Four pounds boost tops [two should be enough], should I worry about top ring gap? Only 2.5 bore so not much ring to expand from higher combustion temp. Stock gap is .007-.017. Gasoline fuel, stock cam, ports worked alot. I guess my motive is more torque [and having a supercharger on a Crosley] to maintain mph on hills.
Ok, I am curious. What do you supercharge a Crosley with? Please post some pictures of this setup. Even if we have to wait until you have it together, please post some pictures then.
Ring gap on a blown engine becomes an issue when the rings get too warm, because you're making a whole lot of power. I don't think you're there with only two to four psi boost! Stock specs should be fine. Err on the high end, but don't go past.
Supercharger will either be a Judson Vane type [W11] Or a AMR300 rootes type. Judson did make a kit for Crosley in the '50's and ***eol&Crofton had Pepco Rootes type kits, the 45hp ***eol had a pepco [pic]. I found a Judson and a guy an hour from me has been rebuilding them for over 30 yrs. Gathering pieces for mock up pics. Will post.
Judsons were popular with the Triumph MG crowd. I might have a look around their chat rooms for some advice. I have no site names to give you for a place to look. It has been years since I had my TR-3 on the road. If I remember right they were just installed on stock engines. But that was a kit with probably correct drive pulleys to do it that way.
The best solution is to talk to the ring manufacturer and tell them your application and get their response. Another thing to think about is too much ring gap yields just a little more blowby, too little can be catastrophic.
Your not making enough boost to get carried away. If it were mine I would go for the high end of the stock spec.
The Judson unit for a Corvair only produced 4-5 psi. As mentioned the high end of stock spec would be correct. The X factor would be what type of pistons you have( cast,forged,hyperutetic) as they have different expansion rates.
Pistons are stock cast NOS. Stock [Hastings] top ring, cast no chrome. Piston clearance comes in at .003. Compression ratio I'm shooting for 9:1, still working combustion chamber/valve seats and ports. Slow going.
I went down this road with a blown alky dragster. The ring spec was around 25 thou as I remember. When the ring end gaps but, terrible things happen. It blackened the cylinders something terrible. I ended up with 40 thou. I would start out with the 17 or 20. Your cylinder cir***fernece is about half of what mine was. However, your temps on gas are way higher than alky. If I was doing it, safe rather than sorry would be my pick. A few thous aren't going to make a huge difference in the blowby going to the 2nd ring. I would make sure that the 2nd ring was on spec. I never had to open them up.
Not trying to be a smarta** with this question. Won't it take as much hp to drive the supercharger as it will make with 2lbs of boost on a small engine?
I think it's more about the cool factor with a Judson blower. They aren't something you see everyday.
Yes and no. As long as you end up with the "more" you want all is good. I cry more about the weight, Judson has a Cast Iron body and has some weight to it.
The Judson from a 36/40 VW application, sitting on a 948cc BMC engine Cannon manifold which just happens to fit a Crosley [and deritives] with very little machining. Thinking on a Aisin AMR300 rootes type also.
Even at idle, @ 700 RPM thats 12 strokes per second , how much do you really p*** thru a warmed up top ring gap anyway, most blow-by comes from out of round cylinders after warmup
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