Re: V4 Flat to bubbleback conversion
OK, cool. We'll assume you're going to use it as a stock recreational motor -- about 5800 rpm or so. We'll further assume that you're using a block with 115 style porting, not an older 90.
First off, don't worry about the inserts. You'll actually get slightly more rpm without them.
Lay the inner exhaust gasket on the back of the block. You'll see that it only covers part of that rib. The part it doesn't cover can be, but it's not absolutely necessary, machined away. That part of the rib was still there on the older 135's but removed on the 140's. At sub 6000 rpm I doubt you'll see any difference.
After that it's just a matter of bolting on the 140 style exhaust.
