2 Trick Rick

Running a 15 1/2 x25p Hydro at 8200/8300rpm at 84/85mph.

I would really like to lower the rpm's while keeping the speed at 84/85 (class 4 limit).

Would a 15 1/2 x 26p or 15 1/2 x 27p Hydromotive lower my rpm's to 7700/7900 and keep my speed?

Reason I'm asking is no one in MI has a set I can use and I would hate to buy props that don’t work.

hoozeyurdaddy

what's your gear ratio?

2 Trick Rick

2.1

hoozeyurdaddy

buy my figures, the 26P is the better choice, 2.1ratio, 9% slip, comes out to about 7875 rpm at 84 mph

2 Trick Rick

Thanks, But I might try a 15 1/2 x 27 cut down to a 15 for acceleration.

We shall see...

bbladesprops

I agree with the acceleration part.

If you are at the speed you need, why do you want to decrease the acceleration by going up in pitch? What engines and rev limit?

2 Trick Rick

2.5 / 260 - Rev limit from the factory is 7500. I replaced the ECU, rods and pistons with 280 parts so I should be good to 8200/8300 but I just dont like taxing the engines at the hi rpm so I wish to lower it a few.

bbladesprops

If you go up in pitch, acceleration will go down. Decreasing diameter, blade area and cup heights will give some acceleration back but speed may come also that could take you past the 85 mark if you can pull them high enough.

2 Trick Rick

Well I went with the 27's and I may have to lower my drives 1/4 - 1/2 inch to slow her down some. I'll know more after this weekends Metro race.

It's all new to me!!