Difference between a 4th gear pull & 5th gear pull on dyno

I've seen where everyone says a dyno pull on a S550 GT manual should be done in 5th gear. What happens when you do a pull in 4th gear would it read higher or lower power/torque than it really has?

Thanks

4th gear still has a reduction ratio. 5th gear is 1:1 and will give the most accurate reading of engine output.

So a run in 4th would give a higher power/TQ reading or lower than 5th?

Thanks

Higher

4th would have a mechanical advantage and theoretically show more torque than the 5th. Theoretically...

Typically running in 4th shows about 10hp/tq less than 5th gear. A few guys have run both back to back.

Keith_PDX said:

4th would have a mechanical advantage and theoretically show more torque than the 5th. Theoretically...

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HP is calculated at the rollers by various methods (depending on the dynamometer type) and translated back to engine RPM to calculate engine torque. Gearing (4th gear as opposed to the direct drive 5th) only adds more unaccounted inefficiencies which would result in a lower value.

Automatics do not have a direct drive ratio.

TexasRebel said:

HP is calculated at the rollers by various methods (depending on the dynamometer type) and translated back to engine RPM to calculate engine torque. Gearing (4th gear as opposed to the direct drive 5th) only adds more unaccounted inefficiencies which would result in a lower value.

Automatics do not have a direct drive ratio.

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That's a new one. Many do have a 1:1 ratio.....

From Ford

Optional Six-speed automatic with paddle shifters
Gear ratios
First 4.17
Second 2.34
Third 1.52
Fourth 1.14
Fifth 0.87
Sixth 0.69

The clutch & planetary system never directly connects the input shaft to the output shaft.

Ah, yes, that particular automatic....I was speaking beyond the realm of S550.

Correct on the clutch/planetaries, but the gearing in an auto definitely comes into play in many aspects.

Strokerswild said:

Ah, yes, that particular automatic....I was speaking beyond the realm of S550.

Correct on the clutch/planetaries, but the gearing in an auto definitely comes into play in many aspects.

Click to expand...

;)
Well yeah. That particular automatic is the only one in the S550.

Until recently, all automatics had a direct drive... It wasn't that long ago direct drive was the highest gear.

I dynod my car one pull in 4th gear and another in 5th gear and the 5th gear pulled gave lower numbers like 10whp less

FYI for the '18 folks, the 10 spd is 1:1 in 7th gear, at least what's currently in the '17 F-150 and Raptor. I doubt it would change much, but it might.