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Old 07-26-2012, 09:05 AM   #16
itsatdm
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One other fly in the ointment with the Nuda pistons. They provide a 13.1 compression ratio in the Nuda. The 800 seems to have problems running 12.1 CR with out engine meltdown with poor gas. The Nuda also has bigger valves and more radical cams. Having more valve overlap mitagates the effect of higher compression ratio's as it shortens the time the engine is really at that ratio. So assuming the Nuda piston will fit, you may introduce other problems.

Outside my knowledge base, but how are you going feed your big bore? The amount of fuel is determined by how long the injector remains open. That won't change. It seems you run the risk of leaning out the mixture with more cc's to feed.

I did a 2mm big bore on my 650 single. It netted me 28cc. A welcome boost in torque across the rpm range. Top speed actually went down a few mph. 2mm on the 800 will get you 48 cc.


A bore job on my single was $85 for one cylinder a few years ago. I have seen the cost to replate a single nikasil cylinder at $250. Double that for the 800 and then throw in the cost of new gaskets along with what ever the cost of new pistons and I just do not think it is worth the mod.
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itsatdm screwed with this post 07-26-2012 at 09:13 AM
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Old 07-26-2012, 02:55 PM   #17
ebrabaek
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One other fly in the ointment with the Nuda pistons. They provide a 13.1 compression ratio in the Nuda. The 800 seems to have problems running 12.1 CR with out engine meltdown with poor gas. The Nuda also has bigger valves and more radical cams. Having more valve overlap mitagates the effect of higher compression ratio's as it shortens the time the engine is really at that ratio. So assuming the Nuda piston will fit, you may introduce other problems.

Outside my knowledge base, but how are you going feed your big bore? The amount of fuel is determined by how long the injector remains open. That won't change. It seems you run the risk of leaning out the mixture with more cc's to feed.

I did a 2mm big bore on my 650 single. It netted me 28cc. A welcome boost in torque across the rpm range. Top speed actually went down a few mph. 2mm on the 800 will get you 48 cc.


A bore job on my single was $85 for one cylinder a few years ago. I have seen the cost to replate a single nikasil cylinder at $250. Double that for the 800 and then throw in the cost of new gaskets along with what ever the cost of new pistons and I just do not think it is worth the mod.
I guessed about 50cc gain.....Sounds like you did the math.... The reason the nuda have higher compression... is the stroker crank... Or should I say...most likely. The BB will not alter the compression as the stroke is not changed. As far as the fuel delivery... You would need the PC-5 or equivalent.....with in my case....the autotune module. Only reason you lost top end is your fuel delivery is not correct. Nothing going back wards with a BB. Many people forgets that when you BB a bike..... your main jet will meed to be decreased.....Or in case of fi......Not programed correct.
The BB way is the easiest way to increase the out put with the least amount of intrusion on the motor.... Thais is of course..... factoring in the facet that there is enough room for the bore increase.....in the cylinder skirt....... and that.... I have no clue....
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Old 07-26-2012, 04:25 PM   #18
itsatdm
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Sounds simple, just buy and bolt it on.
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itsatdm screwed with this post 07-26-2012 at 04:43 PM
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Old 07-26-2012, 05:01 PM   #19
ebrabaek
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Sounds simple, just buy and bolt it on.
........ Ehhhh...uhmmmmm.... Trouble here is that there are no r/d available...... Son the first step would be to check the clearances in the cylinder case.....to make sure there are room for the bore... Then contact some one like cylinder works in Denver,CO......and see if they could do it....and what they charge for it plus the nikasil plating......then get the parts...... ( very expensive ....I think)..... PC-5+autotune...... It is somethink I would like to do.... If there was room.........
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Old 07-26-2012, 05:19 PM   #20
itsatdm
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I think those engines may be more different than what we think. I saw a schematic of it and it looks like they went back to a counter rotating balance shaft.

You never know what you will find. A KLX 650 and KLR 650 have the same bore and stroke. You would think the KLR 685cc piston would bolt right on.

Only if you run diesal. 16 to 1 CR in a KLX. Different deck height.
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itsatdm screwed with this post 07-26-2012 at 07:50 PM
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