It shouldn't be much oversquare. If the bore is exactly 4" that's 101.6mm. IIRC the stroke is 99.7???? That would give a capacity of 4849.8cc... maybe the stroke is a bit less.
It's still a 20% increase. Maybe it'll be restricted by the head casting... normally with such a bore increase the chambers would be widened and larger valves fitted. I'm not sure if Joe has the resources to do this, but he already does porting & cams for the I6 so will be able to at least partially compensate.
The relatively small valves should mean high intake velocities at relatively low rpm, so it probably will be torquey. I reckon a centrifugal blower would help overcome any flow deficiency at higher revs...
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The Frankenfalcon... AU1.5 Wagon, BA brakes, AU2 booster, BA2 XR6T engine, stock from airbox to turbo, 8psi/98 octane tune 240RWKW, BF XR6T cat, quiet 3" zorst, Pex BSO660 & BSO439 mufflers, 84 db, built BTR box, 3.08 LSD, Emer SVI LPG, AU1 XR8 alloys, Momo wheel, JVC KDR746BT head unit, Aerpro steering wheel control wiring.
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