5.0L OMC TOP Speed at WOT.....

[hg849]

I have a 1988 21 ft Four winns with a 5.0 and an OMC cobra....I'm only doing 32 mph at 4000 rpms ...I think I should be doing much more than that I think the prop that I have ats a 14 * 19 pitch ....

ANY IDEAS WHAT WOULD BE A GOOD PROP TO GET BETTER TOP END SPEED???????

 

[Howard Sterndrive]

Re: 5.0L OMC TOP Speed at WOT.....

is that gps speed? is the prop beat up?

you won't gain any serious speed by changing props unless your current one is quite damaged
something isn't adding up... 19P and 4K rpm should have you going around 42mph if you have the correct gear ratio outdrive

 

[Don S]

Re: 5.0L OMC TOP Speed at WOT.....

Trim the drive up.

 

[hg849]

Re: 5.0L OMC TOP Speed at WOT.....

is that gps speed? is the prop beat up?

you won't gain any serious speed by changing props unless your current one is quite damaged
something isn't adding up... 19P and 4K rpm should have you going around 42mph if you have the correct gear ratio outdrive

Yeah the one thats there is a little bit up, the mechanic told me it needs to be replaced. One of the blades is a little bent and everything...Yes thats GPS speed.....do you think the wear and tear of the prop will reduce spped by that much ???? we are talking about 10 mph .......

 

[gbeltran]

Re: 5.0L OMC TOP Speed at WOT.....

Yes, a bad prop can cost quite a bit of MPH. Is your tach accurate?

 

[HT32BSX115]

Re: 5.0L OMC TOP Speed at WOT.....

I have a 1988 21 ft Four winns with a 5.0 and an OMC cobra....I'm only doing 32 mph at 4000 rpms ...I think I should be doing much more than that I think the prop that I have ats a 14 * 19 pitch ....

ANY IDEAS WHAT WOULD BE A GOOD PROP TO GET BETTER TOP END SPEED???????

When I had the 460 Cobra in my 87 211 Liberator, I had a 19P (cupped and repitched to 20) prop.....I also have a 17p SS prop but never used that was too low for the 460 (that I kept for a spare).

You might be a little high on the pitch for a 5.0L engine in a boat that size and weight......


If your engine is otherwise running correctly, you might try a 17 and see if it gives you a little better performance.....Stainless steel props also have thinner blades and can perform better than aluminum props.....most prop shops will allow you try different sizes if you buy one and don't ding the "trial" props!

 

[Don S]

Re: 5.0L OMC TOP Speed at WOT.....

To be honest, there is a lot of things that can cause low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[sw33ttooth]

Re: 5.0L OMC TOP Speed at WOT.....

i have a 5.8l 23 foot sundowner does about 40 half tank 1 person 37 with full tank and up to about 5 people i think i am a little low but i am pushing 4050 rpm and 5l-5.8l i think should be running in the 4k-4400 rpm range at wot

 

[HT32BSX115]

Re: 5.0L OMC TOP Speed at WOT.....

i think i am a little low but i am pushing 4050 rpm and 5l-5.8l i think should be running in the 4k-4400 rpm range at wot

Most of those engines want to turn around 4200-4800 at WOT. If you do not have one of the problems in the list above, (except #2........ and your tach is verified accurate ) it probably is #2 and you're a little under-propped.....