350RX........should i do it?

[ryanh250ex]

title pretty much says it all. i'm in the process of acquiring a '86 350X motor bored out to 405, ported and polished head, etc etc. i also have a friend with a spare TRX250R frame. i have read up a little bit on the 350RX conversions and it's something i'm interested in doing.


has anyone ridden these machines? if so, are they any good?

for those that have ridden a 350X, was it pretty fast?

i want something powerful and unique for my area. i can build one pretty cheaply, and i'm in need of a serious machine, so i'm really looking into it.

thanks in advance.

- Ryan

[86atc250r]

In this day and age, that would be an exercise in wasting one's time.

400EX's are dirt cheap used, and the 400EX engine develops more power. Chassis parts prices for a 250R or 300EX are also immensely more expensive than for a 400EX.....

I know, I know, there are those that will argue, but no one has been able to show evidence why a 350X engine develops the same or more power than a 400EX --- and there are certainly a number of reasons a 400EX will develop more power than a 350X.

Anyhow - if you're really wanting to do a 350X conversion, do it to a 300EX. Easier & you will not be going backwards in a chassis (i.e. putting a less powerful, heavier engine in a chassis than it was originally intended for).

We've done a 250X/300EX conversion - it's a huge torque increase over a 250X/300EX engine, but still is not nearly as strong as a stock 400EX.

Even the engine you're talking about at 405cc's with some work is likely to be less powerful than a stock 400EX with a pipe. The 350X engine is also heavier than a 400EX engine.

The reason for the power difference is the 350X engine had smaller ports, a less efficient combustion chamber, smaller valves, a smaller carb, smaller intake, and heavier hardware than a 400EX engine. It will take significant modification and lots of $$$ to compete with a 400EX based machine.

My thoughts would be to buy one of the ~$2500 400EX's out there and not waste any time or money trying to piece together a 250R / 350X machine, because you'll spend more than that even if you get a free engine and frame.

[ryanh250ex]

Originally posted by 86atc250r
In this day and age, that would be an exercise in wasting one's time.

400EX's are dirt cheap used, and the 400EX engine develops more power. Chassis parts prices for a 250R or 300EX are also immensely more expensive than for a 400EX.....

I know, I know, there are those that will argue, but no one has been able to show evidence why a 350X engine develops the same or more power than a 400EX --- and there are certainly a number of reasons a 400EX will develop more power than a 350X.

Anyhow - if you're really wanting to do a 350X conversion, do it to a 300EX. Easier & you will not be going backwards in a chassis (i.e. putting a less powerful, heavier engine in a chassis than it was originally intended for).

We've done a 250X/300EX conversion - it's a huge torque increase over a 250X/300EX engine, but still is not nearly as strong as a stock 400EX.

Even the engine you're talking about at 405cc's with some work is likely to be less powerful than a stock 400EX with a pipe. The 350X engine is also heavier than a 400EX engine.

The reason for the power difference is the 350X engine had smaller ports, a less efficient combustion chamber, smaller valves, a smaller carb, smaller intake, and heavier hardware than a 400EX engine. It will take significant modification and lots of $$$ to compete with a 400EX based machine.

My thoughts would be to buy one of the ~$2500 400EX's out there and not waste any time or money trying to piece together a 250R / 350X machine, because you'll spend more than that even if you get a free engine and frame.

a 350X conversion is something i've kinda always wanted to do, and being that the motor is being taken OUT of a 300ex frame currently, i'd rather not stick it back in one. i believe that a 250R frame has better handling potential than a 300ex ever will.

i already have a spare frame i can buy off someone who doesn't have a motor in it (it locked up so it sits unused), and i need a serious machine, so i'm putting two and two together.

like i said, i want something fast, yet unique. 400ex's are everywhere around here, i'd like something that will get a weird stare as i idle by.

[86atc250r]

If it's what you want to do - then go for it.

However, keep in mind that you'll be building a machine that's similar in handling and power performance to a stock 400EX and the expense of building and maintaining it are going to cost much more than a 400EX.

My 400EX was red - I wanted something unique as well. It now has green race cut Maier shiny plastic with a black frame - it's easy to pick out of the crowd at the races & I've met people from all around that say "You're the guy that rides the green 400EX, aren't you". Other people have a hard time figuring out what it is....

Then there's my CR500 powered 400EX, but that's a whole different story ;)

I just have to question the expense, time, and sanity of building a 350X powered 250R with the availability of the quads out there today. You'd be FAR better off to get that 250R chassis, and find a cheap 250R engine to build up, then customize the bike to make it look unique if you're stuck on the 250R's geometry.

[250rider]

these r all false statements, a 350x un worked will out run a stock 400, i know from experience. the 350x motor also has the six gears so it is better for racing and it has a lot of potential, i have also seen a 432 stroker the 350x motor, kill a 440ex.

[86atc250r]

I knew someone would have to..

Tell me then......

How does the 350X produce more power cc for cc when it has smaller valves, smaller ports, smaller intake, smaller carb, less aggressive cam profile, forked rocker setup, heavier rod & crank assy, and a less efficient head design than a 400EX?

What black magic does the 350X engine contain that makes it develop more power?

Why doesn't our 300EX conversion quad even come close to outrunning our 400EX? Note that we built our conversion from a brand new 350X engine that had been stored in our barn for something like 14 years (we bought it from the VoTech it was donated to & they did not touch it) -- not some worn out POS.

Why won't my stock ATC350X outrun my stock 400EX, even though it weighs 50lbs less?

Why does the 350X put out less power when dyno'd?

Why does Pam at Powroll herself say the 350X doesn't produce more power?

Why is the 350X, even though it has 6 speeds, still geared substantially lower from the factory than a 400EX?

Why don't racers replace the 400EX engine with 350X engines if they have more potential?

Why did the "350RX" conversion quads all but disappear from racing after the 400EX's introduction?

If you really are developing more power with your 350X based engine - then how have you geared it to compensate for the very tight ratio transmission that has likely become a problem?

I would like some answers, granted you can provide them..... Don't take me wrong, we've owned numerous 350X's over the years - some since they were brand new. It's one of my very favorite old rides. However, the stories about it's engine nowadays are more legend than truth.

I don't doubt that you may have seen a modified 350X outrun a "440EX" - however, you must be aware that many "440's" out there do not run any better (if better at all) than a stock 400EX. Not because the 400EX engine isn't capable of responding well to mods, but because of some of the aftermarket piston setups & poor parts matching some people try. More than likely, if someone has a 432cc 350X they had a professional engine builder do it - many "440's" are done by people in their own garages - results can vary...

CC for CC - true compression ratios matching & with similar cam profiles - the 400EX engine will outperform the 350X every time.

[ryanh250ex]

i know there has to be more that have knowledge on the 350X machines......

this could be an interesting discussion, i'm curious to see what the argument is as to why the 350x would make more power than a 400 if atc250r is indeed telling the truth.

[dnj400ex]

I have a 400ex and the only mods I have are WB slip on and K&N filter. My friend rides a 1986 ATC350x. Not only is it stock, except for a supertrapp slip on, but the motor has been ridden very hard for the 14 years he has had this machine and has never turned a bolt on the engine. It is bullet proof!! As far as racing him, I win every time in a straight line but in the trails it seems like he has twice the torque. I would not trade my 400 for a 350 anyday but it is very impressive especially in the hill climbs where he can usually pull me. I'm not an expert by any means nor do I know much about all the engine specs but I love riding the 350.

[quad_62]

just a little advice on the 350x idea.......


listen to 86atc250r, he knows what he's talking about. I know this from experience. He's got more brains about 3 & 4 wheelers in his pinky toe than most of us will ever totally have. I also have been around these machines for years. He's right about the 400's too, why spend all the extra time and money to end up with a moderately competitive 350RX when you can spend the same amount of money on a used 400 and some mods, but have a superior machine. In my opinion, being an "individual" isnt worth all the extra coin or hassle. Save yourself some money and time and just get yourself a decent 400.

but... like i said, this is only my opinion and it's your wallet, so go do whatever you want. I'm just giving my 2 cents.

good luck on whatever you decide.:confused:

[bradley300]

be different, mod the hell out of a 300ex until most people dont even know what it is your riding, seems to get me some confused looks

[86atc250r]

Originally posted by dnj400ex
I have a 400ex and the only mods I have are WB slip on and K&N filter. My friend rides a 1986 ATC350x. Not only is it stock, except for a supertrapp slip on, but the motor has been ridden very hard for the 14 years he has had this machine and has never turned a bolt on the engine. It is bullet proof!! As far as racing him, I win every time in a straight line but in the trails it seems like he has twice the torque. I would not trade my 400 for a 350 anyday but it is very impressive especially in the hill climbs where he can usually pull me. I'm not an expert by any means nor do I know much about all the engine specs but I love riding the 350.

Thanks Andy...

dnj400ex - Yes, the 350X is a very good engine. It is actually built heavier than the bulletproof 400EX engine.

It also develops a little better bottom end, but rolls off more quickly thru the mid and top (due to the smaller valves, head porting, less aggressive cam, and heavier hardware).

Another reason it seems to have great trail torque is because of it's close ratio transmission - it is substantially lower geared than a 400EX and the gears are spaced closer.

It was one of my favorite trail machines & I spent many hours on one. At the time it was one fast bike.

Here are my gearing calculators if anyone's interested:
http://home.earthlink.net/~gellett/400ex.htm
http://home.earthlink.net/~gellett/atc350x.htm

[rs169300]

I know a mx pro that used to race a 350X aginst yam426 quads. This was when he was a pro-am and i think he won the title that year. I have rode his quad and it HAS more power then any 400ex I have riden.

[86atc250r]

No one said it wasn't possible to build a 350X that would beat a 400EX - I said the 400EX - cc for cc is more powerful, easier to extract power from & there is no point in trying to build up a 350X anymore.

Heck, I can build a TRX90 that will beat a 400EX - but you won't find me wasting my money doing it.

If your buddy was truly competing at that level, his 350X engine was FAR - VERY FAR from stock. He would have been better off with a different engine no doubt. The 350X was heavy and had no where near the power level required to win a national MX or TT when stock. It roughly develops 1/2 the HP of a YZ based engine stock for stock.

With a 350X based machine he was at a serious mechanical disadvantage to the other riders - even if the peak power it developed was near that of YZ engine (because of it's delivery).

What was your buddy's name and what year was he racing this beast?

[rs169300]

Look at exriders home page and go down to the pict Jan 25, that is him in the middle. Jason. I think the year was 01 when he ran the 350X based quad, he then went to the 426 yam. then to a c-dale last year. This year his ride is the yam.

[ryanh250ex]

i think i'm still going to do it. i can realistically build this thing for 1700 or so.

everything i need to make a 350x motor run= 350$
250R rolling chassis=$ 800 negotiable
"Ultimate RX conversion" from Rocky Ridge Racing= $550
look on people's faces when they see a 4-stroke 250R rumbling by them: priceless

even if i do some other slight modifications, it still will be under 2000 total.

[dnj400ex]

good luck and let me know how it turns out. Thanks for the info 86atc250r. I guess the reason my buddys ride feels so strong to me is because where we ride, you rarely can get over 30mph. Lots of hole shots and hill climbs

[brandonpeake]

86atc250r was giving factual info that is true, and alot of his comments were disputed by taking one sentence of what he said and trying to twist it around, he is very knowledgeable and knows what he is talking about

one tip of advice , i have helped some of my buddies with some custom bikes w/ strret bike motors etc, toy always always end up with way more in it than u think, there is always something you will need where the part you got or the stock part wont work right for the different weight or power and will break

one more question are you buying the 350x motor?
why not put an r motor back in it

[ryanh250ex]

Originally posted by brandonpeake
86atc250r was giving factual info that is true, and alot of his comments were disputed by taking one sentence of what he said and trying to twist it around, he is very knowledgeable and knows what he is talking about

one tip of advice , i have helped some of my buddies with some custom bikes w/ strret bike motors etc, toy always always end up with way more in it than u think, there is always something you will need where the part you got or the stock part wont work right for the different weight or power and will break

one more question are you buying the 350x motor?
why not put an r motor back in it

yes, i am buying the 350x motor. it is owned by the same person who previously owned the z50 i recently bought, so i know him pretty well, and he is giving me an excellent deal on it.

i dont have a 250R rolling chassis as i type this, but a friend of mine has two R frames, one of which he needs to get rid of so he can make more storage space for his other machines. he is wanting roughly 800 for his '86 R frame, with works shocks on front, good tires all around, lsr axle, etc etc, with just about everything there except for rear hubs. there is a very slight twist in the frame, which i am nervous about, but after searching all the ends of the Earth to find a OEM R frame that hasn't been beaten to ****, i think this is the best one i'll find for a good price. he showed me himself that 99% of all R's have been raced at one point or another, and 99 out of every 100 R frames out there have been cracked/bent/welded at some time.

i could buy an R motor, if i really wanted to. i just dont know if i can get one that is in decent shape for in the ballpark of 350 bucks, since that is what i'm paying for the 405X motor. most R's have been handed down from racer to racer, it seems to be getting harder and harder to find one that isn't on its last leg.

these are the reasons i'm doing this conversion: 1. it would be a great project, 2, there are shops (i.e. Rocky Ridge Racing) that have done these swaps many times before, so i can be assured that it can be done the right way, 3, i would like to have a unique machine, and 4, i am getting numerous good deals simultaneously, and in my opinion, they are offers i cant refuse.

sorry for the long post.:D

[PhilMoore]

My 350X is on the stock sleeve, but overbored once with a rebuilt head.

It will not out run my stock 400EX.

[brandonpeake]

hey man its your cash and i agree with you im glad you gave the long post so we know the whole story, no way you will get a nice r motor for 350 more like 1000-1250 and you prob will still not know much about it, i think you know what u want so go for it i love 350x's i d like to have one to play around on, but dont have the extra cash for it right now, i used to have a 250x bored into a 330 and would have loved to had the 350x conversion back then but before the 400ex was out also, if i could have it for under 2g's in an r frame i might do it also, be something different and you could probaly part it out and get you money back if need be pretty easy, 800 for that roller is a sweet deal
go for it man and post us some pics, but on the performance issue atc250r has told u what to expest accurately, 440 kits have a bad name to me in one regard you can see one j@ck@ss with one who has the bore and thats it nothing else even a stock exhaust telling everyone he has a built 440 and its slow so people wil judge all 440s by the same regard knowing a duncan or sparks 440 is a whole nother story

[Juggalo]

theres a guy whos got that set up at the grass drags. hes even got custom stickers for the quad that say it. he races in a ton of classes (some of the big bore 4 stroke classes too) and always does good. he cleans up everybody in the warrior/blaster/300ex class, he usually does real good in the 400 class, and he does well in the upper classes too. i dunno what hes got done to it but its probably something similar to the motor your getting. it'll be a nice fast quad.

[wilkin250r]

The 350RX conversion was very popular before the 400EX, and I would have to assume it was popular for good reason. The end result was/is a 4-stroke 350cc with much better suspension and handling than a Warrior could ever aspire to.

Be honest, how many projects have you completed where your final costs were anywhere near your estimated costs? The bulk and most flexable cost is the rolling chassis, most other costs are fixed. If you do pay $800 for the rolling chassis, my bet says you have at least $2500 into your project BEFORE you add any major cosmetic costs into the mix, like powdercoat and/or new plastics.

[ryanh250ex]

Originally posted by brandonpeake
hey man its your cash and i agree with you im glad you gave the long post so we know the whole story, no way you will get a nice r motor for 350 more like 1000-1250 and you prob will still not know much about it, i think you know what u want so go for it i love 350x's i d like to have one to play around on, but dont have the extra cash for it right now, i used to have a 250x bored into a 330 and would have loved to had the 350x conversion back then but before the 400ex was out also, if i could have it for under 2g's in an r frame i might do it also, be something different and you could probaly part it out and get you money back if need be pretty easy, 800 for that roller is a sweet deal
go for it man and post us some pics, but on the performance issue atc250r has told u what to expest accurately, 440 kits have a bad name to me in one regard you can see one j@ck@ss with one who has the bore and thats it nothing else even a stock exhaust telling everyone he has a built 440 and its slow so people wil judge all 440s by the same regard knowing a duncan or sparks 440 is a whole nother story

thanks for the encouragement.

believe me......i'd LOVE to have a real 250R, motor and all. i almost bought one a year ago for 2700, but i had to pass on it.

i wrote the long post because i wanted everyone that read this to know why i was even considering doing this swap in the first place.

the kid i bought the Z50 from was buying a used quad, and he found a 350ex ( a 300ex with a 350x motor under the plastic) for sale right in his price range. he wanted a newer bike motor in there in the 350's place, and so he asked me how much the motor was worth. knowing how old the motors were, i said 300. a few minutes later, i was talking to another friend , who has multiple trikes and a trx250r in pieces, and he tells me they are really worth alot more than the number i gave him.

so the kid throws me an offer - everything i'd need for 350. now knowing i was getting a good deal, i say i'll take it, but i need to raise the money. so now i am driving myself crazy to get 350 bucks in the matter of a few weeks.

i tell my buddy chris ( the 3 wheeler guy) about the deal and how much he wants, he offers me a 250R in reasonably good shape for 800.


like i said- 2 deals i cant refuse.

[ryanh250ex]

Originally posted by wilkin250r
The 350RX conversion was very popular before the 400EX, and I would have to assume it was popular for good reason. The end result was/is a 4-stroke 350cc with much better suspension and handling than a Warrior could ever aspire to.

Be honest, how many projects have you completed where your final costs were anywhere near your estimated costs? The bulk and most flexable cost is the rolling chassis, most other costs are fixed. If you do pay $800 for the rolling chassis, my bet says you have at least $2500 into your project BEFORE you add any major cosmetic costs into the mix, like powdercoat and/or new plastics.

the only project i've previously done is my Z50, which has proven to me a little bit more than what i was looking to spend.

and actually, when i get the frame converted to take the 350X motor, it will be also sandblasted and repainted, along with being magnafluxed, rewelded, and reinforced. all of this is going to cost me 550 + shipping. so the painting is already taken into account. i dont know if the rolling chassis will include plastics, so i have not taken THAT into account.

i'm willing to bet my project will not go over 2500