Difference in RWHP between manual and automatic?

[Bandit]

I know a manual transmission frees up power over an automatic transmission--but how much, percentage wise? For example, going from a TH350 auto with a 2500 stall converter to a manual TKO-600 5-speed, as I did with my car. I know the best way to tell would be run it on a chassis dyno with both setups, but since I never had the chance to dyno the car before the swap, I can't do that.

Also, is rearend gear ratio a big factor in rear wheel hp? Say, if you swapped from 3:08's to 4:11's.

I am sure there are other variables, like autos with lockup converters that would change the results, but I am just looking for a general estimation.

(I am sure this has been discussed here before, but I couldn't find it with a search.)

[John McIntire]

I cant answer your question about the gear differences, but as far as the loss between an auto and a stick, The general rule of thumb is 20% loss for an auto, and a 15% loss for a stick.
I'm sure someone else will chime in about the gear differences

[Steve Chryssos]

The difference between manual and auto is 5%-10% depending on transmission type and converter efficiency. Some say more, but that is probably attributable to some sort of transmission problem or tuning defficiency. Biggest differences between automatic and manual are in the converter (slippage) and trans fluid pumping (parasitic). TH350's are fairly simple and efficient, so figure on the difference being less than with a heavy TH400 or complex 700R4. Your converter, on the other hand, was probably not capable of 90% coupling efficiency. So the biggest losses probably came from the converter.

[greygoose006]

well gearing wont effect power, but it will effect torque, and the dyno might interpret that as more power.
the torque difference will be exactly equal to the difference in gearing in the gear you are in.