80s 247 Refit Suggestions Needed
#1
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Joined: Oct 2002
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From: Bowling Green, Kentucky
I recently purchased a 247 Superboat knowing the engine took a bath and needed to be rebuilt. I have always had cats and know not a lot about good set up on these small Vs. The boat must have been the only Superboat in Havasu and surprisingly is all dry. I boat at Lake Cumberland and want to build something that is reliable safe and run into the 70s. I also plan to use it to ski the Catalina Ski Race in 2026. I have stripped the boat and am planning what to do to optimize the set up with a reasonable budget.
The boat has a 454 4 bolt main with 990 iron heads flat tap hyd cam. I have already taken the block to the machine shop and they are going to bore 30 over, line home, new cam bearings etc..I am going to use the original GM forged crank and dimple rods. I am going to use Promaxx 317 rect heads with 119cc chambers, pac springs, inconel exh valves, wiseco pistons that will give me about 9.7:1 CR with a standard thickness head gasket. Im going with a Edelbrock Airgap intake and 850 carb.
The boat had an electric shift Merctrans 2 which the tail stock is leaking. A TRS drive with a nose cone. The drive seems good, but I am going to pressure test it. The transom assembly looks good and tight. I want to shoot new gelcoat on the transom while Im at it. The boat had the cheesy bennet tabs.
Tenative plan.
Hydraulic dual ram steering
280 Kplanes
Borg Warner transmission change.(I am going down a bit of a rabbit hole with this because I am going to have to move the engine forward about 6 inches find a new drive yoke, new shifter)
I have managed to gather a bunch of used parts to lower the cost of the project. I like the old graphics and want to keep the nostalgic look. I know that the transom is going to be full of hardware and the steering rams may restrict the location of the tabs. I dont know if moving the engine forward would adversely affect the CG?
I know it wouldnt be good for top speed but may help it to fly more level.
Please let me know your suggestions.



The boat has a 454 4 bolt main with 990 iron heads flat tap hyd cam. I have already taken the block to the machine shop and they are going to bore 30 over, line home, new cam bearings etc..I am going to use the original GM forged crank and dimple rods. I am going to use Promaxx 317 rect heads with 119cc chambers, pac springs, inconel exh valves, wiseco pistons that will give me about 9.7:1 CR with a standard thickness head gasket. Im going with a Edelbrock Airgap intake and 850 carb.
The boat had an electric shift Merctrans 2 which the tail stock is leaking. A TRS drive with a nose cone. The drive seems good, but I am going to pressure test it. The transom assembly looks good and tight. I want to shoot new gelcoat on the transom while Im at it. The boat had the cheesy bennet tabs.
Tenative plan.
Hydraulic dual ram steering
280 Kplanes
Borg Warner transmission change.(I am going down a bit of a rabbit hole with this because I am going to have to move the engine forward about 6 inches find a new drive yoke, new shifter)
I have managed to gather a bunch of used parts to lower the cost of the project. I like the old graphics and want to keep the nostalgic look. I know that the transom is going to be full of hardware and the steering rams may restrict the location of the tabs. I dont know if moving the engine forward would adversely affect the CG?
I know it wouldnt be good for top speed but may help it to fly more level.
Please let me know your suggestions.



#2
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Joined: Feb 2007
Posts: 1,555
Likes: 81
From: Columbia S.C.
Congrats on the purchase. It looks good in the pics. I just moved from a twin outboard Talon cat to a 23' Kryptonite with 300XS. I
look forward to following your refresh of the boat. I don't think you will have any problems getting answers on setup as those hulls have been around a long time. Keep us posted on your progress and congrats again!
look forward to following your refresh of the boat. I don't think you will have any problems getting answers on setup as those hulls have been around a long time. Keep us posted on your progress and congrats again!
#4
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Joined: Oct 2002
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From: Bowling Green, Kentucky
I have twin ram Imco hydraulic steering ready to go except I need one of their back cap mounts, Thanks for the suggestion. I have some 280kplanes as well. I am going to have to fill in some screw holes and regel the transom.
The machine shop is about done with the block and the new Promaxx 317 heads are arriving tomorrow.
I tore into the 71-c velvet drive this weekend. The used unit I bought had some water in it and it is marginally rebuildable. I was lucky enough to find a 72 that was working but had a seal leaking. So it looks like I will rebuilding that one. I had never opened a velvet drive up. Wow beefy units. Much better than the Bravos cone clutch but they add a lot of weight and have to have a lot of parasitic power loss.

The machine shop is about done with the block and the new Promaxx 317 heads are arriving tomorrow.
I tore into the 71-c velvet drive this weekend. The used unit I bought had some water in it and it is marginally rebuildable. I was lucky enough to find a 72 that was working but had a seal leaking. So it looks like I will rebuilding that one. I had never opened a velvet drive up. Wow beefy units. Much better than the Bravos cone clutch but they add a lot of weight and have to have a lot of parasitic power loss.

#7
I good friend of 42yrs, I lost last September. He has 24superboat 79. 502 about 550hp TRS drive 280 k planes and 2yrs ago put external Hyd steering. There's a nuff.have room. I have the Baja AirTime boat, had shortie bravo with hyd steering. 509 650hp did mid 80s. Also own 28Saber with Dean Gellner 1100SC 572cu. 380 ks Oops Oles 24 did 75mph, might have gone faster. But he was 80 last 2 yrs ago. When I went with him. Going g to suck without him. He was the older brother I never had. We ran Harleys too.
Last edited by AIR TIME; 04-14-2025 at 11:29 PM.
#9
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Joined: Oct 2002
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From: Bowling Green, Kentucky




Making progress.
i have all the holes in the bilge area filled and it sanded ready for new coat of gelcoat.
i dynoed the engine and it’s ready to go.
I got a mock up block and I’m fabricating the motor mounts and getting them installed.
As you can see I ditched the TRS stuff for the Konrad drive with a Huber 1050 drive.
I refinished some 280 K planes and have IMCO dual ram steering ready to go.





