MillerModSaws and the PS-7910

I've promised several people I would do a build thread on this saw. So here we go. Please be patient as I am slow with these. This will be my first build of this model. So I'm always open to suggestions and everyone's knowledge. I have this same thread going on AS so hopefully I keep them straight. Lol. Here's my victims. A brand new pair of 7910s.

 

Ok I started off by muffler modding one saw. And i did a thread one this just a few days ago

 

A few pics of tear down. You can see the small crankcase volume these saws have.

 

Here's the intial numbers. Ex 106, trans 130-132 slant, intake 76. Squish .025" with base gasket .015" without. Comp 165. I have not did a 7900 either but I have looked at the numbers. They have 27 deg blowdown. I'm guessing the 7910 has a shorter blow down because of the SLR system which I have removed.

 

I started by taking .032" off the base and .038" off the squish band. The saw is getting close to free porting at these numbers. We will see what kind of comp it has.

 

My plans for this first saw is ex 102, trans a flat 129, intake squared and widened a little at what ever the base cut ends me up at. Then I will use the second saw for a base line then try to out build the first saw. Then I will gasket match the lower trans. I think i will just raise the uppers for now due to the small case volume. Works in my head anyway. Lol.

 

Well here's ya some numbers to play with. Lol. The second saw I will try a 25°blowdown and if that dosnt work I will simply raise the exhaust to 100° to get my blowdown back.

 

On the exhaust I pushed a ring up in the cylinder and market it at 102° and then marked my intial widening. I marked the width a few more times after the first pic. I ended up leaving about .078 between the exhaust and piston skirts. I ended up right around 60% exhaust width to piston diameter

 

Now the exhaust outlet takes a lot of blending. But i was very careful not to touch the base next to the piston being I am close to free porting anyway. I may go back in and fully take out the slots were the muffler slide in but it's at a good start now.

 

Here I've marked out my upper and my lower trans. I will just case match and blend my lowers. I will not take any out of the trans tunnels.

 

One final pic for the night. I roughed in one upper trans before calling it a night.

 

Rookie question, how do you get your target #s?

 

Looking good !! Let that metal fly LOL !

 

Why keep the slots in the exhaust if you removed that metal chamber ?
A gasket between the cylinder and the now flat muffler should allow you to loose them slots, no ?

 

On this saw I aimed for the 7900 numbers with a slightly higher exhaust to move my rpm range up.

 

I probably won't by the time I'm done but I also have to watch my gasket. By the time I would take all the top slit out my gasket maybe to thin. When I go to port match the exhaust it'll tell me a bit more. I will bolt the heat shield and gasket on and see where I'm at. I'm just getting started.

 

If it's like the 7900 muffler the gasket and muffler flange will be very thin if you go that far.

 

http://www.permatex.com/products-2/...-temperature-rtv-silicone-gasket-maker-detail

I have used this stuff on many collectors and headders, including air injection, nitrous, and turbo applications .............. this stuff is right at home with thin flanges

 

A little progress tonight. I got the upper trans done. I squared them up a bit more from last night and finished them with a diamond burr.