Ok I started by doing a muffler mod. Know while I've never built a 7900 I see it has higher blow down than the 7910. And I'm guessing it has something to do with this SLR chamber thingy. But i heated up and opened the muffler up. I cut out the SLR unit but tack welded the flange from it back in from spacing and support. Then the area you see that I open up for the exit in a factory indentation. If you open it up you'll wind up right about 80%.
A couple pics of tear down. You can see the tiny cranckcase volume everyone always talks about on these.
Ok so I started by cutting .032" off the base and .038" off the squish band. I will be running this one without a gasket. With this amount off I'm getting really close to free porting at the bottom of the exhaust.
On the exhaust side there is a huge amount of blending to do. I was careful not to take any from the floor right at the piston. I may go back in and take the top and bottom slots all the way out from where the muffler slid in but this is a starting point.
I have the lower and upper trans marked. I'm not going to widen the uppers as of yet. Just raise them o a flat 129°. I don't want to add to much width on them because of the cranckcase volume. That's sounds right in my head anyway. Lol. And this is as far as I have gotten.
Had just a little more time this evening so I went ahead and roughed in one side of the trans.
Yes it does. Lol
When I do my final polish I use silicone rubber polishing burrs and oil.
