My "Big Bore" motor in progress.
For a "Big Bore" Corvair, you use 94mm VW jugs and pistons, machining the Corvair case and heads as required.
Below is a side by side comparison of a VW 94mm jug, piston and head gasket (left), and the same for the Corvair (right).
Below you can see a little better how much difference there is in size between the Corvair and VW pistons. The Corvair piston "rattles around" inside the VW jug! (left photo) Also notice how the Corvair jug sets down inside the VW jug with ease, (right photo)
Below is a photo showing the difference in length between the VW Rabbit Rod I am using, and the Corvair rod. I shortened the VW rod as much as I could, and it is still around 0.300" longer than the Corvair rod. Most guys, when building a Big Bore Corvair, will use the Corvair rods, and cut the VW jugs down shorter. I chose to use the VW rods for several reasons. First, they are much stronger than the Corvair rods. Second, with the longer rod, the piston will be slowed down compared to the short rod. Since I will have a shift point with this motor of around 7200 RPM, the longer rod was the better choice. The VW rod was also made to be a full floater, and was made for the .866" VW pin. The Corvair rod was made as a press fit pin, and was sized for a .800" pin. Also, by using the VW rod, I do not have to shorten the jugs.
Here you can see a piston at TDC in my mock up case. It could be a few thousandths off from what it will be in my motor, (given production tolerances), but will be very close. The piston is just barely coming out of the jug by a few thousandths. This is about perfect. I can use head gaskets to get the piston to .040 from the head surface. I was also concerned that the head studs may be too short. After careful review, I can see that they will be just long enough. I will need to get new studs, as I need the threads good to the very end, but at least I will not have to get studs custom made, (read BIG $$$$ to go with Big Bore!).
The jugs fit VERY closely in the Corvair case. So close, that I have to "clearance" the area for the head studs. Below you can the area before I ground for clearance, then in the next photo you can see the clearance that was added. It is not a lot, but things fit that tight that it is needed.
