93 Four Winns Horizon LOW top speed

I have been searching all over and have found different scenarios but I am finding my symptoms are different:

1993 Four Winns Horizon 190 Bow rider
5.0 OMC Cobra Engine/Outdrive
OMC Book says desired Operating RPM at WOT 4000-4400 RPM

I just bought the boat and he said it was tuned up 5 yrs ago. He was the original owner. The boat had a 14"x19P prop (not sure of make) on it and would rev almost 5000 RPM and just over 35 MPH. This was with 3 people and almost full tank.

I switched to a Michigan Wheel 14.25"x21P prop and the boat will still rev 4700 RPM with 4 people and 3/4 tank of fuel. The boat still barely runs just over 40 MPH. If I throttle back to 4500 RPM the speed is closer to 30-35 MPH.

Both Scenarios are trimmed just under the 3/4 mark on the gauge as any closer to 1/2 it will porpoise.

When I read online usually it is not enough RPM and a tune-up is suggested with a smaller prop. I am afraid to go to a 23 P prop as I plan to pull skiiers as well.

Why the high RPM's and Low Speed?

Thanks

Re: 93 Four Winns Horizon LOW top speed

Ultra-high prop slip, or inaccurate RPM readings could cause that. Also improper final drive ratio.

Using a slip of 15% and calulating the drive ratio those numbers indicate a drive ratio of 2.0, which is not right for a V8. Usually a V8 would have a 1.5 or so. This would explain your situation.

When I use a drive ratio of 1.5 and then calculate slip I get 25%-35% slip which with 2 different props is unlikely.

This could also be a tach problem, not showing actual rpm's. Verify RPM's first, if the tach is accurate then I would verify the drive ratio. If it is a 2.0 then you will have to run a 23p and be resigned to the lower top speeds until the drive ratio is changed out.

Re: 93 Four Winns Horizon LOW top speed

I tried a few calculators and was getting the same. The numbers did not seem to make sense. Thanks for the quick reply I will verify the RPM and I will take a GPS with me the next time out as well.

Re: 93 Four Winns Horizon LOW top speed

UPDATE! = I installed an autometer tachometer. Come to find out the factory one was 1300+ rpm off.

Last night I ran with almost full tank and 2 people (150 lb + 175 lb) and here are my results.


I am now running a Stainless Mich Wheel Apollo 19Px14 1/8" Prop
WOT: 4000 RPM 42/43 MPH

I tried a Mich Wheel Aluminum 19Px14" Prop and got
WOT: 3900 RPM 40/41 MPH


This is GPS Speed. Holeshot seems good, the Aluminum stands the bow up higher, the Stainless comes out of the water flatter.

~ With a 4000-4400 RPM guideline from OMC, should I be going down a little in pitch to bring the RPM up so when I have more people and am pulling skiers it doesn't lug the engine too hard?

Is this speed about it for this boat? I feel I should be closer to 50mph with a V8

Thanks again

Re: 93 Four Winns Horizon LOW top speed

With those new numbers, and using 15% slip I get a 1.46 drive ratio which to me seems in range and normal for that combination.

With a 19p if you could get to 4400rpm that would get you to 44-45 maybe.

A 21p shows 50mph at the 4400 rpm, problem is your engine cannot turn those rpm's even with the lower 19p prop.

At this point it seems that 1.) Engine is down on power or 2.) Boat is heavier than it should be.

Re: 93 Four Winns Horizon LOW top speed

The drive ratio is actually 1.59 .... I guess I will tear into plugs/Dist Cap/Fuel Filter.

Any easy places to see if it is waterlogged?

What are your ideas on going to a quadrajet 4 barrel vs. the 2 barrel carb?

Re: 93 Four Winns Horizon LOW top speed

My 1992 Horizon 200 with 5.8L and 4bbl is driving a 19p 3-blade prop; this is the factory recommended prop. New it was rated at 49mph. It's all original including the manifolds and risers. It now does about 45mph on gps at 4100rpm.

I also use a 18p 4-blade when I have heavy loads and it still gets above 40mph.

Re: 93 Four Winns Horizon LOW top speed

The 4bbl change would probably not help much. The HO 302 had different heads and intake and cam.

I ran your nmumbers again with the 1.59 drive ratio and slip is below 10% so I think the numbers are in line so to speak. If you cannot get more power from the engine then a drop to a 17p would get more RPM at about the same top MPH, and a little better holeshot.

Re: 93 Four Winns Horizon LOW top speed

I just am having a hard time believing that a 19 foot boat with a v8 can't swing a 19Pitch prop... We will see what the tuneup looks like and I will check the timing

Re: 93 Four Winns Horizon LOW top speed

Well, I installed a new cap, rotor, plugs, and wires. no improvement in performance.

The plugs that were in it were completely wrong (were not a croos for the original plug type). They had a .050" gap when it should be .035" I was ver surprised when I only gained 100 rpm or so.

I am now at 3900 RPM 40 MPH (4 people this time and 7/8 of fuel).

I would like to gain 200-300 rpm and think an 18 pitch would be good, but all I can find is a 4 blade. I am unsure if it is the route I want to take.

I feel a 17 would be way too small...

Re: 93 Four Winns Horizon LOW top speed

I have been checking into prop Diameter vs. Pitch and the 17" Michigan Wheel is 15" in diameter. so will going down 2 in pitch be adversely affected by going up to a 15" diameter? (has a 14"x19P now)