Does anyone know or seen any changes in RWHP #'s after doing a rear gear swap or tire diameter?

 

I've heard you get lower tq #s with a lower gear. (higher numerically). Not really sure about this though.

 

Anybody else have any insight?

 

I would think it is the other way. The few times I have dynoed, I have got a lower tq # compared to people with comparable engine mods. The difference being I have 3.23s and they have 3.73s or whatever.

 

That is exactly the results I would expect due to a higher numerical gear multiplies tq. The actual change would be very little i'd imagine, The main thing would be, on the dyno anyway, the lower rpm you are having to spin up your tires/wheels which would save some HP.

 

Going to 4.10s from 3.73/3.23s increases your torque multiplying capacity do to having more leverage on the tires. Less rotating mass would also do the same for your rw numbers since you can feel in the SOTP difference with shorter tires or lighter wheels so that translates into faster times and in ANY 1/4 time calculator whether by E/T or curb weight it will tell you that you gained hp with a faster time if the weight of the vehicle stays the same.

 

MJ,

A chassis dynos will show lower numbers with high numericly gears because of drive train losses. It's like running your truck in 3rd gear for a pull then then running it in 4th gear for the next pull. 4th gear will show better numbers because there is less drive-train loss then 3rd because it is 1:1 where 3rd isn't. The difference to 3.73 to 4.10 will be the difference in drive-train loss, you won't see a difference from torque multiplication you will just run up in rpm faster. Next time your at the dyno give it a try and you will se what I'm talking about.

 

Third gear is 1:1...

 

Not in a 5-speed, which is what Mjhoward is running