cj9694

Well I'm glad I listened to you guys. It really came down to the dump can and some operator error. The OD on our dump cans was too big and was blocking the filler neck vent. We shifted the nozzle to the side and dumped 5 gallons in 15-20 seconds. So those expensive fittings are getting sent back. Thanks for all the help guys!

cj9694

Hey guys, I was hoping for a little help on something else related to the fuel tank. I read an article on Grass Roots Motorsports a few months ago about how they modified the "in tank vent tube" to allow for more fuel in the tank. Basically where the vent line is located in the fuel tank is rather low, they put some pipe fittings on the tube and moved the termination of the vent closer to the top of the tank so that all the air could vent during refueling. There by guaranteeing that you get approximately 14 gallons of fuel in the tank. My thought is to just slip a 10-12" piece of fuel hose onto the line and aim it up at the highest point in the tank.

So two question, is this a really bad idea? I can't foresee it causing any leaking issues. And does anyone know the diameter of that pipe in the tank. I thought it was about 5/8" but not totally sure....

Dunning Kruger Affect

Two things to consider; two very big things:

1. What happens when people notice that you can easily go 2 hours per stint while driving faster if your previous stints were fuel limited to 1h40m?

2. What happens when your vent tube starts siphoning gas from the tank because you're now filling the tank all the way to the brim?

cj9694

1. Its lemons not spec Miata. So that aspect isn't going to be examined that closely. Right now we get 2hr to a tank and when we had the 1.6 engine we were getting 2.5-2.8hr per tank. You are right, if we were to be looked at, it could be suspicious.

2. Isn't that an open line inside of a closed system. The vent line inside of the tank does not vent to the atmosphere, it starts in the tank exits to a hose that runs to a bull head in the filler neck. I guess if there is zero air in the tank you could be creating a vacuum but that would already be the case with the current system right? The gas cap is a one way valve correct? When you consume fuel air goes in and when you roll over (God forbid) the cap keeps the fuel in.

Midtenn

iTrader: (15)

It's pretty common for Miata's to go past 2 hours on fuel in Chump Car. Chump also allows for the factory vent to be modified. Now if we can just figure out how to make it 3 hours on a single fuel stop, we'll be golden.

Dunning Kruger Affect

You have to change drivers every 2, but it's advantageous for Double 7s.

cj9694

If you switch to a 1.6, you shouldn't have a problem getting close to 3hr. To make up for not having any torque, swap the rear gears from a Kia Sportage. I'm guessing you are running 4.10 gears? The shortage front gears get you 4.778 changes the way it accelerates dramatically.

cj9694

in lemons we don't have a maximum drive time or put time limit (but we also can refule in the pit lane, we have to return to our paddock spot). I'm hoping to get to 2.5 hrs with this tank and a newer engine.

Midtenn

iTrader: (15)

True, but every time you take fuel, you must stop for a minimum of 5mins. If you don't take fuel, you can just change drivers (takes us around 2-3 minutes). So with a 3hr + pit window, you can change drivers at 1.5hrs and gain 2-3 minutes of time (1-2 laps) on the other cars stopping for 5 mins every two hours. There was a E36 318 at National Corvette Museum earlier this year that could do over 3.5hrs on fuel (so one fuel stop per 7 hour race) and we had to stop 3 times. That equates to about 4-6 minutes of laps they gained on us assuming the laps times were similar over the race (they weren't equal lap times, they were also running faster lap times than most of the field).

We run a 1.8 with the 4.77 gears and it is just enough to keep up with the fast cars coming out of the corners and down the long straights. That is more important on the 7 hour races. The 1.6 even with the 4.77 wouldn't be competitive (that's why Chump now allows all NA's to run 1.8's at no points). We are going to add a max size surge tank (.5 gal) and potentially swap out the ECU (if/when it becomes no points) to see if we can save some fuel up top.

Dunning Kruger Affect

I don't buy it. Doing a 1.5 hour strategy depends largely on the format (Double 7 vs a Single 12, etc) and how good your pit stops are in general. It's completely possible to get a new driver into the car quickly, but the theory doesn't hold up with 3 minute driver changes.

If your driver changes are 2 minutes on the dot, for a 7 hour race, you'll save a minute. For a 12 hour, looking at 2 minutes.

wannafbody

iTrader: (1)

On my car we hogged out the flapper door but left the rollover ball in and it only takes about 35 seconds to dump 5 gallons from a Hunsaker or a modified (vented) fuel jug.

Midtenn

iTrader: (15)

Let's break it down based on a 7 hour race. Chump Car rules state that you are going to have to stop at least 3 time to change drivers. So if you stick to the 2 hour rule, you have to stop at least 3 times (2hr, 4hr, 6hr). That means you are spending 15 mins mandatory in the pits, not including the time you spend driving down pit road.

Now, if you can drive 3+ hours on fuel, you still have to make 3 drivers changes, and fuel at least two times. You could stop at 2 hrs, 4hrs, and 5.5hrs. Hours 2 and 4, you take fuel (5 mins each, 10 mins total). On the 5.5hr stop you only have to change the driver (3 mins). Now you've only spent 13 mins in the pits. So you've gained at least 1 one lap on the rest of the field.

We can do a driver change and fuel in about 3 minutes. We've lost races by less than one lap. So that one lap gained could have won us a few races.

Dunning Kruger Affect

My math is based off of 1.5 hour and 2 hour stops.

2 hour stops, total time: 15 min
1.5 hour stops, total time: 14 min

For an 8 hour race, it's 15 vs 16. For a 12 hour race it's 25 vs 28.

JBH

This is apparently a very common modification for endurance. How exactly have folks plumbed this vent into the top of the tank? I've seen an AN fitting into the lid suggested, but clearance of the cover is apparently an issue. Would appreciate a suggestion from someone who has done it before stumbling around with this. Thx

curly

iTrader: (25)

Reach in and bend it up. We did a 1.6 to 1.8 tank swap before we realized that’s all they really did. Bent the 1.8 vent up and gained a bit more, fuel cell ftw. Fwiw, the design of the 1.6 vent looked difficult to bend vs. the 1.8.

JBH

If you just bend the vent upward doesn't it just fill to that level and you still have a 1 gallon air bubble in the top of the tank? Don't you have to move the vent position to the top of the tank?

Thx