Fuel consumed during races

[Hollowpockets]

Hi all,

So far my races have all been 20 minutes or less and I've never had to work out the volume of fuel needed, just throw in half a tank or so and never work out whats used, my fuel guage is a dip tube sender but its not accurate, the tank has baffles and a collector pot with a couple of one way valves in it. it feeds two externally mounted Bosche 044 pumps.

I plan to do 45 minute races next year where no re-fuelling is permitted and need to work out if my tank will be capable. I don't know of any calculations and cant really do any testing until feb/march.

Its a 60 litre tank, 45 minute race so have upto 1.33 litres per minute to burn. (plus the litre or so in filler neck)

car will be running 500bhp 450lb/ft or there abouts, its 3 litre turbocharged, runs 1 bar of boost and revs to 7500rpm. car weight is 1170kg full of fuel with me in it.

can someone clever with this info give me a rough idea or point me to a genius who can, as my 'it'll be fine' attitude might not pay off with this gamble.

cheers

Graham

[HustleRussell]

In my opinion it won't be possible to 'calculate' fuel consumption in a way which is accurate enough for you to bank your entire race weekend on the result.

I suggest you firstly drain the tank until no more will come out using the in-tank lift pumps. Observe/mark gauge location. Now you know where 'completely empty' is. Then book a test day, or experiment on the test day before your first race. See how long you can go without letting the fuel level drop to your pre-determined 'completely empty' marker. It is probable that fuel surge will start to be a problem before the thing actually runs out of petrol anyway.

Also, on a track/test day you could calculate fuel consumption using the traditional method i.e. brim to brim comparing amount of fuel used to the number of laps/minutes/miles etc done.

If you can find anybosy using a techncally simular car, ask them obviously!

[Auntieroll]

The fuel consumption is proportional to the power produced, do you really think that the F1 fuel loads are guessed at?
Look up BSFC on Wiki all the information needed is there.

[mrmr96]

Auntieroll said:

The fuel consumption is proportional to the power produced, do you really think that the F1 fuel loads are guessed at?
Look up BSFC on Wiki all the information needed is there.

It will also depend on the circuit and what proportion of time is spent at what throttle position.

[CharlesElliott]

In club racing, you generally have the issue of starvation as the baffles are not perfect. So you may have 10 litres left in the tank but no fuel after a long left or right hander depending on where the pump is.

[norwichphoto]

Adopt what single seater drivers do and is to pump out the fuel between sessions and fill with a measured quantity. You soon come to a conclusion on fuel consumption per minute and can plan accordingly, leaving in the necessary for fuel sampling etc., Weather and track does make a difference, but its something you can rapidly learn.

Of course, these cars tend to have bag tanks rather than a rigid tank with possibly baffles.

Edited by norwichphoto on Wednesday 11th December 14:46

[Web13]

mrmr96 said:

Auntieroll said:

The fuel consumption is proportional to the power produced, do you really think that the F1 fuel loads are guessed at?
Look up BSFC on Wiki all the information needed is there.

It will also depend on the circuit and what proportion of time is spent at what throttle position.

And what lambda the car runs at WOT? and does it have run down fueling? or anti lag? does it have high amounts of valve overlap sending un-used charge down the exhaust?

If it was me I would do a track day before the weather gets bad if your exhaust/intake noise allows. you only need to do a couple of runs. probably best to go to a power track like silverstone to get a worst case scenario.

[mrmr96]

Web13 said:

mrmr96 said:

Auntieroll said:

The fuel consumption is proportional to the power produced, do you really think that the F1 fuel loads are guessed at?
Look up BSFC on Wiki all the information needed is there.

It will also depend on the circuit and what proportion of time is spent at what throttle position.

And what lambda the car runs at WOT? and does it have run down fueling? or anti lag? does it have high amounts of valve overlap sending un-used charge down the exhaust?

If it was me I would do a track day before the weather gets bad if your exhaust/intake noise allows. you only need to do a couple of runs. probably best to go to a power track like silverstone to get a worst case scenario.

Good points.

The bottom line for the OP is that, as you've said, it will be much more useful/accurate to actually go and run the car and see what it does, because there's far too many unknown variables to be able to be able to calculate it.

PS - WRT to F1 teams not guessing, you're correct, they CAN calculate accurately because, whilst there is still the same number of variables, they actually know what the values are. The OP doesn't.

[Web13]

mrmr96 said:

Good points.

The bottom line for the OP is that, as you've said, it will be much more useful/accurate to actually go and run the car and see what it does, because there's far too many unknown variables to be able to be able to calculate it.

PS - WRT to F1 teams not guessing, you're correct, they CAN calculate accurately because, whilst there is still the same number of variables, they actually know what the values are. The OP doesn't.

+1

Its possible to get a guesstimation if you have an after market ecu and some data, you could calculate actual injector flow rate by dividing actual fuel pressure in the rail with the pressure the injector is calibrated to, get the square root, times it by the injector flow rate at test pressure to get actual flow rate.

Now here is where it gets really complicated, you have to look in the data to see how many milliseconds in each rpm/throttle zone position is having of injection, then see how much time each one uses over a typical lap, add them all up. throw in your flow rate, a rough litre per min. rough because it doesn't include injector dead time or over run, tip in enrichment or any of the many other enrichment factors, or lambda control. the more I think about it the more i think its a terrible idea, Just go testing.

[Hollowpockets]

haha, thanks guys, I thought that would be the case.

The car will be getting mapped again in January so I might be able to get an idea of the worst case scenario from him based on duty cycle and fuel pressure and the map. will have to wait for the prep work to be finished and get out on a dry track asap.

Problem is if the tank is not big enough, theres not really any space to make it bigger and it would need chassis bars moved or the tank put where the passenger seat was and another bulkhead adding quite a bit of weight.

The tank has a central collection point then piped to two external pumps, no internal pumps. The baffles were designed and fitted last winter by guys who previously set up a few similar Nobles for the factory so its a tried and tested design I believe.

[Web13]

Hollowpockets said:

haha, thanks guys, I thought that would be the case.

The car will be getting mapped again in January so I might be able to get an idea of the worst case scenario from him based on duty cycle and fuel pressure and the map. will have to wait for the prep work to be finished and get out on a dry track asap.

Problem is if the tank is not big enough, theres not really any space to make it bigger and it would need chassis bars moved or the tank put where the passenger seat was and another bulkhead adding quite a bit of weight.

The tank has a central collection point then piped to two external pumps, no internal pumps. The baffles were designed and fitted last winter by guys who previously set up a few similar Nobles for the factory so its a tried and tested design I believe.

well, going off what you said originally about only using half a tank and doing twenty mins, and i was being positive about it, i would say;

• you don't pick up all the fuel anyway, there is always a little in left over no mater how good the system is. so you get slightly more for your second half. plus you have the filler neck and what not.

• you only have one set of out laps and in laps regardless of how long the race is. so a little saved there in your second half.

• you could try to save fuel across the whole race if needs be.

• you fit a swirl pot to add a liter.

• ask your tuner to take make a leaner map for endurance, this obviously has risks associated to it, like needing a new engine because some of your old one melted and came out the exhaust

• failing all else you could do a Smokey Yunick and have twenty feet of the largest diameter "fuel line" you can find coiled up in the boot.

[woof]

The longer distance races we did last year used less than we thought compared to a 20min race.
On average it was 45mins - 40-45ltrs of fuel, so you'll be fine

Hollowpockets said:

Hi all,

So far my races have all been 20 minutes or less and I've never had to work out the volume of fuel needed, just throw in half a tank or so and never work out whats used, my fuel guage is a dip tube sender but its not accurate, the tank has baffles and a collector pot with a couple of one way valves in it. it feeds two externally mounted Bosche 044 pumps.

I plan to do 45 minute races next year where no re-fuelling is permitted and need to work out if my tank will be capable. I don't know of any calculations and cant really do any testing until feb/march.

Its a 60 litre tank, 45 minute race so have upto 1.33 litres per minute to burn. (plus the litre or so in filler neck)

car will be running 500bhp 450lb/ft or there abouts, its 3 litre turbocharged, runs 1 bar of boost and revs to 7500rpm. car weight is 1170kg full of fuel with me in it.

can someone clever with this info give me a rough idea or point me to a genius who can, as my 'it'll be fine' attitude might not pay off with this gamble.

cheers

Graham

[SimonMason]

If your getting 1.3Ltrs a minute at the moment, no it wont last 45 minutes on 60Ltr tank, no chance unless you change driving style and drop pace and revs slightly. As suggested already it doesn't sound like your picking up all your fuel anyway, so that needs looking into.

Strip the tank, foam fill it and fit an internal collector/trap (if not already there) or add additional floating lifter pumps at each side. Then fit bigger filler pipes and maybe a 2Ltr swirl pot to increase capacity. You need that baby carrying a minimum of 65Ltrs to do 45 minute races reliably in all variables on 1.3Ltrs a minute average.

[Hollowpockets]

Sorry Simon you misread that.

I said I think the car has been using just over 1 litre a minute, with a 60 litre tank and a 45 min race that gives me a possible 1.33 litres maximum to burn over 45 minutes. During a 20 minute race plus out lap and In lap I think I use 25 litres. So around 1.14litres a minute (should be close to actual)

I had FIA baffle foam in the tank last year and it did absolutely nothing to stop fuel surge, it was terrible even with a couple of baffles the gauge moved by over 1/4 tank either way, so the foam was removed and several more baffle plates were added, and a fuel collector pot with 2 take off pipes to 2 bosche 044 pumps, if I can avoid fitting extra pumps and swirl pots I'd rather not. The tank has never suffered fuel surge this year and I've finished races with less than 10 litres. My new ecu will run wideband lambda and knock sensing then will back out the power, so I'll know if it's starting to run lean.

Something else I forgot to mention, during the races this year I have also used my 'push to pass' button which bumps power up to 600bhp, to do some overtaking. I won't be able to do that in GTcup so won't use that extra 100bhp and 100lbft worth of fuel for about 10% of the race.

After some thought I think if I'm starting with a full tank and the neck brimmed I will be able to get round most tracks and have around 6-10 litres left. I can always short shift and use the torque when I've not got someone on my tail to help.

Will let you know how I get on folks.

Thanks for the advice so far though!

[woof]

can I have your push to pass button please

[itdontgo]

If you're running out of fuel you'll know about it before it conks out. I ran my single seater out of fuel in my last test intentionally and felt a misfire through a corner at the start of the lap. I got back to the pits in fourth with what was left. You should try that on a test day but do it during the last session ;o)

[Web13]

itdontgo said:

If you're running out of fuel you'll know about it before it conks out. I ran my single seater out of fuel in my last test intentionally and felt a misfire through a corner at the start of the lap. I got back to the pits in fourth with what was left. You should try that on a test day but do it during the last session ;o)

In a highly tuned turbo car its a bit risky, even a very short period of leaning out as the fuel pressure drops can lead to engine damage.

[SimonMason]

Ok on those figures I have you ending a 45 minute race with less than 10Ltrs so you should be OK on a 60Ltr tank. Foam filling a tank only ever works if you have a baffled collector in the centre of the tank to hold the fuel for the pumps. All the foam does is slow the movement down not stop it! You are only aloud one swirl pot outside the tank of a maximum of 2Ltrs so you can do no more there anyway, so sounds like your on normal the limit of capacity.

1.1/1.2Ltrs of fuel per minute is pretty amazing from a engine like that. Our Supercopa was 320bhp and does between 1 and 1.1Ltrs per minute although it does weigh nearly 1200Kgs and has the aero drag of an 18tonner.

[anonymous-user]

I have a two liter turbo, running 450BHp and car weight 638 KG and I use almost exactly 1 liter a minute, (which is 2 Km a liter, I run a big surge tank, and a baffled main tank to avoid surge problems, but still allow about 10 liter as a reserve, remember fuel for sighting, warm up, and in lap, (ok not at full power),

[itdontgo]

Web13 said:

In a highly tuned turbo car its a bit risky, even a very short period of leaning out as the fuel pressure drops can lead to engine damage.

This is true! I was running a FF1600