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Building Tips and technical articles. => 1/2 A building. => Topic started by: Jim Roselle on July 17, 2013, 05:38:57 PM
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I recently purchased a Tee Dee .049 with a tapped backplate. I run surgical tubing bladders and love the performance, I have never used crankcase pressure. What advice can anyone give on running with crankcase pressure. Can I use a drilled out Venturi? I have several small perfect tanks I could use.
Thank you,
Jim
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Tapped backplate runs fine, you can open the venturi. Recommend a one way valve in pressure line, and uniflow tank. Suggest you stay with bladders if they work to suit you. Just plug the tap. There may be a one way valve in the tap.
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I agree with Jim as far as he went.
Personally, I prefer the crankshaft timed pressure output. That funny nipple on the side of the crankcase can be drilled out, and gives non-flooding, gentle pressure fuel feed.
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I would think the crank pressure would give more pressure than backplate pressure. Backplate pressure changes from positive to negative, and back again as the piston goes up and down. Crank pressure should be timed to give only positive pressure. I always cut the nipple off as it gets in the way of my motor mounts.
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I never did the measurements, but was told that the place where the pressure port is located yields only a little positive pressure feed. You can select how much pressure you want by where in the stroke you locate the port.
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My theory of crakcase pressure is this:
On the downstroke the piston sends A LOT of pressure into the tank.
On the upstroke it sucks a lot of air in through the venturi and allows a minimal amount of pressure to escape the tank.
But the net result is still PLENTY of pressure in the tank.
More than enough to drown any engine in fuel, even with a giant venturi.