Oldbe needs some help

[NAMBA860]

if I placed the fuel tanks in the back against the transom would that be to far from the carb? What would be a good pipe length to start with in an x mono K&b .91 x460 3 blade prop K&b h.p. Glow plug and 50% nitro and where are you measuring it from?

 

[Andy Brown]

I have a small amount of experience with that and it is not good. Unless you run a really small carb the engine will go lean when the boat accelerates.

It's not the distance. It's the position in relation to the carb. Tank in front is best, at the side ok, behind not to good.

 

[NAMBA860]

Ok thank you Andy I'm actually running a venturi

 

[Brad Christy]

Shane,

Something else to throw into the mix: With the tank at the transom, even if you can get the engine to like it, the CG of the boat would change dramatically as the tank was drained, making dialing in the boats handling a nightmare.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[Andy Brown]

Ok thank you Andy I'm actually running a venturi

The same physics will apply. If it is small enough it may work ok.

 

[Ian Inverarity]

I don't run a fuel tank at the transom but I have run a few monos with the tank behind the engine in front of the radio box, including my current 45 mono. This complicates installation somewhat as the flex shaft, tuned pipe and throttle linkages run thru that area, but the engine runs fine and the boat is a lot more consistent in trim than a boat with the tank in front of the engine. This is because as the tank gets emptier and lighter the whole boat gets lighter (and wants to run looser) but the CG moves forward to compensate. With a tank in front of the engine the boats gets lighter and the CG moves back as well, both make the boat run looser.

FSRV boats carry a lot of fuel for long races and all (that I am aware of) have the radio box at the back and the fuel tank behind the engine.

 

[Andy Brown]

I don't run a fuel tank at the transom but I have run a few monos with the tank behind the engine in front of the radio box, including my current 45 mono. This complicates installation somewhat as the flex shaft, tuned pipe and throttle linkages run thru that area, but the engine runs fine and the boat is a lot more consistent in trim than a boat with the tank in front of the engine. This is because as the tank gets emptier and lighter the whole boat gets lighter (and wants to run looser) but the CG moves forward to compensate. With a tank in front of the engine the boats gets lighter and the CG moves back as well, both make the boat run looser.

FSRV boats carry a lot of fuel for long races and all (that I am aware of) have the radio box at the back and the fuel tank behind the engine.

A short distance behind the engine is normally fine, but a long distance behind the engine will reduce fuel delivery upon acceleration. The quicker the acceleration and the longer the distance from the tank to the, spray bar ( to be specific), the more the fuel delivery will be reduced. It is the same effect, but in reverse, as head pressure on a fluid tank that is influenced by gravity. The higher the fluid level above the outlet the more the flow.

There is certainly a benefit to having the tank on the CG. My first 21 Mongoose riggers had the tank right on the CG and they were also even with the spray bar.

The CG did not change with fuel level, nor did the fuel delivery change due to acceleration/deceleration.