Despite space for a more conventional V engine, Porsche opted to use a 3.6-litre VR6 for the Cayenne
Engines built from a recipe of experimental out-there engineering and heaps of personality usually result in flaky, unreliable units. But in the case of the VR6, it seems there have been no sacrifices.‘ They’ re not a weak engine.’ Tom Walker of Retro Resus, a performance car and engine specialist who tunes VR6s, tells me.‘ You have to keep on top of timing chains. In the early days, there were a lot of stories of the Mk4 Golf R32 timing chains failing at 40,000 miles. I’ ve personally never seen one at that sort of mileage fail, but I have seen failures.
‘ They do give you warnings, normally. Rattly start-ups, noises from the chains, they’ ll put the engine management light on because the timing is too far out. The chains physically stretch, and then the tensioners need to overextend to keep up the tension. But that’ s just part of maintenance, though.’
Heat is something else that needs to be managed, but not until you start modifying them. And, for Tom, there’ s only one logical way to get more power from a VR6.‘ In naturally-aspirated form, I’ m not a huge fan. When you look at horsepower per litre, they’ re not amazing. Unless you build a full race spec not-for-the-road engine, very rarely are you seeing 300hp. But stick a turbo on them and they come to life. They are fantastic.
‘ Supercharging is an option, but I’ ve never been a huge fan of it. The best way for these is turbocharging and an aftermarket ECU.’ And the results are quite astonishing.
‘ If you want to go to 600hp, around that, you can get away with a half build. Put a set of rods and pistons in it, what we call“ drop-ins”. You can even do it with the bottom end still in the car. That’ s 650hp, no problem at all. And you can run a standard valve train.
‘ But if you’ re going to use it on track, we’ d recommend doing exhaust valves and springs. They do tend to run quite high exhaust gas temperatures, so you would run an Inconel exhaust valve to try to cope with the extra temperature. And then uprating the valve springs.
Depending on the boost that you’ re running, you can get valve float. The standard spring is not designed for forced induction, as it’ s not designed to have pressure on the back of the intake valve.’
While all VR6s are durable enough, there are more desirable factory parts.‘ Some of the Mk4 R32s, and some Audi TTs, have a forged crank in them from the factory. If you’ re doing an R32 turbo build from scratch, you’ d choose to go and get one of those cranks if you’ ve got a Mk5 engine. The Mk5 isn’ t a forged crankshaft, but they will still do circa 600hp, not a problem.’ They’ re a highquality, well-finished engine, that’ s for sure.‘ They’ re pretty well balanced out of the factory too, they’ re pretty good compared to a lot of the other VAG engines.’
A fine balance doesn’ t necessarily make them rev happy engines.‘ I think most people are setting the rev limiter to about 7200rpm. If you’ re putting cams in them, you’ ll go a little bit further. But, if you go“ R30”, which is a 2.8 crankshaft with bigger pistons and different rods – so short stroke it with big cylinders so that you’ ve got a much better rod angle and bore-to-stroke ratio – you can rev them better. With a solid lifter conversion, a really lairy cam in it, you can rev to 9000rpm quite happily. We did an R30 build for Mk4 R32, and we ran that at 1250hp.’
So proud of the VR6, VW couldn’ t help but put it into everything. Including its van …
26 The Engine Rebuilder Issue 05