decking limits

[jimbob-mcgrew]

how much can you safely deck the smallblock 8v's ? (14NV in particular, if it makes any difference)

cheers :thumb:

[garyc]

I would think you could go about 20 thou pistons out the top of the block. On our autograss 1300's the pistons are 10 thou out the top of the block.

[jimbob-mcgrew]

the setup i had in mind, would leave a niagra-falls cavern in there.

i was thinking 3mm ish, is that do-able ?

[Royston]

Surely 3 mm deck would result in the pistons striking the head, or are you talking about skimming the head, seems extreme either way

A standard head gasket is @ 1.3mm thick when compressed.

The last 1.3 engine I built I planned to deck the block to get the piston crowns flush, but ended up with @ 15 thou proud, engine runs OK, Was @ 25 thou clearance before machining.

Need to allow for expansion and stretch in the conrods under load.

[jimbob-mcgrew]

the piston heads i had in mind are shorter, and would be 4.8 mm lower down in the bore.

actually... it will be more like 1.5 to 2 mm deck drop, as the 14nv pistons have a fairly big dish in the crown (3.4 mm over 70% of its surface)

also, can you trim down the head bolts to match the new height, without weakening them too

[Royston]

I understand what your doing now, I would suggest building the crank and pistons into the block and measure accurately the piston depth in the block (depth micrometer) in 4 places with each piston at TDC, you an then calculate the average across all cylinders and therefore how far to go with the block to achieve the amount of piston exposed you want, (10 to 20 thou max, I suggest)

I would hope a few other engine builders will offer guidance

[Will F]

What CR are you aiming for??

[Andy]

Dont cut headbolts ffs.use spacer washers if you really need to.you will need to make sure theyre high tensile though and not copper washers for eg lol probably obvious but some people would lol

[garyc]

why not build a normal engine rather than some weird hybrid that probably wont work?

[jimbob-mcgrew]

What CR are you aiming for??

about 10.5:1 ish would be ideal.
would need to be run on super unleaded at that.


Dont cut headbolts ffs.use spacer washers if you really need to.you will need to make sure theyre high tensile though and not copper washers for eg lol probably obvious but some people would lol

very good point.
some 5mm, solid washers is way easier, with no drama involved :)


why not build a normal engine rather than some weird hybrid that probably wont work?

probably for the best gary, but im a bit retarded most of the time, and struggle to grasp the concept of normal :)