The 3.2 Carrera Engine Rebuild: Part One
The thing about Porsches is that buying one tends to be the beginning of a long and happy relationship. Something more meaningful than you’d experience with a more mundane car.
The thing about motors is that they harvest the power of explosions to convince our rear wheels to push us about. And despite the fact that Porsche has one of the best service reputations in the industry, the parts that spend their days exploding and moving about frenetically will eventually wear themselves out and require some love.
So what do you do when they do?
As sad as you may feel when your beloved motor starts to age, it’s actually quite an exciting time; like planning out the next phase of life with your new love. What new go-faster bits do you want? Do you want more capacity? Performance cams? Lighter internals? Better breathing? Let your imagination run wild and you’ll build a pretty wild motor.
This motor is an excellent example of typical 3.2 Carrera engine wear and what can be done when it comes time to rebuild. We’re going to follow its progress over the coming weeks as it makes its way through a rebuild and into our 911 SC Group 4 replica project.
The engine has been stripped down to the crank and will receive anything new it requires. This will include special cams, performance valve springs, a displacement increase from 3.2 to 3.4 litres, extrude honed manifolds, 3mm + increase in throttle body size and custom Motronic mapping to bring it all together. To help it all breath we’ll be fitting a new bespoke exhaust system.
To kick things off we’ve had the barrels bored out from 95mm to 98mm and re-plated.
This normally sets the thought process in motion about using twin or single ignition as 3.4 litres is often regarded (more so in the USA) as the tipping point to go to twin plug. The reasoning is as follows; when you go to a larger combustion chamber, the spark has a greater area to ignite, so single ignition (1 spark plug) may not entirely ignite the air/fuel mixture. This is why the factory used twin ignition (2 spark plugs) in air-cooled engines larger than 3.6 litres.
So, back to our comment about the USA. In the US, fuel can be of varying quality and they often struggle to obtain a true 98RON fuel. This is why Americans like to use twin spark with larger engines that are running anything above 10:1 compression ratio. It lessens the risk of detonation (bad) if you get a poor-quality batch of fuel.
In Australia, our fuels tend to be of much higher quality than the US and the consensus here and in the UK is that you can safely run higher compression ratios of 10.3 – 10.5 to 1 without twin spark ignition in a 3.4 litre engine, provided that you know what you are doing.
This is where our experience in building many, many, race engines comes in very handy. For this 3.4 litre engine we will be using a piston set of our own special design which allows a very even burn across the whole combustion chamber, hence being perfectly suited to single plug ignition.
Stay tuned for more updates as we put this beauty together.