350x top end options

[f76]

My 350x top end is getting tired and I'm exploring options for rebuild or replacement. I'm aware of the 500cc big bore from Mickey Dunlap at four stroke tech, but it's out of the budget. My research has come up with kraft Kustoms as an option for a big bore but I'm unsure if it requires case boring, which I would like to avoid. Are there any other options to look into?
My original thoughts were a wiseco 10.25 0.50 over with fresh valves. But if I can go with a big bore that doesn't require case boring or mad mods that will easily go over budget, I would be interested in that route as well.

I'm not looking to build a super high horsepower unit, I don't have money for that. I want a reliable machine with some mild upgrades to help it out performance wise. I already have a 400ex carb and supertrapp exhaust.


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[yaegerb]

What's your budget?

[f76]

Good question, I see I left that out. I would like to keep it below $600, finished and ready to ride.


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[oile]

Mickey does other setup's besides the 500 give him an call.

[El Camexican]

Did you mean Kustom Kraft?

[Shawn Powell]

The kustom kraft 452 does require case machining. Also high compression and race fuel. Not sure on the 426. Mickey has kits that fit in your budget. Also he has some. I've 11 to 1 comp pistons like 1 or 2 over with a cam and some mild porting you'll scream. That's my plan for next summer


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[yaegerb]

Personally, if you can stretch that a bit and ensuring your crank is still in good working order I would do a 10.25 piston, 162-30 cam and springs from mega cycle and get a port/polish with 5 angle valve grind from Jeff at fast racing. That will be more power than you will ever need.

[BOB MARLIN]

The 10.25 piston is what I put in all my 350x's. They just seem to run better than the stock ones. That piston with the stock cam, Supertrap or DG pipe and a properly jetted carb turns these things into torque monsters, with minimal spending.

[Shawn Powell]

The 10.25 piston is what I put in all my 350x's. They just seem to run better than the stock ones. That piston with the stock cam, Supertrap or DG pipe and a properly jetted carb turns these things into torque monsters, with minimal spending.

Add a 400ex carb and a k&n to that would be well within your budget and you'll have a super reliable bike that moves real nice. That's my build basically.


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[axeman24]

The 10.25 piston is what I put in all my 350x's. They just seem to run better than the stock ones. That piston with the stock cam, Supertrap or DG pipe and a properly jetted carb turns these things into torque monsters, with minimal spending.

What piston do you prefer for this type of setup

[Shawn Powell]

I went with wiseco. Although if I were to do it again I might look at four stroke tech by Mickey Dunlap. He has some nice light weight 11 to 1 comp pistons that run on pump gas.


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[atc007]

The 10.25 piston is what I put in all my 350x's. They just seem to run better than the stock ones. That piston with the stock cam, Supertrap or DG pipe and a properly jetted carb turns these things into torque monsters, with minimal spending.

Absolutely. Simply rebuilding a worn out 350X turns them back into a monster. 10.25 Wiseco, take your time on a good valve job,clean up the ports and I promise you it will be all you want. You already have the carb and exhaust.

[BOB MARLIN]

I use Wiseco. If you end up running a K&N type filter make sure you use an "Outers" type cover over it.

[barnett468]

My 350x top end is getting tired and I'm exploring options for rebuild or replacement. I'm aware of the 500cc big bore from Mickey Dunlap at four stroke tech, but it's out of the budget. My research has come up with kraft Kustoms as an option for a big bore but I'm unsure if it requires case boring, which I would like to avoid. Are there any other options to look into?

I'm not 110% certain just yet but I think there was once around a 393 cc kit that consisted of a custom made piston and a sleeve in which the orig sleeve was bored out and a new thicker sleeve was installed that had the same od as the orig sleeve on the bottom so the cases did not have to be bored . I also saw a used one on ebay and and a company that claimed to have a custom made 86 mm piston for your bike that is made by JE but there was no mention of a sleeve so it looked like they simply bored the stock cylinder out to 86 mm which i not what I would suggest doing if you plan to ride it hard at all as my guess is that it would have a high potential for seizing but I don't know this cylinder that well . I actually emailed the place that has the piston and am waiting for their reply.

You could also call LA Sleeve and ask them . They no longer list any big bore kits for those bikes but they can make a sleeve if you need and can also install it . They have been making sleeves for 2 and 4 strokes since at least 1976 when I started buying them from them . They probably made them for Powroll as well.

One problem with many big bore kits is that they do not make oversized pistons for them in which case, once the piston or cylinder needs to be oversize, you need to start from scratch and get a new kit, however, if did make the pistons for the shop I emailed, they could easily make an oversized one if you needed . Just call both places and ask.

https://www.lasleeve.com/

https://jepistons.com/



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[f76]

Thanks for the info guys. I went down the rabbit trail of thinking I needed a big bore to make it a capable machine by today's standards. A fresh 10.25 piston and valves should be more than enough for what I want. Perhaps if the budget allows, a cam and valve springs from mega cycle could be added as well.


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[atc007]

J&E pistons does still make big bore pistons for 350X. They are a work of art. But you don't need that. You are then looking at boring cases etc. If you do ever go down the road of wanting a 350X that just flies. Contact Tom Carlson at TC Racing,,although ATM he is very overworked correcting mistakes of one of his four stroke competitors. One of my friends is awaiting a TRX 250R engine Tom is doing,and he said it is sick the garbage that he is busy cleaning up.

[barnett468]

Thanks for the info guys. I went down the rabbit trail of thinking I needed a big bore to make it a capable machine by today's standards. A fresh 10.25 piston and valves should be more than enough for what I want. Perhaps if the budget allows, a cam and valve springs from mega cycle could be added as well.

I would start by doing a compression test with a good gauge . I can guarantee you that the difference in performance between a stock engine in good condition and one that has higher compression is small if all else is the same . Of course if you have a stock pipe and replace it with less restrictive high performance one it will also have more power but that increase by itself will also be small but the increase in sound/noise will be huge and some people don't want an extremely loud bike . If you have a stock pipe, you can remove the muffler and ride it around and see if it is too loud for you before you buy a pipe . The aftermarket silencers will quiet the exhaust a little but not a lot.

In general, the more high perf parts you put on a bike, the more power it will have, and making several changes that by themselves only make small increases in power will add up to make a big increase in power.

As far as cams go, in general, the "bigger" the cam, the LESS low end power an engine will have . The bigger the cam, the higher the rpm range becomes which is one reason why people often install numerically higher gears in their differentials to compensate for the loss of some low end power etc . It is incredibly easy to "overcam" an engine and end up with something you are unhappy with.

If you rarely or never ride your bike wide open in top gear, you should consider installing a numerically higher gear ratio . This in itself will make the bike feel like it has more power and it will accelerate more easily and will climb hills more easily etc.


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[barnett468]

J&E pistons does still make big bore pistons for 350X. But you don't need that. You are then looking at boring cases etc.

That is not what I have found, but as I mentioned, I wouldn't bore a stock sleeve that much . I emailed these people 2 days ago to get more info but haven't heard back from them yet.

http://www.xlintperformance.com/performanceparts.htm


"Big bore kits, 10-1/2 to 1 compression pistons

CNC machined from lightweight alloy and manufactured by JE to our specifications. These piston designs were first pioneered in the 70's by the top XL tuners, but, over the years, the designs have been refined.

You simply bore your cylinder and fit the pistons for an immediate increase in horsepower and torque. For maximum effectiveness you should mount an aftermarket exhaust and do some slight carb re-jetting, but the pistons perform well in a stock configuration."



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[Dirtcrasher]

I have an LA Sleeve 452 kit from Mark at KK. It is not high compression; Mark said it did not need race gas. It took me a little bit to tram in my mill to bore the cases. Now I have a jig so it's easy.

I'm only building the 452cc for Flat track and TT where you must break the tires loose and slide often.

My other 350X that has lots of mods, with nice suspension as well, is plenty enough.....