Decking the Block

[Anthony]

What measurement should I be looking for when decking the engine block?

I thought I'd read its a good idea to have the pistons 10thou out of the block


Is this based on anything particular?
ie: Squish
Or is it down to dynamic or static compression ratios?

[rotoflex]

I would like to be the first to suggest at this most wonderful time of the year that the procedure be undertaken with boughs of holly.

[JohnD]

And remembering the old Christmas refrain, "Caput apri de fero" (the head of iron is a pig)

John

[JohnD]

Anthony,
The height above the block is irrelevant.
What is important about decking is that every piston must rise to the same height in the bore, which may require machining of all the other pistons so that they all rise as much as the lowest, and then machining the block top, so that they all are at the desired height in the bore.

You are confusing that with obtaining 'pop-up' pistons, which further reduce the combustion chamber volume by occupting some th eof the head gasket volume and promote squish. Then, the measurement that is important is the minimum piston to valve distance, which should be - ten thou!

John

[Anthony]

Thanks John

I thought I had to get the pistons to stand out of the block by 10 thou when at TDC


My head is currently.......

Overall Height = 3.272"     (originally 3.300, giving a 0.0280" skim)
Chamber CCs = 32cc
Chamber Depth = 0.38"

Static Compression Ratio = 10.77:1


Cam is undecided as of yet



How to I measure the 10thou from Piston to Valve?
Do I use the fully open valve lift and the Piston height at TDC?

[JohnD]

Putty.
Put some on the piston crown.
Assemble the engine with a used gasket.
Turn it over.
Disassemble and cut through the impression of the valve in the putty, with a sharp knife.
Measure the clearance.

No one said that high performance engine building was easy or quick.

If your existing static CR is 10.7, you will need an octane booster if you raise it any more, by going pop-up.
No available pump fuel will stand much more than 10.5.
I'd stick to decking the block, to ensure max and even performance from all your bores.

John

[James]

JohnD wrote:

No available pump fuel will stand much more than 10.5.

Depends on which cam is used — a high performance one needs a decent CR to work — and will in fact have a lower dynamic CR.

[Anthony]

jcarruthers wrote:

Depends on which cam is used — a high performance one needs a decent CR to work — and will in fact have a lower dynamic CR.

From what I've read so far i'm thinking of aiming for ~9:1 dynamic CR