250x motor need help and thoughts

[jdb8297]

i'm trying to build my thirteen year old an hotrod 250x but its seems hard to find aftermaket parts for these engines! what i'm trying to figure out how much can you bore a stock cyl. does any on offer tit valves. and is there any cam companies who know their cam profiles i have called two and asked their opening and closing number at .006 .010 .020 .050 .100 on differ cams and all they can tel me is lift and duration at .050 by the way i design camshaft for v-8s and these overhead valve engines are a whole differ animal but the only way i can determine what i want to put in this motor i need to know these figures, to compore with my flowbench numbers after i finish porting the head. I haven't found anyone thats knows what springs to use or how to set them up what i would like to do is order three different springs and put them on my spintron and check the harmonics in them with different weight valves at differ rpms. If their is anyone out their who could lead me in some direction and know these engines pretty good could you PLEASE HELP!!!! I look foward to all comments.
thanks

[2muchquad]

yeah unfortunately if your a serious tuner your gonna have to do some footwork to get all the details.Usually when you buy a camtheyare labeled "all around or high speed track Mx etc".As far as the 250x motor goes,a lotof stuff such as the topend fromthe 300ex will interchange.there are an assortment of companies that make big bore kits and strokers for it.

[wilkin250r]

I hate to say it, but I think you're fighting a losing battle. It's going to be rather difficult to get the types of numbers you're looking for. Most builders, even those that design cams and port heads, don't get into the details of duration and lift at .006, or harmonics of different valve springs. They'll obviously calculate and consider lift at different valve openings, but I think they're more concerned about rocker-arm angles and longevity rather than specific flow patterns.

I think a few different companies make heavy-duty valve springs, but I think you'd have to buy them and test them, I doubt you'll get any useful info from the manufacturers.

However, I CAN tell you that the largest piston you can get with the stock bore is 76mm. If you're willing to put all the time and effort into the camshaft and porting, you may wish to throw some time and energy/money into the lower end and get the cases bored for a larger sleeve, or even a stroker crank.

Has anybody ever told you that you can put a Honda ATC350X engine into a 250X chassis with very little modifications? If you're looking for all-out performance, that may be an option worth looking into. Check www.powroll.com

[ghak99]

Just by reading your post, I can tell your knowledge level is higher than that of many engine builders.

Good luck on getting the specs you are looking for. Many cam makers won't turn loose any more specs than hey have too.

You might consider going with a big bore kit instead of maxing out the stock sleeve, they tend to get weak when bored to their limits.

Good luck, and if you have any easier questions ask away....lol

;)

[bradley300]

i built a 300ex (identical to a 300ex, just a different crank stroke) so mabey i can help.

use kibblewhite valve springs, and there arent any specs that i am aware of, there just heavy duty, but they work

white brothers and TC racing both make good 300ex cams, tell them where you want the power and they can help yopu get the cam you want.


80 over is about the max on a stock cylinder, but with a sleeve you can go all the way to 350cc (380 on a 300ex)

and you can get oversized intake valves, none for exhaust and they are not titanium.

dont waste your money on hard weled rockers, there not needed.

[jdb8297]

Originally posted by jdb8297
i'm trying to build my thirteen year old an hotrod 250x but its seems hard to find aftermaket parts for these engines! what i'm trying to figure out how much can you bore a stock cyl. does any on offer tit valves. and is there any cam companies who know their cam profiles i have called two and asked their opening and closing number at .006 .010 .020 .050 .100 on differ cams and all they can tel me is lift and duration at .050 by the way i design camshaft for v-8s and these overhead valve engines are a whole differ animal but the only way i can determine what i want to put in this motor i need to know these figures, to compore with my flowbench numbers after i finish porting the head. I haven't found anyone thats knows what springs to use or how to set them up what i would like to do is order three different springs and put them on my spintron and check the harmonics in them with different weight valves at differ rpms. If their is anyone out their who could lead me in some direction and know these engines pretty good could you PLEASE HELP!!!! I look foward to all comments.
thanks

[dork]

the problem with atv's is that you only have so many options when you get into performance parts like this. its not like a small block chevy or something where there are hundreds of cam choices. you could call web or megacycle and see if they could spec out the cam at the lifts you want on v blocks or something, but its unlikely. on megacycle's website they at least list the opening and closing points at .040 and the intake and exhaust centerlines. you could call FST or TC, they have lots of experience with 250x's, and have their own custom grinds different from whats on the mega and web websites.

[jdb8297]

Thanks for all the comment and help keep them comming. I have found tit valves for this engine all i need now is a couple of more spring manfactures. Guys let me tell you in my twenty years of designing v-8 cams and building cup motors your horspower is always in the head and let me explain why springs or the most important and why! First thing is i run a machine called a sprintron and it has optron lasers that check the harmonics of whats happening to the spring as it opens and closes the valve. The things that affect these harmonics are: first: the weight of the valve in a cup motor 20grams per valve can mean 300 more rpm and about 12 hp not only that bouncing the valve off the seat makes bigtime horsepower and you do that with peak postive acceleration in the cam design. and what that means the faster the opening ramp of the camshaft to max lift makes a extreme amount of horsepower (rev like a two stroke with very wide power band) the tricky part here is designing the closing ramp with negative acceleration which means closing slow at the beginning then slamming the valve real fast to bounce the valve off the seat. Second thing that is so important here is setting springs at different height to have different openning and closing pressures so thats why i need three different spring is to test each of them with different heights and cam designs. Third is the cylinder head flow how much is too munch and not enough and alot of that depends on how the bottom end is built. Cup motors love big bore short stroke which the 250x crank is as far as i can tell RIGHT? KEEP THOSE COMMENTS COMMING I NEED TO THINK AND YOU GUYS ARE MAKING THAT HAPPEN!!!!!!!!!!!

[bradley300]

also, on a 250x/300ex motor, you will gain more power from boring than you will stroking, stroking dosent seem to do much on these motors

[dork]

if you really want to turn some rpm and make horsepwer, you should've got a mojave lol..where did you find titanium valves? with the cr250x dirt bike out, the 250x name is popping up again and can be misleading.

if you want to go big bore short stroke, then go with the 86 or 87mm piston and resleeve, that should work good with the smaller ports and bigger valves. the 250x has a longer con rod than the 300ex and shorter stroke, so its better for high rpm breathing.

[jdb8297]

I found some tit valve blanks froms my good friends at ferrea valves of course i will have to grind the head down to what i want but after putting my head on a sunnen vgs20 and geting a good radius on the seats i should have know problem grinding the valves down to what i want.

[jdb8297]

Originally posted by jdb8297
I found some tit valve blanks froms my good friends at ferrea valves of course i will have to grind the head down to what i want but after putting my head on a sunnen vgs20 and geting a good radius on the seats i should have know problem grinding the valves down to what i want.

[wilkin250r]

I'm intrigued. Can you explain the mechanics and details of exactly HOW bouncing the valves make big horsepower?

Also, at that point, would you possibly be severely affecting longevity and reliability? I wouldn't think that bouncing the valves off the seats would be very good for extended periods of time.

[2muchquad]

i was always under the impression that bouncing the valves off the seats caused severe"cupping" of the valves.those are the problems you run into with soft valve springs.the idea is to have a stiff spring to hold the valves against the cam lobes.how can valve float be good for horsepower?sound like a accident waiting to happen.:confused:

[jdb8297]

Guy's you are both right! I didn't explain myself earlier because I put the cart before the horse because I thought everyone knew what I was talking about. FACT all valves bounce period when you turn the RPMS know matter how stiff THE SPRING!! Please let me explain: No matter how stiff the spring if the valve such as stainles valves that are heavy the are going to bounce no matter what. That's the reason you play with different spring pressures is to see which presures elimate the domint harmonics in the spring and this can be acheived by changing differ installed heights and open pressures. By acheieving a lighter valve such as tit with no weight you can run more of an aggresive cam (very fast openinng and closing ramps) these camshafts acutally trick the motor into thinking it has more compression because of the shorter seat timming. And because of the valve being so much lighter and so strong when you use a copper valve seat you will not see any cupping in the valve. But you actually having less valve bounce because of the lighter valve. I said that all wrong in my previous post I got excited and got way out there i'm sorry.

Please guys understand I'm not saying boucing the valve is good but what you have to understand is all valves bounce when you turn a decent RPM thats the reason four strokes can't turn the RPMS of a two stroke. But with todays spinstron an optron laser and being able to put mini cameras in the intake and exhaust ports to see how much the valve is bounicing thats why we can change different spring pressures and recheck to see what the valve is actually doing!! By the way a spintron is an electric motor the only spins the engine the engine does not run but you can speed the engine up and down and run different RPMS and you can actually program a race track into and how a driver will drive it with lifting the throttle and check the horminics in the valve train.
Guys some day we will turn a four stroke like a two stroke with a wide power band with a whole lot more torque though!!!!!!!!

Why do you think all these new 450's have tit valves in them?

[oriclez]

Personally, if I where you I'd do a different quad to hot rod. Sounds like you want to spend a lot of time into it? Same thing I did with my 300ex. Sure its rewarding in the end(when stuff quits breaking.) But I'd suggest do something that has more potential. Maybe a banshee? But than again thats just me, no clue what you plan on doing to the 250X.

[jdb8297]

i'M PLANNING ON LETTING MY SON RACE THIS IN THE 300CC CLASS LOCALLY HERE. AND THE REASON I HAVE GONE WITH A 250X BECAUSE I GOT A HECK OF A DEAL ON IT. AND I'M A LITTLE HARD HEADED I'VE BEEN TOLD THAT THE 250X IS OLD AND WANT KEEP UP AND EVERY ONE HAS TRICKED MOTORS BECAUSE THE TRACK DOES NOT TECH SO I WANT TO KEEP UNDER 300CC AND SMOKE EM AND I WILL DO THIS BY ACHEIVING MAX HORSPOWER OUT OF THE VALVE TRAIN AND PROPER CHASSIS SET UP WHICH I HAVE NOT EVEN STARTED ON THAT YET!! I WOULD LUV TO BUILD SOMETHING BIGGER AND BETTER BUT THE TRACK HERE WILL NOT LET HIM RACE ANYTHING OVER 300CC DUE TO HIS AGE.
THANKS FOR YOUR THOUGHTS.

[oriclez]

Ahhh good point. I am running a 406 stroker on my 300ex right now. I was thinking of entering a 300 class on it.:D Haven't got into track racing though. What is the age cut off of the 300 class?

[jdb8297]

AS FAR AS I KNOW ITS 13 AND UP I HAVE SEEN GROWN MEN RACING 300'S. I JUST WANT MY SON TO BE THE BEST HE HAS A NATURE BORN TALENT TO RIDE QUADS. WE DID THE GO-KART THING FOR ABOUT SEVEN YEARS BUT HE JUST NEVER GOT INTO THE WAY HE SHOULD HE WAS TRACK CHAMPION FOUR YEARS IN A ROW!!!!! BUT IT DOES NOT SEEM TO EXCITE HIM LIKE QUADS DO!
I ASKED HIM IF HE WANTED A SPRINT CAR AND HES WANTS TO RACE QUADS SO QUADS IT WILL BE. HE'S THE ONE THAT HAS TORN DOWN THIS MOTOR AND IS EAGER TO LEARN AND WANTS TO LEARN HOW TO BUILD THEM SO WE ALREADY HAVE RUN THIS ENGINE ON THE SPINTRON AND FOUND ALOT OF INTERESTING THINGS ABOUT JUST BY PUTTING THE OPTRON LASERS ON IT. WE KNOW WHAT DIRECTION WE ARE GOING JUST WANTING MORE COMMENTS ON PEOPLE WHO HAVE MORE EXPERINCE THAN US.

[jdb8297]

Does anyone know if wiesco make a std bore pistion with dome on it?

[2muchquad]

wiseco makes a 12.1 compression piston for your 250x.good luck with your endeavor..:D

[jdb8297]

does je pistons make pistons for 250x and how about aftermarket rods? Doesn't powroll make a billet rod?

[ghak99]

I had a .020 over ,12:1 or maybe 12.5:1, domed Wiseco piston, but I am not sure about a stock bore. Check with GT Thunder on a rod. I know the one he put in my stroker was very impressive looking.

[jdb8297]

GHAK99 i NOTICE THAT YOU A 400EX CARB ON YOUR 300EX MOTOR HOW HARD WAS THAT? AND I ALSO NOTICE YOU HAVE AN 350X SWINGARM IS THAT SOMETHING YOU CAN DO WITHOUT OF ALOT MODIFCATIONS?

[notfastenuf4me]

the 350x takes some modding to make fit the 250x chasis like making spacers and what not too sure on what it all contains
the reason i know is because i was gonna do it on min
my opinon is if u want a longer swing arm id get a lsr +2 swingarm thats jus my .02

[jdb8297]

Right now i need to stay focused on the motor! I know after looking at this cyl head that all the power is in the head and camshaft!!!!!!!!!!!!!!!!! I'M still waiting on all of your comments and imput on cams and cylder heads and carbs!
THANKS

[notfastenuf4me]

wiseco should make a high comp stk bore piston go to there website wiseco.com also for cams look into web that what im buildin my 350x motor wit also with all the work ur lookin to do i would purchase the 400ex carb i also bought one of them for mine got it for 60 bux shipped used off of this site

[ghak99]

Originally posted by jdb8297
GHAK99 i NOTICE THAT YOU A 400EX CARB ON YOUR 300EX MOTOR HOW HARD WAS THAT? AND I ALSO NOTICE YOU HAVE AN 350X SWINGARM IS THAT SOMETHING YOU CAN DO WITHOUT OF ALOT MODIFCATIONS?

The 400ex carb is a very easy swap. It basically bolts right on, I used the 350x air boot, between the carb and the air box, because it fit the carb neck better and would flow more air than the 250x stock carb boot.

If you do a search you should be able to find a post on how to swap the 350x rear end that I posted a year or so ago. It is fairly simple and cheap. I have less than 100 bucks in the swingarm and shock. The stock 350x shock is completely adjustable and rebuildable. The swing arm is 1.5 to 2" longer depending on who you ask. Sure beats a $500 aftermarket shock and $450 dollar aftermarket swingarm. The aftermarket set up probably rides better, but I am not sure it would ride 850 dollars better.

[bradley300]

you can use a 400ex carb, its a cheap easy mod, if you really want power, try a 38mm FCR, they are a pain to keep jetted properly, but it should help the power quite a bit more than a 35.5mm like the 400ex's

and gthunder makes a heavy duty rod, i had one in my 300ex. its not on thier site, but the phone number is- www.gthunder.com

[2muchquad]

when you start porting on your head,try not to take too much material out of it especially on the intake side.the idea is to try and keep velocity up for better volumetric efficiency especially since you plan on running a short duration cam.there may be some performance to be on the exhaust side but again you'll want some back pressure.i would try to get the compression up to 13to 1 or so if you can.this is your best bet in building performance from a middleweight 4 stroke.I would run the stock carb if i was you.again too big of a carb will hurt your intake velocity and throttle response.i have a 300ex myself thats pretty much stock excepty for a 11 to 1 high compression piston and exhaust.i also run no base gasket for a tad more compression.its not a hot rod but it runs good because all the components work together in a system.But reading your posts im sure you knew all of this..:D

[jdb8297]

2muchquad apreciate your comments I will tell after bascially smothing up the intake ports and putting a little more contour in it the airflow munbers picked up quit a bit (whole lot) and smoothing and slicking up the tops of the exhaust ports seem to do wonders! Thanks for the comment and keep them comming i'm new at all this and need any comments and help in any way.

[2muchquad]

you sound like you know everything you need to know.help us out..:D

[jdb8297]

DOES ANYONE KNOW FALICON PHONE NUMBER

[dork]

727 797 2468

[jdb8297]

Looking to buy a stroked crank and rod along with head and rocker assembley if anyone got any good used parts laying around let me know i maybe interested

[bradley300]

gthunder can stroke your crank, and they sell a nice HD rod. www.gthunder.com

[willow2679]

Back in the days where no other 4stroke was available the 250 4 stroke class was the best (not considering 2 strokes), there was lots of mods made to it, they remove the reverse fgear and if I'm not wrong the first gear too.
later the 400cc four strokes were ok for the pro class and there tom carlson made a 250 (for jeremy schell) with a 350 x head and hopped the displacement to 400 (with a stroker rod I supose) that head was way better than the 250 because it has four valves and let make more displacement on the motor
don't forget BIG oil cooler to maintain it cool during the hole race
(now that I think the 250 has four valves?):ermm: but the thing was that that head had lot more potencial to make big hp numbers (remember that the quad has to have the power that your kid can ride) so maybe more torque is needed than a piky powerband

[jdb8297]

Does anyone know what the difference between a 250x pistion and a 300ex is it pin location?

[bradley300]

Originally posted by jdb8297
Does anyone know what the difference between a 250x pistion and a 300ex is it pin location?

yes, i beleive the 250x pin is a tad higher? could be wrong, but i do know the piston pin is in a different spot, weather is higher or lower i'm not sure on

[jdb8297]

dOES ANYONE KNOW IF A 300X CRANK WILL FIT IN A 250X BLOCK?

[wilkin250r]

Originally posted by jdb8297
dOES ANYONE KNOW IF A 300X CRANK WILL FIT IN A 250X BLOCK?

The 300EX crank won't work. Electric start.

[jdb8297]

GOTCHA!!!!
Thanks Wilkin

[quadfamily]

How is the progress on that 250X ?