F

flow

New Member

• Feb 11, 2007

• #1

Hello all. I have a S3 904xxxxxxx engine that should have a 7:1 compression head. It has been reco'ed and some one has put extractors on it so I'm wondering if they didn't put an 8:1 head on it. The only numbers on it are 568750 and 12G. Is this a 7:1 or 8:1 head? Or can I get a rough idea from the results of a compression test?

Thanks in advance.

 

M

monkey wrench

New Member

• Feb 16, 2007

• #2

do not quote me on this but i was told that the difference between these are 7:1 is the old leaded head and 8:1 the unleaded, the diff being 8:1 harder valve seats to cope with hotter running fuel ( unleaded ).

 

A

AJM610A

New Member

• Feb 16, 2007

• #3

I have heard that the 8:1 compression heads hav a square cast on the side of the head (manifold side)

 

A

AJM610A

New Member

• Feb 16, 2007

• #4

Or another way look at what plugs are fitted..... THe plugs are different depending on the head....

These are the plugs for a series II but i believe should be the same for a III

7:1 heads have Champion N8, NGK B4ES, Bosch W10C or Denso W14E
8:1 heads have Champion N9Y, NGK BP5ES / BP6ES, Bosch W7DC / W8DC or Denso W20EPU / W16EPU

 

Slippery

New Member

• Feb 16, 2007

• #5

You could phone padds and ask them for a service kit, and they will talk you through idenifying you engin.

 

F

flow

New Member

• Feb 19, 2007

• #6

Thanks every one. I found a 7 on the machined flat in the middle of the left hand side of the head. Also the compresion tests point towards a 7:1. I just did a 400 mile trip with a 1.5 tonne boat in toe and got 15.5 mpg. Must be the 750 tires, extractors, free flow exhaust, and airfilter doing some good. If I were to plane the head how much imporvement on that do you think I would get?

Can you get any more than 8:1 out of a 7:1 head?