help with outdrive

[Maclin]

Re: help with outdrive

Your gear ratio is off!! The 1.98 ratio is killing the motor. Running the data you supplied thru prop calulator (10% slip) the speed is pretty close. The data plugged in at 4600rpm @1.5 ratio pops you back at 45mph.
http://www.byuboyz.com/boats/prop.htm

MH11 says his engine cannot get past 3100rpm with whatever ratio is in the drive, say it really is the 1.98 ratio. If he puts in a 1.5 ratio the problem will get worse.

That size boat with a good running 350 cube engine should be able to stay at or above 19 on the pitch and still get to 4400rpms in my opinion.

Also, the cracked exhaust hoses indicate it has been run hot at some point, maybe it was with the previous engine but maybe with this one. In any event those hoses should have been changed if the cracking is causing exhaust/water leaks on the inside.

If the engine was ran hot then there could be cylinder sealing problems. A compression check is the first thing to do. A new intake and the rest is not justified at this point. Do the compression test with the throttle open so as not to restict the intake stroke.

Backfiring thru the carb? That thing needs a full tuneup including fuel system and carb. The carb needs to back to specs as far as fuel metering, and needs to be operating correctly. Backfiring thru the carb can also come from an intake valve sealing problem.

FIRST ORDER OF BIZ: Do the compression test correctly and report back before doing ANYTHING else to the engine.

 

[chiefalen]

Re: help with outdrive

I missed cracked hoses where?

 

[Faztbullet]

Re: help with outdrive

MH11 says his engine cannot get past 3100rpm with whatever ratio is in the drive, say it really is the 1.98 ratio. If he puts in a 1.5 ratio the problem will get worse.
Please explain how this will make problem worse as all Mercruiser V-8's come from factory with 1.5 gear ratios? If the engine turns @3100rpm with a 1.98 with 17p that works out to 23 mph. Same rpm, pitch,slip on a 1.5 =30mph a 7mph increase.
http://continuouswave.com/cgi-bin/propcalc.pl

 

[chiefalen]

Re: help with outdrive

Faztbullet good catch.

I looked it up, it is a 1.50 standard on the V8.

 

[Maclin]

Re: help with outdrive

If the engine cannot spin up to it's operating range with a 1.98 drive it sure as heck will not be able to with a 1.5 drive. That is the point I was trying to make. His drive may already be a 1.5 now, nobody knows. He has a problem getting the engine to run good enough to hit the top range.

 

[Maclin]

Re: help with outdrive

37mph at 3100rpm and 23 pitch prop with 15% shows a 1.5 ratio, so that is probably what he has now.

I would guess that a 21 or 23 pitch prop would be about right once the engine can hit 4400rpm reliably.

 

[Don S]

Re: help with outdrive

3) I am on a budget, so I really don't want to take apart the outdrive to check it, I just know that the stamp on the upper case says 1.98r, and that Bond-o said the cases are the same and they could have replaced the upper case for some reason. Is there a way to check the revolutions of the prop by turning over the motor to estimate the gear ratio?

You can find out the actual ratio without taking the drive apart. Pull the spark plugs out of the engine, Put the shifter in forward and turn the engine over by hand in the proper direction of rotation. Now, turn the engine and count exactly how many turns it takes to turn the prop one full revolution.
If you turn the engine almost 2 complete revolutions, that's a 1.98. If it turns one and a half turns, then you have the proper 1.50 ratio gears in the drive.

 

[Maclin]

Re: help with outdrive

Chief, this is where I got the idea about overheating, from the original post...

"5) Also, I am thinking about putting the high rise GM manifold, k&n flame arrestor, and the later year manifold aluminum kit to drop weight by about 80 pounds, and get more horsepower since both my rubber boots between the riser and y-pipe both cracked, figured I would improve performance and save weight at the same time, does this make sense?"

 

[mh11]

Re: help with outdrive

Thank you so much for all of your help, I will do the compression check first thing when the season hits, and post the results. This is a really nice boat in really nice shape.

I'm not really looking for a ski boat, just a boat to pull my little kids around the lake, and cruise at tahoe. I figure if I get 45-50 mph, that is fine by me.

Thanks again!!

 

[chiefalen]

Re: help with outdrive

Maclin ^5 didn't see it. See everyone why i tell you that open forums are the best place to get advice.

A lot of great minds can view it and chip in. I always tell the people who pm me that.