Fuel strategy for endurance racing
#1
Elite Member
Thread Starter
iTrader: (41)
Join Date: Jan 2006
Location: Seabrook, TX
Posts: 2,417
Total Cats: 20
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.
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.
#2
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.
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.
#3
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?
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?
#5
Elite Member
Thread Starter
iTrader: (41)
Join Date: Jan 2006
Location: Seabrook, TX
Posts: 2,417
Total Cats: 20
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
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?
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?
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.
#9
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.
#12
Elite Member
Thread Starter
iTrader: (41)
Join Date: Jan 2006
Location: Seabrook, TX
Posts: 2,417
Total Cats: 20
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.
#13
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...
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...
#14
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.
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.
I hope you find a solution, quite an interesting debacle!
#16
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...
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...
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.
#18
Elite Member
Thread Starter
iTrader: (41)
Join Date: Jan 2006
Location: Seabrook, TX
Posts: 2,417
Total Cats: 20
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!
I hope you find a solution, quite an interesting debacle!
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.
#20
Elite Member
Thread Starter
iTrader: (41)
Join Date: Jan 2006
Location: Seabrook, TX
Posts: 2,417
Total Cats: 20
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.