As the reader may realize, pistons are the basis of engine performance. So if you want or need piston kits now or soon, you will have to cope with CP's or JE's turn-around time which I am told is about a month. The good news? Gen I through 1100 piston kits in .5mm incremens in half point compression ratios. That's '81 to '83 750 from standard size through 87mm; that's 823cc, up to 13:1 compression ratio. 920 and thousand in 96mm (a full liter) in 11:1. Thousand (and TR1) up to 99mm (1065cc) 11:1 and 1100 in 99mm (1155cc) in 11:1. Frankly, these can be had in higher compression ratios, but 1) I must buy in quantity and I don't think I can stand behind the spares, 2) I don't want to be tempted to sell 14:1 hand grenades. Besides, I don't think that it would be possible to turn the engine fast enough to start.
Keep in mind that while the American market 920s and Virago 1000s had combustion chamber volumes of 63cc, the Eastern Hemisphere TR1 had a more sporting 55cc. As a rule of thumb on the 96mm and 99mm pistons, reckon the TR1's CR to be a point and a half higher. Thus when looking at pistons that we have listed at 11:1, they will run about 12.5:1 in a TR1. There are many bikes in Scandinavia and Australia running this figure on pump gas without problem.
The maximum sizes that can be run in the various cylinders are as follows: 750s: 86mm (87mm will theoretically work with a copper head gasket but NO warranty).
750s have 20mm rod eyes althought the stroke and geometry was the sane as the bigger bikes which have 22mm rod eyes.
Swapping out the rods (not an easy job) can open your ride out to enornaous displacenents,
It is a matter of hogging out the spigots and - if you waanted to go fast - swapping out to larger heads (for the valves).
920s: 966mm - there is just not enough metal to go bigger. You can remove material from your case spigots and run 1000 cylinders.
1000s and 1100s: 99mm, not enough meat to go bigger. Later we will explore sleeving out 920 and larger motors to at least 105mm; this will probably be costly as I think only a plated-on bore can shed the heat fast enough for this much twin.
These pistons _require_ special head gaskets, and these are included in the "bare" kit ae well as with cylinders. These are high compression pistons and require greater holding power.
The risk fee I mention below is to cover my vulnerability. I must buy in quantities of four and I may have trouble selling the remaining pair. 99mm 11:1 for the 1000s carry no risk, but anything for a 750 is very risky. Anything 12:1 or higher is very risky. If what you want is just plain bizarre, I might require you to buy all four. Before I get too far afield, TR1s and 1100 Viragos seem to thrive under high compresssion: I'n heard of TR1s going over 14:1 reliably and 1100s coming alive at 12.5:1.
Coming up: piston kits with bored-to-size cylinders and an Athena gasket set. Figure an additional $400 for a 920. Thousand cylinders and gasket sets are costlier, so figure on $500 over the piston kit price.
At this point it may be a good idea to mention starting. All XV series bikes had marginal at best starting mechanisms. If your starter is weak, it is possible that it will spin without turning the bike's engine. See here.