Faster Refueling for Lemons Racing
 

Hi Guys,

I have spent quite a bit of time researching this topic over the last 6 months. Let me try to explain what I am trying to do. I have a NA6 with 1.8 swap that we have prepped for Lemons endurance racing. We have already gutted the flapper in the spout to allow for Hunsaker 2” fill cans. The problem we are having is that the stock fuel tank cannot vent as fast as the fuel is coming into the filler neck, which causes the fuel to back splash or we end up with a 12 minute fuel stop (SLOW AS HELL). I know that there has been discussion about slow refueling for street cars could be the result of a plugged roll over valve which causes the fumes to not vent properly. In the picture below, someone was kind enough to label the lines running to the charcoal canister (I think) and what to cap off.


https://www.miataturbo.net/attachmen...ine=1456789988


It looks like they cap off the roll over valve (doesn’t sound like a good idea, although putting those two hard lines in a loop doesn’t seem like a horrible idea. In theory I can then run a hose from the ROV out through the trunk at rubber panel where the filler hose is and then down to ground at the rear of the car right? I would be cutting out the restrictive charcoal canister allowing for the fume pressure to escape easier.

https://www.miataturbo.net/attachmen...ine=1456789988

My other idea (and I already have the parts) is to drill a hole in the top of the fuel pump assembly with -8an fuel fittings (start with a discriminating ROV) and a 90* elbow but the assembly doesn’t clear the service lid.

https://www.miataturbo.net/attachmen...ine=1456789988

https://www.miataturbo.net/attachmen...ine=1456789988

I could make a custom service panel but that kinda draws attention to the fact I have modified the stock system (we aren’t supposed to but I want faster refueling).

https://www.miataturbo.net/attachmen...ine=1456789988

Any suggestions will be very helpful!

Don't do anything stupid is my suggestion.

You're doing something wrong if it takes you 12 minutes. We're using ~1" hunsiger hugs and it takes us less than 5 for 9.x gallons.

You say don't do anything stupid. Which is what I am trying to avoid by posting. But what you are telling me doesn't really help. putting fuel in a car isn't rocket science I know. Which is why when I use the smaller 1" spout Hunsaker Jugs I am still getting significant back splash and slow fueling. I'm a little lost here. I have talked to another Lemons Miata team (two of the guys are mazda engineers) and they complain of the same issues. So I thought I would post on forum to see if someone else has more info. I have been researching this off and on since June (flowing a 24 hour race).

Possibly hazardous and definitely ignorant question from an engineer with no first-hand experience in wheel to wheel racing or the rules appertaining thereto:

You're trying to pour a lot of liquid into a tank rapidly. It needs to displace the air that's already in the tank. The faster this air can be evacuated, the faster the liquid can enter.

The stock vent / rollover valve consists of a big hole which necks down to a tiny hose. What if that assembly was removed, and replaced with a vent line whose diameter is roughly equal to the fill line, and vented directly to the exterior of the car (say, the trunk lid for example)?

You'd need to do some creative fabricating to keep this all within the LeMons-prescribed metal bulkhead, and you'd need to fabricate a new rollover / overfill-preventer valve, using something about the size of a golf ball which is heavy enough to not be pushed up by rushing air, but still positively buoyant in gasoline. And made of a material which does not readily decompose when immersed in fuel or fuel vapor.

Does the car overflow when you fill it from a regular gas pump in < 12 minutes?

--Ian

no because Im not putting in fuel fast enough for any pressure to build. And when I say 12 minutes I mean that's how long our pit stops are (includes a driver change which takes only a minute maybe 2). Other teams are ALOT faster with 24 gallon fuel cells.

Also Joe, I would never accuse an engineer of being ignorant (I think that's how I was meant to read that). What I have is an in tank discriminator valve already just a little smaller then what's in the link.
discriminator valve, -8
I am brushing up on my fluid dynamics (its been a few years since I took fluids). I know that gasses behave similarly to liquids per ideal gas law. However, Grahams Law basically tells us that a lower molecular weight gas will evacuate faster then a higher molecular weight gas. I think this can be applied in this situation as well although we are talking about "fluids". Obviously if the vent is the same size as the fill then there will be no problem but based on what I just read the low density gas should evacuate faster then the high density liquid. Which brings me back to the vent line on the OE filler neck being ~20% the size of the filler neck opening. Am I doing that head math right?

I have modified both NA and NB tanks to accept the enduro jugs I use. They will dump 5gal into an empty tank in ~17sec. The only modification is gutting the vapor/backflow flaps in the filler neck. 100% stock tank vents, no aftermarket discretionary valves, no other alterations. If it takes you more than 20 seconds to empty your current can into the tank, you need to solve the issue you have before making it worse with a bunch of mods.

See that's the thing, at our last race, the driver could NOT be in the car if the fuel cap was open, and we'd get a 5 minute egg timer slapped on our car at the beginning of the pit lane. So we'd pull in, hit the kill switch, driver would climb out and open gas cap (kept us from doing anything before the driver was out), put ~1.9 of the quick fill 5 gallon jugs in (maybe .5 gallons left?), strap the driver in, start the car, pull to the end of pit lane, and have 30-40 seconds left before our time went off and we were released.

Our only change to the stock system is putting in a 2-piece filler hose to go around our cage's rear upright.

My point is you're over thinking this, and/or something is wrong with your car.

Have you replaced the valve?

Several of the crap can teams I bang around with use a vent line with a ball valve. Refueler opens the valve before turning the first can upside down and closes it when fuel comes out the valve.

You're doing something wrong on the pits stops man. We do ~13 gallons of fuel, driver change, check/fill oil, change gopro, and clean windshield in roughly 3 minutes, depending on how far we are from pit entrance.

HEEEEELP me figure this out! I don't want to put holes where they don't need to be. I figured something is wrong. I have looked for a replacement valve online but can't find it anywhere. I don't know if I'm calling it the right thing or not in the search field.

Also the Previous owner was a dick and I am pretty sure he booby trapped the car. Diff blew up after the first 20 laps. The shocks were bent and toast. drivers side wheel bearing was missing 2 balls (AND WE DIDNT LOSE A WHEEL AFTER A 16 HOUR RACE!!!! I immediately went and bought a power ball ticket but apparently I spent all my luck on the bearing) part of me wonders if he didn't screw me on this too. As far as vapor evacuation goes, the two locations which vapor gets out is the roll over valve through the charcoal canister and the vent line that's near the top of the filler neck right? The vent at the neck I can blow out with some compressed air but how do I make sure the gas is escaping through the ROV properly?

Have you taken the filler neck off and confirmed that the plastic backflow valve at the bottom is removed?

Look up revlimiters blog. What's funny is you quoted his picture above.

I have read a few of his things, the fuel vent isn't one. Thanks for the tip!

Edit-

I have actually read this before. Kinda forgot about it.

All I can say is that you need experiment. Make a mock up of the tank and use water. Get creative, find creative friends, try it even though its stupid.

Unfortunately a lot of top teams aren't going to share their fueling secrets. That is were you can make up a lot of time on other cars. We can easily refuel our car in under 2 minutes and we solved one of our problems with the tops cut off of Gatorade bottles. Fuel, check oil, change driver, and a once over of the car in under 3 minutes should be your goal.

ill start with checking all the check valves. The car is originally from CA so it might have 3 valves lol. I wills start by cleaning everything out. Thanks guys for all of your help. Love this community, everyone is super helpful!

My can empties in roughly 20 seconds for 5 gallons and it was only a few mods that have been listed above. I can definitely improve it

Some drilling was involved with the filler neck and the can itself, no other mods, still have the orange plastic ball thing in the filler neck (trying to decide whether to take that out, anyone have suggestions on whether to leave it or take it out?). It can be done. there is obviously some issue you are having. As to what, not sure, but it being a CA car may be it

I have not. Its located where the filler neck meets the tank?

Yes. Take the filler neck out, remove the flapper on top, dremel it out as large as you can if you haven't done this already. Remove the ball valve just before the rubber elbow to the tank and reinstall filler neck. It will still vent through the little overflow hose on the side of the neck and will empty a 5 gallon can as quick as it can get out of your fuel jug. We usually weld a 2" ball valve and hose on the bottom of steel fuel jugs and vent through the original opening on top. It will empty in a tank as quick as it can get out of the jug.

We've done all types of mods.....
my recommendation is do not mess around with fuel tank unless you have to....and know what you are doing. They cause leaks, fire......

with most crapcan racing, you have way too much time to refuel anyway. other than dremel out flapper and remove ball valve, don't mess around with fuel tank please.

that's the plan. I wont modify beyond the above recommendations.