Changing gear ratio affect RWHP on a dyno?
 

Going to a higher gear, say 2.73 up to 3.42, and then having the car dynoed, would RWHP or TQ show up on the graph. :bigears

higher ratios reduce rwhp

:lurk:

:yesnod:

So would 3.42 gain more HP over 3.15

:lurk:

I think you should gain some torque. I'm sure I will be corrected if I'm wrong. :lol:

Other way around...

Peace
Chip

Actually, lower gears produce lower dyno numbers. 3.42 is a lower gear ratio than 3.15.

:iagree:

It's kinda like this!

When you try to remove your LUG NUTS with a 3/8" ratchet and socket it will take a ton of arm strength to remove them and if you had a dial gauge on your elbow the needle would move tremendously with the effort being used.

Now if you were to remove that same LUG NUT and used a long bar with the dial gauge on your elbow it would read less in the effort needed!

So to answer your question you will loose some dyno numbers because the 3.42 gears will make it easier to move the dyno, therefore the gears are utalizing what you already have and it takes less effort to get it going:D

In real world though it is ONLY a number but the results are better performance and quicker times and it takes lees to move your Vette from point A to B thus making it quicker:thumbs:

But the results are like adding 50 HP but it does not show up on the dyno just at the track and on the street!:yesnod:

I hope this helps:leaving:

You just described the effects of torque, not horsepower.

Higher final gear ratios reduce wheel horsepower because of increased friction loss

Okay! It was just a real world like way to help someone get the idea!

Much in the same way it loses HP too, that is in an illustrative way!:D

I would like you if you could give us an ILLUSTRATION to help us understand the loss, if that would be good for you :thumbs:

Please respond! So I wont make this mistake again:D

Thanks,Matt

Summary: You'll loose some numbers on the dyno, but the car will be faster on the street. You want the 3.42 :thumbs:

3.42s are no good. You know you want 4.10s. So i have a question then. I dynoed at 424rwhp with 3.42s and now have upgraded to 4.10s what would my dyno numbers be now?

415:crazy:

Nice post! Too many folks get wrapped up in a HP number. The most important mod is the driver. The Corvette is quick enough out of the factory.

This would be true if the percent decrease in hp/tq correlated with the gear reduction. Just like if went from a 1' breaker bar to a 2' breaker bar, The dial guage on your elbow would read exactly half of what the 1' breaker bar read given the same amount of tq at the lug nut. Going from a 3.42 to a 3.90 is a 14% difference which means you would loose 14% of your tq on the dyno and I don't think people lose that much.

I don't really have a theory for why you lose power but it may have to do with engine load. Like maybe you have more power when the engine is under a higher load.

OK. You lose #s on the Dyno because with lower gears it takes less effort (torque) to turn the roller. The way Dynos work HP is derived from torque so the HP #s will also drop a little.

Dynos #s are also affected by wheel/tire sizes and unsprung weight.

People seem to forget that Dynos are really a tuning tool and to some extent you can use the information for vehicle to vehicle comparisons but it is not 100% accurate.:cool:

fixed it fer ya :D