performanc question

[roberto alvarez]

Hi, i wnat to know if i am right or wrong,my boat (see my pictures) did not have a awesome top speed,in the lake were she was, the max speed after solve the planing problem was 24 knots

some friends told me that in a closed lake the boat not perform as must because the water here is not dense as salt water

this boat came with the omc 225 stern drive unit with a 350 GM and a carburetor from a omc cobra 5.7L

as i can read here on the registry this hull is faster and safer and was used with smaller engines with better performance, just before try it on a 100 miles trip,

NEED I REPLACE MY ENGINE??? it have good compression and no internal wear, good oil pressure, may be frozen rings ( i dont see any smoke from the valve covers), any hel will be considered , this boat was stock as was in 1977, thanks

[David]

What size & pitch prop are you using and how many rpm at wide open throttle?

[roberto alvarez]

Hi, the prop is a 14X18 and the rpm at 24 knots is 3500, before i was using a 14X14 with a max speed of 16 knots and 5000.
if i can get 40 knots at ????, the problem is that the propellers for this unit are not easy to find,on my las discussion i ask a similar question as my boat hull was hard to planing, i mean the transition from the bow up to planing was too slow, the ignition timing was wrong, that solve my first problem
i really did no want to remove this engine and install an outboard, did some one else have this set up?
my second chance option is modify a 13.5X19 prop with removable hub and try, but if another user have best performance.

[David]

With a 350 Chevrolet you should have better performance. RPM at wide open throttle should be between 4,000 and 4,500. I think 40 mph is realistic. Many things determine boat speed including bottom, prop and engine condition as well as weight and water conditions. Outdrive trim angle can make a great deal of difference in speed and handling. Boat needs to be trimmed enough to lift the bow out of the water. If you have good compression then the rings should be OK.

Trim the boat until you reach maximum speed at WOT then check engine rpm. Should be between 4,000 to 4,500. If it is more than that move up in pitch, if it's less, move down. 2" should make about 300 rpm difference. It's possible that with your 18" prop you could reach 4,000 rpm if you trim the boat properly, if you can't then try a 16" or 17" prop.

If your engine is in good condition, check and make sure your timing reaches about 36 degrees total advance at 2,500 rpm.

[roberto alvarez]

Hi David, now i see a new deatail, reading a copy of the omc 225 manual for the 1977 i read that the 350 was not used on that model
i will remove a head and measure the cylinder diameter and stroke and then see were i am

[roberto alvarez]

3970020 is the casting or number on the engine block