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Workshop talk with Richard den Brinker – RP968, the Champion of WTAC 2018.


Owned by Rod Pobestek, Driven by Barton Mawer

I think within 6 months of starting this project, we had our sights set on this car you see here, it has just taken us a couple of goes to get here.

Overall this is the second iteration of the car, I’ll run through the changes we have made over the years to get here. There has been two complete fronts and rear wing configurations while the under tray and the diffuser have stayed the same. Mechanically we have gone from the standard/modified 968 engine to a completely billet unit, gone from a standard torque tube which connects the engine to the gearbox, to a carbon torque tube and carbon drive shaft internally in the torque tube. We’ve tried multiple turbo setups and we have changed ECUs, from Motec to Emtron.

This is the car we wanted to run last year but we simply didn’t have time on our side, we had the billet engine in hand but we had some technical issues that we couldn’t solve in time to get it on the track, so we ran the old engine. The new       carbon torque tube was also in but we had a problem with that as well. The current brakes we installed (ceramic) and the bodywork was as you see it here.

This year’s car is basically last year’s car, refined.

What stopped us last year was a steel interface driveshaft that connects the carbon unit to the engine, inside the torque tube, was sheering off. The problem with that is, the torque tube is very hard to get out of the car – it’s ten hours work to change it, and we didn’t have limitless time or spares. We broke the steel interface on the Carbon shaft first and then we went to the standard torque tube with the standard 968 internal shaft and unsurprisingly broke that as well.

The old (non billet) engine was performing amicably last year, we were running around 700kw at the engine. When it was decided that we could not get the billet unit ready for last year’s event, we only had a day to put the old engine in and rebuild it. So it was a case of, pull it apart and put new bearings in it and put it back together – a rattle gun rebuild if you will – but it ended up being the drive shaft that let us down at the track.

So we made a new steel interface, and remounted the gearbox this year and we got the ‘Thor’ engine going, the main issue was oil pressure, it was usable but we weren’t happy that we were going to be safe. We tightened bearing clearances up and changed the oil pump ratios and solved the oil pressure problem, we simply didn’t have that little amount of time last year to solve that issue. The essence of this car is constant problem solving. Every part of it car is pushed to the edge of its tolerance – so when there is progression in one area, that progress has an effect – nearly everywhere.

This year we ended up running about 1000kW at the engine in its higher boost mode. You have to quantify that figure, in that you are not running 1000kW all the time, you are running maybe 600kW in 1st& 2nd gear, 700kW in 3rd etc. As you go up the gears you are increasing boost and increasing power, because it just hasn’t got traction to unload 1000kW in second gear. Until you get up to any decent speed with the wings working, the car hasn’t got enough down force to allow the engine to put the power to the ground. So its not until the top gears that you can utilise the maximum amount of power. We could (and will) wind it up further but it would only be useful in 5thand 6th gear.

We were surprised that we had that much power on the track, as we didn’t have that figure on the PR Technology dyno. It is due to the duct at the front of the car, force feeding the air cleaner, which is providing a few pounds of pressure pre turbo, which is free power in essence.

The Billet Thor engine was really good in most regards on its maiden WTAC voyage. Though it didn’t escape unscathed – right now I think we have a bent valve. Which stopped us running the last session and shoot out, and that can happen for a variety of reasons but one of the big problems is on these cars when you do a sequential change or an air-shift change with the paddle shifts on the wheel, you commonly get a back fire, the back fire is caused because the inlet manifold is full of fuel and the exhaust is red hot so if any extra fuel goes into the exhaust system, you get an explosion, the pressure will go down the pipes and will hold the exhaust valves open when they are not meant to be open and there is basically nothing you can do (if it back fires) to stop the popping of exhaust valves and if a piston is anywhere near them you bend a valve. With more testing and programing, you can refine the shifts and work to make it better, it could also be a broken valve spring, which could allow the valve to drop down and bend. At the time or writing this, we haven’t pulled it apart yet to confirm.

At the 2018 World Time Attack Challenge event we ran seven of the nine sessions and it was Saturday morning that we achieved the best time. Traditionally the best track conditions happen on Saturday morning of the event. Friday you get some track time, you learn the car a bit more, you get some rubber down on the track and then Saturday morning, being cool and these cars love cool temperatures as they have very soft tyres – the softest road tyre really that you can have – R spec compound. And every degree of track temperature is critical.

We have a single turbo currently, on this billet 4 Litre four cylinder, we have had a twin turbo set up on here and in a way we feel like we are pioneering a little in that this is a very large four cylinder engine and on paper the single and the twin turbo set up have the same power, but in reality you have a 1 litre piston for each of these cylinders and every time it fires, gasses going into the smaller diameter twin turbo set up, just doesn’t seem to be big enough to accommodate the flow. It comes on boost wonderful and does everything really nice with the twin turbo, it just didn’t have the top end, and we were about 100kW down with the twin turbo set up. So once again in a time critical situation, in the week before Time Attack we decided to go with the single turbo set up and remake the whole exhaust system and intake system, which is why we only had heat shielding with tape rather than proper Inconel heat shielding.

There are no commercially available parts on the engine now, so the crank, head, cams, valves and flywheel are all custom made. The 986 engine is tilted in the car the same as this, but on a 968 the inlet manifold would be on the left hand side of the car and the exhaust would run under the engine to the turbo, and then the inlet manifold is on top.  So we turned the head around to make a cold and a hot side, in the engine bay, which really helps us from a packaging point of view. The hot side is so hot that you could assume that it is on fire the whole time, so there is no point having an inlet manifold on top of that. Plus the cold and the hot side make for very short pipe work. From the turbo charger to the intercooler it is only a couple of hands away and it is the same on the other side making the total pipe work about a metre long.

We stiffened up the mounts to the gearbox, to take any excess load off the carbon torque tube, it has enough load and force on it as it is without the gearbox leaning on it.

The throttle bodies here are electronically controlled, so there is no conventional wire to operate them, that task is done electronically. We were having problems with them at Time Attack in testing and it wasn’t until Friday night that we decided to change that totally. By replacing them with a Bosch motorsport unit, I came back to the workshop and changed all the mounts and the team at the track rewired the car and Matthew had to reprogram the car to work with the new unit, all on Friday night. It was quite a risk; you don’t need much to go wrong for it not to work. We took the risk and we were back in business on Saturday morning, a real credit to all involved.

The problem was the amount of air running pushing past, the original throttle body motors couldn’t open the throttle anymore, if you closed it for a gear shift it the throttle would slowly creep open because the motor that runs it wasn’t up to the task.

The aero on RP968 this year is mainly the same, but with the addition of wheel plates on the inside face of the wheel. There is a significant amount of wheel wash which, it turns out was preventing us from achieving the modelled down force in Sammy from DAS Aero Solutions initial predictions. With the addition of the plates this year, we gained 10% down force on last year! Or put another way we stopped loosing it. And once again we had them last year and didn’t have the time to fit and test them.

So this year is a culmination of all the parts and ideas we had been working on – all implemented on the car. It was a fantastic moment when Bart pulled into pit lane having achieved the record World Time Attack Challenge 2018 time of 1:19:8250 in the Porsche #RP968.

A note from the Owner Rod Pobestek:Wow it’s been a long journey, the ‘blue car’ went back to the shop in April 2014 but the actual build of the physical RP968 didn’t start until March the following year, it has always been a difficult thing, oh so rarely does it give! This year has been particularly difficult with reduced resources, but most of the groundwork was in place from last year, but up until Friday morning we had yet to run a full lap with everything functioning correctly, but the guys at PRTech Racing kept going and everything came together to give us a chance to show that this car will go. I think over the years everyone at PR Technology has worked on RP968 but I would particularly like to express my gratitude to Richard den Brinker, Matt, Ben, Mitch, and Bowie, you have all just had a great attitude to the whole project, and Richard especially has been incredible at dealing with everything that never seems to stop happening. Dejan at TT Suspensionhas been great, the active dampers we put in last year have been a huge assistance in coping with the demands of the downforce that Sam from Dynamic Aero Solutions has produced. This year was the first time for the Thor engine from Elmer Racing, which has added so much to this whole project it’s and great to see and hear it in the car. Of course we would never have got the 1:19.8 laptime without Barton Mawer, it’s been a pleasure and you are a great member of the team on and off the track.

See you next year.

_DNW2939 _DNW2962 _DNW3004 _DNW3010 _DNW3019 _DNW3029 _DNW3031 _DNW3050 _DNW3054

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  1. What a great story guys wish u well in the future.

    - by Paul in August, 2019