Question for all you head guru's Options

[rtalich]

Can anyone tell me if these heads have been modified and/or why they have a little 'step' bored into them? The first picture shows a 'normal' head. Notice the flat surface shown circled.


These next two pictures are the heads in question. Have these been machined/modified in any way? If so, why?




Thanks,
Rob

[HAM Inc]

Rob the head with the step has been flycut. Stepcuts were never std with any O.E. T4.
I am a big fan of the step cut. The biggest reason being that more material is left in the head in the weakest areas of the chambers: 1) beneath the ex. studs 2) on the side plug heads (1.7 and especially 1.8's) the area closest to the spark plug. By cutting a step you increase compression with out removing as much material from the head. The head seal seems to hold up better over time with a step as well.
If you have a .75mm (.030") step in the head you need a .25mm (.010") deck ht in the cylinder, for a total deck ht of 1mm. The deck ht. volume in the cylinder and the head can be calculated. A 1mm total deck ht in a 94mm bore will be 6.94cc's a 96mm bore will be 7.24cc's.
The heads in the pictures have not been cut too deep as the top shoulder has not been cut to prevent cylinder fin interference. The heads will need new seats and some crack repair to be made reliable.

I do offer a 10% labor discount to all 914 club members.