milled oz 250 head for cc's

[grocery getter]

my oz 2v head is at the machine shop. from what i've read I need 48 cc's

52 to get it to the correct C/R . and the extra 4 to make up for the head gasket.

this is on a non-decked 200 block.

am I correct? if not, what's the target?

 

[kirkallen143]

A 0.010" mill cut is apprx. equal to 2cc's reduction in volume size.

You would need to mill 0.025" to compensate for the 0.050" gasket thickness to maintain same CR.

 

[CobraSix]

I guess the question is what is your target C/R? Current CC? Bore on the block, etc?

Plug and play here:
http://falconperformance.sundog.net/compcalculator.asp

 

[grocery getter]

I guess the question is what is your target C/R? Current CC? Bore on the block, etc?

Target? i'm looking to keep it at the stock '66 C/R.

 

[kirkallen143]

I guess the question is what is your target C/R? Current CC? Bore on the block, etc?

Target? i'm looking to keep it at the stock '66 C/R.

So 9.2 to 1 CR?

 

[CobraSix]

Being as there are so many variables, I'd take the measurements the calculator is looking for and go from there if you can.

 

[grocery getter]

I guess the question is what is your target C/R? Current CC? Bore on the block, etc?

Target? i'm looking to keep it at the stock '66 C/R.

So 9.2 to 1 CR?

Yes...

from what i've read that's the '66 CR. if it's not, please chime in.

 

[addo]

That's a pretty heavy cut on the head. Is it worth so much "pigeonholing" the head to make it work with an average block?

I would compromise a little, so if you build a block with some positive deck later, the head isn't junk.

 

[Mustangaroo]

How about looking for a NOS metal headgasket I have gotten them on ebay and even someone on this site was selling some a few years ago. Yes they are had to find, but I'd look for one before cutting that much off my 2v head. Another idea is have a custom headgasket made, last I checked one could be made for about $120-$150. Just my 2 cents

 

[grocery getter]

Thanks for the replies.

you can always take it off, you can't put it back on

 

[CobraSix]

Look on the plus side...a lower CR means you can run with cheaper gas. My CR is calculated at 9:1, and I just run 89 or 87 (if I'm really cheap). I was always told that when determining octane needed for a engine, take the CR and mutliply by 10. So 9.2 = 92 octane.

Granted, I'm not sure if it's an 'old farts tale' (like and ole wives tale) or not so feel free to debunk that if I'm way off.

 

[grocery getter]

Look on the plus side...a lower CR means you can run with cheaper gas. My CR is calculated at 9:1, and I just run 89 or 87 (if I'm really cheap). I was always told that when determining octane needed for a engine, take the CR and mutliply by 10. So 9.2 = 92 octane.

Granted, I'm not sure if it's an 'old farts tale' (like and ole wives tale) or not so feel free to debunk that if I'm way off.

what's the CC's on your head, what gasket and is the block decked?

Thanks

 

[CobraSix]

I'll have to check my notes, but it was in the low 50s, want to say 52. I know it was higher then my old log head that had been milled to 48. The reason I didn't want to go to that again, was the 48CC combined with a low thickness head gasket, I had the #1 piston hitting the spark plug at high revs. I actually had to index that plug until I swapped out heads.

I don't think my block was decked...The measurements were almost exactly like stock.

I just used a standard Autozone gasket on my OZ head.

 

[grocery getter]

thanks, that sounds like the way to go.

I still haven't heard from the shop.

 

[grocery getter]

A 0.010" mill cut is apprx. equal to 2cc's reduction in volume size.

You would need to mill 0.025" to compensate for the 0.050" gasket thickness to maintain same CR.

it cc'd at 55. he's going to make a pass and recheck.
i'm going with hardened seats and he needs to source an exhaust valve.

 

[CobraSix]

Did you have the valves enlarged?

 

[MustangSix]

Look on the plus side...a lower CR means you can run with cheaper gas. My CR is calculated at 9:1, and I just run 89 or 87 (if I'm really cheap). I was always told that when determining octane needed for a engine, take the CR and mutliply by 10. So 9.2 = 92 octane.

Granted, I'm not sure if it's an 'old farts tale' (like and ole wives tale) or not so feel free to debunk that if I'm way off.

That's the rule of thumb for old style iron, wedge heads like these. If you have a high swirl chamber like a Chevy Vortec you can add a point and/or if you are running an aluminum head you can add a point. So an aluminum, vortec head can usually get away with 10:1 compression on 89 octane fuel. With full electronic engine management some late model cars like the Corvette LS3 can run on 87 octane even with a 10.7 CR (at reduced power). The LS7 is 11:1 and can run on 87 octane if need be, and although performance suffers, the engine is capable of doing so.

 

[grocery getter]

Did you have the valves enlarged?

no, since I only need one i'm going to replace that. i've got draw the line somwhere it will be in great shape when he's done.

 

[grocery getter]

it came back @ 52cc's 8)

 

[addo]

Put 15 thou of positive deck on it and you'll be equal to high forties in chamber volume on a stock motor...