OMC 5.7 4200 rpm WOT?

[ShawnR]

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]

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]

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]

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]

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