Dyno Numbers and Gears

[Shelby3]

I have always been told that gears affected the dyno readings in terms of horsepower and torque. I finally have some perceived sense of how much. The first run in the dyno sheet below is with 3.73 gears on blower only. The other run is blower only with stock 3.07 gears and approximately 10 degrees lower air temperature.
Some of the gains are likely due to the cooler air but a chunk must be in the gearing. I'm hoping with additional tuning I can get to 700 RWHP without the juice. Sean, when are the water/**** kits available?

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[Ulysses]

What were the temps during the first run and the second?

 

[Shelby3]

What were the temps during the first run and the second?

60 on the first and 50 on the second.

 

[STUGOTS]

So the stock 3.07's showed more power correct?

I always it was the other way around.

 

[Shelby3]

So the stock 3.07's showed more power correct?

I always it was the other way around.

You are correct, you were incorrect.

 

[Ulysses]

You've got approximately a 16.7% decrease in temperature and a 15.4% increase in RW Torque. I'ld have to say that most of that is due to temps.

 

[joe117]

The gears will change your torque at the wheels and they will change your rpm at the wheels, right?

With a 3.73 you will get more torque at the wheels but the wheels will not turn as fast.

Horsepower is a measure of torque at some given rpm. Tell me a torque reading at some rpm and I'll tell you your horsepower.

So the torque at the wheels going up and the rpm at the wheels going down,
these numbers, when fed into the hp formula,
will give you the same horsepower with either rear end gear.

Now, that being said, you might see a small difference due to more gear tooth contact in one rear ratio compared to another.

But gears can't change horsepower at the wheels.

 

[KenH]

The dyno numbers are SAE corrected, so that should factor out the temperature difference.

From what I understand and have seen, lower gears seem like they tend to read 5-10HP lower on the dyno. Whether that is a real loss due to more friction loss or something or not, I don't know.

I think you have some other factor at play here to account for the 62HP difference. Perhaps the blower was heat-soaked on the earlier run.

 

[Ulysses]

I completely agree with Joe and Ken. Other factors are in play. Good catch Ken.

 

[Shelby3]

The dyno numbers are SAE corrected, so that should factor out the temperature difference.

From what I understand and have seen, lower gears seem like they tend to read 5-10HP lower on the dyno. Whether that is a real loss due to more friction loss or something or not, I don't know.

I think you have some other factor at play here to account for the 62HP difference. Perhaps the blower was heat-soaked on the earlier run.

I did three pulls in each configuration. The two displayed above reflect closely in the range for each three pull set. It wasn't heat soak as we allowed adequate time between pulls to avoid potential impact.

 

[Ulysses]

Somethings different though, it looks like the AF goes from 12 to 13 between the two runs. Or is that expected to vary that wide. I would think that the AF would be pretty close if it were only a gear change.

 

[Shelby3]

Somethings different though, it looks like the AF goes from 12 to 13 between the two runs. Or is that expected to vary that wide. I would think that the AF would be pretty close if it were only a gear change.

Good catch. Could that be due to the ambient air temp difference?

 

[Ulysses]

Could be,

I'm not quite clear on how the IAT interacts with the O2 sensor intake in the calculations for AF. I thought that the PCM would try to keep AF close to the programmed value.

 

[2MANYTOYS]

I have always been told that gears affected the dyno readings in terms of horsepower and torque. I finally have some perceived sense of how much. The first run in the dyno sheet below is with 3.73 gears on blower only. The other run is blower only with stock 3.07 gears and approximately 10 degrees lower air temperature.
Some of the gains are likely due to the cooler air but a chunk must be in the gearing. I'm hoping with additional tuning I can get to 700 RWHP without the juice. Sean, when are the water/**** kits available?

You must be registered for see images

Good numbers Jim! Glad to finally see that your getting close to the numbers you were promised in the beginning. Are you going to be the next Viper tuner?

 

[Shelby3]

Never gonna be a tuner Brian but I am learning a bunch working through the list of issues with my car. Looking forward to the water/**** kit from Sean.

 

[Larry Macedo]

Wow, great numbers, Jim! For all of those who didn't think gear ratios skew dyno numbers, the proof is in the pudding!