Gti Cylinder Head Original Thickness

[mattbenselin 0]

Hi all,

 

I have just sent my head off to Stanwoods in Bawtry to have it skimmed, 3 angle valve seats, new cam shimme in etc.

 

BUT looking over the engine at home have discovered that it is a DKZ block rather than D6B, this was confirmed when I looked at the standard camshaft from that engine which was identified as DKZ also.

 

Now I know this means a lower CR of 9.2:1 (D6B 9.6:1) due to deeper dished pistons. The head has been rebuilt and skimmed before but unfortunately I don't have time to measure everything and cannot be sure its all DKZ and not a mix, but assuming it is all standard then I believe a skim on the head of 1-1.2mm should bring CR up to about 10:1 or thereabouts.

Here is a pic of the DKZ block and pistons, can anyone confirm they the pistons are definitely DKZ?

 

My question is does anyone know the original thickness/size of the head before it had ever been skimmed? For example from the camshaft centre line to gasket face. From this measurement I could then work out how much has been skimmed off before. Do the piston crowns come to the top of the liners?

 

Thanks any help would be very appreciated,

 

Matt

[DamirGTI 342]

Hard to tell from the picture really even if you place a DKZ and D6B piston next to each other you'll hardly notice the difference as the DKZ pistons (dishes) are just a touch deeper than D6B ones so you'll need to measure the dish volume in order to rule this out ..

 

Damir

[mattbenselin 0]

Think I've sorted it now...

 

...spoke to Neil over at DES Developments and he has informed me that the original depth of the combustion chamber from the gasket face was 7.5mm. Using some clever equations we worked out that if you take 1mm off the head face the CR would rise to 10.55:1. Now I did explain that I have a DKZ short engine but I think he did the calculation for a D6B. So a raise for a D6B to 10.55:1 would equate to a raise for a DKZ to 10.15:1. Does this sound right?

 

Neil said the most you should go for using standard pistons etc. should be 10.55:1 so should I take some more off to reach that? Or stick with 10.15:1. Would there be a measurable change in performance?

 

Cheers

[welshpug 1,657]

I wouldn't take it too far, as the cam timing is taken further away from its standard setting the more you skim the head.

 

(That's if you don't fit a thicker gasket to compensate, which isn't the aim here)

[DamirGTI 342]

Neil said the most you should go for using standard pistons etc. should be 10.55:1 so should I take some more off to reach that? Or stick with 10.15:1. Would there be a measurable change in performance?

 

Cheers

 

Well , i'm on 11.1 CR with std. pistons without any problems so far so i guess it's about how you tune up the engine afterwards

 

And yes , i agree with welshpug regarding this skimming stuff .. i'm not a fan of heavy head skim cos while skimming the head you're retarding the cam timing as well , cheap and effective way to up the CR on D6B or DKZ engine is to fit DFZ pistons (from an 1.9 CTi engine ..) ..

 

Damir

Edited November 25, 2008 by DamirGTI

[welshpug 1,657]

Not a problem if you fit a vernier pulley however

[mattbenselin 0]

Well the head will be running Piper BP285 and a Kent vernier so should be able to sort the timing out fine. I don't have the time or the arsed'ness to change pistons so skimming the head seemed the easiest and most practical option.

 

So all sounds good for the go then...?