the power curve will converge at the top end. Anybody run the direct gear and another gear back-to-back? I ran in 5th (=direct on 15-17 mt82) and the torque was so much higher than 4th but I stopped at a lower rpm for mph concerns.

What do you mean by “the torque was so much higher”? What sort of numbers are we talking?
You need to think of power (hp) and torque as inextricably linked in a sense. Eg. For a given rpm and hp, the torque figure will ALWAYS be identical, practical example, 500tq @ 7000 rpm will always equal 666.4hp
The crossover at 5252rpm is because of the math behind the calcs. If the two aren’t intersecting at that point, it’s purely the result of using different scaling for the two parameters (which happens a lot here in Australia) example provided below.

 

[Meatball]

What do you mean by “the torque was so much higher”? What sort of numbers are we talking?
You need to think of power (hp) and torque as inextricably linked in a sense. Eg. For a given rpm and hp, the torque figure will ALWAYS be identical, practical example, 500tq @ 7000 rpm will always equal 666.4hp
The crossover at 5252rpm is because of the math behind the calcs. If the two aren’t intersecting at that point, it’s purely the result of using different scaling for the two parameters (which happens a lot here in Australia) example provided below.

In 5th it’s about 30 ft-lb higher than 4th. You would think the shape of the torque curve would be identical between gears with a simple vertical shift. But again some knowledgeable folks have said that the hp doesn’t show higher at high rpm, I don’t understand why. If that’s true the shape of the torque curve must change slightly between gears.

according to others, like the person who responded here, there is a difference in peak hp. I didn’t rev 5th as high as 4th out of concerns about over speeding my tires/the rollers and am curious what my 5th gear power would be based on 4th. Maybe I’ll just bite the bullet and try it in 5th next time.

 

[Burkey]

In 5th it’s about 30 ft-lb higher than 4th. You would think the shape of the torque curve would be identical between gears with a simple vertical shift. But again some knowledgeable folks have said that the hp doesn’t show higher at high rpm, I don’t understand why. If that’s true the shape of the torque curve must change slightly between gears.

according to others, like the person who responded here, there is a difference in peak hp. I didn’t rev 5th as high as 4th out of concerns about over speeding my tires/the rollers and am curious what my 5th gear power would be based on 4th. Maybe I’ll just bite the bullet and try it in 5th next time.

Do you have a copy of both the sheets?
If we assume you’re making 600tq at peak, a difference of ~30 is ~5%
Basically, if you apply that to your hp figure, you should’ve gone from something like 700whp to say 735whp. Substitute the math to fit the example more precisely of course.
Worth remembering that it’s unlikely that you’ll get two identical runs, so there’s a certain error margin that you need to keep in mind when trying to make predictions.

 

[Meatball]

Do you have a copy of both the sheets?
If we assume you’re making 600tq at peak, a difference of ~30 is ~5%
Basically, if you apply that to your hp figure, you should’ve gone from something like 700whp to say 735whp. Substitute the math to fit the example more precisely of course.
Worth remembering that it’s unlikely that you’ll get two identical runs, so there’s a certain error margin that you need to keep in mind when trying to make predictions.

Unfortunately I only have a print out and it’s not where I am now. The question is is the torque curve identical between gears just shifted vertically, or does it converge at high rpm? Patriot Six showed a difference, but I don’t know if that difference carries throughout the rpm range.

I did see some difference bw 4th gear runs but they were very close, within a few ft-lbs. 5th showed a big difference.

Anyway thanks for responding

 

[Burkey]

Unfortunately I only have a print out and it’s not where I am now. The question is is the torque curve identical between gears just shifted vertically, or does it converge at high rpm? Patriot Six showed a difference, but I don’t know if that difference carries throughout the rpm range.

I did see some difference bw 4th gear runs but they were very close, within a few ft-lbs. 5th showed a big difference.

Anyway thanks for responding

I wouldn’t lose any sleep over it.
The most you can say about a dyno figure is that this is what it made on a given dyno on a given day. It’s just a number. It’s a tuning tool, not the arbiter of absolute truth.

 

[beefcake]

10-20 each gear down typically

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