endeavour32

I want to upgrade the drives on the 39 I just bought (bravo XRs), and I'm torn on which way I want to go. To begin with, the 39 Top Gun came with 600 SCI that are now 700's.

My two options are: SCX uppers with my Sportmaster lowers and run bravo props. If/when I install a stage 3 whipple kit, I'll replace the Sportmasters with the new twin shaft IMCO lowers, which at that point maybe I would run #6 props. My other option is to use the SCX-4, and run the better #6 cleaver props. I know there have been several guys with 39's that have ran both the SCX with SCX 1400 lowers, and didn't seem to lose much speed, which shocked me, as well as then switching to the SCX-4's. I know the 39 with 750 Zul engines, that Lipship built was rigged with Bravos, SCX and SCX-4's. I've messaged a few of the guys that have posted that they ran the various set ups on their boats, but I've yet to hear back from them.

So do any of you know of anyone that has used any of these set ups, and how the boat ran? I know the boat will be better running offshore cleaver props in the rough water, but is it a substantial improvement? Any info is appreciated, thanks!

SecondWind

Damn, nice purchase! My experience on a single engine cat w/ SCX upper and SC lower wasn't great. The SC lower is definitely the weak link. The gears in the lower would produce a lot of wear in just one season. The SCX upper was great but that wear from the lower circulates in the upper and that can't be good long term. I also cracked an SC lower case somehow with that setup. The boat was running 800HP roots style blower motor. I did run the boat fairly spirited but I thought that drive combination would hold up better than it did.

F-2 Speedy

I'm in the first stages of this myself, Ive talked to IMCO a few times and my drive guy, its a big purchase so planning is key to not make a 10k mistake, Ill be following your thread.

endeavour32

I talked to Jerry at IMCO yesterday, and his recommendation was to run the SCX upper with my Sportmaster lower. He thought with the power I have, it would be fine. Then when I bump up the power, switch out the lower. His thoughts on the SCX-4 is its a great set up, but harder to dial in and obviously more expensive due to the props. My bravos are currently surfacing, and bravo props don't really last a long time if ran that high. So I'm not sure that the added initial cost will really matter that much in the long run- bravo props vs offshore props. But I'm curious who has experience with this boat and these various combos.

endeavour32

F-2, what was the input you received so far?

I talked to Marc Jacob about this, and based on his experience, if I'm going to run in rough water, go SCX-4's. His experience was the cleaver props would make the boat feel completely different (better) than a bravo proper boat. That is the way I'm leaning now, but it would be great to hear from someone that actually did this swap, or knew someone that did and their opinion of it. However you can also run #6 props on a standard SCX, but I don't think they can be as big of diameter as what can be run on a SCX-4. I asked Jerry this, but he was pretty vague on the max diameter on a SCX.

F-2 Speedy

I'm still gathering info at this time, but the discussions have been around the SCX upper and lower or possible the SC lower, with the SCX-4 being a true surface drive I think the prop shaft would be to high on my boat, I don't want to have issues getting on plane, just need something more than the XR's for my power.

offshoredrillin

When i took the tiger to whipple 4.0's I did scx uppers and standard xr lowers, boat ran great. then a friend needed xr lowers and had some imco sc -2 lowers, put them on and ran even better. I'm going to re-tune it with more boost and will see how they hold up, i also have 1/4 inch spacers if needed and trying bblades new 4 speed props with bigger diameter.. I also went with imco transom assembly and gimble rings as they are more beefy.. im at 92 now with 7lbs boost and on the rev limiter.. i have a straight hull though.

F-2 Speedy

Curious what the 39 TG weigh ?

endeavour32

They used to claim 9800, but I don't believe that. With 565's and bravo's they are now claiming 11,200. Construction hasn't changed, so I think 11k is an accurate number.

frickstyle

You're going to be running in Lake Michigan, correct? I would lean towards the bigger lower and the #6 props for the ultimate setup. there's a lot of stress on that drivetrain, and I doubt you would want to be running a "bravo" setup (props, shafts, and lowers) with the power turned up. I think you have a pretty solid plan to end up with the dual shaft lowers, but take a little time to get there by running the sportmaster lower at your power level. Will probably be a learning curve going from the Bravo setup to the #6 style setup ($$$). I'm constantly chasing a prop setup with #6 props.

I cannot speak on the specific equipment you are asking about. I run an old 38 side by side non-step but with 18" dia props and for Lake Erie / Great Lakes I would want surfacing props, big diameter, big drives. your boat runs completely different than mine, but the basic physics / hydronamics / theory should be relevant. I know when I'm out of the water running above 70 or 80, you can really feel those props bite hard. I run #5s and just under 1,100hp per side, old heavy setup.

Give Phil a call? Or Tres Martin. They may be able to speak on the differences per the specific drive setups on those boats. I wish you luck, and hope to see the boat sometime out on the water. The 39 TopGun is such a sweet setup.

Where's the prop shaft in comparison to the bottom now? That may be a major consideration for future equipment.