WTAC Porsche RP968 Powertrain Now Twin Turbo!
With the World Time Attack Challenge Sydney on 13th -14th October 2017 coming up fast, the bag of tricks on the Porsche RP968 is getting deeper.
The current engine runs a large single Borg Warner turbo charger, the biggest of that series which tops out around 900 horsepower. This year we are going to be running a new configuration with a power increase up to 1200/1300 horsepower, running two of the smaller Borg Warner turbo chargers which is the same turbo teams run on Indie cars. They have an aluminium core and they are actually lighter than the big single. In running the 2 smaller turbo chargers and the different exhaust system, we actually save 7 kg in turbos alone and a further 7 kg running the exhaust thru the door. We also get another 300/400 horsepower capability. The new engine is larger in capacity up to 4 litres from 3.1 litres. We are planning to have either configuration available to us at the event.
In the steel work in the exhaust manifolds, it’s all equal length and very specific with regards to sizing, the material selection is very specific because it runs very hot so you have to make sure the welding is nice and it’s all purged properly so you don’t end up with cracks. You have to be very careful when building the system, as it can break apart. Don did a great job with building it.
The exhaust system exits earlier out through the side of the door, so we are shortening the exhaust system which also makes it lighter and it saves a bit of heat load from under the car as we are running carbon torque tube and carbon drive shaft. The carbon floor was quite close to the exhaust before so that was all compromising the carbon work. It’s a general rethink and the new turbos also run internal waste gates so we save weight there also. With 2 turbos that are smaller you have less inertia with regard to how quickly they wind up, so you have less lag. You put your foot down and something happens quicker because the turbines are small plus the Borg Warner turbines run titanium exhaust wheels on them so it makes them lighter again.
We’re making two complete engines with a billet block, billet head, the whole cradle for the bottom of all the bearing caps and sump are all one-piece integrated. The crankshafts are being made, aluminium con rods, aluminium pistons, camshafts and valves, everything is custom made, there’s nothing off the shelf. We are also making it so we can change con rods at the track, we can pull the cylinder off quickly and there’s cover plates underneath the sump. We can pull the individual cover plates off and access the con rods so we don’t have to pull the sump off to get the pistons and con rods out the top, so over night we can do con rod changes because of the aluminium con rods we are using. Steel isn’t strong enough, so you need to run aluminium but then you have a life issue so maybe 300/400 km is maximum life of the con rod. It’s really pushing boundaries.
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