Fuel tank design?

[Cobra Dude]

Anyone here know about fuel tank design? I am rebuilding my Cobra tank from scratch with 1/8" aluminium. Two purposes are more capacity, and dual in-tank pumps to eliminate the noisy in-line T-rex BAP.

The tank is already designed from an external-shape perspective, with the pumps close to center towards the rear of the tank. They are as far back as possible considering the slope at the rear of the tank.

I need to tweak the design for better sumping though. Instead of sumps (which will steal capacity and be difficult to implement cleanly), I was considering baffles surrounding the pump pickups and angled towards the center -- sort of like a pyramid with the top half cut off.

Thoughts?

Cheers,
-Neil.

[Back in Black]

But I would never use anything but a top flight fuel cell in something like a cobra. Why make your own tank if it's going to be dangerous? (all gas tanks are dangerous, but a home made one?)

[Richard Hudgins]

Originally posted by Cobra Dude
Anyone here know about fuel tank design? I am rebuilding my Cobra tank from scratch with 1/8" aluminium. Two purposes are more capacity, and dual in-tank pumps to eliminate the noisy in-line T-rex BAP.

The tank is already designed from an external-shape perspective, with the pumps close to center towards the rear of the tank. They are as far back as possible considering the slope at the rear of the tank.

I need to tweak the design for better sumping though. Instead of sumps (which will steal capacity and be difficult to implement cleanly), I was considering baffles surrounding the pump pickups and angled towards the center -- sort of like a pyramid with the top half cut off.

Thoughts?

Cheers,
-Neil.

Neil,

First thing. Pumps need to be forward in the tank. Braking is the critical area for fuel pickup. You will never have the G's in acceleration that you will have in braking.

Second thing. You can buy fuel cell foam from any of the fuel cell manufacturers. Use this as your baffle system. Put the pumps forward in the low part of the tank. Cut the foam to give you a sump type area around the pumps.

Third thing, buy a fuel cell top fitting with the filler and pickups included. Much easier to use this than try to fab everything.

[Cobra Dude]

I looked at fuel cells, but with the shape of the area available to me for the tank, I would never get a decent-sized fuel-cell in there. Just completed a welding class, so I trust my welding quite a bit. Also, have very good tig and other equipment at my disposal, so I'm not worried about the welding part.

"Pumps need to be forward in the tank"
Why? As far as I've always known, the tanks are always rear-ward since it sucks most fuel during hard acceleration. During braking, the throttle is usually closed, so I'd be surprised if it consumed even the residual fuel in the lines. Can you please explain the theory behind this?

Cheers,
-Neil.

[Richard Hudgins]

Neil,

You will just have to look at the dynamics of the systems to understand why the pickups have to be in certain locations.

If you are on an oval track they are in one place, if you are a drag guy another, road race as I stated.

You would be best speaking with someone that builds fuel cells and that you trust. This way you can obtain answers that you will be comfortable with.

[Cobra Dude]

Richard, you're right about the corner pickups for oval tracks, etc, but I still haven't found anything on forward pickups for any purpose.

Anyone else have thoughts or pointers to info on baffle/sump design?

Cheers,
-Neil.

[Fred]

Neil,
I added a baffle to the fuel tank of my CR Cobra. I was loosing fuel pressure during hard acceleration. As I did not want to cut the entire tank open, I made an 8 inch diameter cylinder and welded a flange to the top. Cut an 8 1/8 inch hole in the top of the tank. The flange bolts to the top of the fuel tank and also has mounting holes to bolt the intank pump to the same cylinder. There is 1/2 inch between the bottom of the tank and the bottom of the cylinder. The front half of the cylinder is perferated and the back is solid.

I have not lost fuel pressure since installing the piece.

Fred

[Bob Putnam]

This is how we do it:

The longitudinal baffles have one-way doors in the front section, forcing the fuel toward the pickup. The transverse baffle is just high enough to keep the pickup covered at 1G accelleration.