22 replies to this topic

[Carl]

Can anyone tell me approx. how long I should be able to drive a 1990 Spec Miata on a full tank of gas?  Cal Club has a 90 minute enduro coming up in November and I am wondering if I can make it the full time (with a mandatory 5 minute stop in the middle).  I know my 1st gen RX7 would make it, but I don't have any enduro experience with the Miata.  

 

Any suggestion (other than if it goes more than 4 hours call 911) would be appreciated.

 

Carl

[Ron Alan]

It will make it! Especially if you drive it like an enduro...short shift and running corners you can in a higher gear. The early cars have a very small tank...like 10 gallons stuffed. Not sure when Mazda went to the next size tank which is more like 12.5 gallons stuffed. But even at 10 you will make it!

[Carl]

Sounds good!  Just fill it as full as possible and ignore the gauge reading empty near the end?

[gerglmuff2]

i dont think it can do it. esp considering it will starve in corners with under 1 gallon in the tank. you'd really have to baby it. 

[speedengineer]

No crew available to splash a few gallons of fuel in during your mandatory 5 minute stop?  I think you would make it regardless, but it sure takes the guesswork out if you can add a few gallons.

[William Keeling]

we did 1:55 in our chumpcar 1.6 all the time

[Carl]

If we could just put in a splash without getting out the car, I would do it.  The driver has to be out of the car though during fueling, so I think I will be taking a chance since it seems likely the car can make it.  Also by not fueling I can avoid the chance of a penalty for spilling fuel.  Last time I did one of these with CalClub I got a 3 minute penalty for spilling literally 3 drops of fuel outside my catch basin.  

 

Thanks for the advice.

[Michael Novak]

You will be fine. Short shift when possible and save fuel if you get a yellow.

[Ron Alan]

Sounds good!  Just fill it as full as possible and ignore the gauge reading empty near the end?

If you plan to run more Enduro races you should be pretty comfortable with your fuel gauge...test it! Best way is to empty tank...add exactly 2 gallons...note if the gauge moved. Go run a session until the car stumbles...watch the gauge during this and count your laps/time. Once it stumbles slow down a little and get back to the pits in 4th/5th gear. Try and pump out and see what you get! I've done this and got less than a pint of fuel! Obviously if you stumble and dont make it back to the pit...make a note  

[Danny Steyn]

Carl, with all due respect, if your intention is to DRIVE for 90 minutes then you are on the right track. You can do it for sure  

 

However if you are planning to RACE, then you need to think again. 

 

To RACE, you need to be fast, light, and on the throttle, in the power band - short shifting a 1.6 is not the way to make it go fast.

 

Having done lots of enduros with 5 min compulsory pit stops. It is really easy to get in and out, and refuel you car in 5 mins, with only one crew member doing it, without rushing the refueling.

 

You can even change 4 tires in that time and we have done it, but it does require two crew over the wall.

 

This way you can run you car light, with slightly over 1/2 tank for 45 minutes, come in to the pits, get out, drink, stretch and get back in again, and you will have a faster car for each stint, since you are lighter an you won't have to short shift.

 

But thats if you want to RACE!!! 

[Carl]

In this particular instance I do not have a pit crew, so that means me getting out of the car, refueling (borrow someone to hold the fire extinguisher)  and getting back in the car and belted on my own.  Definitely do-able in 5 minutes, as I do it all the time with time to spare when there is a crew and a new driver is going in.  I have also done it once on my own (two hour enduro where there was not enough fuel to go 2 hours) and it went OK, just hectic.  

 

Since I normally run +7 hour enduros where starting with 1/2 tank of fuel is not an option, the thought of of starting lighter had never crossed my mind.  That makes some sense and I will have to take that into account.  

 

I guess my question has been fine tuned a bit.  Can I drive at race pace (no short shiftiing, etc) for 85 minutes without fueling?  If I can, I will have to decide if starting the race 30 lbs lighter gives me enough benefit to do a mid-race re-fuel.

 

Thanks  

[Jeff Wasilko]

I have a 1.6 tub with a 1.8 drivetrain (that runs in ITA). We were getting 1:45 on a tank at Watkins Glen with AER.

 

Early cars had 11.9G capacity vs 12.7G on 94+/

[Steve Scheifler]

You said it’s a ‘90, so small tank as Jeff noted. It depends on the track, but what Danny said. That isn’t an enduro, it’s a double sprint, and if you drive it like one I expect you are at risk of coming up short unless tuned really lean. Depending on the track we’ve sometimes burned close to 1 pound per minute in our 1.6s tuned a little rich, but I also seem to recall completing the MW Council Loooong Race on one tank. Dave W, chime in here.

[Steve Scheifler]

Ah, the council race is only 50 laps (~97 miles) so that wasn’t a problem in the 1.6 at full pace. Without good data for your car at that track I’d recruit help and refuel.

[Jaysz28]

Wouldn't the fuel consumption be based more on the track?

 

I burned through 3/4 tank in my 90 miata in 45 mins - 1 hr at Daytona this past May.

 

I grabbed a fellow SM driver who wasn't competing in the enduro and asked them to fill the tank while I held the extinguisher. You have more than enough time to throw in 5 gals and grab a drink in the 5 min mandatory pit stop.

 

-jason

[William Keeling]

if the stop is optional then then straight thru on a full tank will be fastest -- if the stop is not optional then Danny may be right

[luvin_the_rings]

Lucky for you, I have done this exact experiment. Unlike the 1.8's, I have consistently measured our tuned 1.6 to use, on average, including going in and out of the pits, about a gallon every 10 minutes.  That is at BRP 13 CW, however its all the same at most of the SoCal Tracks. 

 

The tank holds 10 gallons, so that's 100 minutes of running, minus 5 minutes for the pit stop and you're looking at about 15 min, or about 1.5 gallons to spare using a full tank. Don't forget about safety cars. The tank also uses almost all the fuel before cutting out. 

 

An extra 5 gallons weighs 45 lbs. That could average to 3 or 4 tenths a lap maybe? Loosing a second every two laps to the guy in front who is running a half tank. 

 

hmmm... 

 

Those tenths sure add up. 

 

Spec Miata's run 2:06's in sprint races at Buttonwillow 13 CW, so probably 2:10's in endurance racing in the evening. So that's about 40 laps total, best case including pit stops. 

 

You will be running an extra 5 gallons during the first stint compared to the equivalent fuel stop strategy, so that's 20 laps with the extra weight, loosing 1 second for every two laps, that's about 10 seconds disadvantage you have over the 90 minute race by not re-fueling at half way.  

 

That's assuming you're loosing half a second a lap with the extra 45 lbs. 

 

of course, once off track excursion is worth 25 seconds so... there's that too. haha

 

pick your poison!

[davew]

We have never had an issue with running out of fuel at That loooong Race. 50 laps / 100 miles at Blackhawk. Takes an SM about 70 minutes.

 

When doing other enduros, I have done an extreme short shift, easy on throttle to save fuel. Gotten 2 hours on about 8 gallons of fuel. About 1.5 seconds slower per lap. This saved us 2 pit stops or 10 minutes. 600 seconds divided by 1.5 seconds per lap is a 400 lap equivalant point. So if I am running a 6 hour race (360 minutes) on a 1:30 lap track, I will do 240 laps. In this case a slower lap time with 2 fewer pit stops gains us overall time.

 

Couple secrets:

 

Blow up the gas tank. Remove the fuel pump access plate, using a rag as a seal, use compressed air in the fuel filler neck to expand the tank. Watch what the tank does through the access panel.

 

Remove fuel pump assembly, reach inside the tank and you will feel the 1" diameter vent tube. It is about 2" off the top of the tank. Bend it up to as close to the top of the tank as you can. You can only fill to the vent tube, moving the vent tube up gets more gas in.

 

I have seen Miatas hold 14+ gallons of fuel in a tank done this way. YMMV

[Steve Scheifler]

Great tips Dave!

Increasing tank size aside, the rest of the endurance norms don’t seem to apply here. He’s doing 90 minutes less a 5 minute mandatory stop. To short shift or do anything else to save fuel seems like conceding the race if anyone else is really trying. At absolute worst those lost seconds could be added to the pit stop and you still have the advantage of running lighter.

So if it can be done with one tank then fine, maybe it’s worth carrying some extra weight to avoid the risk of a fueling mishap, but it’s not an enduro where the tortoise wins by making fewer stops.

[davew]

I agree Steve. The original question was about a 90 minute/0ne stop race. But the conversation veared away to general enduro stuff. I agree with Danny, if you want to win; start light, add fuel, go fast. If you want to have fun the easy way; modify the tank, short shift a little and walk away grinning!!!!!