just picked up a 670HO and was wondering how fast they are also what if any mods are needed to make them really cook.

they are very competitive with 7's and even some 8's. Depending on what you would like it to do , the best mod is an 1 1/4 track. Clutching , gearing, and good maintenance.
I have an MBRP wide kit on the front end of my flatland HO and love it.

Ufo's have their good points and bad. Love the throttle respone, hate the gas mileage. Going to give them a go again with some changes and see if I can get the mileage up.

go here to see what to do to really make that sled cook--

http://mxz670.tripod.com/99670HOTH.html

Even though it spots some 30cc's to the larger 700s, it is a really quick sled. On the bottom and mid-range, it really moves, but the top end suffers a little.

On my old 670, I had a goodwin performance clutch kit, and one tooth smaller gear (the small gear). It was studded with 144 studs, I had the shorter intake boots and had tried a couple of different rotary valves. I always did very well in grass drags with the machine, and even could beat SRX's up to about 75-80mph. After that, the top end would drop off.

All in all, a great motor!!

Fastest twin Skidoo has ever built! :hallo3:

can't say I agree with that,I had both and my 700 is faster.the ho would win to around 60mph past that its all series 3.

thanks for the info guy's i'm thinking about getting the 740 big bore for it any info on that would be great.

If you dont even know how fast it is why do you want to modify it before you even ride it? Just curious.
Ryan

RNM2399
because there is no replacement for dissplacement thats why.let's see 145hp 740 vs 127 stock,i need all the juice i can get.

With a little bit of grinding in the right spots, a stock bore 670 will make 145hp with the stock pipe and muffler.

I 'm sure it will but i dont want it to burn down after 500ft.The Crank S hop has dyno'd the 740 @145hp with 98ft lbs of torque,it sound's to me that the 740 is alot less radical than a standard bore 670 would be makeing the same hp as the 740.

paidncash, I have 4500k(2796miles) on my modded 670(non HO) with no reliably probs what so ever.

If you bought it to ride it...then ride it. If you bought it to build out the motor, then that is another story. That motor is definately a drag race king, and will do well in that type of running, but if you want top end, the reed motors will develop more top end. But then, if you just want top speed, he with the most money wins...

Just remember, the more mods you do, the less reliable a sled becomes... (if you are just going to trail ride it).

Recently I spoke with a couple of the bigger rotax specialty shops, DNE, CrankShop etc. They would love to do the 740 bigbore but the they freely admit that the best bang for the buck is a tunnel and cylinder porting job with matched cases, slight bump in compression, timed rv and rv cover mod.

If your topend is ready to be redone the price isnt that bad. But if you have a good motor spend $900 Can or $600Us and send it to Don and let him do his thing.