Skoda Rally Blog

The head is the part of the engine that everyone seems to know everything about – the kind of thing that people would say “back in the day” that you’d need to get a “Stage 3 Porting Job” or similar. Not that anyone had any idea what that actually meant, and in many cases what would be a good idea either!  I’ve seen some horrendously badly-done “porting” jobs in my time, looking like they’ve been done with an angle grinder, or some kind of garden machinery.  The idea is to get more air into the engine, and that doesn’t just mean “make the holes as big as possible”, there’s a LOT more to it than that.

However, as with just about everything else on the engine, there are limits, and once more they’re prescribed by the FIA.  Many of the things that a “normal” tuner would do aren’t allowed – valve and port entry sizes have to be kept as per the paperwork, which does allow for some minimal changes to be made, but they’re exactly that – minimal.  In a case like this, every little helps (hopefully), and the head I have has been prepared to an excellent standard, and within the letter of the rules, which is a good thing.

Cylinder Head, bare and ready to build

As you can see, it’s a nice bit of work, but there are things to be done to it; the first of which is to check the compression ratio.  This is how much the air and fuel that goes into the engine is compressed, and the volume in the cylinder head is the main way of changing this; I’ve had the head machined to increase this, BUT need to check it, and to do that the valves need to be refilled, and then the cylinder head placed on a flat surface and the volume measured by putting liquid in from a burette.  The volume I was looking for was 24.6cm³, giving a compression ratio of 11.5:1, which will mean two things – firstly an increase of about 8% power with no other changes, and secondly that we’ll need to run it on good quality fuel!  However, this means fitting the valves to it, otherwise (obviously) you can’t fill the chamber up!  So, in they all went…

Cylinder Head, with valves and ready to measure

… and measurement found that it was spot on – precisely 24.6cm³, so that calculation was perfect.  Great.

Next up, fitting the manifold;  this might sound like a “bolt it on, Darren” instruction, but there is a small amount of play in the holes, meaning that alignment can be an issue, and in addition the ports in the head don’t line up exactly with the ports in the manifold; in addition the ports in the manifold are actually slightly smaller than they are allowed to be, so opening them up slightly to align them should pay benefits; again it’s only a small thing, but every little helps; I’m hoping for 100bhp from the engine, which is a 20% increase over the old one, and with the restrictions that running to International spec place on us, it will not be easy….