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Discussion Starter #1 (Edited)
Alright, so ill bring you guys up to speed, see if you can help a guy out.

What i have, is an old 87 virago that was ready for a ring job. started out simple, but after finding nearly zero aftermarket and reading the viragotech forums endlessly i decided a hybrid was the way to go.
you can see the current thread here:
http://viragotechforum.com/viewtopic.php?f=14&t=48187

this is just engine components comparison. it also happenes to have the info on the PCS 10.6 pistons if your interested in that.

the original plan was to make the PCS pistons work, somehow in all my reading i missed the different rod heights. the Vstar is 1.5mm longer.
after tearing down & comparing, i decided to ebay myself some rods, and a crank to go with it.
im using the vstar jugs because they are just.. better.
the current plan is/was to stick with the virago heads, mostly for budget reasons.

But everything ive been able to gather is other then the cam profiles being different, internally they are basically identical.

here's my problem:
if you look at that thread, you will read that the difference in compression height between the pistons is roughly ~0.110" (2.8mm)

i know i can make up .06" (1.5mm) using the vstar rods. no big deal.
the jugs on the vstar are every so slightly taller. (.01 mostly irrelevant can be turned.)


so, what happened to the last .04 of deck height? the cranks are identical other then the snout for the clutch basket from what i can tell.


Any engine guys know what im missing here?
 

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If the crank throw is identical and the rods don't make it up, then its got to be deck height. Pistons may ride different height from bottom of cylinder.
 

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Discussion Starter #3
its possible. id love to get the heads side by side and see if the chambers are different enough to change the CR.
 

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I wouldn't go the Hi comp route, been there with the PCS 10.6:1. Too much heat for the stock heads. Ended up losing part of the top of the rear piston. Don't get me wrong they are a great part just too much for this application.
 

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Discussion Starter #5 (Edited)
yeesh. thats not cool.(zing)

for the comparison, i was going stock to stock. the PCS is looking like a pipe dream at this point.

really need to figure out where my height is missing.



EDIT: just dawned on me that while the total height is lower by .04, the bottom of the stroke is that much lower. keeping the CR where its suposed to be, in theory. (i think)
 

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Wait am I misunderstanding??? you have it assembled and your piston crown is above the cylinder lip or a ways below the lip?
 

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Discussion Starter #7
ive still got everything disassembled, i was doing the maths to see which parts could, and could not be swapped.

i was trying to figure out the total height difference. my concern was the difference in wrist pin center to deck.(piston compression height)
About ~0.100" ( virago to vstar stock)
originally i was all worried because the vstar rod only makes up .06" of the difference

i was all worked up over the last .40"
in my rum induced pondering, i realised it doesnt matter. while the piston might not get as close to the head as it does in the virago, it also sits lower in the sleeve on the down stroke.

thus the CR is still At 8.3

making sense? or do i need another rum?
 

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Without seeing everything, the math works slight head changes and gasket thickness changes could make that up. Search this board or the Yamaha motorcycle forum. I remember a guy that was doing what you're doing. Mainly because he wanted the chain drive. I think he started with a 920 though.
 

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Discussion Starter #9
i would need thinner gaskets to get the piston up higher.

stock ones are fairly thin already. i suppose i could use copper or brass sheet..
 

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Discussion Starter #10
Alright, i got a hold of a head to compare. im happy with using the virago head, though the extra fins couldnt hurt.

now my question is about cam profiles. vstar rods and pistons with a virago cam.

you know the profile differences by chance?
 

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Not right off hand. I switched cams to the PCS XXX2 when I put in the Hi-Comp pistons. When I switched back I left the uprated cams in. I would be safe to say the Virago cams would be the more aggressive as the Virago made more horsepower. The timing of the Virago might be slightly different so if you can get a Virago Engine Computer. The mating of them with the Dyna3000 really woke the bike up. The biggest bang for the buck since you have that covered would be the POD style filters on each carb with the associated re-jet..
 

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Discussion Starter #12
Not right off hand. I switched cams to the PCS XXX2 when I put in the Hi-Comp pistons. When I switched back I left the uprated cams in. I would be safe to say the Virago cams would be the more aggressive as the Virago made more horsepower. The timing of the Virago might be slightly different so if you can get a Virago Engine Computer. The mating of them with the Dyna3000 really woke the bike up. The biggest bang for the buck since you have that covered would be the POD style filters on each carb with the associated re-jet..
i should be okay for ignition, going with a modern C5 ignition.
 

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Whats a C5 ignition?
 
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