I've got a 'big bore' B20 in my PV. This was done originally way back when using an IPD kit and some specially made pistons that worked with the 22mm wristpins of the old style B20/B18 rods (the late production 8-bolt B20's and B21's all used 24mm wristpins and different rod bearings). I needed to rebuild it more recently and found that I could use normal b21 pistons with my 6 bolt rods by having a machine shop remove the small end brass bushing and reaming the steel slightly for an interference fit on the 244 mm wristpin. Then the only 'special' item you need to get is a 93mm bore head gasket. KgTrimning sells Elring bigbore gaskets, another alternative is to have a copper head gasket place whip you up one.

2130cc motors will have a noticeable added amount of toque and power. How much and how far up the RPM scale that added power goes depends on all the supporting modifications. A stock B20 head is severely limited in flow by the exhaust ports, and the extra CC's can't breathe that well through them so the added power drops off as the rpms rise. You'll need some head work and/or a better cam to get more than just a low end torque bump. And possibly some different needles in your SU's. MPG is affected only by how fast you drive the car, how often you use the added power. Power is gas burnt, no way around it. There's nothing intrinsically less efficient about a 2130cc b20 vs the normal B20.

If you are doing a full rebuild on a motor anyhow, a big bore won't really cost that much more than a regular rebuild would if it requires new oversize pistons and a rebore anyhow. Although machine shops might look at you funny when you tell them you want it punched out 3 mm. They'll charge extra for removing so much metal (takes several passes) but not *that* much more. And stock B21 pistons won't cost much more (if any) than B20 pistons. Might as well do it to get the added low end oomph, and if you ever tweak the breathing some (I/H/E) you'll get more results.

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'63 PV544 rat rod, '93 Classic 245 + turbo