This is what I did for my mod sled in the Vet class here in Alaska.  I put an off the shelf, RMK 600 motor in my '04 ProXr 440 chassis.  I say RMK 600 but it is a motor my local dealer has on the shelf, brand new.  They come complete with Y pipe, carbs, ignition, straps, recoil, spark plug, readt to bolt in and put gas in and start. They come with oil injection and all the fittings and hoses already attached.  Without the octane key switch plugged in to the ignition box the dealer told me it was set to the Premium setting .  I did not have a key switch so I went without.

1. I used the straps off the 440, this placed the motor exactly where it needed to be in relationship to the jack shaft and CG.  By using the 440 straps the motor sits very low in the chassis and at a the exact same angle as the original motor,  This angle is very different than on an RMK chassis and strap configuration.

2. On this motor using the 440 straps the carb boots faced at a more downward angle than the 440, kinda facing directly into the jackshaft.  I used a carbide bit and trimmed on the airbox to carb inlets and used the IQ 440 airbox boots and made a perfect fit, If you use the rmk proX style boot they have to be trimmed down at least half as thick because the airbox is real tight to the carbs. The stock strap holds the airbox in place and if done properly it is a perfect fit.  The PTO side carb is very tight to the chassis near the torque stop and jackshaft bearing.  It almost touches, the airbox just holds it away from the chassis.  Dont trim to much on that side of the Airbox, the boot needs a little lip to catch on, but you have to trim to within about 1/4" to 3/8" from the edge if you know what I mean.  Both airbox holes have to be trimmed and widened but a little more on the PTO side of the box. You can put the airbox in place and mark exactly where it needs trimming.

3. You should use the fuel pump from the 600, cus the 440 has two outlets instead of 1.  I started out using the 440 pump and both lines but wasn't sure if it was right.  Then after the first race I bought a new 600 fuel pump and swapped it out.  It made no difference in plug wash, jetting or performance but I had piece of mind.  Ether pump will work if done properly, but you must use both hoses if you use the 440 pump.

4. The Y pipe that came with the new motor was at a slightly upward angle.  It didn't hit the Shock Tower Brace but it made getting the motor in and out almost impossible with the Y pipe on.  The 440 y pipe has the right angle and appeared it would bolt on but it has much smaller tubes in the manifold.  I chose to raise the Shock Tower cross brace for proper clearance.  I used a cutting wheel and removed the weld on the PTO side of the brace.  I then removed about half the weld on the Mag side of the brace.  Then I put a 1” square tube spacer under the brace on the PTO side and welded everything back in place.  By only lifting one side the brace did not interfere with on the pipe side  If your Y pipe has a more downward angle like the 440 then you should have no problem with the brace, if your y pipe angles up slightly, just about 6deg., more than the 440 then it is best to modify the brace..  You will be able to tell immediately if the motor is difficult to get in and out. 

5. The stock 440 pipe and can work amazingly good, it looks good and has a deeper throatier sound than with the 440 motor.  You should plug the temp sensor with a pipe plug, I just left the pipe temp probe in and tied up the wire so it wouldn’t flop around.  You are giving up just a few HP to an SLP or aftermarket pipe but not that much, and it will work better than a stock 600 pipe for sure.  It fits and looks perfect, there is a very slight angle diff. at the Y pipe but it works good.

6. I used self taping sheet metal screws about 1.25 “ long and mounted the coil to the top of the Mag side of the airbox with the plug wires facing forward.  One plug, and remove the caps and the airbox comes right out and it looks like a factory fit, even better than the factory tie rap job of the 440.  I removed the 440 adj. timing switch and CDI and bolted the 600 CDI right in place of the 440 CDI.  The spacers from the adj. switch work perfect for mount spacers for the CDI.  It mounts vertical with the harness plug facing forward.

7. I went to a Sno-Go junk yard and bought a Oil Inj tank from a 1993/94 A/C Prowler.  I barely modified the stock prowler mount and it bolted it a little above and in front of the CDI right next to the Puke tank and steering post.  The prowler tank mount bolts directly to the chassis near the recoil with just a slight modification.  A new piece of tubing and you are set.  The stock 600 tank may work ok to but it is heavy and gets pretty nasty. I don’t know if the stock tank will work with the ProXr steering and tank set-up.  The old prowler tank was $15 and it has a much larger cap than the polaris tank.  Every person who sees under the hood can’t believe how clean the setup looks.

8. For clutching I went with a full SnoX set-up with a $180LB titanium spring and 70grams on the toe of the heelclickers in the Primary ,  and I put about 6 g’s on the heel. This weight was adjusted for the track conditions.  I clutched for 8250rpm at all times.  The secondary was different depending on the track we raced at but it was set up for Mod SnoX racing.

I used the stock 440 gearing but you should gear it up if it is just a play sled.  The 600 would pull to about 85 to 88 MPH in about 6 seconds with this setup .  I ran premium in the tank and jetted down to as low as 310 at warmer temps.  At 20deg I ran 330’s at a sea level track. I know that sounds lean but we were snoX racing and that’s what it could handle for short bursts.