My 950 Refresh or Mission Creep...

[buffallodan]

My Husqvarna TE610 has an FCR41 and it has a choke as well as a hot start button. Am I missing something here or are the twin carbs the difference. I'll go ahead and declare my noobness .

Dan
BTW great work very inspiring build.

[sakurama]

Originally Posted by buffallodan

My Husqvarna TE610 has an FCR41 and it has a choke as well as a hot start button. Am I missing something here or are the twin carbs the difference. I'll go ahead and declare my noobness .

Dan
BTW great work very inspiring build.

Yes, you have a different carb. The MX version has a choke. The downdraft does not. Well, it didn't...

G

[Katoom119]

Originally Posted by sakurama

Chris is a rare person in that he he grew up in his fathers garage, then became a mechanical engineer and then a machinist. Typically the three won't agree - theory and reality and practicality - but Chris can see things in a way most can't and that's more valuable than his skill in either individual disaplin.

Okay, we ran the bike with the 41's and... Well, I was hoping to hear some guesses. Okay, right after dinner with Gino I'll post the dyno charts. Plus I got my old 950 mill apart. Interesting stuff. Stay tuned.

Gregor

I'd say the 41's were better across the board. As long as the stoichiometric ratio was correct I would think that engine would be able to burn any amount of fuel mix efficiently. More fuel, more power. The only way I can think that the 41's would sacrifice anything would be if it dumped so much fuel in at a low RPM that it bogged the engine down.

[max2]

+2, I'm going with the 41's = more power everywhere

[sakurama]

Originally Posted by Katoom119

I'd say the 41's were better across the board.

Ding, ding, ding. Winner, winner, chicken dinner! (Yeah, I don't understand that either but I like it.)

Katoom and Max2 are right - the 41 FCR's stomped the 39's... everywhere.



You could say that my bike is a formerly FI 990 SMR and you might be right that my engine is more able to take advantage but considering there was no point anywhere that the 39's worked better I don't think so. Without testing a more stock 950 engine of course we can't say unequivocally.

I'd still like the chance to ride them back to back but it's really only to satisfy my curiosity. There's a chance that the 39's might offer a cleaner pickup off idle or below 2K rpm but I don't think it could do anything to offset the gains the big carbs give everywhere else. It's also possible that Chris' velocity stacks and the correspondingly larger filters are letting the carbs capitalize where before they couldn't but I will say that in the next month or so the first set of 39mm FCR's with chokes will be for sale. Just sayin'.

The 41's also narrowed the gap to Gino's 990R - depending on the pull I'm making the same peak now (albeit about 500rpm sooner) or I'm 2rwhp behind. In torque it's just no contest. It also seemed to smooth (ever so slightly) what was an already smooth torque curve. That's pretty stuff.

So what do you do after you've fixed your carburetor woes and made a solid 10%+ gain - go looking for another 10% of course.

Gregor

[Katoom119]

Sweet. I like being right.

That's the 2nd flattest torque curve I've ever seen, with the first being my RC8 after it got dyno'd and remapped. It wants to pull my arms out of the sockets and it's not that far off of your bike. It must be a hoot to ride.

[sakurama]

So Chris is behind on some jobs and we couldn't get the other carb done or the parts to finish the choke plunger body but it gave me some free time to drag my old engine out from behind the lathe and put it on the table.



Dirty and tired - ridden hard and put up broke.

My shop manual is on my ipad but for some reason in the switch from my old to the new it didn't make the trip. I looked up something about the engine fixing bolt and put in a 5mm allen like I saw in the photo on the internet and then promptly rotated the crank and snapped the wrench in two. It's not often you can break off a tool inside your bottom end and just shrug and say, "Oh, well..." and move on.

Since one of my cam chains broke it wasn't like I was going to be keeping anything in line anyway so I just started unscrewing things willy nilly.



Cams looked nice. Since 950 cams are supposed to be a "good thing" I'm glad for that. Not sure that I'll ever put them in but it might be nice to try some time down the road.



Umm, yes, that is disgusting dirt about to fall into the bottom end. It didn't. I wiped it away but I will say that when it counts I'd clean the engine before I took it apart. This is scrap.



Ugh, that is so ugly and dirty. It's even worse when you consider that's all Canadian dirt! Much worse for engines it seems.



Free at last!



Overall it wasn't bad until I found this big scratch.



Then it was over to Mr. Fixit for some analysis. Hi Chris!



The big question is "Is there room and if so how much?" The wall thickness at the top of the cylinder contains the greatest pressure so being sure a larger bore won't compromise that is key.



Chris has built several singles from Ducati twins and so there were some spare 999 and 1098 cylinders to compare with and from what we can tell right now it looks good to do a big bore. Since we know at least someone has done a 105mm bore and since 105 yeilds a nice round 10% increase we're looking at that. It seems like there really wouldn't be room for more and less probably isn't worth the trouble. As we were explaining to Gino today a 10% increase in displacement should yield a 10% increase in power and torque - there's no replacement for displacement - as the saying goes. That's the 999 on the top right and the 1098 in the middle and the 950 up front.



Issues are mainly the head gasket and the space between the cooling ports and the cylinder wall. Chris has worked with Cometic before so he's reached out to his person there to see if they have a KTM 990 head gasket. If they do making a modified one should be pretty easy. Since the bore is so similar to that of a Ducati in size Chris isn't worried about the piston as he would simply spec one to be made. Something I learned tonight that I never knew: Pistons aren't round. They're actually oval. Yup. Surprised me too. They're made oval so that as they expand with heat the areas of different thicknesses will expand so that at operating temperature they are round. Did not know that until tonight.

So, it seems like a big bore kit will be possible. 105mm on a 950 will give 1040cc and on a 990 will give 1080cc's. If you have a 950 and you want the 1080 you have to change your crank to the 990 crank. Or get a 990. Too much is never enough.

Gregor

[sakurama]

Originally Posted by Katoom119

Sweet. I like being right.

That's the 2nd flattest torque curve I've ever seen, with the first being my RC8 after it got dyno'd and remapped. It wants to pull my arms out of the sockets and it's not that far off of your bike. It must be a hoot to ride.

I've ridden an RC8 and it was one of the hardest pulling bikes I've ever ridden - silly power.

Yes, my bike is now a full on hoot and kick in the pants as well. Today coming over the Williamsburg bridge I flashed the clutch in third at 60mph and she stood right up. Much like a dictator I find myself abusing my newfound power. I'm just hoping not to be toppled...

As an aside I never mentioned the lighter throttle springs. They're better. They're nothing like the one finger throttle of an injected bike (oh, how I wish) but it's now only slightly heavier than stock. I suppose the fact that it never occurred to me to mention it is probably worth the mention as it means the pull is just this side of normal now. Good stuff.

Gregor

[LocuL]

So close to 1150cc. Would it be reliability issue that stops you from pushing more? Would a crank be able to stroke it further or would it tumble?

Great write up, quality in both picture and writing is standard top.

[kamanya]

Originally Posted by sakurama

The 41 FCR's stomped the 39's... everywhere.

Ahh no!

I rather have not read that. I now will be haunted by a mere 2mm.

[sakurama]

Originally Posted by LocuL

So close to 1150cc. Would it be reliability issue that stops you from pushing more? Would a crank be able to stroke it further or would it tumble?

Great write up, quality in both picture and writing is standard top.

It's hard to say. The Ducati pushed the bore to 2.17mm walls but it also left more at the very top of the head where it's most important. 105mm in the KTM would leave just over 3.5mm per side and you're also bumping the compression ratio so it's more pressure held with less gasket. The difference in the 950 to 990 is 1.25mm in stroke (60 vs 62.5mm) and 1mm in bore (100 vs 101mm). Small changes but they give 50cc. Certainly there's probably room to have the crank reground to increase the stroke again by 1mm but then there's a whole host of things involved with that; grinding the crank offset and rewelding it, shorter rods, and then checking and changing all the clearances inside the case, the cylinders and the pistons. Quite a lot of work. At that point it's time to go down your path and find the RC8 engine. Chris' interest is to make a viable kit with minimal work for maximum yield.

Bore on the other hand could be just a bore, replate, custom head gasket and piston. It's more gain for less work. In looking at the cooling passages most are blocked off by the head gasket so their thickness isn't the limit as far as cooling but it's about if there's enough gasket to hold the pressure. Chris said he could design a new cylinder casting that could decrease the width of the passages to gain space for the gasket but it still seems like 105 would be the safe limit.

In reading the article in BIKE about the new 1190 it seems they intended to continue to develop the 990 into a 1090 but when the economy crashed they shelved the plan. In 2007 when they introduced the 990 Ducati went to 1098 and KTM said they planned to go to 1090 but stopped development. After shelving the plan they decided to start from scratch with the new 1190. It would seem that the LC8 was intended to be pushed to 1090 but what changes the factory would have made isn't known. It's certainly easier for them to do stroke than for us.

Interestingly the cooling in the head doesn't even go down the full length of the piston travel. Much like the new boxer it's concentrated at the top of the cylinder.

I'm going to try to get in touch with the guy who built that 1080 and see how it's holding up. I want to see who else has done it and what issues they found. I'm curious why it's not been done (more) and want to avoid any obvious pitfalls but I'm also willing to give it a go.

G

[davesupreme]

those 41mm's can be bored out too!....... read the RFS section at KTMTalk, all the big bore guys bore them, i think you can do it ovally too, or tapered.....

you never mentioned much about the cam differences.... i bet that the FI cam is different than the one for the carbs.... lotta voodoo there....

[sakurama]

Originally Posted by kamanya

Ahh no!

I rather have not read that. I now will be haunted by a mere 2mm.

Flanny's bike is still a 950 so perhaps we can arrange dyno time with the 41's for his bike before they head back home. Where is he anyway? Damn job promotions...

Interesting that there's room to push the 41's even more. I was considering boring mine but it seemed more trouble than it was worth. I would need to really dial my lathe in or Chris would have to do it on the Bridgeport. I gotta limit my "creep" somewhere.

Gregor

[Flanny]

Originally Posted by sakurama

Flanny's bike is still a 950 so perhaps we can arrange dyno time with the 41's for his bike before they head back home. Where is he anyway? Damn job promotions...

Gregor

Yeah - buried with work-work these days...All work and no play makes for a very grumpy Flanny

I think the 950 could do with both a big-bore kit, AND probably a 41mm carb bore...just need to find time to get some attention back on the fun stuff!

[LocuL]

So do this mean that you will settle for "only" 41mm? Serious how much can these babies take(off)? RFS/XC4 bikes would be 43mm as an maximum, but i´m not sure.
I get the idea with stroke would be to much since the engine runs fine. Lots of work involved in that. Do you have any timeframe of this build?