Repower prop question

[legend 550]

First post here on iboats, So hello all. I recently acquired a 1987 Wellcraft 210 classic project boat. It had a 4.3 OMC Cobra with a bad lower end in the drive. I have replaced the complete drive unit with the drive from a donor boat.
The new 5.0 Cobra drive came from my 87 Bayliner 2550. The Wellcraft had a 14 1/2x17 prop with the 4.3 and the Bayliner has a 15 1/2x15 prop. Question is what prop do I need on the Cobra 5.0 drive in the Wellcraft ? I positive I need to prop up as the Wellcraft is less than half the weight of the Bayliner, I just don't know how much I need to go.
Thanks

 

[steelespike]

Re: Repower prop question

What is the hp rating of the 5.0 and 4.3? The 4.3 and 5.0 probably overlap.
Do you know the 5.0 gear ratio? Usually on the outdrive.
I'd start by testing lightly loaded with the 17" prop.Remind us of the prop size,gear ratio,hp.
Get us the wot rpm and gps speed.

 

[bimmi]

Re: Repower prop question

Like steelespike said need more info throw the 17 on and give us some numbers to help you I can tell you i;ve had 2900 lbs boat 1.61 drive 4.3 motor it would pull a 21 wheel at 52 mph i;ve also had same type boat 5.0 1.61 19 wheel 52 mph 5000 rpm.

 

[legend 550]

Re: Repower prop question

You are probably correct. I need numbers to be sure. The 4.3 was rated at 185 hp with a 21.19 upper 984541 and the 5.0 was rated at 225 hp with a 21.17 upper 981542. The lowers are identical. The previous owner said he saw 46 mph on the Gps with the 4.3. Boating season is over here in Southeast Michigan so it will have to wait till spring. I'll try the 17 and get some numbers.

 

[bimmi]

Re: Repower prop question

we do;nt kned the split case number;s just the reduction number on the side of the of the drive it;s on a tag such as 1.51 1.61 and so on weight of type of hull w.o.t. numbers some other thing;s to think about how many people; gas; wind ;current 3 blade or 4 type of material ss or alum.