I did a track day yesterday and basically ran the car out of fuel 3 times and I also ran out just as I pulled the car back in the garage, it's likely a case of idiot me just not putting enough in but the mileage seems a bit high.

The 5 gallon cell was full to the brim, I did two 30 minute sessions and with about a minute to go in the second session the car starved out in a high G turn. I just made it back to my pit. It's a 3.4 mile course and I get 8-10 laps depending on traffic so that's between 54 and 60 miles. So I'm getting 12 mph tops and possibly as low as 9.5, does this sound about average. The showroom stock Miata I raced only managed 9 mpg so it's not unthinkable that it's this low.

Note this is an A15 with flat slides, 278 degree cam with .420 valve lift ported GX head 37/30 valves revving between 4800-8000 rpms making around 105-110 at the wheels.

Tom

I'm note sure on mileage but my twin 32/36 webers main fuel jets run 180's on the primarys and 220's on the secondarys at WOT. That's a lot of fuel.
The guys at the import shop had never ordered 220's and said they were surprised that they even made them for a DGV 32/36.

I use about 7 gallons (29 Lts)in a 28 min race with the A12 turbo on E85. About 50 Kms. (23laps of 2.2Km circuit)

29 liter/50 km = 4.1 mpg (US)

I'm doing a little better than sikyne with a rate of 6.1mpg with a similar but very docile A12 turbo running on E85 jungle juice compared to Simons beast.
More to the point ...who cares how much fuel we use in the race cars anyway??Got to be cheaper than sex

I seem to remember the A15 is a recent addition. The more power made, the more fuel burnt. So you might be spot on, especially as you compare it to the MX5 Miata getting about the same. The E85 fuel mentioned is an ethanol blend, so the cars run richer & get worse economy than pure petrol. Maybe you can find a bigger tank to make sure this doesn't happen. You could also go through the fuel system & check for fuel leaks. Nothing is worse than wasting fuel you really need. I think this is one of those things that seems like a problem but is just a change due to other things.

I pretty much wanted a reality check: I have 165 mains in the carbs which are not huge by any means. What I think is tripping me up is the vintage events are only 20-25 minute sessions whereas the track days are 30 minutes per session so the extra couple of laps is just enough to run the cell dry.

I'm hoping to get the car on a dyno in the next few weeks to see where it's at. I have procrastinated on installing an air fuel ratio gauge in the car for years. It's now our off season for the next 3 months, going to hit 107 F this week and won't go back below 100 till September. I'll get the A/F gauge installed over the summer.

I at least know I'm not way off, if Simon's 200 hp motor is getting 4mpg then my 105-110 whp motor getting 9 mpg sounds par for the course.

I come off turn 2 at 78 mph and 2400 ft later the car is up to 111mph, this up 9-10 mph from when I ran the A12 and was getting roughly 15mpg.

Tom

Engine makes maximum power somewhere around 13:1 to 12:1. You may find that leaning it out to 13:1 gives the same HP while using 8% less fuel

I was going to suggest a run on the dyno, just to check mixtures. I can't remember what jets I had in my A15, but I'm sure it was smaller than 165. You probably have big air corrections too, which gives the correct fuel to air ratio, but gives more fuel than the engine can burn. I'll try & get the carbs out of the shed for a look, but it's cold & wet here in Sydney, after a warm dry autumn(fall).

Yes, there are 200 main air jets and I think 90 slow air jets. I experimented with the smaller air corrections but as described on the Factory Pro jetting guide for FCR carbs the just seemed to worked better with the larger air jets.

Tom