has anyone put a newer model CR250 motor in their quad? If so, how do you like it, does it vibrate heavily, how is the power, do you like it better than a 250R engine?

 

You never hear of the CR or YZ (2-strokes) being put in quads. We're rebuilding our 250 right now, form the bottom up. These engines really are sprinters, and aren't engineered for the long haul (although lots of them get ridden XC anyway!). Just ask yourself why the manufacturers havn't done it??

A quad dishes out a lot more abuse than a light little MX bike. It's just not what these engines would be good at. But, if someone has done it, we would love to hear form you!

 

A couple things going against the motor swap...nothing that cant be worked around.

As mentioned the vibration issue... Work around: put a CR cylinder on a TRX bottom end. www.ftzracing.com

Transmission ratio differences... Work around: put a CR cylinder on a TRX bottom end. www.ftzracing.com

ESR www.esr250.com offers a CR ignition for the TRX engines. I'm wondering now if you were to do the CR/ESR swap then you would be able to drive the powervalve servo. Or does the PV run from crankcase pressure for the years that the cylinders that are being used to swap with. Not too sure there....

I think that for relative costs, a Pro-X cylinder would be a likely better canidate than a CR cylinder would be. Especially now with the 350cc Powervalve Pro-X cylinders. www.lrdperformance.com

In a nut shell, your taking a good 2 stroke engine (the TRX based) and replacing it with another good 2 stroke engine (the CR based). Is that swap really necessary? You're looking at about the same price for a Pro-X swap. FTZ is getting $1600 for the std CR cylinder, and 1995 for the late model(nikasil) CR swaps(it also requires case welding) I think that price is in line with what a 350PV will cost. Comes down to really what are your expectations of power and desired power characteristics, but at least in this kids opinion nothing that cant be tuned to with the TRX based engine.

 

Backcountry:
The CR powervalve set-up will not be able to function when put on a TRX bottom end. Before PRO-X cylinders where available (way back when), it was advantageous to use the CR cylinders because of the port layout. The powervalve was blocked using a "plug", and the porting was done accordingly. The powervalve is mechanicly actuated from within the bottom end of a CR, and the TRX doesn't have the capability for adaptation. So, you end up with a powervalve cylinder with no powervalve. If you're looking towards using a CR engine because of the powervalve, theres other things to consider. The NEW cr's (2002) have a powervalve actuated electronicly via the cdi and a servo. This has huge potential for TRX owners who want a powervalve set-up (this may actually work, where "other" attempts at a producing powervalve cylinder have failed to yield results). The current powervalve kits available to TRX owners offer no advantage over a conventional cylinder with good port job, the correct pipe and the correct carb for the application, regardless of all the hype the current powervalve cylinders have. This "conventional" set-up would also be about $600 cheaper! We've been testing with our 2002 CR250 for a couple of weeks now, and initial tests are discouraging. The 2002 is down on power (per the dyno). There is no doubt that power delivery is smoother, and definately more "ridable" in real world testing at the track. The bottom line is, though, that it doesn't produce the HP numbers (right now, anyway, in "stock" trim). If we're looking at utilizing the 2002 powervalve set-up for TRX applications, we have to determine wether the lack of power is due to the new powervalve design (which might be trading horsepower for ridability), or related to any of the other changes that where made this year (of which there were many). Time (and testing) will tell. As you stated, there is no advantage to putting a CR in a TRX, but there is the obvious drawback of added vibration (significant). The CR's are totally capable of dealing with the added weight or any "extra" abuse of a quad, heck, the micro-sprints weigh a good 750 pounds!

Just my $.03 worth....

lump-dog

 

No advantage to a CR motor over a 250r motor? I have to say otherwise I think. I rode my friends 97 CR the other day and it had WAYYYY more power than any R I have ridden. The bottom end from the CR is amazing for a 2-stroke. I rode another friends LRD 300r and it has bottom end, but not like the CR. The CR is also FAST on top end too!
Also, replacing a 1986 motor with a 1996 motor makes sense to me. However, I dont know if the vibration would be worth it.

One question about the vibration though, wouldnt a 4-stroke dirtbike motor also vibrate like crazy and if so, then why are the pros running them if its so bad? I would think that if you added a steering stem with anti-vibe stuff on it, got a wristwrester maybe, a steering damper, and built rubber lined motor mounts, you wouldnt notice the vibe much. Unless the 2-strokes somehow vibrate more than a 4.

 

Yes, a CR in a dirtbike is going to be faster than a TRX in a quad. There are some funny little laws regarding physics (like weight, rotating mass, etc) that come to play here. The bottom line is, a CR and a TRX are going to perform very much the same in a QUAD. The differences that would come in to play would be things like ignition, carburetor, pipe, etc. These are all variables though, and shouldn't effect what we are discussing here, is a CR engine better than a TRX engine......


-doug

 

Thats a good point about the weight of the quad I suppose. I never really took that into consideration. However, I still think that the newer CR motor will make more HP than a TRX motor. If nothing else just due to new technology in the last 15 years or so. How much HP does a stock 96 CR make compared to a stock 86 CR? Then you would have your answer I think if you could find both those figures.

 

One of the dirt bike magazines said that the current 125's are as powerful as the old 250's. So that means the new 250s are......

Again though, I bring up the point that the manufacturers don't use these engines in quads!! They have the engine R&D done already, so wouldn't it be cheap to just throw it in a quad frame??? I think they know something we don't, like the things wouldn't hold up!

 

They would hold up in a quad, the pros are running YZ motors arent they? Anyway, the reason that they dont throw one in a quad is a combo of 2 things. First, the reason they stopped making them in the first place, too many people getting hurt. Second, the new laws cracking down on 2 strokes. Honda has already said that they will not produce any more 2 strokes except for closed course competition dirtbikes, that rules out quads. I would say that within the next 10 years, there wont be any more 2-strokes being produced. The AMA is pretty well trying to phase out the 2-strokes by allowing 440cc 4-strokes and only 265cc 2-strokes. The only 2-stroke motor that is going to produce as much power as a built YZ426 motor bored to 440 is maybe a Sparks 265 powervalve (obviously it does, Jerimah Jones just won with one) but normal ones just really cant hack it anymore. There are still a few tracks that 2strokes dominate, but not many. Just look at #2 and #3 this year, both on 4 strokes.

I think the day is coming when we wont have any 2-strokes. Hell, its already here, the ones we have are 15 years old!

 

here's my main reason for the inquiry about swapping out the motors. A TRX motor would cost you at least $3000.00 to build brand new, when you can get a complete 2001 CR250 engine assembled, with electronics for $1800.00. A new CR motor has roughly 45 horsepower stock, while a TRX motor I believe is in the mid 30 horse range in stock trim, which in turn you need to shell out more $$$$ to get the TRX up to par. If the CR motor will work you save money, i'd like to talk to someone that has tried it and see if they liked it or not and why. Thank's for all the helpful info!