As today it is crazier than ever, and yesterday, the carbs that did get proper venturi are in a museum worth a million dollars...
I am trying to build an air intake to put on top of my 1781cc boxer...and realized dimensions are endless.
1. materials: plastic equals warm. aluminum is electrically conductive, and carbon fiber is a 1960s boat recycled. I would just assume use aluminized exhaust pipe and thorough paint external..WELDED venturi.
2. temperatures along the route. Venturis can cheat this..but it must win. It is easier to make a loser. the carb is in the center of the engine, the inlet a cold outside source...indirectly, where a modern cone filter will go.
3. cam timing. A delay like injection needs a gigantic air plenum. Carbs do not...but what math to apply exactly? My cams are the classic 3 degrees snapper.
here is some math I apply free from the net:
this number is "air capacity"
below is max hp rpm. it is 90hp at 5200 on a 109 cubic inch engine.
5200X109 /3456 = 164 cfm at 5200 rpm. That would need hardly anything.
but the engine does climb to 7000 easy enough:
7000 x 109 /3456 = 220 max cfm, the rest is a legendary whistle.
here is max torque figures for "air capacity"
2800 x 109 /3456 == 88 cfm. and that could breathe through a one inch straw.
with above figures, no engine uses all of it. that is where volumetric efficiency equations comes in. again cam timing/lift and temperatures, compression, thermal dissipation (I love to mention this when speaking of a liquid cooled boxer) etc.
Now I am stumped. What size pipe do I need, and what perfect strain of venturi, given what I have written....from one end to the other, about 18inches...
At what speed is the cold air at the end of a 3 inch venturi, and at what speed makes it equal towards the middle of the hotter engine... before trial and error, I am welding this custom plenum, and need a roundabout math to get started...and it is certainly not subarus by oem plenum (it was as ridiculous today as 22 years ago when it was new). Anyway, thanks for ideas. My goal is not to allow a heated intake at the center of carb..therefore venturi is a helper. It would be easy to reply with "a pipe big enough" but that is like saying fual injection was a winner.
