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Big Bore

1896 Views 9 Replies 4 Participants Last post by  SCCTrim
Anyone install the Wiseco Big Bore 988 or 904 kits in their standard Bonnie? What kind of power gains can be expected. Any idea on the gas mileage afterward?
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The 988 kit is actually a big bore and stroker combined. Uses stock rod length by moving wrist pin further up in the piston, but requires stroking the crank 1/4". I plan on doing it to my bike this winter. Will let you know how it goes about March, as our racing season starts then.
To "stroke" an engine, the crank pin(where the lower end of the rod attaches) is moved towards the outside of the crank weights, so that as the crank rotates, the piston moves farther up and down in the cylinder, thus increasing displacement. Usually, this requires a longer cylinder to accomodate the increased travel of the piston upward, but in the case of the Wiseco kit, this step was eliminated by fabricating a piston with the wrist pin located farther up in the piston( the exact amount of increased stroke) therefore simplifying the process. Power increases should be substantial, not only because of the increased displacement, but because of the mechanical leverage advantage the stroke angle provides. In high RPM motors, piston speed becomes excessive, but in an engine like the triumph, that is not a concern. However, if all you are interested in is horsepower, and not the type of bike it is delivered in, you are better off changing to almost any other bike, as they are all more powerful than our triumph twins.
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988 wiseco kit (includes gaskets)-$500
Carillo rods -$654
Falicon Stroking (balancing included)-$545
Installing and prepping cylinder-$160
BUT!-You would also want to install cams-$900, bigger valves and port-(do it yourself~$200; someone else~$1000)
and probably carbs-$500
See what I mean about wanting it in your bike or it's not worth it? For me, it's winter therapy and the desire to be competitive in BOT racing and surprise track day participants(they hate it when you pass them with what appears to be a relic!) :-D
Any problems matching the 42's to the manifolds or did you get aftermarket manifolds to accomodate the bigger bore carbs? Where did you get them from and what was the cost?
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