In Reply to: Re: But what I've never understood is....... posted by Roops on August 31, 2001 at 03:21:21:
On the S14 they are pretty close. The head itself is very good, and the exhaust and intake ports are also very close. However, you will find that once you start to run big exhaust manifolds or increase your throttle body sizes there will be some big steps that need attention. Obviously the more metal you remove the more marginal reliability comes, especially when you couple it with high compression and lots of heat, hence the reason manufacturers tend to be quite conservative.
....why don't the engine manufacturers make the ports the right size in the first place? Or are we talking about fractions of a thousandth of a millimetre? (ie outside normal manufacturing tolerances?) Having said that you'd have thought on an engine like the S14 they'd have spent the time to get them accurately matched?
The terms "flowed head", "porting and polishing" all relate to cylinder head modifications. Very basically, tuning attempts to allow and engine to flow more air (that's why bigger capacity engines tend to make more power than smaller engines). Gas flowing (flowed head) means that any restrictions in the cyclinder head are machined away to allow more air to flow through. "Ported" relates to the intake and exhaust ports, these are usually matched to the internal dimensions of the intake and exhaust manifold. Again this allows air to flow better on the way and exhaust gases on the way out. "Polished" is a term and technique that has died away a bit. It was thought that by having shiny ports and head the air flow would be accelerated thereby allowing better air flow. It has since been deemend that fuel and air mix better when the surfaces they are passing over are not totally smooth.
That's about it.
Additionally, what is a flown head?