Maximum head milling

[Spike56]

I’ve got a big log 1969 head need to get cc’s down to around 48. I read for every 10 thousandths milled will reduce cc by 2.4. It’s had 20 milled off already and I’m at 59 cc’s. I read 90 is about max to mill off. I’m thinking another 50-55 should put me where I need to be. 48cc’s with a 6.8 cc dish piston with a 1.5 compression height piston. 50 thousandth head gasket. Wondering what everyone is using for piston rings. Cast? Molly?
Thanks you in advance

 

[pmuller9]

I’ve got a big log 1969 head need to get cc’s down to around 48. I read for every 10 thousandths milled will reduce cc by 2.4.

That is not correct.
On the big chamber 300 heads, it takes about .007” to reduce the chamber volume 1cc.
A small chamber, small six head will be even less.

Have you measured the volume in the chambers?

 

[InlineDave87]

That is not correct.
On the big chamber 300 heads, it takes about .007” to reduce the chamber volume 1cc.
Have you measured the volume in the chambers?

He said big log tho. I think he is talking about a 200

 

[pmuller9]

He said big log tho. I think he is talking about a 200

That's correct
If I can only get 1 cc for every .007" on a 300 head, how in the world would a 200/250 head get 2.4cc for every .010"?

 

[Spike56]

He said big log tho. I think he is talking about a 200

It’s a 20 over bore 200
The short block is a 78- head is a 69.I took it apart and it has 20 thousandths cc dish pistons with a 66 head- at 48 cc. The piston to deck height is 4 thousandths down the hole. So it’s either been deck milled or pistons have more compression height to bring it up the hole a few thousanths? putting a 69 head on and changing the pistons to the stock 6.9 cc dish and a 1.5 compression height piston. Pistons are not here yet to check deck height. I’m not looking to send this thing into orbit I just need a close idea of where I’m going to end up

 

[Spike56]

It’s a 20 over bore 200
The short block is a 78- head is a 69.I took it apart and it has 20 thousandths cc dish pistons with a 66 head- at 48 cc. The piston to deck height is 4 thousandths down the hole. So it’s either been deck milled or pistons have more compression height to bring it up the hole a few thousanths? putting a 69 head on and changing the pistons to the stock 6.9 cc dish and a 1.5 compression height piston. Pistons are not here yet to check deck height. I’m not looking to send this thing into orbit I just need a close idea of where I’m going to end up

Oh and yes I did cc the combustion chambers and the dish in piston

 

[InlineDave87]

That's correct
If I can only get 1 cc for every .007" on a 300 head, how in the world would a 200/250 head get 2.4cc for every .010"?

Ok. So how much can be taken off a 300 head safely?

 

[pmuller9]

Ok. So how much can be taken off a 300 head safely?

I’ve never taken more than .025” off the head.
I figure that the thicker the head surface, the better.

 

[alwill923]

I have found it is better to order custom pistons with the correct piston height to make the top of the piston flush with the deck rather than milling the block. Also you can get the piston dish size to give you the CR you are looking for.

Yes expensive but a better solution.

 

[powerband]

'keepin it simple', here's some useless related anecdotal info:

cc'ing the head and confidently predicting comp. ratio by milling, along with simple back-cut valve job, V8 springs and inspex/replace of any suspect parts will ensure driving rather than wrenching down the road ..
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'63 has a '71 Maverick 170 from a Craigs List low-miles rotted car, with a donated D7DE (1977) era 250 head (@62cc's OEM) milled @.070 to 48 cc chambers. The original 'steel shim' thin head gaskets are still available for the smaller bore 170 and the stock 170 mated to rebuilt/48cc head yields a SCR @ 9.5:1.

Tight 170 gets good mileage (with 91+ octane.) With the progressive 2Bbl carb, Hooker Dual Out headers and a T5 OD transmission, the170 runs strong and the OD-T5 enables best use of the torquey' small block six's powerband .
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[powerband]

... should mention the head being cc'd in previous pic is a 'small chamber' head CODE is off the '71 Maverick 170 C8DE engine. Chambers were measured at @ 54cc's . Also the 144/170 uses a flat top piston and smaller bore which skews compression ratio calculations different than 200's with larger bore dished pistons.
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