EW12J4 with EW10J4S head project. Compresion ratio question

[ammm84 0]

Hi,

 

I'm building a trackday 206 GTI. Here is the idea (a lot os parts bought):

-EW12J4 from a Citroen C8, without balance shafts

-EW10J4S Head

-XU10J4RS (RFS) cams, or 2 units of EW10J4S exhaust cams, since i'm not going to use the vvt, due to my car ECU cannot manage it

 

I have been measuring the EW10J4S head chamber, and I get 48cc. I have measured also the piston spacing, and this gives me a (poor) CR of 10,3:1 using the stock 0,8mm head gasket. I can't find any other thickness gasket, neither aftermarket high compresion ratio pistons (and those probably will be expensive), so I think the only way to get a better CR will be to grind the cylinder head 0,8mm, wich will give me a CR of 11,1:1 (more or less, due to my calculations).

 

Any advice to get the correct CR before machining the head?

[petert 586]

That seems surprisingly thin for a standard head gasket.
 

How far down the bore is the piston at TDC? I'd deck the block before anything else, to at least get zero deck height.

[ammm84 0]

Head gasket thickness is 0.8mm according to the workshop manual (see attached image, and sorry about the language, but can't be changed easily). It could be wrong, but can't find any other manufacturer thickness for this 02090H Citroen gasket.

 

The piston on the TDC has almost 0,95mm of clearance to the top of the block

 

Edited January 3, 2021 by ammm84

[welshpug 1,657]

I'd be inclined to use the ew12 head, the ports aren't much different to the ew10 and you know the compression is going to be 10.8.

 

what is the chamber size of the ew12?   48cc seems rather large, though I do recall the valve reliefs being tiny/nonexistent and pistons come up to deck possibly?  with very little dish,  quite unlike the 2.0 Mi with its flat top piston and cavernous valve reliefs 

Edited January 3, 2021 by welshpug

[ammm84 0]

Yesterday I  measured the EW10J4S chamber again (47cc), and also measured the EW12 (47,5cc). I can't find where do I lose 1cc last day. 

 

If I assume that the main difference in the CR is due the height of the piston, and its shape, with the OEM head gasket (0,8mm) and taking in account the difference of 0,5cc, machining 0,2mm the head will make a CR of 11,06.

 

@welshpug The EW10J4S ports are a bit bigger than EW12, but the bigger cam followers are the main reason of the election, for a future choice of aftermarket camshafts.

Attached you will find images of the piston an head chambers (chambers are almost identical, invisible difference to the naked eye)

[Gaz7612 1]

How are you getting on with the build? 
Have you had the bottom end balanced now? 

[ammm84 0]

No major advances. The project goes a bit slow due to the big workload . I sent the crankshaft to the workshop to be balanced, but I haven't received it yet. The EW10J4S head has been done, and the block is clean, and ready to start the assembly