We trundled off to Barkston Heath airfield to test the latest changes to the car last week. The short version is things worked really well, the timing change and the addition of an anti-lag setup both really helped improve the drivability. The performance still really shocks me, data logs say 0-100mph is <6sec and it really felt like it this time. We ran some pretty poor tyres and at anything above half boost it was a big handful, spinning the rears all the way down the straights.

Previously you could see on the data logs two problems coming out of a slow corner, both cases you would say are lag. The first was a delay from throttle opening to really seeing any boost appear. This I would estimate as 1/3 sec and second was the rate of boost increase was poor, perhaps taking a further 1 to 1.5 secs to build up, so worse case 2 secs to reach full torque. That sounds a lot but of course the car is still accelerating in that 2 seconds, it’s just not accelerating as quick as you know it can and want it to.

With just the timing change on everything was a bit slicker, I would estimate worst case fell to more like 1 second to reach full torque. Better, but not enough for our needs. With the anti-lag turned on things felt much better when it worked. The logs show cases of instant boost, i.e. torque available as soon as you press the loud pedal. This was such a great feeling given all the struggles we have had with the engine setup, finally a properly responsive engine package.

The problem with the anti-lag was that it didn’t always work, some post analysis of the logs showed an interesting behaviour, when the anti-lag should be operating the rpm would die like the engine was going to stall. This would trigger the anti-lag to turn off and the revs would instantly rise, sometimes high enough to start the cycle all over again sometimes not.

The theory I have about this is that I programmed in too much timing retard into the anti-lag settings. The system I am using involves an electronically controlled throttle blipper and custom fuel and ignition maps. When the anti-lag is active the throttle is effectively opened a small amount, say 10% by the blipper to let air into the engine. This would normally cause the car to surge forward so at the same time the ignition is retarded very significantly, in this case to 25deg after top dead center.

With these setting the combustion should not really be pushing the piston down much but more chasing it, and so the engine makes less power. The energy in the combustion gases actually exits more via the exhaust valve port and so it is used to drive the turbo and not the engine. So with too much retard I suspect there is not enough energy being used to drive the piston and so the engine rpm goes into free fall. The solution of course should be simple, use less retard so the revs don’t drop off a cliff when anti-lag is on. Something to test on the next outing.

We did test a few other changes, notably paddle gear changes, but it was getting close to an effective anti-lag setup that I was most happy with. Without that I don’t think we would have looked at running this car this year.

The long term concern here is going to be burning the turbo out or the exhaust valves, they don’t particular like anti-lag setups. I am trying to mitigate that by only running a very mild system where we don’t add an extra fuel to really heat things up. That felt quite nice to drive on, frankly full power on the exit of a slow corner is not something I want to experience, that’s for the straights only.

The turbo was/is already showing signs it needs a re-build via blue smoke, maybe I will need to take that on before the competition season starts to make sure we in the best possible position to enjoy the car. Next & last testing session is at the end of the month so time is running out to get this spot on.

Update: I have since discovered that during some re-wiring the throttle blipper was disconnected. This would have been having a big effect on how the anti-lag setup was working, I thought it was rather quiet in operation from what I was expecting after testing the garage. Also spotted a interesting article on how an anti-lag like setup is being used on F1 cars to “blow diffusers”, certainly worth a read.

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