Putting in a stroker crankshaft changes everything. Ideally, the engine should have been built from the start with one. I know that buying these parts doesn't always coincide with when they should be bought, due to things like life getting in the way - wife, kids, home... So, when this happens after the engine has been built there has to be some trade-offs.
In this case the barrel is a Pro-X. Those barrels already come at zero deck - the piston is at the edge of the liner when at TDC, so the piston will have to come above the liner further. It would be nice if adding a stroker to an engine didn't require this, but it usually does. That is, unless the engine build is for top end power only. So, a +4 mm stroker puts the piston 2 mm above the deck when at TDC. No problem.
A new dome will have to be made. A new dome that considers the new deck height, the amount of squish thickness needed along with the rest of the design parameters, such as the squish velocity and compression ratio. It'll need to be cut so as to allow the piston to fit inside it somewhat and not physically hit it. The combustion chamber will have to be made a little larger than the bore to accommodate this.
The porting of the Pro-X barrel can not be perfectly optimized, after the porting has already been cut for use with a standard crankshaft stroke. The key word here is "perfectly." It can usually be modified to work very well though. As long as the transfer ports have not been raised too far it is likely the porting with the stroker crankshaft can be made to work pretty well.
Sometimes a long rod style piston will have to be used. The long rod piston, with its piston pin location 5 mm higher will offset some of the additional spacer plate needed. Without it expect about 1/2 of the stroke increase to be added to the plate.
At this time it might be good to think about a custom cut piston to go along with that newly designed combustion chamber. It's all gain - no pain.
If you had a 72 mm bore and a 72 mm stroke (293.1 cc's) and switch to a 76 mm stroke you'll pick up about 16 cc's (309.4 cc's). The change in displacement from a +4 mm stroke increase is not that great. But it is about 5% - so expect about a 5% gain in power from that alone. What is great is the amount of usable power it will make available. We don't usually stroke crankshafts to get a displacement increase. We stroke them to get a power stroke increase - or, less of a loss of power stroke due to extreme porting.
The engine cases will likely have to be clearenced and/or trenched depending on the rod length used.
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