A few engine questions

I am new to this, I hope these don't sound too dumb.

On a schnurle ported engine, which port is the boost port if it has one? I have an OS.40LA, and I think it doesn't have a boost port, how do I tell for sure? I also have an OS.25FX, and am pretty sure it does have a boost port.

On an engine with a boost port, how do you block/plug it?

Thanks in advance,
Ed N.

The way I have always understood the nomenclature, the two intake ports themselves are opposite each other, more or less to the front and rear of the engine. The boost port occupies the spot where an older style baffle piston engine ("loop scavenged") would have had a single intake port, directly opposite from the exhaust.

Engine tuners have adjusted the size and shape of the ports for years, and with various metallic epoxy compounds can make plugs and partial plugs to fill bypass channels. Not being in that business, nor interested in going into it, I have never tried to make such an alteration myself, but I assume you would merely block off the boost port's channel to the lower end of the engine crankcase with a plug of one of these heat-resistant products.

K.

The boost port, if there is one, will have the top edge (the timing relative to crank rotation) lower than the bypasses. I haven't tried it, but I would be inclined to block the boost port with a fitted block of soft balsa. As oil soaked in, it would swell to completely fill the port, and if a bit of it came loose, it would not be a catastrophe like a chunk of epoxy. Some LA .40's have boost ports and some don't, LA .46's don't. The boost port isn't required to make it a Schneurle. Steve

>The boost port isn't required to make it a Schneurle.

. . and the intake ports don't necessarily HAVE to be fore and aft, as was the case with the 40, 45, & 46 OS-FSR's. George Aldrich is my source for the description of the Fox Big Case 40's porting as "Schneurle;" that's what *he* called it when he designed the upper end (the lower end is a Fox redesign, since the original prototype had a twin-BB crank).

I have one, and never paid a lot of attention to where the ports lined up in the cylinder. If they are still more or less opposite to the exhaust, it is nevertheless my bet that the DIRECTION of air flow from them is STILL fore and aft into the combustion chamber!

Kiwi