Cylinder head work

Hi guys. We know the benefits of cylinder head work. Can it give a good increase in power?

"Headwork" covers quite a wide range of work; from polishing the ports a bit, through to gas-flow work and fitting enlarged valves.

If you mean just polishing the ports yourself, then go ahead! Won't make much difference but it won't hurt either and it's a good experience to have a go yourself.

If you mean professional porting / gas flowing then it's about value for money. A well flowed head is always beneficial, but it becomes more beneficial the more power you are aiming for. Both the 16VT and 20VT can make well over 400 bhp without any headwork. However, if you are aiming for figures above 500 bhp then headwork begins to become essential.

then just a good polishing (and take 1 mm of material per side) does not make much difference in an engine of about 300-350hp??
 

doing the work yourself can be a bad idea if the meat taken out isn't the same across all 5 otherwise you will have different flow rates between the cylinders etc etc. I saw some early flow work on coupe engines a few years ago that people had paid good money for and it was shocking, i always have the heads check to what flow before fitting

Also note that good headwork will pay for itself if you're doing a fairly decent mileage in the car. When I first had mine done, my fuel consumption decreased by about 5mpg. Because I was doing 25-30k a year, the cost of the headwork was recovered in a couple of years

Something that is definitely worth doing is port-matching the exhaust ports in the head with the exhaust manifold - as standard there's a considerable step which can't be doing any good for gas flow. You can also knife-edge the collector in the manifold

However - I'f you're trying a bit of DIY porting, be extremely careful - headwork is all about flow - you'd think that opening up a port will flow more gas (be it intake or exhaust) but if you're not careful, you can create vortices (called laminar separation IIRC) through too-tight radii and you can also slow down the gas speed which can play havoc with turbine speed.

If I had my time again (and a fair bit more cash than I spent originally), I'd be giving a cylinder head to Guy Croft. He's already spent some time on a 5-pot Coupe head and of course he's done countless twin-cam four-pot heads (including Begbie's). IIRC, he had quite a few positive comments on the 20VT head, but he still found significant improvements.