20 Eliminator Scorpion Engine prop setup help

[jmess13]

My friend has a 1990 eliminator scorpion with a freshly built 260 Mercury that is putting out an estimated 300hp. We have tried a wide variety of props 3 blade 4 blade anywhere from 25-30 pitch and we have played with the jack plate and engine setback. We can’t get the speeds or RPMs we are looking for. When I trim the engine to get the boat out of the water to try to make some RPMs the boat porpoises horribly. I had one lucky run one day where I caught a little bit of air under the boat along with a little chop on the water where the boat ran perfect and I saw 85 mph. I could never get it to do it again. The boat feels heavy or under powered to me. I was wondering if anyone has any experience with a similar set up and has any kind of recommendations of what we can try? Possibly a five blade prop?

[Charli]

I don't have much to add, other than I believe a 21 Daytona with a normal 260 will run in the low 90's, 90-94. What is your setback? What was your rpm on the one good run? What is the rpm that you think is too low?
There is a guy on Instagram @River _jonkyle who has a setup like yours and seems to run really well. Reach out to him maybe.

[Motv18]

Was the hull weight checked or a survey done.

she could be wet. Depending on how wet she could be 1000# over weight.

what rpm and assume it’s sporty lwp type lower.

[DangerNewb]

Concur it's worth checking for moisture. You can buy a moisture meter at lowes for $50. My experience has been props with larger blades seem to work better once you get a hull bigger than an stv ot mirage. In other words, a merc et or spinelli dr4 may not have enough traction. I ran a Hill Eagle 4 blade on my seebold that worked better than anything else I tried. Little more diameter and larger blades than other ET style props. I'd think you want to stay with a 28 pitch if 1.87 lower unit for a good balance of acceleration and top speed. Larger blades/more traction can help with the porpoise also. Maybe narrow down your variables. Set the prop shaft 1 inch above the center pad and leave it. Focus on 27, 28 pitch props. Change one thing at a time.

I'm no expert, only been messing with fast boats for 4 or so yrs. Just sharing what my experience has been. Good luck.

[Dave Strong]

Boats water logged, set up all wrong, 260 is not putting out 260hp, seat time needed. Not enough info to really help.

Dave

[fasteddies69]

Dave, I own the boat. Where would the boat be water logged? One owner boat, driest boat I have ever owned. No false floors, stringers are nice, front and rear dry as a bone. Explain what is wrong with the set up? Engine is fresh. New crank, 260 small rods,sps bolts, HIPO 260 bearings, Wizard 2 ring pistons TIN rings Milled heads,Compression 145 all cylinders, .075 gaskets, Factory reeds External Brucato ACU, lighten and balanced flywheel. Big bearing 260. 20" off shore mid, 1:87 sportsmaster.

Set back was 15" made new mounts and tried moving it forward. Now 10" set back. I called Eliminator they said to try 8 to 10 inches and about an 1 or 2 inches higher than the bottom of the boat.

I have been working on the boat all year testing. 10 different props. 23 which of course over revved the motor 25 thru 30 pitch props cleavers, choppers 3 blade and 4 blade.

How much to come to Columbus Ohio in the spring. Set it up and drive it. This offer is for anyone. If you have the tools and equipm

I'm going to recheck the compression over the weekend.

Any more help would be appreciated. I had a Mirage with a 280 that ran 122 mph. I just like the Eliminator if it would run 90 mph I'm happy.

Thanks Ed

[Dave Strong]

What greacase is on it?

Dave

[David - WI]

It doesn't sit low in the water versus other Scorpions I've seen, but they are kind of heavy boats. You can weigh it right on the trailer in a few minutes: http://windmillclass.com/static/weigh.html

The motor looks low (in the photo) compared to others, like this one:


Also (no offense intended) it's not making anywhere near 300hp if you're turning less than 9k rpm.

[David]

The core could be wet. Or the bottom not flat. You could check that with a straight edge. Although lots of tunnels porpoise, I did not expect the Eliminator to.

[fasteddies69]

Thanks Dave. Some STV boat racers stopped by and looked at the bottom. Said it looked flat had a 6' level. They were worried about to much hook. Said it didn't have two much.

Ed

[fasteddies69]

Dave, WI. I agree with you I think it makes 275ish. rev limiter is set at 8250 but we can't get more than 6800 to 7000 out of it. I weighed the boat and tandem axle trailer Weighed 2800 lbs. I think the trailer is about 900 lbs if I remember right Your boat looks great I have seen it before.

[fasteddies69]

Here is where the motor use to sit

[jmess13]

Here are a couple videos of it running. One video I trimmed it as much as I could without it porpoising like crazy. As you can see it pretty much just plows through the water. The other video I trimmed it up to try to get it out of the water and get some speed and RPM. https://youtu.be/zVAkbhuEYY8

https://youtu.be/eM_GNgjQCRs

[Capt.Insane-o]

Did that boat come from Michigan and had a 200 OMC on it?

[DangerNewb]

You've got more problem than switching props is going to solve. Motor looks low in the above pic but hard to tell from angle. Is that where you're running it now? Have you measured prop shaft compared to pad?'