Fuel strategy for endurance racing
 

We do a lot of chump/lemons racing in our 94 Miata. At lemons we have a much more relaxed attitude to the racing, but Chumpcar is a different story. They allow a maximum of a 2 hour stint for each drive to be on the track and to be competitive we need to move closer to there from our current hour and a half stints. We are trying to figure out the best way to increase our fuel efficiency without sucking the fun out of it.

Currently we are throwing around a couple ideas. One would be to run with an SM throttle body plate and another is to install a shift light to shift at 6700 instead of winding it all the way out. Is our logic flawed in thinking that the smaller intake of air will result in better fuel economy for the drop in power? A programmable ECU seems like it would do wonders to give us both better fuel economy and more power, but sadly that option is off the table.

The main thing is that we need to use the entire capacity of the 12.7 gallon fuel tank. If we can put 11.5 gallons in consistently, that will help immensely as it will be about 1.5 gallons more than what we were putting in before. A programmable fuel gauge will help this as the damn OEM one shows empty with about 2-2.5 gallons left.

We came in second at our last lemons race with just fast pits and mostly penalty free drivers. Mechanical reliability was great too. Again, we were having to pit every hour and a half though.

Why don't you just not drive %100 all the time, It is a 24 hour race with manditory 5 minute fueling pit stops. We usually make it 1:55 minutes on a tank of fuel, and especially at tws, you will feel the car hiccup in the stooges, that will tell you that the car has about a lap of fuel left. Any other questions feel free to PM me, But of course, I have some secrets that I just cant tell you:hustler:

How about just setting up a throttle stop and fine tuning it over time? Much easier to eliminate a "soft-footing it" variable, especially when racing and someone is pulling away and you mentally want to chase them down. You are still being able to use WOT.

You can't use any ECU mods at all? Can you use a variable rate fuel pressure regulator to manually reduce fuel pressure at the rail which could allow you to lean it out a fraction of a point in AFR?

What year is this rharris? If its the early trapdoor maf, you can crack her open and tighten the spring a click or two. it will lean the whole fueal table out, and you can actually pick up a few hp. although I am willing to bet you already knew this from sm.

The guys on this team are good sprint drivers. Telling them to go easy will be like telling the fat guy he needs to work out. They know it and they may try it, but will give up because they think it sucks.

That may be a viable solution that I was trying to get at with the restrictor plate.

They see the car as a $500 car as is, so no performance mods are allowed at all without penalty. Some people get away with it on various cars, but our will stay 2 legit 2 quit.

The car is 94, so we have a maf. I know plenty of the 1.6 guys do it and most never get caught in SM.

Its actually legal in sm. I know its a new rule change, but it is in fact legal.

Did not know that. I know people where getting in trouble that hadn't actually touched it.

Yeah, its in the GCR now.

Edit: although I cant seem to find it currently. I recall reading it in some form way or shape of gcr

We have put 3 cars through chump racing. 2 1.6's and 1 1.8. Have always managed to squeeze 2 hours out of each stint. Of course full course cautions and lots of traffic typically help a good bit too. We agreed to a 6500 rpm limit for the majority of the race for our last event in October and it seemed to help a good bit. Most of our drivers would make their last two laps of a stint with the car coughing on fumes however.

Flawed. No different than part-throttle.

Can you run 100 octane and run it leaner with an AFM signal modifier?
Or reduce fuel pressure by 10 psi or so?

I second the notion of flawed. Just from an engineering standpoint, you are going to want as much excess air as possible to ensure a more complete burn of the fuel. Less air = lower efficiency, IIRC.

I am not saying that it will lean it out, but trying to limit that air coming in to effectively keep it at partial throttle to lower fuel consuption. I was hoping it would be about the same and the result would be less fuel used. My question though is how much.

We could run a higher octain and do that but the cost for 100 is around $9 a gallon at the track. Using around 175 gallons would get crazt expensive.

How about a low level warning light, or a better readout instead of a needle for the fuel gauge? Most senders are simply a variable resistor, so if you can get a repeatable resistance value at low and high levels, it should give you a little more resolution on how full your tank is. A super cheap (aka lemons legal) way to do it would be to wire in a harbor freight multimeter ($4) and use the resistance measurement as your gauge. I know it's not as easy as looking at a needle, but it should give you a better idea of how much fuel is really left. Just a thought.

The other option would be to wire in a dummy light as a low fuel warning when a certain resistance is reached, but off the top of my head I can't think of a super cheap way to do that...

Unfortunately, limiting air is more likely to decrease mpg as opposed to increasing it. You are going to be injecting the same amount of fuel with less air, and just combusting that air less completely. I do not anything about throttle limiting per say, but I do know that choking your engine of air is not going to do it, or at least not what you would like.

I hope you find a solution, quite an interesting debacle!

What's the point? The car is going to stumble during high load corners and it will be real obvious you need to pit. Tone down your last few laps to avoid fuel slosh and starving. No need for a warning light. Assuming typical Chumpcar drama you will have some full course caution laps likely during everyone's stint to conserve fuel.

Limit your rpm use to 6500 for most of the race and you should be able to make it 2 hours for each driver. We've never had issues. It will be close and the car should literally come into the pits sucking rust from the bottom of your tank. Drive wisely let the 6 and 8 cyl cars duke it out and hit the pits early for fuel. The pack will "Darwin" itself out a few hours in and then it's time to start pedaling when the track clears up.

I assume you have a com system? Your crew chief should be calling the shots on the pace you are setting and be giving you an idea of timing while you relay fuel situation back.

in LeMon, is it a 5 minutes mandatory as in Chump ?
is there a limit (like NASA) on how much gas you can put in per stop ?

better mpg is not the goal, it is about getting better mpg at same power level..

I would really fail to see how it would be different from partial throttle and save fuel on a car with a MAF and not a MAP sensor. The ECU only injects what the MAF tells it is getting in air and if the air is restricted, then it will be injecting less.


LeMons is as fast as you can get in and out of the pits. Chump requires a full 5 minutes if doing anything with fuel.

You can get as much fuel in as the tank can hold. LeMons allows much larger fuel cells where Chump says they must be within 2 gallons of OEM. With the OEM tank being 12.7 gallons, that really only leaves 12 gallon cells. Plus a fuel cell system with FIA/SFI certs costs around $900 when all is said and done.


I agree that's the way it should be and would love to have that as an option, but it is looking like I may not be able to have my cake and eat it too on this one due to the limitations. Since the OEM ecu is worthless for tuning anything other than a higher redline, all that I would be left with to maintain the same power would be reducing drag.

Lean it out with 1.6 injectors? I have never tried to do this, but plenty of people do the opposite to make a 1.6 run rich.

I thought about getting a smaller injector and trying it out, but I am worried that going to the 1.6 in a 1.8 may prove to be too lean. I could try it out and hook up my LC1 to see what the numbers look like and if they are acceptable.

Time to start the chump car FAQ with injectors rated between 230cc and 265cc. People will be scavenging pull-a-part for the rare sets.

Adjustable fuel pressure regulator would be better than trying random injectors. Just tune it on a dyno (or road tune with a wideband) and be done.

I'll argue power level is meaningless (obviously to some extent) in chump/lemons racing. Strategy (protecting the vehicle) is your top priority. There are plenty of yahoos that will make clean laps difficult to come by and jeopardize the car's safety simultaneously making that last drop of hp useless. Consistent, "fast" laps that aren't throttling the equipment for every oz of effort and avoiding flatspotting tires will get you into position for the last few hours. Then you make the push.

Wanna burn less fuel?

https://www.miataturbo.net/showpost....4&postcount=17

Nope. If saving fuel is higher priority that power in endurance racing, then you simply short shift and slow down. You never want to go slow, you simply want to use less fuel while going fast.

It boils down to this:

Endurance racing is gaining as much track position for fuel mass burned. Everything else is secondary.

Just going slow and high mileage is as pointless as hauling ass and getting terrible mileage. Track position:fuel mass used

Agreed. It seems to be a careful balancing point and having limited resources is mildly frustrating, but breads ingenuity.

That's too lean for my liking in an endurance car. If I could find a way to stay around 12.5 on the oem ecu I would be golden. Based on that graph it gets even richer than I thought at high rpms

I don't recall ever recommending going slow? I read some of the posts as "use up every bit of the vehicle at all times" and responded accordingly.

I could have sworn I posted our rpm regulated strategy earlier in this thread that the team I was on for an Oct Chumpcar event used. I even suggested consistent fast laps which is what we aimed for. Maybe I missed something? I guess it worked for us?

I'm all ears to learn and be corrected but it seems as there was some misinterpretation.

"I'll argue power level is meaningless (obviously to some extent) in chump/lemons racing." I interpreted that as an argument that you thought reducing power to gain mileage was OK. Also that adding power was less useful that increasing mileage due to difficulty in using the gained speed in traffic.

On our team, we go fast in traffic both being passed and passing. We spend a lot of time and money training our team drivers, poring over data. This is part of enduro winning strategy. If we can get power we take it. In NASA PT however, we have a lbs/hp cap so any extra power means more ballast. The lower weight helps more than the power does. If we weren't lbs/hp capped, we would weigh the same and definitely make more power. In Chump, we want as much power as possible.

FWIW we won a 24hour chump car in our first try with a 95whp street car on Flex's and junk tires. We were in EC class but actually a tad slower than Eyesore. They broke, we didn't.

Another reason we use chump for training because we like to learn to pass in turns. We're not always the fastest car in a straight line in Chump believe it or not.

Flex is certainly a step up from our Chump suspension setup. Can you say kyb gr2's, no front springs, BMW 5 series bumpstops, and rears were random H&R race springs. :rofl:

Anyways, what you said makes sense. I appreciate the insight and can certainly attest to the "we're not always the fastest car in a straight line in Chump". At PIR (a relatively HP advantageous track) we had our work cut out to keep up with the faster cars.

In the end though protecting the vehicle (not getting collected up in those large clusters of cars where chaos happens), 4 cyl fuel economy aided by 6500 rpm limit (extended driver stints to the full alloted 2 hours) and tire conservation (not flatspotting Star Specs) kept the machinery relatively "fresh" for the last few hours of the race where we really made up in the position department. That was my reasoning. Not pedaling your way around the track as perhaps it come off as.

You have the right idea. Keep pace without using up the car. In the my pre-race drivers meeting, rule #1 is "protect the car". Every other goal is subservient to that.

I think the real focus for me on this needs to be for me to get all the "spare" weight I can out of the car. As it sits now, it's around 2025 caged and I am not sure how much else I can take out, but I need to take a second look. That will really be having my cake and eating it too.

Rarely are we held up by traffic and use 95% of the car 95% of the time. I am amazed at how well chump and lemons have taught us to pass in the turns and how to do aggressive but safe passes in traffic.

Looking at the data for our last race has helped us understand the line even more. I thought after a good 500+laps at TWS I wouldn't have much room to grow, but the data doesn't lie. The more experience we get with this, the more time we find ourselves spending trying to understand how to get all we can out of the car. It really bumps it up a notch.

At TWS we top out around 108 on the front straight while others are hitting 140, so the frustration is very high to have to turn around and pass them again 2 turns later.


Same thing I say to them is that the #1 rule is to keep in a position to where you are in as much control as possible of your safety and the cars safety. You can't win a race in a car that is wadded up.

Really appreciate the reading and input in here. We'll be taking the Piñata down and adding a Civic Si to the mix for the 24 hour LeMons race in May @ ECR.

At TWS we put down some quick laps, but 7 trips to the penalty box pretty much killed any hopes of a top-10 finish. :(

Can you run lean and use water injection?

NASA yes, Chump it might be hard to show it doesn't add value. Wouldn't help mileage though. Do the math for latent heat vs BSFC. You lose more than you gain. Plus you would need a might big tank and safeties built in. Relying on water level to keep your engine from exploding, well, lets just say that's it's not an optimum strategy. Myriad other ways to improve the TP:FMB

btw, that Miata was DRIVEN to the race track....
it is a daily street Miata.

later, 949racing / 2nd Chance Roadster built a dedicated Chump car. This Miata was faster, due to 300LB less weight.. It won the last Chump race by 6 laps...

I think that is about as succinct as the situation can be described. Word.

Robert our rule has always been shift at 6500-6700. Period. In the BMW it was shift @ 3800 (325e).

Another thing I'm a believer in is the underbody aero. I think a flat airdam front, sideskirts and whatnot helps. Anything to keep air from going under the car. :)

I have done 3 races in our 1.6L (2 LeMons and 1 Chump) all with a dyno proven 84 whp. I have never seen over 1.5 hours out of a tank, how are you getting 2+? Is the early 90's tanks smaller? I dont think ours holds 12+ gal. I also think timing your stops in the long haul will be more beneficial than anything, we lost 3 spots in the last 45 minutes of a 24 hours race at VIR to come in for a splash of fuel...not cool. Still 7th made us happy!

I've never weighed our car, now knowing yours I have a benchmark. I bet due to the E-30 front end on our car it will be heaver. We also contended with 100*+ heat both days at VIR last summer and I dont think any of us could have lasted 2 hours even if we had gas. Thermo in the car was always over 140! The cool shirt was the best invention EVER!

90-93 had a 11.7 gallon tank and 94+ had a 12.7 gallon tank. Where you guys driving until you got fuel starve or until it read empty on the gauge? We found it still had about 2+ gallons when the gauge read empty. You can recalibrate the gauge and we will probably do that for the next race.

next time. during one of the track day. drive the car till fuel light comes on (if you have a NB), start your count. next drive till car hiccups...write down how many laps that was. then drive till the car stutters so bad that you are losing 5+ seconds. write that down.

my point is, ignore the fuel level gauge...it really is irrelevant...

+1

What matters is how far you can go at race speed. Find out. Record it carefully. Keep track of distance traveled on track during race. OEM dash gauge is useless.

Dang, This discussion is still going on....Good to know that no one else knows our secret:fawk:

Let me take a guess. Run a bigger fuel cell ? Chump allow stock capacity +2 gallons (more depending on tank size, but for Miata it is 2).

Nope, we run a completely stock fuel tank...for that matter, a completely stock car.

Enlighten us oh wise one.

1. Hide aftermarket ECU (I.e. megasquirt) in stock ECU box.
2. Lean out
3. ???
4. Profit

Just put one of those magnet pill things around the fuel line. Supposed to increase mileage by up to 30%. That should do it.

That is what I was looking for.


Combine that with a Tornado and I am golden.

Well I would, but mr.harris is one of our competitors.

You dont have to use that big of a crystal...
The other way to do it is to get the ecu reflashed.

https://www.miataturbo.net/attachmen...ine=1331353986

and and and and

https://www.miataturbo.net/attachmen...ine=1331353986


LIKE A BAUSSS

We run a 95 325i in Chump.
With the stock diff (3.46 gears), we can go 2 hours. We changed the rear end to a 3.73 from the junkyard and the car started sputtering through turn 4+5 in Portland after 1:20h.
While it was the perfect ration for that track (just hit redline at the end of the straight), not being able to run the full 2 h cost us.

So slightly lower gearing might get you through 2h.

Tell him your secrets or you will be banned. Severely.

Let the banning commence! :jerkit:

We calculated it the easy and safe way....fill the tank to the brim....run like hell for 20 min straight...flat out 7000rpm shifts...etc....

fill with fuel...

do maths

assume the shitty miata will only run down to 10-11 gallons...

The run it till it hicups hard has run us out of fuel on track before...which sucks in the summer.

The secret is Eric and John are cheatin turds who have a team full of drivers who are better than everyone.

BOOOOOOO!!! :p

I like your thinking David.:idea:

Except for the fact that we have NEVER truly cheated a Lemons/Chump Car event ever.

Weigh-In-Motion?

Attachment 240060

Your cheat IS the better drivers....we're screwed. The cheatin car i hear (though legal by the rules) is the SHO motor 2nd gen RX7