Prop for 23 SeaCraft with transom-mounted Merc 250 EFI

[rdoaner123]

Originally Posted by Bigshrimpin

EZ . . . The simple answer is setup and weight My old 225 mariner carbed engine was a 1997 and had the 1.75 ratio lower. Both 3.0L 225hp and 250 are closer in hp rating than you might think. The later mercury 225EFI's were known to dyno at 242hp. You can run those Rev4 props higher without blowing out . . . less lower unit in the water means less drag (and more rpms). See the Hijacker fixed jack plate on the back of my boat with the 225.

100lbs in the wrong place can slow you down a few mph. Every 100lbs extra will make your top end suffer. Waterlogged foam in stringers can add several hundred pounds.

T Tops can be the absolute worst performance killers!!! Poorly designed Tops will catch the wind and act like a giant parachute. Just picture a 4x8 sheet of plywood flying through the air at 40mph. Tilt the front of that sheet up 5 - 10 degrees into a 15mph head wind . . . what happens?

We are talking about 25year old motors. If we were comparing both engines using the exact same hull in a controlled environment then we could say more definitively that your 250efi was tired. 46mph is respectable with a 250.

Here's a video of my boat with a 1987 vertical reed chrome bore 2.4L 175. Running light the boat would tickle 43/44mph. Those 2.4L engines weigh under 400lbs. Early fingerported 2.4L 200hp horizontal reed mercs would dyno at 218hp from the factory. That vertical reed 2.4L was real strong too . . . I'd bet money that engine was over 200hp on a dyno (despite the sticker on the cowling) and had good bottom end torque. (here's a few mods for the 2.4L . . . https://www.chattanoogafishingforum....=39864&start=1)

https://www.youtube.com/watch?v=jg7cdv1w1vE

I don't think weight is an issue (the boat was fully rebuilt), but it does have a large t-top. That and the fact that the engine could still go up 2 holes probably.

BTW, going by your picture, looks like you have a 25" shaft motor on a 30" transom (at least mine was exactly 30" after I filled the "second notch" in). That could explain how you were getting those rpms!

Looks like I'm gonna raise the motor and try the REV4 in 17 pitch first.

There's no worry that the 18 pitch Eco and 19 pitch Highfive won't decrease rpms?