Fuel Tank Sloshing ? ...

kfalk · 06-22-05, 11:26 PM

I've done some searching, but haven't seen any discussion on this, so here goes.

Given the longitudinal fuel tank arrangement, isn't there a problem with the fuel sloshing forward under braking, and backward while accelerating? I would have thought that there would need to be baffles in the tanks.

No one seems to be complaining about this, and I don't think that any tanks come with baffles. Is this a non-issue?

Gary Gibbs · 06-22-05, 11:51 PM

Some of this might be helpful. More weight on the rear tires on accel????

kfalk · 06-22-05, 11:57 PM

Well, there are two consequences. One is the handling issues. Slamming on the brakes, and having a secondary weight transfer when the wave hits. This will be at its worst when the tank is half full (or half empty - depending on your outlook).

The other is that it could starve the fuel intake.

DC · 06-23-05, 02:00 AM

The GTD tanks have two deep baffles which in effect only allows a relatively small amount of fuel to flow backwards past them. Also there is a filling of explosafe (like loose aluminium wire wool) in the front two compartments.

I have not experienced any 'sloshing' though have run out of fuel and had the engine stall on a long downhill road when light on fuel. The car would not restart until level again for a small distance. This is somewhat fail safe as the hill was steep enough to coast forwards.

The longitudinal fuel tanks is an issue as you need good rear venting arrangements to avoid air locks which can cause fuel to be 'pushed' out of the fillers on hot days.

I am sure this has been discussed before, try the search facility.

Phil · 06-23-05, 02:01 AM

Kelly
I filled my tanks with Explosafe foam, No sloshing at all, and the loss of volume is negligable. If the tanks had baffles the foam would never have gone in completely, but I used senders with no moving parts to avoid any interference with the foam. I guess there are trade-offs with every design.
Phil

norman falkiner · 06-23-05, 02:09 AM

Can't talk for other owners but my RF has baffles in the tanks and I have never noticed any movement of fuel whatsoever. The three way valve system keeps the third tank full so starvation cannot happen and also enables the excess fuel in the fuel rails to return so that vaporisation is not an issue. Similar to the setup as used on the V8 Supercars raced in OZ. Regards

Kalun D · 06-23-05, 03:14 AM

Safety foam, as others have mentioned takes care of some of the problem.

Also some systems have a swirl pot, like a 1 gallon tank fed by low pressure pumps from the main tanks. It's baffled and shaped so the high pressure pump running from it can't suck air. It doesn't matter if the low pressure pumps occasionally get air with this system.

On the advice of Kinslers I set up a baffled chamber in each tank, sort of like a built in swirl pot, with a one way door and in tank high pressure pumps. It saves some room in the already crowded engine bay, but is harder to work on.

Andy Besic · 06-23-05, 10:26 AM

My GTD only holds about 8 gallons each side. I don't think there is enough weight/mass in the given space to make any real difference vs. the mass of the car. I have killed the engine during severe 100mph to zero brakeing but I would bet that was fuel starvation in the Holley float bowls rather than tank starvation.

kfalk · 06-24-05, 01:10 AM

Encouraging info - thanks everyone.

I wasn't aware of a "third tank" - is that standard on an RF, or was that added?

As to whether or not the fuel weight is significant, with both tanks half full - ie 10 gallons on board, thats about 75 lbs of material sloshing around. Not enough to run you off the road, but certainly noticable if not managed with foam or baffles.

norman falkiner · 06-24-05, 01:19 AM

Kelly. Yes it is standard on the RF. One of the tanks is longer and the third tank is the extra bit and is a seperate compartment. Needless to say it is at the rear near the engine. Regards

Peter D · 06-24-05, 08:41 AM

Kelly, my DRB has baffles in the tanks & they are ok in terms of stopping major surges under braking / acceleration, but you can almost use the tank gauges as "inclinometers" on long up & down hills runs ! If you keep the car pointing down for long enough with low tank levels (like parking on a hill), there could be trouble.

I have an EFI setup, so there is a surge tank which buys enough time to get things back on an even keel (feed & return lines to the tanks are at the top of the surge tank, so it doesn't drain back). A simple surge tank is cheap & would be good insurance against getting stuck - whilst you might be pointing in the right direction (down hill), rolling the car down to the bottom of the hill to wait for the pumps to grab fuel can be embarrassing - that happened to a mate of mine recently.

Kind Regards,

Peter D.

MichaelHarvey · 06-24-05, 12:20 PM

My RCR40 holds about 15 gallons on EACH side, and there are baffle plates throughout the tanks (although I'm not sure how many).

I agree that tanks with no baffles or foam would make for some very quirky handling under race or heavy street use conditions.

06-26-05, 06:01 PM

DELETED!

Craig White · 06-26-05, 08:05 PM

Flatchat in his old DRB had an extra tank installed under front clip to give him enough range(fuel) in endurance events. Once it was fitted, I think it was the only tank he used for his normal street driving.

Kalun D · 06-27-05, 01:58 PM

""My GTD only holds about 8 gallons each side. I don't think there is enough weight/mass in the given space to make any real difference vs. the mass of the car.""

It's not the size of the tank that matters, it's the shape. The shape allows the fuel to slosh away from the pickup easier than a conventional shaped tank. Also the mass/ inertia problem is secondary to the pump pickup problem.

Safety foam could almost be considered mandatory from a fire suppression standpoint alone, sort of like seat belts. Especially considering the dangerous location of the fuel tanks in your typical GT40. You might as well get the added benefit of slosh control.

""I have killed the engine during severe 100mph to zero braking but I would bet that was fuel starvation in the Holley float bowls rather than tank starvation.""

Electronic fuel injection is much more problematic when it comes to supply. With carbs you essentially have a reservoir in the float bowls which doesn't exist with EFI. Fuel injection pumps at a faster rate also because of higher pressure and the return system. If it sucks air it's not good for the high pressure pumps and means the injectors will surely be delivering that air leading to certain driveablity problems and possible damaging lean conditions.