Deck height, compression ratio, and valve relief flat top pistons, In a 2.0 Options

[emerygt350]

Ok, my question of the day:
Put my new 96mm pistons and cylinders on and measured deck height, .033 all the way around. Let's say .032 to be conservative.

I will not be running head gaskets.
The calculator gives me
8.8 CR at .033
8.6 CR at .043
8.4 CR at .053


The pistons have a valve relief (pretty large) cut. I am shooting for 8.4 CR.

Heads are in the shop so I can't check the CC yet.

Everything I read says .04 - .06 for deck height. With the valve relief do I need to worry about going lower? If I had dishes would you measure from the edge of the piston or the dish?

[technicalninja]

I believe you are leaving 5-10 hp on the table with a quench distance that high.

.040 is what I use for customer engines where I'm being a bit more conservative.

Cast hyper from a reputable company on decent H-beams can often work at significantly lower distances.

One builder I know runs hyper-eutectic "claimer" SBCs at .029 without trouble.

Yes, I know this is not a T4 and is probably more dimensionally stable than a VW boxer but .029 is too tight in my book.

The tighter the quench the more detonation resistant the engine becomes.
It can run fuel with less anti-knock resistance and commonly requires 5-7 degrees less total timing to make MBT happen.
Compression increases slightly.
The piston crown and combustion chamber stay cleaner as well.
The only drawback IMO is you have to be far more careful during assembly and really nail the deck height measurements.
It's less forgiving for trash running through the engine as well but if you have foreign objects entering your intake track you deserve what happens...

The "quench" argument is a moot point if you're running a fuel that has extremely high detonation resistance. For a methanol or nitromethane application this distance is far less important.

For folks running pump gas it is the single most important "blue-print" distance to get right IMO.

This measurement for me is "the smallest clearance possible that has the ability to turn at 110% redline without the piston crown touching the head."

If this ends up placing the piston crown too close to the opening/closing valves then the valve pocket in the crown needs to be deepened/modified.

It is possible to build a 10.5-1 flat top Datsun Z motor that can run regular with less chance of detonation than the stock 8.3-1 motor has.
It also requires a much larger duration cam profile (has to with the compression) and makes 40% more power than the stocker.

I believe the quench phenomena starts about .065" and only gets better right up to the point of contact.
At which point it all comes apart.

I've built multiple engines (not T4s) with a quench of .035-.040 and had no failures.
I'm also beyond anal regarding engine clearances...

One thing to remember. Changing deck height on a T4 is EASY!!!
Doing it on almost anything else requires adjusting rod length, offset grinding the rod journals, decking the block: significant machine shop processes and if you go too low...
It sometimes requires a new/different block.

Being able to place shims between the cylinders and the block is a very welcome change for me.
Gives me options I've never had before...