If you do decide to do this you can purchase a new 350x motor from east coast atv. I think they are $1500. Then reliability is not a Question.

 

A stock 350X engine puts out around 22 RWHP
A stock 300EX engine puts out around 16 RWHP
A stock Warrior engine puts out around 17 RWHP
A stock 400EX engine puts out around 27 RWHP

A 350X will not outrun a 400EX

A 350X will outrun a Warrior.

A highly modified 300EX will have trouble outrunning a stock 400EX. It will take every bit of that 330kit, pipe, cam, high compression piston, port and valve job, and carb to match the stock 400EX. Then, as I said before you have a modified race engine that needs frequent maintenance to remain in a good state of tune, and you have spent more than the difference that the 400EX would have cost. It takes some good planning and lots of tuning time to squeeze 11 more RWHP out of a 16 RWHP engine (that's like trying to squeeze 45 RWHP out of a 400EX, it can be done, but you're in the realm of race gas only, frequent rebuilds, and a finicky race engine that is not reliable for everyday riding)

The 350X engine, I feel, puts out a little more bottom end than a 400EX, the mid is probably close, but on top the 400EX will eat the 350X's lunch.

 

Gabe is right on with the HP estimates and lack of reliability when building a "race" engine. More care is nessesary too keep a "race" engine up to par.

But the one thing he forgot too mention is rider skill. The machine is only a tool, and it's up too the rider too use the tool too his advantage.

A 400EX is a GREAT machine. But I have seen Blasters run circles around novice riders on 400EX's. Keep in mind that rider skill plays a bigger part in the equation than the machine that he is riding.....

Don't ever forget the story about the turtle and the rabbit......


Chris 00' TC Racing 300EX

 

hey I say a nice 350RX for sale......it says 13:1 compression. does that have to use race gas? its $2900 and looks good......I'm think abuot gettin it......later

 

I did this 6 to 8 months ago in my 250x I even got custom exhaust for the conversion from powroll racing, It is definatly faster than the old 250x, but not like I had hoped for, I have it running about 65 right now, I put a little smaller front sprocket on for more getup. the engine has tons of torque on bottom end, but the top end is a little weak, where I notice a big difference though is going through a field where you can get it toped out, the 250 would almost not have enough torque to run wound out in 5th, the 350x has no problem maxing out though. its also nice for jumping because there are more gears to choose from when going up toward a jump, its hard to explain but someone may know what I mean. anyhow, the exhaust was like 400 bucks and it has already broke once accualy. you have to consider the oil cooler as well, that was a bi*ch for me I had to get custom hydrolic lines made for it and the still aint the greatest. in my opinion, if the 300ex bike and motor is fine, then dont change it, if you want more power, sell it and save up for the new 660 or a 250r (you could be like everone else and get a 400 though) thats my 2 cents, later

91 TRX350X
Works front shocks, skids all around, k/n filters+ outerwear, 86 350x motor, custom exhaust, lonestar bearing carrier, blue flames seat cover, + other little shi+

85 ATC250R, all stock but exhaust
will dust any 400

94 DR350 enduro bike, just picked up, needs carb work

later

 

I HATE the kickstart of my 350X with 12:1 compression piston, but the starter on a high compression big bore 300EX will not hold up long. That I do know as true.

The 350X will not out run 400EX's unless it is heavily modified I suppose. (i"ve never seen one outrun a 400 and I know mine doesn't)

My buddies 400EX low end was killed with heavy 6 ply tires all the way around whereas mine doens't seem any different, so I don't know what to take of that. The high compression piston in mine I guess is what saved my low end.

You cannot buy a "new" 350X motor anywhere. Those are motors that have been taken apart and put back together by hundreds of motorcycle mechanics during their schooling. I know someone who bought one and it came apart after 6 months of riding. If you do buy one, you need to completely take it apart and make sure it is put back together right.

The 350X motor is also a lot heavier than the 300EX motor. I have been trying to find out how much but I haven't been able to find it yet. This definately changed the feel of my quad when I switched to the 350X powerplant so it has to be heavier.

nosaj
96 350XX
#94 MHSC
#401 SOIL

 

the weight difference is true, my 250 is a lot heavier than before, hasent really seemed to effect flying though, she is balanced well. the decompression cable is a bi+ch, it dosent fit on the 250x frame, I bent it to make it work but it has now broke and I havent worried about it since, I know the feeling of kicking the beast over, (almost always takes 2 kicks too) I have gone through one pair of boots already from kicking her. I have also played with jetting, I am running a 140 main right now in the 250x carb, they say it works better, i dunno, I would like to try a 350x carb to see if it could be the carb holding it up. also no air box lid w/ k/n filter, sounds better like this but not much help

if anyone knows if there is a difference between the 2 carbs and one is better, let me know, thankx, later

K Krabill
91 TRX350X
85 ATC250R
94 DR350

the workers
85 250 Big Red
84 200 Big Red

 

Why wouldn't the starter hold up on the 350ex? Cuz I know rittercycle offers to bore it to 350 with the works for 1100+ dollars.
I think if they do it all, which is more than 1100 you got a quad with a reverse, that eats everything else up that doesnt have engine mods.

 

hehe Chris, see my post in the Sport Quad section on the subject of riders.... You basically just repeated what I said

The above examples were given with the rider taken out of the equation because there is no way to quantify rider skill in an internet posting and it would further confuse the subject to try.

Later

 

Ahhh,

I didn't think many people knew about the Vo-tech donated engines.

I got one of those 350X engines, but the instructor held it back, didn't let the students touch it, and used it on his own bike for about 30 days. Got it for spare parts, never needed it, what a great engine the 350X was. Bought it for $200 several years back. It's collecting dust right now... What a shame.