performance issue 1900 sr 5.0 220hp

[slow95gt]

First post here hopefully someone can shed some light on my situation.

I have a new to me 1999 1900sr with a 5.0 (2 barrel carb) with a alpha one gen two outdrive (1.62)

The prop that was on it was a mercury 14" x 23p that was cupped, this prop would only allow it to rev to 4000rpm and a gps speed of 40mph (with this setup you could not trim up at all without it porposing). It was also terrible on the holeshot and would only plane at 3/4 throttle.

I changed the prop to a 14 1/4 x 21p from michigan wheel and it now revs to 4500rpm but also only a topseed of 42mph gps. With this prop the holeshot is amazing compared to the cupped 23p, and also planes at a much lower speed. I can trim up with this prop also to the point of cavitation before porposing.

to me it seems like the rpms could potentially be right where they should be by going to a 19p but i dont feel my mph is going to increase to where it should be. I am going to check the timing this afternoon if the wet stuff stops coming down. Im leaning towards it just being down on power seeing as the rpms are increasing but speed is still 10mph slow.

any ideas

Thanks in advance

[mmwjr]

Slow95gt, first of all welcome aboard.

So slow by 10mph is what you believe, therefore expecting top speed of ~ 52mph. How many folks on board? How much gear weight? What are sea conditions?

Unless you are on a lake 50 +mph on a 19' boat is a little scary to me. I would expect this boat to do mid to high 40's with 4 or less people. If I recall you engine package is rated at 220 HP. The 19p prop should get you into this range.

Why the need for that much speed? What activities do you use the boat for?

[slow95gt]

Its really have no need for that speed, im satisfied with mid 40's. I just feel that something must be wrong or at least that there is a reason my boat is almost 10mph slower than ones similar.
I am on a fairly large lake, when i last went out with the 14 1/4 x 19p the water was glass, temp was 72*... it was my wife and I and our 3 small children (5 people total combined weight around 430 lbs). practically no gear as of yet.
Its used for weekend tubing with the kids...knee-boarding..occasional skiing, eventually teach my 7 year old to wakeboard.

my ultimate goal would be to find a top speed prop...and get another for holeshot. I'd rather not settle for something that i feel is good enough if theres a good chance im leaving performance on the table.

This is my first boat although i have an extensive drag racing background most of this is new to me

I did check the timing today and the base was set at 18*, I can tell the intake had been removed previously. My guess is they just didnt set it right. I have it set at 10-11* base and am getting approx 28-30* total advance. Im taking it out tomorrow afternoon and bringing the timing light so we'll see how it goes.

[mmwjr]

Did the 14 1/4 x 19p give better performance than the 14 1/4x 21p? Doesn't sound like the boat had a excessive load.

18* timing is not correct, not sure what the correct time is but where you have it set to now is close. BTY a boat only has mechanical advance no vacumn.

How many hours are on the engine? I have seen the timing chain stretch on boats that are primarly used for water sports.

[slow95gt]

my mistake i meant 14 1/4 x21p i havent gotten a 14x19 yet...
the 14 1/4 x 21p gave me waayyy better performance than the cupped 14x23, it planes after only a few seconds now and the holeshot is amazing compared to the 23p...but only gained 2mph top speed.

not sure on the hours there is no hour meter

going out in a few hours i will report back then, thanks for your input

[slow95gt]

well it was 6mph slower, but after putting timing back where it was it went the same 42mph @ 4500 rpm

no good, turns out the machined groove in the balancer isnt TDC...there are actual marks ATDC / 0 / BTDC . apparently what i thought was a 10 was actually 0.

I think if i can gain another 2 mph using a 14x19p and gain holeshot at the same time i'll be golden, hopefully thats the case as i have another 2-300 rpm to work with.

[mmwjr]

Dropping to the pitch from 21 to 19 should give you ~250 rpm. I'd check for slack in the timing chain as well. Using a ratchet turn engine to TDC pull cap to verify rotor is on #1 plug then start turning crank counter clock wise until rotor moves and look to see how many degrees the balancer moved. Should be less than 1 degree if 3 or more chain needs to be replaced and can cause timing to vary when the engine is running.

[slow95gt]

Originally Posted by mmwjr

Dropping to the pitch from 21 to 19 should give you ~250 rpm. I'd check for slack in the timing chain as well. Using a ratchet turn engine to TDC pull cap to verify rotor is on #1 plug then start turning crank counter clock wise until rotor moves and look to see how many degrees the balancer moved. Should be less than 1 degree if 3 or more chain needs to be replaced and can cause timing to vary when the engine is running.

Looks like its 1-1.5 degrees, I need to change the gimbal bearing. Do you think that could be dragging it down also. Its to the point of growling and sounds like theres marbles in there now. I'm done messing with it until I fix this issue beforeIt explodes.

[mmwjr]

The plot thickens! If nothing else a gimbal bearing that is about to either lock up or fall apart can damage the outdrives input shaft and cost you even more $'s. Stop using the boat and fix this now.

Then let's see where things stand.

[Bad Ass]

im not sure how you are making out but I have a 2000-1900scz with a 5ltr two barrel carb I run a 21 pitch prop and with two adults and two teens I get about 46mph but have to watch my rpm that is at 5000rpm and max rpm is 5500 for my boat. The only dif I can see is I installed a hydr foil so it gets up and plains at approx. 1/3-1/2 throttle and comes out of the hole real good I find the 21 pitch pulls the kids good on a tube(four place tube) but yet allows me decent fuel usages


Brad

[shrew]

Originally Posted by Bad Ass

.............................I have a 2000-1900scz with a 5ltr two barrel carb I run a 21 pitch prop and with two adults and two teens I get about 46mph but have to watch my rpm that is at 5000rpm and max rpm is 5500 for my boat.

I was under the impression the Mercruiser 5.0 was 4400-4800rpm on the carb and 4600-5000 on the mpi on the 5.0L.

[ss3964spd]

I would definitiely double check that 5500 RPM claim, Brad, these stock engines don't have enough valve spring to spin to 5500 reliably, and the cam is done by 5K anyway. A 5500 RPM blast may float your boat but it'll also likely float the valves.

[slow95gt]

Originally Posted by Bad Ass

im not sure how you are making out but I have a 2000-1900scz with a 5ltr two barrel carb I run a 21 pitch prop and with two adults and two teens I get about 46mph but have to watch my rpm that is at 5000rpm and max rpm is 5500 for my boat. The only dif I can see is I installed a hydr foil so it gets up and plains at approx. 1/3-1/2 throttle and comes out of the hole real good I find the 21 pitch pulls the kids good on a tube(four place tube) but yet allows me decent fuel usages


Brad

I also have a hydroil w/ torque tabs? I think that's what they are called. I did notice I get an extra 150 rpm by taking off the exhaust bellow but that was just another part of my trial and error.

[slow95gt]

Update:

Did a compression test and all cylinders were 115-120psi except lucky #3...which had 65psi. The number s may be a little lower across the board because it was done with the engine cold.

When I pulled the plug it looked a little rusty. Hopefully its just the exhaust valve and I cqn get away with just pulling the heads.

[mmwjr]

slow, it seems to be time to have the heads rebuilt and check the exhaust system (manifolds and elbows) it may need replacement as well.

BTY: compression would go up when the engine is warm. i.e. 120psi cold will be ~140psi warm. Normal compression on a warm fresh engine is ~150psi

[Bad Ass]

sorry guys I ment 4000 to 4500 not sure what I was thinking about

[slow95gt]

Figured i'd update this with my findings, it turns out i had a leaking riser gasket that leaked water down the backside of the valve and eventually rusted the valve seat, causing my low compression on that cylinder. I pulled the head, lapped the valves and everything is good to go now.

Now on to the gimbal bearing

[mmwjr]

That's in line with what I thought.

Have fun with the bearing, are you doing the bellows as well?

[slow95gt]

Originally Posted by mmwjr

That's in line with what I thought.

Have fun with the bearing, are you doing the bellows as well?

yea, bellows, bearing/seal, water pump impeller, u joints are tight for now....just got new trailer tires installed yesterday. pretty soon i'll be able to enjoy it again