SCX or SCX-4
 

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!

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.

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.

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.

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.

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.

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.

Curious what the 39 TG weigh ?

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.

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.

Frickstyle-
Thanks for the input, and yes the boat will be run on Lake Michigan.

I need to get the boat up to Michigan so I can get more specifics on the prop shaft depth. I believe it is even with the hull, but I'm going off memory. Sticking with the SCX upper would be easier, as I could change things in stages. Going to the -4, it all needs to be done at once. However, I want to set it up the right way, not the cheapest way. I can run 6 props on either set up, I just need to figure out if the extra -2" is needed/ beneficial.

Yep, I would start there. Your "cheapest" move to the -4 will be to find someone whos already done it. I wouldn't do anything to your setup until you find that person, or persons. This will save you tens-of-thousands in R&D. Pay them for their time (knowledge), because your ROI would be 10:1 easy.

I can tell you what "experimenting" gets you - because I could probably have a 39 at this point with what I've spent on converting and redoing this old rig....

the most cost effective is the scx, you can run a cleaver on any scx lower, it just depends on the X and i think you can get any scx lower in a -3 depth as well, then if you really bump it up you can switch to the dual shaft.. i may wind up with those as well.

I think the SCX only comes in a -2, I'm sure only the SC is available in a -3. The biggest problem with a -3 if they made one is its going to limit your prop size by 1/2" with the SCX. If a 16.5" cleaver will fit in an SCX with an SCX lower, then that will probably be the way I go, but I want to talk a few people that have one of these combos first.

Yes,

You can run current tech cleavers on Sportmaster and "Bravo Style" https://www.mercuryracing.com/boat-p...d-cnc-cleaver/

Those props are $5600 each and only 15.25". Ha, I've looked into them, I think I would rather run a bigger prop and take full advantage of the cleaver.

Where are you going to be max HP at stage 3..........mine are close to 800

I believe it is right around the same.

I wouldn’t mess with an sc lower, not in big water with good power in front of it, unless you want max speed with an scx upper. I’d go scx-4 with #6 shaft. Get the big bullet as high out of the water as possible. You could go scx 4 with 1-1/4 shaft and use adapter to test cleavers and switch to #6 shaft when you find right setup, then blue print lowers while guts are out, but you’d probably have to mess with spacers for bravo style props and no spacers for cleavers then. There are props out there to test. There are cons to cleaver props but pros outweigh them. Hate to say it but maybe run it for a year as is?

Hard to beat this view, at least on what started life as bravo boat
https://cimg8.ibsrv.net/gimg/www.off...6758072ca.jpeg

https://cimg3.ibsrv.net/gimg/www.off...4463e48a5.jpeg

Get Wet-
Great looking combo! What size props are you running? LOL, I don't think you can go any bigger!

Thanks. 17.25” with 1/2” spacer installed. 17” is max on scx-4 with no spacer, 16.75” for scx

That upgrade package is about half of what I paid for my boat 🤦🏼‍♂️. Looks great though, and I’m sure it’s very reliable.

Drives
 

Check with Mike at CK or Mitch at Custom Marine Service right here in west Michigan , these guys do this stuff all the time.

If the end game is to run SSM props, I’d find out what the prop shaft height is on a 39 700 NXT boat and use that as a starting point, I think the NXTs sit a bit further back, so you might have to go a tick lower than that

That's a good call.

looking at your boat on the trailer in the trailer thread the prop shaft looks to be 4-5 inches below the bottom, unless its just the angle of the pic

after seeing this and going to see the pics, the fact that you have ITS, you will have plenty of water to the props no matter what you do. just have to check with a few people that have them as to how it will get on plane, i know the step hulls tend to run flatter at speed, and kind of have a suction getting going. in theory a -4 should work.

Now that F2 mentioned that I looked at that as well, hard to tell depth but looks like a pretty good size notch in that boat! I haven’t looked at a ton of 39s but I don’t recall seeing that big of a notch in others. That would obviously play a big part in drive height.

I just measured its 4.375 to 4.5 from the bottom of the hull to the center line of the bullet....

Is yours a 38 or 39. A 38 will be set up deeper than a 39.

unfortunately you can’t tell much from those pictures. Even with a great pic it’s almost impossible to tell. Everything needs to be leveled, a pic from a random angle just doesn’t work.

38....but this is an X race boat and Id heard they were set up a little higher than norm...

PBC had the purple 39 center steer for sale 7 or 8 years ago, it had 525’s, I was looking it over pretty good, I do recall the drives being very high, probably only an inch or so below the bottom, I would imagine yours would be in the same neighborhood

the scx is bigger so it sits back a little further

i meant the op's boat has its, so he has plenty.

so does mine.......:D

Is yours running -2 sportmasters? I'll be picking up my boat Thursday, so I'll find out soon, what mine is.

I quickly eyeballed mine when I looked at it, and the drives appeared very close to being even with the hull. However without a straight edge, it's really hard to get an accurate guess.

I would measure mine for you but the drives are not on the boat. I would definitely run big props on your boat if possible. The difference between them and bravo props is night and day, especially on Lake Michigan. Mine also sucks to get up on plane even with big props, I have 17/35 herrings