Fuel level for autocross

[Locust]

Originally Posted by e1_griego

@Locust please share your washer fluid strategy.

Empty before every event and put it back in after. Takes less than 30 seconds to do each. You've all known this for a long time. I've had it measure at 2567 on the SCCA scales after 3rd runs. Could probably still knock another 20-40 off with seats, brake kit, and titanium header. I've added it all back on the driver this year though. Can't empty that as easily.

[Locust]

Originally Posted by strat61caster

Yeah I try to show up with >1/4 tank and I don’t waste any more energy thinking about it until I’m on my way home and deciding where I need to fill up so I’m not overly late to work on Monday.

Pretty much the goal for STX. 1/4 tank = sweet spot and if you end an event with the gas light coming on as you finish then you've hit it just right. For street I'd run it 1/8 tank.

Originally Posted by SCFD

Trying to optimize the car based on fuel levels is probably highly dependent on the driver's skill and competition. You'd need to be a fast and consistent enough of driver for it to matter. Subjectively, I prefer how the car feels with a full tank compared to one near empty. Although every little bit of advantage adds up, I personally never felt my results would've changed due to the amount of fuel in my gas tank.

Have you tried changing some of your settings with a less full tank to see if you can get it to feel the same way? Not discounting your feel for the car at all but if you have the knobs available you probably can get it there.

Originally Posted by Autoxer62

Not all weight is created equal, your problem there is the wrong passenger. I had a friend that had a passenger seat in his EMod car to take "babes" (his term) for ride alongs, he said he went about a half second faster.

🤣🤣🤣

[jcaserta]

Originally Posted by Locust

Empty before every event and put it back in after. Takes less than 30 seconds to do each. You've all known this for a long time. I've had it measure at 2567 on the SCCA scales after 3rd runs. Could probably still knock another 20-40 off with seats, brake kit, and titanium header. I've added it all back on the driver this year though. Can't empty that as easily.

Man if only I'd known this before nationals. How do you empty washer fluid in 30 seconds? I tried searching and came up with nothing. I guess the hose is accessible, or do you use a transfer pump of some kind?

Realistically I just keep it at the lowest level that barely registers on the bottom of the dipstick. That allows me to not mess with it and it's likely negligible weight, but if I need a quick spray there's some in there.

[AustinTX]

I started the super challenge on the low fuel light and ran the 3rd place runoff with the needle even with the red line. Zero issues. Even had enough gas to go and get more gas.

[jcaserta]

Originally Posted by AustinTX

I started the super challenge on the low fuel light and ran the 3rd place runoff with the needle even with the red line. Zero issues. Even had enough gas to go and get more gas.

I added gas before sunday runs since the light was on but it didn't move the level. Then I added a bit more before the challenge, still reading below E. Then midway through the challenge added even more just in case. Even with that I was convinced I'd run out of gas at any moment, especially by the time I ran against you for 3rd place. Then added even more before my tuesday tnt runs, still no movement. Thankfully a little later on tuesday finally it updated. Over half a tank lol. So I ran nats (and I guess the challenge) with more gas. Oh well.

Now I'm wondering if my fuel gauge is wireless and it was reading your fuel level the whole time

[strat61caster]

Originally Posted by jcaserta

I added gas before sunday runs since the light was on but it didn't move the level. Then I added a bit more before the challenge, still reading below E. Then midway through the challenge added even more just in case. Even with that I was convinced I'd run out of gas at any moment, especially by the time I ran against you for 3rd place. Then added even more before my tuesday tnt runs, still no movement. Thankfully a little later on tuesday finally it updated. Over half a tank lol. So I ran nats (and I guess the challenge) with more gas. Oh well.

Now I'm wondering if my fuel gauge is wireless and it was reading your fuel level the whole time

We learned that lesson at Lincoln last year lol, renfield explained it, unless you throw about 3 gallons or more in the tank at once it doesn’t register as a fillup and keeps calculating fuel level based on consumption (I assume to minimize the needle bouncing around it rarely takes a real level reading). Guess it prevents getting a false level if parked on a hill or something? Idk. But yeah if you’re adding 1-2 gallons at a time the gauge will keep going down until you add about 3 gallons at once, might be able to get away with 2.5, I haven’t gotten scientific about it.

We panicked and did the same with an overfill halfway through the pro I think last year.

[steverife]

My gauge seems to pick up any addition of fuel. I've added half a gallon during challenges with the fuel light on and it turns off the light and moves the needle.

But I've talked to several others that will add 2 gallons, not move the needle off E, then add another 2 gallons, and find themselves at like 5/8th's of a tank.

[foshjowler]

The second gen has a similar response, you need 2-3 gallons for it to register anything. Haven't tried it yet in the first gen, but sounds like they probably use the same programing.

[Locust]

Originally Posted by jcaserta

Man if only I'd known this before nationals. How do you empty washer fluid in 30 seconds? I tried searching and came up with nothing. I guess the hose is accessible, or do you use a transfer pump of some kind?

Realistically I just keep it at the lowest level that barely registers on the bottom of the dipstick. That allows me to not mess with it and it's likely negligible weight, but if I need a quick spray there's some in there.

The hose is clipped into the driver side fender under the hood. You can detach it easily at the back clip and feed it into a 1 gallon fuel container (be warned, though, that the overall capacity is above 1 gallon on these cars and is more like 1.4 gallons). After that just turn on your car and pull the lever back until you hear the pump noise change (it'll get louder and kind of higher pitched when it's an empty pump).

[Locust]

Originally Posted by jcaserta

I added gas before sunday runs since the light was on but it didn't move the level. Then I added a bit more before the challenge, still reading below E. Then midway through the challenge added even more just in case. Even with that I was convinced I'd run out of gas at any moment, especially by the time I ran against you for 3rd place. Then added even more before my tuesday tnt runs, still no movement. Thankfully a little later on tuesday finally it updated. Over half a tank lol. So I ran nats (and I guess the challenge) with more gas. Oh well.

Now I'm wondering if my fuel gauge is wireless and it was reading your fuel level the whole time

Originally Posted by strat61caster

We learned that lesson at Lincoln last year lol, renfield explained it, unless you throw about 3 gallons or more in the tank at once it doesn’t register as a fillup and keeps calculating fuel level based on consumption (I assume to minimize the needle bouncing around it rarely takes a real level reading). Guess it prevents getting a false level if parked on a hill or something? Idk. But yeah if you’re adding 1-2 gallons at a time the gauge will keep going down until you add about 3 gallons at once, might be able to get away with 2.5, I haven’t gotten scientific about it.

We panicked and did the same with an overfill halfway through the pro I think last year.

It's definitely some kind of sloshing/uneven ground safety mechanism and it's a total trip running an event with the meter at negative quarter tank. You need to track your fuel consumption across an average 60s course. Once you hit the fuel light you have ~2 gallons and it won't re-adjust until you add 3 gallons. So if you add a gallon after every 3 runs you're usually good to go from there.

And to clarify - It's not an "at once" thing. You can add a gallon, take a run, add a gallon, take a run, and then add another gallon and it'll update. It has to come up a certain amount below the level it thinks its reading at before it'll believe itself. I haven't figured out what the trigger point for when this behavior kicks in is yet but it's at least below 3/4 and above 1/8 because you can throw in gas at near full and it'll update immediately.

[foshjowler]

Wonder if these cars are like the ND Miata where you can plug in an OBD dongle and get to the exact percentage the ECU reads. They otherwise act the same with 2 gallons left when the gas light comes on and don't register a fill up if it's less than a couple of gallons.

[jcaserta]

Originally Posted by strat61caster

We learned that lesson at Lincoln last year lol, renfield explained it, unless you throw about 3 gallons or more in the tank at once it doesn’t register as a fillup and keeps calculating fuel level based on consumption (I assume to minimize the needle bouncing around it rarely takes a real level reading). Guess it prevents getting a false level if parked on a hill or something? Idk. But yeah if you’re adding 1-2 gallons at a time the gauge will keep going down until you add about 3 gallons at once, might be able to get away with 2.5, I haven’t gotten scientific about it.

We panicked and did the same with an overfill halfway through the pro I think last year.

Thanks! I knew that sometimes it wouldn't update if you put in only a gallon or two, but I've never left the light on long enough after that to see it actually go down to any significant degree. I always assumed it would just stay in one place and not go down further. Seeing the needle actually go down a bunch made me think that it really was reading. But what you're saying lines up.

I'll set up the fuel level PID in racecapture and at the next event try to determine if it's like the ND or not (where the dash is inaccurate but the obd signal is correct)

[DocWalt]

Originally Posted by foshjowler

Wonder if these cars are like the ND Miata where you can plug in an OBD dongle and get to the exact percentage the ECU reads. They otherwise act the same with 2 gallons left when the gas light comes on and don't register a fill up if it's less than a couple of gallons.

Yes, you can check live fuel level with an OBD2 reader.

[autoracer86]

Originally Posted by strat61caster

We learned that lesson at Lincoln last year lol, renfield explained it, unless you throw about 3 gallons or more in the tank at once it doesn’t register as a fillup and keeps calculating fuel level based on consumption (I assume to minimize the needle bouncing around it rarely takes a real level reading). Guess it prevents getting a false level if parked on a hill or something? Idk. But yeah if you’re adding 1-2 gallons at a time the gauge will keep going down until you add about 3 gallons at once, might be able to get away with 2.5, I haven’t gotten scientific about it.

We panicked and did the same with an overfill halfway through the pro I think last year.

Well that explains a lot lol thanks