Fuel tank pressure supply.....whats best?

[Foolwitools]

Hi Guys!

Exhaust pressure supply vs. crankcase pressure supply.........

Opinions Please!!

Bob the Fool :blink:

 

[Ron Olson]

A lot easier to tap into a pipe. Going into the crankcase you'll have to tear the motor down then have to clean out any metal filings. Yeah, I'm lazy at that stuff and would hate to mess up a case.

 

[MarkScott]

Bob,

I'm using crank pressure on my K&B .21 that is using the exhaust throttle. On those with carbs, using the pipe setup.. I was told that with the ET setup, the crank is the best way to go.. I'm no expert, just what I'm using.

Mark.

 

[[email protected]]

My B-Hydro OPC has crankcase pressure. Talk about the most pressure you can get. The tanks look like they want to explode.

 

[Joe_Knesek]

My B-Hydro OPC has crankcase pressure. Talk about the most pressure you can get. The tanks look like they want to explode.

So what's the benefit of so much pressure? As I understood, too much pressure is a bad thing. I've always used a smaller fitting on my 20 motors to reduce the pressure.

 

[Bob Kensill]

I used to run crankcase pressure on my K&B 21 outboard with an exhaust throttle. At very high rpm,it would make the engine pulsate like the pressure was going up and down. Now I only use pipe pressure. Make sure you keep your fitting near the largest part of the pipe. In this area the pressure is the lowest,but the most consistant.

Bob

 

[Preston_Hall]

Considering that either method supplies adequate pressure, the pipe is the way to go due to simplicity.

Also, as long as you have the minimum amount of pressure required increasing it should not change anything since the fuel is basically noncompressable.

Going back to Bernoulli's equation, the pressure in the pipe should be the least at the smaller diameters where the velocity is the greatest. Somebody has stated that they placed about a dozen fiittings in a pipe and measured the pressure differences and that it was neglegible over the length of the pipe. I would have to agree.

 

[Bob Kensill]

I think that higher tank pressure would cause an engine to go rich as the throttle is closed,and then lean as the pressure has to "catch up".

Bob

 

[Joe_Knesek]

I think that higher tank pressure would cause an engine to go rich as the throttle is closed,and then lean as the pressure has to "catch up".Bob

Like Preston said, the I.D. controls the flow. You only need jsut enough. Additional pressure does nothing to improve flow. The needle valve controls the flow not the pressure.

Years ago, John Finch ran with no pressure. He only used gravity flow. The boat was the same speed with or without pressure.

 

[Foolwitools]

Hi Guys!

Thank you all for your input. It seems that there is no distinct differance 'tween the two............ ( except those that use exhaust throttles).

I asked mainly because I bought a used motor that had a crankcase tap.

My first thought was that pipe pressure might contaminate the fuel, but that has not been mentioned here.

I guess I'll be taking the "simple is better" approach and stick with pipe pressure.

Thanks again,

Bob the Fool :blink: