A few people have asked me how my quad with a 250R chassis and built 350X motor compares to a properly built 400EX. Sorry it has taken so long for me to respond, but I have been out riding and am spending less time in this forum.

You can read the modifications to my quad at the link in my signature, but basically it is a full race MX 250R with a 500cc modified 350X motor.

Handling: We all know that the handling of the legendary 250R is second to none. The geometry on all aftermarket chassis' are still loosely based on the 12 year old 250R. The center of gravity of my 250R is slightly lower than on a 400EX and I would give a slight handling advantage to my quad over a similary set up 400EX. I will say that 400EX with the normal MX mods such as a-arms, axle, shocks, and swingarm is a very good handling machine and the difference between mine is probably small.

Motor: I have two 350X motors built to 500cc and they are both rather rare. One motor has been modified by GT Thunder to run dual 34mm carbs which I am currently using as a back-up. The other 500cc motor was modified by Powroll and uses the head from an XR500. This is the 1st year I am running this motor and I like it a lot. The XR500 valves are 3mm larger than the 350X head so this thing flows lots of air. I am using a Keihin FCR39 carb and it runs very strong. My motor is definately faster than a built 440EX but the difference is not huge. I plan to put it on the dyno at GT Thunder this summer to see how many HP it is making. The biggest difference between my motors and a 440EX is not how much power, but how the engine makes the power. A 350X motor makes great low-end power but does not like to rev. A 400EX (or 440EX) revs much quicker and higher than my motor. I still prefer the low-end grunt of my motor and I think it gives more longevity by shifting at 5 or 6,000 RPM versus shifting at 8 or 9,000 RPM. A lot of people talk about the 6 gears on the 350X as being an advantage but I don't think so. The width of my powerband is plenty wide enough to handle 5 gears and the 6th gear is not an overdrive as some people must assume. I believe the final drive ratio on both is 1.0 so 5th on a 400EX is the same as 6th on the 350X. 1st gear on the 350X is lower and I never use 1st or 2nd on the track (except for starting in 2nd).

Someone asked how my quad compares to a raptor in a drag race and I can honestly say I don't know. I have never ridden with a raptor and the only riding I do is on a motocross track. The only drag racing I do is to the 1st turn at the start of an MX race. I can pull built 250R's and Banshees but don't always get the holeshot because of all the other factors involved with the start. I will get to see how it compares to the Raptor very soon because one of my MX buddies just bought a Raptor and will be racing in my class at my local races. I also will race against Raptors at the GNC Nationals in the Open B class.

Would I do it again? No. I bought this quad a few years before the 400EX even existed. I have always been a 4-stroke fan and wanted the ultimate machine that did not exist - the handling of the 250R with the low-end power of a big 4-stroke. I have what I wanted but if I was starting over I would probably buy a newer 400EX and modify it. The reason is because there are so many parts available that bolt right up to the 400EX. When I bought an exhaust pipe I had to strip the entire frame down, and ship the frame to TC racing to have a pipe custome made. When I installed the Keihin FCR39 carb I had to heat and bend the gas tank to make clearance for the carb. I also had to make an air boot to run from the carb to the air box out of radiator hose. Sometimes the tinkering is fun but it would be nice to just order something that fits. Not to mention that my frame is 13 years old and the motor is 15 years old. The 350X is very reliable but how long can they keep going? Also kick starting a big 4-stroke can be very frustrating at times. But, knock on wood, so far with the FCR it starts right up on the 1st kick when cold and the 2nd kick when hot! I am waiting until some parts (a-arms, nerfs etc..) become available for the Cannondale and if it proves reliable I may buy one next year instead of continuing to put money into an old machine.

 

Thanks for that info.
It sounds like you have a pretty awesome quad.

Have you weighed it?

 

I have neveer put it on a scale, although I have been curious. It is way heavier than a normal 250R, I would guess the 350X motor adds 30 to 40 pounds.