Got an SR357 with 454 EFi engines an TRS drives that have the prop shaft cetner line 9" below bottom of boat where drives are located---drives are 33 1/2" apart.

I've been running 21P Mirage props with some questions. Like why won't engine turn more tha 4000RPM at wot?

Tried 21P TRS cleavers with some interesting results. Turned 4200RPM at wot but got slippage when hammered the throttles and on sharp turns, took moe trim tab to bring bow down.

Looked at the TRS manual and in X-dimension chart they talk about 14 1/4" X 25P, 14 1/2" X 23P, 14 3/4" X 21P, 15" X 19" props.

I think my 21P is 15"--

So I think my question is-- should I go to 15" X19P or 14 1/2 X 21P ?

You need to spin your motor at 4900-5000 RPM at WOT.
Is your WOT RPM of 4000 trimmed for speed?
You basically need 1000 RPM. which is a lot smaller propeller maybe 4-5 inches of pitch smaller than the 21P you are running now. so with that in mmind you will need to run a 17P or so.

Julie

First of all, the prop shaft center line needs to be measured at the distance below the lowest point of the hulls keel, pad, or sponson. Not from where they are positioned.

Secondly, X dimention can't be given in black and white terms. There are old school basics that still apply but they aren't always right.

You need to look at your performance numbers across the rpm range so a better decision can be made.

Brett I was quoting the TRS Installation manual--the one I have is a 1986 edition. Not sayng I didn't mis-read it but I do know that the new drives I've got are longer than the old ones and WOT are down since change using same props.

I ran again this weekend with the TRS cleavers and the boat is a little squirly with them so I'm going back to the Mirage's for now. THink next try wil be the Revolutions you suggested when it cools down here--we're having the hottest week of the year with heat index'x aroud 105/107 and water temps around 88 in the river. It's just not pleasant boat weahter at all.

All TRS drives are the same length. Maybe you have TR lowers on your drives. TR drives are designed to spin larger diameter props on cruisers so the lowers are longer.

Anything is possible--could you tell from pictures what the lowers are or can I determine that? At this point the differences are color (silver instead of black) and my perception of a 3-4 inch differnce.

Sounds like a TR. Post a picture with the prop on it.

I know you said with props but I had these on computer at office. What do you think?

They look like TRS but It's hard to tell without the prop to judge size. If you measure someone else's TRS and yours is longer, then you have a TR. The upper is the same on TR, TRS, and Speedmaster 2. Only the lowers are different. In Merc code, there was the No. 1 drive, kinda like a Alpha now. Then there was the No.2 drive which was the TR. TR stands for transmission. TRS stands for transmission sport. Speedmaster 2 was based on No.2 drive. The No. 3 drive was a heavy duty drive that has been discontinued. The No. 3 speedmaster was based on the No. 3 drive.

Thanks for taking a shot--I'll check a few other boats in storage next time I stop by there.