XR but soon to be upgrades by max machine worx. The imco extreme is no better than a XR. Its all how you put them together and how you drive the boat.

John,

I believe that the IMCO Extreme and the XR are similar, but not the same.

The upper case on the IMCO is larger and stronger. The torsional vertical downshaft is different, as is the lower bearing carrier. They both use the XR gearset, which is the weak link. The IMCO lower also tends to be more efficient than the XR lower.

The Max-Machine drive uses there own down-shaft, cryoed XR gears, and a Billett case that is much stronger. They also have an extra bearing to aid in driveshaft rigidity.

The weak link in all these drives is the XR gears. No one has come up with a stronger replacement gearset to date. :(

Guys with more than about 700hp and slip below 12% shred all three of these drives on a regular basis.

I believe that the solution is going to be the IMCO SCX drive. This will be a bolt on replacement for an XR, and has much larger gears. Because of the additional size, and weight, speed will probably be reduced by 2-4 mph when set up correctly. They are rated at 900 hp, and there are no reported failures that I know of. Cost is 15K-16K depending on pricing.

I am about to upgrade my hp to around 750 next week, and have been studying this outdrive problem.
If you have any revelations about this subject... I would love to hear them.
I am worried about my outdrive.. it is only about 15% stronger than an XR

Chris

The case is really not much stronger. I know people with 900 hp heats with xr's holding up fine. The scx is strong but slow as hell. You worrying about nothing just be easy on the drive and it will be fine. Also the xr sportmaster uses the imco vertical shaft from mercury. The lower on the sportmaster is slower but much thicker and will hold up much better with higher horsepower. Pm me your number and I can talk to you and give you a few tips.

John,

Here is a picture of an IMCO upper next to a XR upper.

I would appreciate any and all tips you have.

Chris
206-235-4545

Nice looking engine, John. Can't wait to hear how it runs. Here's my prediction, based off of a speed calculator I wrote. Based on a current speed of 87 and using 550 crankshaft HP on the 525, you should run right at 100 under those same conditions with 725 HP.

Hey Bob,
If that's our old formula, it will be interesting to see if it applies to tunnels too. I think OCM ran 112 with a Merc 700 in their Thor.
I think the tunnels are more efficient than our 17HP per MPH (for MPH increase from stock baseline) formula for Heats. It will be interesting to find out and compare the 2.
Best Regards,
Steve

It's a formula that takes current HP, speed and weight and calculates a performance constant. Then, using the new HP rating, projects the speed. The formula has been around for years. I just put it into an XL spread sheet to be easy to use. It will work with any style hull as long as the characteristics don't change with the increase in power. An example would be a cat that wasn't airing out correctly, but with the added power did so, thus becoming more efficient. The formula cannot account for that. I've found it to be very accurate on dozens of projects. It's a great tool to use when discussing modifications with a customer. It takes out the guess work and keeps expectations realistic. If someone comes in and says they want to run 80 and can give me accurate data on the current setup I can project the power they need. Then I can design an engine package to meet that need with no disappointments.

Bob

Sounds like a version of the BAM/gofast/Mercury formula?
Best Regards,
Steve

Motors look great,:ernaehrung004:

Is there any support on the bottom of the oil cooler?

yes there is a bracket.