Ok, I have an 06 Rhino 660. It goes about 42 mph on pavement (about 38 in the dirt) with two rider. I have it set up as a four seater with a cage and rear seats. I don't have any additional weight added on after that. As for mods, I have a BRP CDI and UMP airbox with the stock exhaust. I am running 12" ITP wheels and 25" terracross tires on a mid travel suspension. What should I do next, a KMS sheeve? re-jet? I have seen the topics on the new dry clutch but I am not sure if I want to spend the $1,400.00 for it. On a side note, the CDI may need to be replaced. It may be one of those crappy units since it is hard to start when cold. What CDI do you recommend since this one may be toast?

I have a 4 seat long travel with a cdi,uni,kms sheave,and a tip and I can hit 54 on a flat dirt road. Avg is 47-52. I have a rhino craft cdi and it works good I guess.

I have a Rhino Craft CDI, KMS Sheave, stock exhaust,rejetted the carb, and a K & N filter and I'm hitting 56 MPH on the street. Also my car is a pretty heavy 4 seater.
I would try and change out the CDI Box. What city are you in? If your close by I would let you try mine and see if it makes a diff. before you go out and spend another $200.

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I also have a 4 seater with a cage and 42" rear set. I have a BRP Stage 2 CDI and a KMS Sheave. No other motor mods. I can hit 55 mph on flat ground and 60 mph on a slight down grade (verified with a GPS). I think a CDI and a Sheave are the 2 best upgrades that you can do. I would not mess with the air intake, jetting or pipe. I would do the sheave, cdi and keep your reliability. The cdi and sheave are the best bang for your buck.

Yes, the sheave and CDI are the best. The only reason I went with the K & N intake is because the stock filter sucks really bad in the sand and the intake vent is always getting sand in it. With the K&N filter you can run a Pre-filter and block out a lot of the sand from the motor. Once you do the K&N you have to rejet it.

Do you guys do anything with the clutch spring? I've seen different weight options? Also, I was wrong, I have the DFR CDI. Not sure if there have been any problems with them. Also, the UMP airfilter is awesome. I run them in my Dual Sport. They utilize a larger paper filter. You can run them almost a compete season. All you have to do is blow the filter out every now and then. No oil, no mess. They also trap more dust particles than most airfilters out there.

Do like Lead Dog said and call Larry at Performance Rhino. He has the best head guy, clutch parts and a killer deal on the PWR radiator set up. He did the re-work on my motor and I couldn't be more happy.

You can get a Duners Kit if you run mostly at the Dunes. I beleive it consist of lighter rollers and a heavier clutch spring. It is also made by KMS. The lighter rollers will allow it to shift at a higher RPM which is good in the sand. With just the KMS or stock sheave it will shift a little to early and then the motor will start to bog down. It is better to keep the RPM's up and shift late to keep the power up. The heavier spring will stop it from engaging out of the hole. It will allow the RPM's to climb a little higher before it engages and takes off. A little more hole shot.