rebedro

hey guys i got a 25 foot donzi ragazza i just took the 260 hp motor out and replace it with a 325 hp. the thing is im still using the old 3 blade from the 260 hp motor. it's 14 1/2 x 19. the new engine has a 5000 rpm wot but for some reason im only getting 4000 rpm. can someone tell me what prop would get me to plane faster, my 1000 rpm im losing and a bit more speed on the boat. thanks in advance guys.

Griff

Start by replacing the impeller. Only use a Merc impeller.

mike tkach

iTrader: (3)

right again.

rebedro

its a new impeller in the drive. but what i did was took off the risers from the manifold and they is alot of rust that clogs the water path i wondering if that could be the problem.

PAST DUE

that could be the problem that is the only way that water can get out of the motor if they are cloged it will cause the engine to get hot but......it would do it at more than just an idle. is the 325 hp engine a fuel injected or carb also is the drive a alpha gen 1 or gen 2?

rebedro

its a carb bro but check this out if i let it idle it gets hot then when its hot i raise the rpms to about 3000 the gauge would start going back to cool or if i drive the boat it would be cool. just cant drive slow or idle.

ken3765

Could be that the thermostat counld be clogged as well.

larry da outlaw

check the water inlet holes for obstructions. next check the sea strainers, then replace the impeller. replace the thermostat. last would be replace the circulating pump

rebedro

all the stuff you just asked me to replace are new brand new parts not even 2 months old yet. the only thing is im not running a thermostat at all.

Delta5

Hi guys...the real problem here is that you are getting "hot spots" in the cylinder heads! It comes from not having rnoug block pressure at idle. In the old days we used a 5/8s hole in a restriction plate in place of a thermostat to get the 25 psi needed to coo, under rce conditions, in the 510 cid Reynolds (all aluminum with iron plated pistons, no sleeves) the 526 cid spacer motors and the L-88s and the original ZL-1s as without the restriction air pockets get real hot and boil small amounts of water all through the heads and the steam gets more of it boiling...hes the answer is mor water being pumped in and either a thermostat or a restriction plate for the size engine you have...there used to be a division of Chevrolet Engineering that always had these answers??? Hope this helps cool her dwon might not need another prop just more rpm!