Is head milled or not?

[ochretoe]

I picked up a rebuilt head (casting code D8) cheap today. Everything looks really good but I want to be sure its milled a little to up my compression to 8.5 to 9.0. How do I find out if it was milled when rebuilt and how much was milled and what are stock numbers? Also where do I measure from? The head had new springs, valves,seats and looks to be ported and polished but I see no 3 angle or back cutting. I will get the valves done as soon as I know where I stand with the decking. Thanks
Steve

 

[pedal2themetal45]

I think the only way to bugger that out would be to have a shop CC the chambers.. and see where its at.. Also it wouldn't hurt to cc the block as well so you know for sure what you have for CR. don't forget to add the gasket thickness..
tim

 

[JackFish]

Here's one DIY method of CC'ing the chambers.

http://www.inlinepages.com/%7Einlinefev ... tions.html

 

[ochretoe]

Jackfish, Thanks for the link. That should help a lot. I guess If I can figure the cc's in the combustion chamber then I can decide how much needs milling with which gasket I will use by where I want my compression. This really is a lot of thinking and math for a Park Ranger. LOL Thanks again.
Steve

 

[The Plankster Prankster]

I picked up a rebuilt head (casting code D8) cheap today.

dont you hate it when you try to say 8 followed by a ) and it makes a 8)? - its a real pain in teh butt, aint it!! happened to me a time or 2

well good luck
--josh

 

[JackFish]

Somewhere there is an online calculator that is referred to here on the forums that will do the math...


Found it!
http://falconperformance.sundog.net/compcalculator.asp

 

[CZLN6]

Howdy Steve and all:

The stock cc volume of a D8 head is about 62 ccs. FoMoCo casting and machining was not very precise, so chambers can vary. Anything less than 62 ccs would indicate machining. How much has been been milled off already is a guess. The formula we use is .010" = 2.4 ccs.

So if your chamber volumes are about 59 - 60 ccs, it is likely that your head has been milled .010" to true the surface. A truing cut to level of .010" is fairly typically when doing a valve job.

Adios, David

 

[mugsy]

I installed a D-eight date coded head 250 head on my Mustang's 200 engine. I can confirm what CZLN6 said: I CC'ed the head at 62 cc in the combustion chambers (I measured three of them) and then the machinist milled/removed a total of 0.040 to reduce the volume to 52 cc. So the 2.4 cc per 0.010 cut is about right as well.

tanx,
Mugsy

 

[ochretoe]

OK folks help me check my math. I CC'd the chambers at 59cc's in one and 60cc's in another, so I'm guessing the head was trued by milling about .010. I want to get to about 9.8:1 compression so I will need to mill off another .058 to get to 46 cc's. Is this correct and is it too much? Should I try to stay in the low 9's on compression? My engine is basically stock now with a Duraspark II and a weber 32/36 added this summer. I will add a header and probably a little more agressive cam in the near future as money allows. The head will get a three angle valve job and I will polish the exh. ports befor it goes on the engine. I may also do a direct mount for the weber but that is still up in the air. I'm thinking the extra air travel time may help the gas and air mix a little better. Hit me with some word and help me do this right the first time. This 200 is in a Bronco and I'm trying to get as much out of this 200 as I can and still have a solid daily driver and hunting truck. Thanks
Steve

 

[mugsy]

Can you deck the block? It will be easier to reduce the total volume if the deck height can be reduced. The diameter of the bore is greater than the head's combustion chamber, so that the volume change will be greater with each 0.010 cut on the block than the head.

I *think* you can go about 0.060 cut on a head, but others here should speak up.

Why 9.8:1 ratio? The rule of thumb I have heard is that the octane rating should be 10 time the combustion ratio (again its a rule of thumb). So if you use 93 octane gas go with a 9.3:1 ratio. Plus you will have a safety margin targeting 9.3:1. What would you do if you get 9.8:1 and the engine pings?

 

[ochretoe]

I've not heard the octane rule but in my 289 I built for my 65 mustang we went 10:1 and I ran 89 octane without any problems. When I raced it I went with 105 octane but that wasn't very often. I can't mill the block as I'm running it now. If I get a block to build I'll mill it and not so much on the head. Thanks for the help.

Can you deck the block? It will be easier to reduce the total volume if the deck height can be reduced. The diameter of the bore is greater than the head's combustion chamber, so that the volume change will be greater with each 0.010 cut on the block than the head.

I *think* you can go about 0.060 cut on a head, but others here should speak up.

Why 9.8:1 ratio? The rule of thumb I have heard is that the octane rating should be 10 time the combustion ratio (again its a rule of thumb). So if you use 93 octane gas go with a 9.3:1 ratio. Plus you will have a safety margin targeting 9.3:1. What would you do if you get 9.8:1 and the engine pings?

 

[wallaka]

If you use a gimongous cam the high compression isn't as much a problem.

That being said, I'd want around 9-9.3 on something I drive everyday. If it's an occasional driver, do whatever you feel appropriate. Mustang Geezer has an absurdly high compression ratio and he's doing just fine with it.