Anytime you increase the size of the piston and stroke, the bike will rev slower but build more torque/hp. I was planning on doing the same thing with my 625. Personally if I was going to tear my engine apart, I would go all out with the biggest, baddest kit available. It will have more power than you could ever use :bowdown:

 

Anytime you increase the size of the piston and stroke, the bike will rev slower but build more torque/hp. I was planning on doing the same thing with my 625. Personally if I was going to tear my engine apart, I would go all out with the biggest, baddest kit available. It will have more power than you could ever use :bowdown:

I'm thinking just the 105mm big bore may be the way to go for me (675cc). It will have way more power, but will hopefully rev quicker than if I also got the 80 mm crank shaft. Plus, it saves the price of the 600 Euro crank shaft!

We'll see, I have plenty of time to consider it!

 

I can't seem to get Schneider to reply to my emails, so what kind of results do you think each one would provide (faster revving, slower revving, more top end, more bottom end, etc)? I am very happy with the power and delivery of my 625 SMC, I just want more of it. If I have to choose, I would like the most gains in the mid-range, but I don't want to sacrifice much bottom end. Top end would be nice, but it is mainly a street bike. I'm not sure if a stroker crank is right for me because I don't want the bike to rev any slower. My goal is upper 60's in horsepower after some head work, etc. 70 or higher would be sweet, but is probably asking for trouble with reliability. What do you guys think?

you have to look at the rod ratio. if you keep the same rod ratio or increase bore equal parts to the stroke then the motor will rev the same, but the motor will have more mass and stress on the wrist pin.

this motor will not last nearly as long as stock. its mch more stressed...

 

Engines are built within design perimeters........the LC4 KTM motor is bullet proof as is....

To maximize performance and keep maximum reliability....improve the intake and exhaust systems.....

Engine match porting and the like can help a bit without having a negative on reliability....

As soon as you open the box/engine to gain power, be it cams, valves, bore and/or stroker mods....you pretty much trade off reliability for said gains..........

If you build up you engine as you are thinking....you need to service the bike much more often....more frequent oil/filter changes, valve check/adjust...

The engine will exceed at least some of its original design specs, and there fore will be more prone to fail and wear out faster....

That is just the way it is....no BS........

If you deeply research this you will see what I say is true.....

I suggest you decide what you want to use the bike for, how much and how often you want to service it, how much reliability you need, and how much $$$$ you have toward keeping it going....then build/modify(or not) within these limits

Study the service and repair schedules of full race engines, and you will see that they are only reliable because they are frequently torn down, inspected, and repaired with new components to replace those that are worn.....

good luck
:thumbup:

 

I realize every large performance upgrade will have a reliability trade-off, I just wish I knew to what extent.

Suppose my stock LC4 will last 20 to 30,000 miles before needing a rebuild (I've actually heard much higher mileages than that) - With a big bore and stroker kit, what could I expect? 15,000? 10,000? (I already have 8,500).

I know it is all subjective, but I wish there was someone out there with first hand experience to talk to. I would be broken hearted if I spent damn near 4,000 dollars and it shot craps in 2,000 miles!

Maybe I'll just focus on removing weight and get some head work done. Decisions, decisions!

Thanks for the replies, keep them coming.

 

The key to any race oriented motor is frequent oil changes and valve adjustment. I am running my CRF450 on the street with everything that can possibly be done to it. I know mechanics that wrench for AMA supermoto pros that say my bike is making more power than their race bikes. A lot of the reliability is also in how you ride the bike. Street bikes see much less abuse and over revving like a race bike would so thats something to think about. You dont ride around on the street wide open around every turn but when you want the power, it is there. I say a race motor will last much longer on the street than on a track if the amount of use is the same. How many miles would you say you put on the bike a week?

 

The key to any race oriented motor is frequent oil changes and valve adjustment. I am running my CRF450 on the street with everything that can possibly be done to it. I know mechanics that wrench for AMA supermoto pros that say my bike is making more power than their race bikes. A lot of the reliability is also in how you ride the bike. Street bikes see much less abuse and over revving like a race bike would so thats something to think about. You dont ride around on the street wide open around every turn but when you want the power, it is there. I say a race motor will last much longer on the street than on a track if the amount of use is the same. How many miles would you say you put on the bike a week?

Last year I put about 7,500 miles on my bike, so figure about 145 to 150 miles a week on average. Obiously a lot more than that during the warm months, and a lot less during the cold months.

 

This is an old thread, but have any of you done cams, pistons, and/or cranks in your 625's? I would seriously consider a cam and piston kit, if my baby didn't have to be the guinea pig... 675cc from a 105mm piston, with a bump incompression,s hould net a NICE gain from idle to redline!

 

The other thing you need to think about especially with the stroked crank is that the piston will move 2mm farther down into the crank cavity, it will also move 2mm farther up towards the top.
This means spacers for the cylinder and a longer cam chain will be required to make it work, slong with machining to the piston skirts to clear the crank, and possibly machining to the cases to allow the throw of the crank to clear everything that might now be in the way.
Cam chains do not come in various lengths from the factory so they require you to add a link or 2 to accomplish this. Your stock chain is a continuous link type without a "master" link so you will need the tools required to custom make the chain......I have heard horror stories of cam chains comming apart.....let your imagination run wild here.

 

I am most interested in what the effects of a high-comp, big bore piston, and a cam in an LC4 are, as they should take the least work, be relatively inexpensive, and offer the biggest benefit. The real questions (in my mind)are how the crank and rod will hold up with a (possibly) slightly heavier piston making a bunch more power. Some bikes are fine with this; others have particular weaknesses. I guess I am looking for people with first hand experience building modified LC4's...

I know a couple of engine builders/machine shops that I can bounce some of these questions off, so I will post if I find anything out...

 

Hi, i hope i can help you guys here, i build/tune lc4 engines for road and race in the UK and have been throiugh all the variants you've mentioned plus a load more which i've devised myself.
First of all you really need to decide what you want to use the bike for and how you like the delivery. Secondly, how big is your budget, which leads to the third consideration which is how much can you really do yourself(Dont kid yourself that your a works mechanic when your not or your really going to cost yourself a lot of cash).
On the first point, big singles for racing usually require a different approach than for road use, this may sound obvious but not always in the way you might think. Road going moto's can usually enjoy a much more aggresive delivery than you would want to race with, because in racing usability is far more important than outright power. Also consider where you want the power, some people like to grunt some like to scream some just want it predictable.
On the second point do you just want a quick thrill or is the plan for long term ownership, afterall there is no point blowing your wad on a machine which your going to get rid of in 3 months. If your going to keep it then plan out a tuning regime which you can do over a period of time to help keep the bills managable and in which each stage compliments the previous one.
On the third point, be realistic! If you need to use machine shop services or even a pair of eyes that know what they're looking at, you may need to pay for them so include them in your budget, for example a 105mm piston/barrel kit will require both the head and cases to be machined this will cost and needs to be done by someone who knows how to machine expensive engine parts(as i have found to my cost). In addition to which the use of such a piston will require the crank to be dynamically rebalanced but i dont suppose schneider told you that! If you know where you want to get to i'll be happy to advise on a package that will get you there.