I have the choice of either getting a stock 400ex or a modified 250r frame holding a 350x motor. I know the rx with handle better but which is more powerful and which has a better powerband.
Also good mods for the better bike. I currently have a modified 96 Banshee and it sucks.

 

the 350x motor will dust a 400ex motor (both being stock)

 

Wrong answer both being stock the 400EX makes about 6 more hp. That is based on the dyno readings from GT Thunder. Also I have ridden a 350X conversion quad and it was a powerful machine, but definitely not as powerful as a 400EX both being stock.

Their may be a slight chance that the 350X is a little faster since it is a 6 speed, but the 400EX has such wide ratios and from what I remember the 350X had about the same top speed in a 3 wheeler as the 400EX.

Adam Smith

99 400EX

 

i must disagree i have seen the conversion and comparrison and the 350x/250r combination is surperior more so in handling but also in speed maybe its the six speed?but the 350x motor seems to be in a higher state of tune than the 400ex maybe cdi?

 

the 400EX is much peppier. The 400's can pull wheelies up to 4th gear. I couldn't even pull a wheelie on the 350RX I rode. Instead of dropping a 4-stroke engine into the R chassis, drop a 2-stroke in there. Then you will fly. 2-stroke is the way to go if you want speed and handling. I was unimpressed after riding a 350RX.

 

I think I can help with this question since I actually own and race a 350RX conversion. First of all - power. If both motors are stock then the 400EX is quicker. I have one highly modified 350X motor and a 2nd motor as a back-up which is mostly stock. I ran the stock back-up motor this whole summer and raced against many 400EX's each week. The stock 400EX's could consistently beat me to the 1st corner when I ran my stock motor. A stock 350X motor puts out about 21 HP while a stock 400EX motor makes around 25 - 27 HP. But keep in mind that most people do not race a stock motor and they both have good hop-up potential with maybe a slight advantage going to the 350X motor (it can be bored larger). As far as handling I would give the edge to the RX, especially since you mentioned that RX you are looking at has some chassis mods. The stock 400EX isn't bad in handling, but needs a longer swingarm to be competitive. One last word that you may want to consider - the RX conversion is a custom built machine and this means that you can't just order certain parts from anywhere. The exhaust pipe is a good example. You can order an exhaust for a 400EX from any numerous places with no concerns about it fitting. When I replaced the exhaust on my RX I had to strip my frame down and send the frame to TC Racing so a pipe could be custom made so that it bolted up properly. And I don't agree that you should get a 2 stroke. My 500cc race motor is fully modified and can kill a stock 250R and will run with any modified 250R or banshee. Good luck and let us know what you decide.

 

Now that they allow 440s instead of 416s to run in 400 4 stoke and 250 2 stroke. So that makes a 400EX a little better choice in my opinion. From what I have seen it is alot cheaper to get 440 displacement out of a 400EX than a 350X. Also as far as max displacement Sparks Racing has a 505cc stroker 400EX on their website right now.

I have my 400EX set up with +2 a arms and a +4 axle. I also have TCS front shocks and it really handles well. As soon as Christmas is over I am getting the TCS rear. I also have my motor at Sparks right now getting a 440 National. You could do alot of the work yourself on the motor and save money, but I just want everything to be set up as close to perfect as possible.

I agree with the other 500RX about the ease of modding a 400EX over a conversion. At least if you go with a 400EX you can just order a pipe. Also the FCR carb is very popular on the 400EXs and that thing is really supposed to be sweet, I hope to find out very soon.

Adam Smith

99 400EX