prop and rpm's

[dschifan]

i have a 200xri merc that is turning a 23p tempest plus at 6000rpm, is this to high of rpm for the motor or can i get away with it?. i still have my oil injection. just wondering if i needed to get the prop worked bigger. my boat is a laveycraft sebring and needs lots of lift, any suggestions on maybe adding more cup? i do not have a nosecone and don't think one would work well anyways on my setup.

thanks guys

Dustin

[Jay R.]

as a general rule, but not in stone. cup doesn't work well on fast boats. more in the design of the prop. chopper for bow lift, cleaver for stern lift. extra rake adds a little extra lift i think. tempest is probably about the best type of prop for that boat if it needs lots o lift. 6000 R's is about right for that motor. If your having a problem with lift you could either try lowering the motor a little for more bite. or you could put on a jack plate and balence he boat a little better. that might get you the extra lift you need to lift the motor a little and get more speed. you can block off the top 2-3 holes in your intake and lift the motor a little with a jack plate on.

[pyro]

The Tempest will run very well at higher surface-piercing heights, it's designed for it. Many props won't even see their best potential top end without being surfaced a bit. I used to have a 26p Trophy Plus, and it would not turn over 4800 rpm with the prop "buried". Top end with that prop (at the proper height) was 76 mph at 6300 rpm. You will almost certainly gain some top end speed and pick up some RPM's with the motor up higher! Block off the top two pairs of water intake holes like Jay said, either with RTV / silicone, or by tapping & threading set screws into the holes. If you need more bow lift anyway, adding a jackplate will offer some "setback" to help shift the center of gravity back and help "lever" the bow up without wasting thrust using loads of positive trim. Even if you don't have a jackplate, you can re-mount your motor up higher, start with the propshaft 2" below the hull. Stock intakes should still feed OK at that height. A Tempest CAN be re-worked, with some additional cup, thined leading edges, etc; but it will effectively add pitch and may bring your rpm's down too low, you might lose acceleration qualities, and passenger-loaded performance may suffer badly if it's over-pitched. A Tempest Plus is a heavy-hitting bow-lifter that makes it popular with the bass boaters. It also lifts the rear more than most thru-hubs and choppers, but it relies on a higher running height to achieve some of these qualities. At the correct height, you may actually discover that you don't have enough pitch to stay within reasonable RPM's.

Oil injection is at risk for failure on any gear-driven pump Merc system like yours, particularly on motors running over 6000 rpm. I would highly recommend removing it and switching to safe pre-mixing, 50:1 for up to 6000 rpm or 40:1 for up to 7000 rpm.
Please read my post on oil injection removal in this thread: http://forums.screamandfly.com/forums/showthread.php?t=57758

What year is your motor?

I turn my '89 XRi to 6500 rpm all the time, close to 7000 with a lower-pitched prop.

-chad

[dschifan]

my motor is a 1993 2.5, i do have a hydraulic jackplate with about 17 total inches of setback. i think as it is now that i can jack it up high enough without plugging the holes, cause it will lose bow lift, but i am gonna give it a try. my boat loves trim, it rides pretty flat and takes a lot to get it flyin. thanks for the help.