View Full Version : new setup 18' wMercury 150 hp 2.5 efi

05-30-2001, 02:03 PM
We have renovated a 1983 Galaxie 18'shallow "V" boat. We installed a 95 Mercury 2.5 150efi motor to a CMC Hydraulic jackplate. Our 1st test run was with a 21 pitch High Five prop. The jackplate was all the way up and trim almost all the way down The acceration was way to cool but we ran out of top end.We tacked easily over 6000 rpm (I was afraid of hurting the engine)so we kept it at 6100. (speedometer showing 61-63
We next put on a 21 laserII prop. We had a problem getting it to not cavitate out of hole unless we brought the jackplate down. We were also getting to the 6000 rpm range too quickly maybe mid 6000 before cavitation. We were flirting with mid to high 60's.
The boat (hull) performed well, never once chimewalked.
(1 We want to go faster (we love speed). Do we get a High Five 23 or 25 or any suggestions?
(2 what is a safe maximum rpm (getting different suggestions)
(3 Any and all help would be greatly appreciated.
P.S. our boating days go back to the fifties when my dad would build 14' boats with 45 or 50 hps motors on them going 45+ mph.race all day on the river with guys who would do the same. We are reliving those days now and with alot more hp.

06-04-2001, 11:13 PM
I don't see any reason to spin the stock 2.5 EFI 150 over 6000 rpm. I'd go with whatever pitch Laser II will max the rpm's at 6000. The HighFive may accelerate a bit quicker, but I'm pretty sure the Laser II will be faster on top end.
The late style SST Merc props have adjustable vent holes so you can fine tune your holeshot. My experience is that the Laser II can start off a bit higher than the HighFive......but again, the size of the vent holes makes a big difference. The vent holes should have not effect on top speed or holding after the boat is on plane. For all out speed (but very poor holeshot) a Merc Chopper will run much faster and you can raise the engine to the moon (but keep a sharp eye out for adequate water pressure)!

06-05-2001, 10:45 AM
A 21" is a holeshot/ski prop for that setup. A 23" or 24" will make that thing fly and put you in the correct RPM range, assuming that you weren't at WOT with the 21" at 6000.

06-05-2001, 04:13 PM
You'll probably be happiest with a 25" Laser II prop for that rig. You should be able to buy a new one for around $450 if you look hard enough, and used around $200-250 for a near perfect one.

06-11-2001, 11:23 PM
sosmerc, pyro, jw thanks for the reply, just got back from the lake we went out early jmorning the water was perfect, and we hit the famous 70 +, still with the 21 laser. 6500 rpm. we took pictures and video, the boat is out of the water, riding on the back 1' of vee but the motor was too tilted. I guess we we are nose heavy.
I appreciate the info on props. We will investigate theSST prop. and we thought of raising the motor a little higher. We still want a prop for skiing, and then have a prop so we can get our ya ya's off. Anyway thanks for the replys we will keep all what you said in mind on our venture forward. will try to get a picture of our boat on line when I figure out how.

06-12-2001, 12:30 AM
I have this 16' Challenger Flatbottom with a 2.0 Merc strapped on the back. Sound familiar??? Looks like a race for the pinks?????????? I may need to borrow a prop............
See Ya at the river!