Compression Ratio by Decking Block or Heads

[kospiller]

I would like to hear opinions on the best way to achieve the desired compression ratio. Is it best to zero deck the block and then set the combustion chamber size by surfacing the head or use some combination of non-zero decking the block and surfacing the head?

I am building a 200 cid with:
264/264 108 deg. cam.
Block bored .060"
32/36 Weber
DUI distributor

Want to achieve around 9.5:1 CR.

 

[bubba22349]

For best results yes it's better to use a zero deck on the 170's and 200's good luck

 

[rbohm]

i prefer to leave the block deck as thick as possible, thus for me milling the heads is the best way to increase compression. that and adjust the piston pin height. remember that the block deck is where the threads are that bolt the heads down. you want to skim the block deck as little as possible to prevent head gasket issues.

 

[pmuller9]

The best way is to get the pistons with the correct CH so the piston is at zero deck and with the correct dish volume for 9.5:1.

What piston are you looking at using?

 

[kospiller]

I will be using the stock pistons.

 

[pmuller9]

If I'm figuring correctly
If you use the Silv-O-lite 3328H-.060" piston, CH 1.530", dish volume 8 cc, It will be at zero deck and with a 51 cc combustion chamber the compression ratio will be 9.5

 

[cr_bobcat]

I got to 9.44 with a standard block and stock pistons by milling the head down to 48cc chambers. This was a 0.070" mill on a C9 head. I also used a gasket that has a 0.035" crush height.

 

[chad]

…then there's optimal quench to achieve too...

 

[pmuller9]

Silv-O-lite 3328H pistons are $150 a set and you get zero deck and the correct compression ratio.
You don't have to pay for extra head or block machining beyond a minor clean-up cut.

 

[kospiller]

What would be the optimal quench height for this setup?

 

[pmuller9]

What would be the optimal quench height for this setup?

.040" is recommended which gives plenty of margin to keep the piston from touching the head at high rpm.

 

[CZLN6]

Howdy Kospiller and All:

I've been AFK for a week so late getting here. You've got some opinions so far, I thought I'd add mine. Decking the block has several advantages when the goal is milling to increase compression with a stock piston. 1. For a given cut of say .030" CR will be raised more when decking the block because it lowers the whole size of the bore. Milling the head only deals with the size of the combustion chamber. 2. Decking allows a better quench. Ideal is best measured with machining done and new parts. "Ideal" requires a lot more fine measuring and fitting. Ideal is generally considered to be in the neighborhood of .035". A quench of more than .040" is verging of poor quench effect. With the chambers in our FoMoCo heads good quench is attainable and worth the effort.

So, I'd have to agree with you, Deck the block to zero first, select your head gasket and then mill the head to goal. What is your CR goal? There is plenty of meat on the deck surface to mill the .025" or '030" to achieve a zero deck height and still leave enough for a good bolt hold. The typical head gasket you will likely use will be .045" to .050" compressed thickness. So with this approach your combination will be on the verge of poor quench effect, but way better then stock.

That's my 2 cents for what it's worth.

Adios, David

 

[drag-200stang]

i prefer to leave the block deck as thick as possible, thus for me milling the heads is the best way to increase compression. that and adjust the piston pin height. remember that the block deck is where the threads are that bolt the heads down. you want to skim the block deck as little as possible to prevent head gasket issues.

I agree with this...If you have a good crankshaft grinder in your area you could offset grind the crank...Last one i had done it was 100$..but that was a long time ago..Always check rod to cam clearance especially when a cam is changed.
The 200 deck is thin if you ever plan to up the power keep it thick...Ford made the 250 with a lot thicker deck, why , it uses the same piston,it does not make a lot more power...does anyone know if the 250 weeps water on the passenger side like a 200?

 

[CZLN6]

Howdy Again:

Drag stang offered another good idea. Off set grinding the crank reduces deck clearance and increases the stroke. However, if you were able to off set grind the crank .020" that would leave some deck milling to achieve a level mating surface. If you're planning to have the crank ground anyway, offset grinding is worth considering.

Hey DragStang, how much did you have your crank offset ground?

I should have ask kospiller, what block are you working with? Later seventies and eighties blocks are a tiny bit thinner cast than sixties blocks. And being that it is already bored out to .060" block integrity could become an issue.

Keep it coming.

Adios, David

 

[pmuller9]

Why not use a piston with 1.530" CH for $150 and not have to do any extra machining?
If the 3328H is available, it has the correct CH and dish volume.

 

[CZLN6]

Howdy Back Pmuller9:

I don't know about these pistons so can't recommend. And he said that he is using stock, .060" pistons. Have you used the 3328H pistons? They may be worth a look for the future.

Adios, David

 

[pmuller9]

Hey David
I work mainly with the 300 six so I haven't used that piston.
The 3328H is a Silv0lite Hypereutectic piston made for the Ford Australian engine.
CH is 1.530"
Dish volume is about 12cc
Summit shows it for $150

If the extra machining is going to cost anywhere near $150 then it would make sense to get the 3328H pistons and not violate the block deck. If the stock pistons the OP has now can be returned all the better. If not sell them.

Paul

 

[CZLN6]

Howdy Back Paul:

Looks like it is available in big dish and flat-top. and it is hypereutectic. These pistons are definitely worth considering.

Anybody out there us the 3327 or 3328 Slivolite pistons?

Adios, David

 

[Hot 6t Falcon]

Howdy,

I'll add my 2 cents too. I've done a LOT of expensive testing with our little six... I had a friend (dead now) that I used to 1/4 mile circle track race with. Denny Roy ran an old-timer machine shop.

20 years ago, While brain-storming with Denny one day about the newer thicker head gaskets and what to do about the loss of compression, We decided to mill the top of the block to equal the additional thickness of the newer gasket PLUS a "little" extra. We did NOT account for connecting rod stretch... at 6500 rpm, it cracked the #6 piston, bent the connecting rod, and cracked the cylinder wall.

MAKE CERTAIN YOU HAVE ADEQUATE PISTON TO HEAD CLEARANCE IF YOU DECK THE BLOCK BIG TIME. I think we had cut .035" from the block... but it was long ago on a far and distant planet.

Measure carefully.

 

[drag-200stang]

Howdy Again:

Drag stang offered another good idea. Off set grinding the crank reduces deck clearance and increases the stroke. However, if you were able to off set grind the crank .020" that would leave some deck milling to achieve a level mating surface. If you're planning to have the crank ground anyway, offset grinding is worth considering.

Hey DragStang, how much did you have your crank offset ground?

I should have ask kospiller, what block are you working with? Later seventies and eighties blocks are a tiny bit thinner cast than sixties blocks. And being that it is already bored out to .060" block integrity could become an issue.

Keep it coming.

Adios, David

Hi David,...I had the crank offset ground from ford 2.1236 down to chevy 350 2.100 ,..That gave .020 more stroke but moved the piston up half so .010 higher....You could use a .050 undersized bearing and get .040 more stroke with the piston up .020
Keep in mind that stock ford ch is 1.511 so a replacement piston is usually at 1.500 is going to come up .011 shorter.
Pmuller taller ch is a great way to tighten up the deck height... Looks like they use metric rings.