OMC 5.7 4200 rpm WOT?

ShawnR

Cadet
Joined
Jul 24, 2006
Messages
14
The facts:
The boat is a 1990 Four Winns Horizon 200 (20.5ft / 3000 lbs)
I bought a brand new 5.7 engine from Michigan Motorz last summer and it currently has about 30 hours on it. The prop is a 14.5 x 19 stainless (original).

The problem:
According to the specs, and other owners I have talked to, the boat should max out at about 50mph. The best I can do it about 42 mph at 4200 rpm. I just installed a Delco Voayger EST ignition system instead of the original points system with no difference. I then upgraded the original Holley carb to a new Edelbrock with still no difference. A lot smoother idle and more midrange power, but no higher top end.

I dropped down to a 14.5 x 17 inch prop and gained about 300 rpm with about the same top speed.

Timing is set to 8 degrees as the sheet with the distributor said it should be and the hull is clean. It is a fresh water only trailer boat. New fuel and fuel filter when carb was installed.

What else am I overlooking?
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: OMC 5.7 4200 rpm WOT?

What is the timing advance at high RPM?

Did you put your distributor in base mode when setting the idle timing?
 

ShawnR

Cadet
Joined
Jul 24, 2006
Messages
14
Re: OMC 5.7 4200 rpm WOT?

What is the timing advance at high RPM?

Did you put your distributor in base mode when setting the idle timing?

I hooked up the shunt at a 12v source at idle and set it to 8 degrees. I didn't check to see what happened when I raised the RPM's up. How far should it advance at a specific RPM?
 

wire2

Lieutenant Commander
Joined
Jun 25, 2007
Messages
1,584
Re: OMC 5.7 4200 rpm WOT?

Your performance seems way off.

I have an '84 Glastron V195, 19'+, also close to 3000#, with a 5.7 but a few extra goodies. (1.6 roller rockers, alum intake, stainless headers, thru-hull on switch).

I usually keep it under 4800 rpm but occasionally I'm forced to floor it, as when a Sea-Doo boat tries to outrun me.
With a 21 x 14? ss prop I get 58 mph at 5500. That's with just me in the boat, ? tank of fuel.

Don't everybody yell at once; I know, way too high!

I'm in the process of converting the OMC to Merc and already have a 23" prop for it. If it's still too high, I'll go 25". Hole shot isn't an issue, it planes in 1 second now.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: OMC 5.7 4200 rpm WOT?

I hooked up the shunt at a 12v source at idle and set it to 8 degrees. I didn't check to see what happened when I raised the RPM's up. How far should it advance at a specific RPM?

You should get max advance close to 4600 RPM. Total advance depends on the distribitor that was installed but should be in the 26-30 degree area for a 5.7L V8
 
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