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Old 12-05-2011, 09:26 PM   #1 (permalink)
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800cc 680 engine compression

Hey,

Looking into buying a 680 ultra engine off a guy. It has an 800cc big bore kit, and he sais it has 13.5:1 comp. SLP heads. Just wondering what the cylinder pressures should be with those. He sais it has 145 across, but I would think it should be higher, especially tested at low altitude.

Let me know if you think this sounds right, or should it be higher.

Also wondering what kind of power this should make? It has engine porting done, 38mm ported carbs, ufo inserts, v-force III reeds, pipes.

170 -180 sound about right???

Thanks.
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'03 RMK 800, 159"

'96 Ultra SP 680, a few mods, 144" Leaves the nutsack dragging behind in the snow.
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Old 12-06-2011, 06:12 AM   #2 (permalink)
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I'm asuming that this is being pulled out of a sled ,or already has been pulled ,correct? The horse power shoud be in that range 170 to 180 ,with all that's been done that you mentioned.Compression should be 150lbs. approx, to my understanding .This thing must be burning avation fuel also correct? The price tag on all of this with pipes should be $2000 to $2500 used, correct?
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Old 12-06-2011, 10:51 AM   #3 (permalink)
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It is pulled. It was in a lightweight chassis with a 163" M1000 skid. He said it was breaking the sled apart and has come to the point of no repair. He is also getting into bigger 1200cc watercraft triples, and whatnot.

Sais it has 6-7 rides on a rebuild. Does use av gas.

Bare bones engine is $900. I can get the engine/carbs with pro-jets/and the used PSI pipes and primary for $1300, OR $2000 gets me an extra brand new set of PSI pipes, SLP heads and water pump, also another primary, and electronics.

It is certainly a good deal, and the guy sounds pretty straight.

I also know the shop where the work was done, and he said he can even have it taken back there for a lookover.
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'03 RMK 800, 159"

'96 Ultra SP 680, a few mods, 144" Leaves the nutsack dragging behind in the snow.
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Old 12-06-2011, 07:27 PM   #4 (permalink)
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Sounds like a pretty fair deal. Do you have a newer chassie to put that thing in with a long track ,or are you going to put that beast back in the 96 Ultra chassie?
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Old 12-06-2011, 07:42 PM   #5 (permalink)
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Yeah, it does have a 144" track, fox shocks, etc. though, but should still be pretty scary. I do have 2 800 RMK Edges, but they are still running strong, so no point dropping an engine into them. I was just thinking of parting my Ultra out till I saw this engine. I will probably be getting it for $1200 with the PSI pipes.

I'll keep you updated.
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'03 RMK 800, 159"

'96 Ultra SP 680, a few mods, 144" Leaves the nutsack dragging behind in the snow.
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Old 12-07-2011, 05:39 AM   #6 (permalink)
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Well, I paid $750 for my 96 sp Ultra 680 engine used & stock...humm? That thing is done out, with all the tricks & pipes to . That thing will be a good talk piece & a blast out on some of the rally's around here. Hang on monkey man!
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