Ian928

The head is finished, they had to go all the way down to the limit. In fact the reference is now 23.61mm!

This is a ex-California car probably run on water only and the result is severe corrosion in the cooling system. I have heard about this but never seen it myself! Even the steel pipes are severly corroded... Why would anyone run a new Porsche with tap water in the cooling system, even though the temperature never gets below the freezing point? Obviously you can not do this here in Norway, and when I opened my 928 engine it looked like new inside.

The compression will probably be unchanged now, and the cam timing also. The only thing that is worrying me is the reduced squish distance. Could this result in detonation starting earlier? I guess we will have to wait and see.

Thom

You should be fine.

Alan 91 C2

I know this is an old chain.

I did a quick calculation, and for .3mm shave on the head is only about .25 degree retard assuming 6" diameter on the cam wheel.

The shop milled my cylinder head to 23.65mm. I am installing a wide fire HG, and a 4 degree advance offset cam key. The loss of space is around 2cc, and may bump the compression to 8.2.

TonyG

That's all well and fine... but your shop is may not be the first shop to mill the head considering it's a 30 year old head. You need to measure the pad on the back of the head to see how much has been taken off from new.

TonyG

Alan 91 C2

Hi Tony,

The measurement is based on the Porsche guidance. The before dimension was stock at 24mm.

KevinGross

Why not measure the effect to timing by putting a dial indicator on the intake and exhaust tappets?

TonyG

Can you even get a dial gauge on the tappet?

TonyG