Big transfer ports vs big bore???

[twinrock101]

Ok so i was wondering in the case of a big bore cylinder, the transfer ports are always compromise by the fact the bore/sleave has increased..how detrimental is this.. everything else being equal is any benifit of a bigger bore cancelled out by the decrease in transfer volume...should the transfer volume be as big as possible..or is flow more inportant than over all volume..or do different sizes benifit different areas of performance thanks

[hoggyis]

Depends on the port size and shape mate. If they are able to flow the increased air they will be fine. Airspeed through the ports will increase slightly too.
If they cant flow the air, its time for a port job/ flow

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[2TInstitute]

Ok so i was wondering in the case of a big bore cylinder, the transfer ports are always compromise by the fact the bore/sleave has increased..how detrimental is this.. everything else being equal is any benifit of a bigger bore cancelled out by the decrease in transfer volume...should the transfer volume be as big as possible..or is flow more inportant than over all volume..or do different sizes benifit different areas of performance thanks

First ,nothing "flows" through the transfers, intake charge only flows from the transfer duct to the cylinder. There simply is not enough time for the common misconception of a molecule of air/fuel going from the carby to cylinder in 1 cycle.
With the big bore the more you cut into the duct volume the more you limit the potential hp. The increased pressure drop(or vaccum if you will) under the piston from a big bore is offset by poor control over the speed and direction the intake charge takes exiting the transfer windows. From the poor duct geometry/volumes
Flow out of the transfers is dependent on the pipe, and the pressure in the front of the pipe being the lowest in the engine at BDC when the transfers are fully open. Pressure goes from high to low.
At no stage ever does the decending piston "push" intake charge through the transfers.
This is why the bigger bores don't make as much hp per cc as a square bore and stroke............but they still make good power but its usually lower in the rev range the more you rev them the less hp they make.