dcrighton

I installed a pair SCX drives mated with the stock merc sportmaster lowers on my Fountain 42 PR and also saw no speed loss. Currently running approx 750-800hp per side and no issues so far.....I should also mention that I ran the boat in a race for 50 miles in 2.5-3' chop with Hering 6 blades and nothing came apart. In the same race last year I didn't make it 10 miles before I sheared the upper gears with the same power with stock XRs

NWPC

My Fountain lost no speed going with the SCX / SC setup. It is much faster then being towed in with a broken xr or Teaque.

Uncle Dave

Has anyone other than Kap done a third party radar tested run with the drives back to back the same day?

I trust Kaps implicity.

Of note: CB-BLR (Chris) is usually pretty damm methodical about his testing as well.


I suspect with a mere 700 HP I dont have enough power to really push the drive, but would likely see a decrease in mileage if in fact its a "hard spinner."


Uncle Dave

kap328

Reply:

Mr Gadgets the input shaft turns freely and I have now put on a second SCX with a shorter cav plate. The loss on the top end is still the same HUGE.

I have checked the engine and it is running perfectly ran the SC with the SC lower and the boat was hauling azz 115-118MPH easily with that combination. I then swap and put the SCX upper on with SC lower and it can barely hit 110MPH. I do not get it but have two theories on the why it is doing this.

Everytime I ignore my gut feeling I regret it and my gut is telling me something right from the get go.

Boatcrzy:

Your right I ran a X-Power Drive for almost a year. We have parted ways and I did yank that drive and put on a SCX/SC combo. It's OK your not confused but rather observant and quite correct.

I have won three years of Shootouts with a modified IMCO/Max Machine Works drive and I want this SCX to work as the bigger gears are stronger.
____________________
Solutions and Proposed Theories:

Reply to those that have V-Bottoms and found no speed loss that is encouraging to hear. However, I have an idea about why you have not found any significant speed loss. It is because your not pushing enough HP/torque to make the following in theory 1 happen.

[Note:These are the two theories I have]

Theory #1 This is my gut talking to me!

I learned running the X-Power Drive that if you set the input pinion gear to deep in the ring gear it will bind up when you really push the HP/torque levels up past a certain point ie... 1000HP. Thus, I believe the input pinion gear is set to deep initially on the ring gear in the SCX drive and when you put serious HP to it the pinion gear is pushed into the ring gear creating a binding effect on the drive.

Hence, those running less than a 1000HP do not have the HP to make the pinion push into the ring gear---thus no speed loss. When I hit it--- 5500RPM++ and above with serious torque the drive is binding up----it seems like I am hitting a wall and I can barely hit the rev limiter with a prop that I always hit the bump box with.

Theory #2

The SCX drive holds a lot of RTF fluid and you need a larger bottle to accomodate the expanding fluid coming out of the drive. It may be that the fluid is expanding too quickly and the line to the bottle does not have a large enough diameter hose/fitting to relieve the pressure quick enough---thus causing a hydraulic lock up of the drive at very high RPM.

Note: The drive fluid expands dramatically when your above 100MPH i.e. about a quarter to a third of a quart in fluid expansion.

Now my gut tells me it is theory one versus theory two.

Lastly, I cannot be the only one to have this problem unless all the drive people out their are keeping it hush hush or do not know really what the side by side comparisons are with a boat pushing this kind of HP.

If you have any ideas please chime in.... now is the time to impress rather than sitting back and waiting when the answer finally surfaces by then I don't want to hear stories just solutions. I am frustrated with this dilemma especially when you read the sidenote below.

Sidenote: 26Redline had the same application and ran 128,129 respectively in his boat on video. He had no significant power loss on the top end and he is pushing 1010HP in a lighter closed bow cat. Albeit, he lost a lower gear set after four hours of boating---his initial runs were demonstrating no power loss. This causes me to question why I am having such power losses.

Any real help and input is welcome you can PM me if you want to run something by me in private rather than in an open forum.

KAP

Mr Gadgets

Kap have you pulled the pinion gear to look at the wear pattern?
with that much power I would think, binding, would show some signs of uneven wear.
Can you shim the pinion out by .005, and see if it helps.
That may prove your theory.

rvrrat

I put the SCX with Imco lower on my F26/Teague 800. My boat did not agree with the SCX. I normally run a labbed 32 and the boat rolls over nicely. I had to prop down to a 30 with the SCX and even then it required much more RPM's to roll over. The biggest issue was my boat developed a porpoise from 65-80 that I could not overcome with trim.

I never took it past 80 to see if the hop went away. Personally I did not see a reason to if the boat would not behave at lower speeds.

I think the SCX is the solution to breaking XR based drives, but with the handling issues I experienced, I ended up pulling the SCX and going with a built MMW XR based drive.

I sincerely hope Imco finds out what the compatibility issues are and resolves them. I am not looking forward to breaking another XR based drive. Because its only a matter of time.

Airpacker

Which lower were you running. The SC or the SCX ?

Same gear ratios? Same lenght lower?

Airpacker

Two thoughts. One) wouldn't the pinion try to push away from the ring gear under load?

Two) Is it possible the the drive is getting really hot and the gears are physically expanding causing the binding you speak of?

kap328

Yes we pulled it and no wear pattern was evident. However, I thought about this and concluded that a wear pattern would not necessarily develop as you do not hold the throttles pegged when nothing is happening speed wise.

Hence, it would not stay there long enough to develop a wear pattern. I could be dead wrong but so far I have not heard of anything to dispell my theory. A good way to see if any movement occurs is to pull the set apart coat with an ink or dye the ring gear and see if the pinion goes in far enough to where it would wear off the dye in the valley of the gear.

Shimming the pinion is the solution I would know in about 10 minutes and/or one run if that is the problem.

I checked the drive cap once I came off plane at 100+ runs and it was warm but not anything excessive.

I was thinking about the fluid type 26Redline did not run RTF he ran a synthetic gear lube of some type perhaps the RTF is the culprit but I suspect not. Note, RTF is used in Number 6 drive but that unit is a dry sump gears are not running through it like a SCX.

My money is on shiming the pinion out away from the ring gear .005+ and see what happens. Hell, we can do it all in one trip to the lake shim, and change out lines and fluid.

I am not a principal of IMCO they should be the ones at the forefront of this issue.

Honestly, I have grown tired of banging on my motor trying to make things work---spent an entire day at Havasu and again on the lower Colorado with same results.

KAP

Airpacker

Kap, I cannot really believe the line to the res bottle is the issue. If that drive built up so much pressure from running, seals would pop or the plastic adapter thru the transom assembly would pop.

It is too bad that IMCO didn't take the concept one step further and dry sump the SCX isn't it?

On a side note, Dave at IMCO suggested it may take as much as 25 hrs use to "wear in" the drive to free it up completely.

Its real hard for me to do any comparison runs as I had 350 less HP and a Black Hawk drive before I bought the SCX /SC combo.