Mark Straker writes:
After 12 months spent rebuilding the Darrian after a minor ‘off’, it was decided to compete in a couple of Sprints, before returning to rallying in Ireland.
First off was FDMC’s Rushmoor Sprint, with some very well organised weather by the club!
Running in ‘rally spec’ with the 34mm turbo restrictor fitted, the Darrian set fastest time on every timed run, ultimately setting FTD by nearly 2 seconds.
However, we had a few electronic niggles during the day, such as the radiator fans not working correctly, several instances when engine power was totally lost and then immediately reinstated, and also possibly a problem with engine boost.
So it was decided to enter the Abingdon Sprint, to see whether these issues had been resolved between the two Sprints.
The engine power loss turned out to be a faulty wheel speed sensor, causing one wheel speed reading to spike, resulting in the ECU seeing an instantaneous front/rear wheel speed difference of 160mph. This caused a massive traction control event, hence cutting the engine power very aggressively. This issue was easily resolved.
The radiator fans issue was present at the Rushmoor Sprint, but not at home either before or after the event – a strange one, so it was decided to attend Abingdon without any further investigative work.
The boost issue was initially thought to be related to a sluggish electronic wastegate, but with three of these having been tested in total, and with all three providing the same boost readings, this was then ruled out as being the cause.
After a lot of head scratching, two conclusions were drawn:
- |The further beyond 5,250rpm that the engine is revved, the more the ECU backs off the boost, to prevent the turbo from overspeeding – this is a feature of running the restrictor ahead of the turbo. What can happen is that if the air through the restrictor goes supersonic, then the turbo will spin out of control and disintegrate, so the ECU has to reduce the boost from a certain engine speed (approx. 5,250rpm), in order to prevent this from happening.
- If running a high target boost value of say 1.9bar, then the step up from perhaps 1.2bar (with the engine revved to maybe 6,000rpm) to 1.9bar is quite large, and sudden, with the restrictor preventing the turbo from drawing in enough air quickly enough to enable it to achieve the target boost. This turns out to simply be a feature of having to run the restrictor, and revving the engine too high, combined with a high target boost setpoint, resulting in significant fluctuations in manifold pressure.
So, onto Abingdon, and we were met with a dry day to start with, with slicks being used on both the practice and the first timed run.
The rear tyres were not in the best condition, with poor traction and poor lateral grip, so we expected to have sacrificed a few seconds as a result. However, we were surprised to see that after the first timed run we were sitting 8th Overall (from around 100 starters).
But then the rain came – and with it an opportunity to test various different boost, launch, traction and anti lag settings, to try and optimise the setup in wet conditions.
At this stage we swapped to Michelin MW1 tyres, which turned out to be excellent.
With a less aggressive anti lag setting, and with a lower target boost setting, the car was superb to drive, with the engine feeling very strong, with our wet fastest time only being 4 seconds slower than our dry timed run. Others had been much slower in the wet (or chosen not to run at all), and looking at the wet run times alone, we set fastest time overall on both.
The ability to vary launch, traction, boost and anti lag settings via dials within the car proved to be very useful, and apart from needing to find more suitable rear tyres for the dry, the car and engine now appear ready for a sterner challenge.
In terms of the issues encountered at Rushmoor, the radiator fans behaved perfectly all day at Abingdon (not sure what was going on there), and the wheel speed sensors worked perfectly, so we had no loss of engine power.
And in terms of the boost issue, as an experiment it was decided to run a lower target boost setting of 1.5bar, and to change gear at 5,500rpm in all gears. This resulted in hugely improved boost delivery, with an absolutely flat line of 1.5bar being achieved right through from corner exit in 2nd gear, to flat out in top gear, something we have never seen when revving the engine higher and when running a higher target boost setting.
It feels like this lower boost / lower revs combination provides more stable boost, but we shall continue to investigate whether a higher boost level may still be beneficial.
We were running with the 1.6L EcoBoost engine in rally spec at both Sprints, with the 34mm restrictor mounted ahead of the turbo, providing around 325bhp & 510Nm.
Straker Performance Engineering Ltd. was established to develop the Ford 1.6L EcoBoost engine for stage rallying, but we can in fact supply this engine, or kits of parts, for unrestricted road, sprint, hillclimb, or race use (currently providing around 400bhp in this spec).
Please find us on Facebook if you would like more information on this engine, which is proving to be on a par with the factory R5/Rally2 engines, and also reliable, with high mileages between planned rebuilds.
Posted by Geoff Wade, FDMC Media
