I'm just starting to plan the restoration of my '68 which hasa plain vanilla200 cidI6. I've rebuilt the wimpy Autolite 1100 1V and have just about got it working as well as I can get it working through my $20 investment in a rebuild kit and nominal investment in a new automatic choke heat tube.

I've discovered that the head is from a '73 Falcon, #D3DE. (And, as a side note, the bore in the head, looks to be about 1 3/4" vs. my carburetor throttle bore of 1 7/16". Whoever changed the head, 'modified' the original carburetor spacer to bolt on the'73 head) My math says that a change from a'68 head to the the '73 head alonewould have dropped the compression ratio from 9.0:1 to about 7.6:1. (assuming that the combustion chamber on the '73 head is 62 cc vs. 52 cc for the '68, and the replacement of the original Ford stock steel shim 0.027" gasket was replaced with a composite head gasket with a compressed thickness around 0.050", and assuming the '73 head was not milled.). I haven't measured anything yet, I'm just trying to figure out what I have make a plan for the restoration. I'd like to get back to something close to the original compression ratio when the car was new and not spend a ton of money.

My question is: What is the most cost-effective way to restore the compression ratio to something around 9.0:1? If the answer is: "milling the head," is there a simple way to determine (say, through a measurment of some kind) whether this has already been done, and how much material can safely be removed?

I'd like to do this restoration in stages and wonder if it's a good idea to work on the head first and save the engine overhaul for a future year...maybe even next year. Is there a lot of risk to refurbishing the head and doing a valve job without doing anything significant on the bottom end? I'm not looking for a mean street machine, I'm looking for something that runs reliably. On the day that I purchased the car and drove it home, the speed with the pedal floored was 71 mph.

I know I can do better!



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7.6:1 PERFECT FOR A TURBO![8D]

And to answer your question no theres no real rule of thumb when it comes to milling heads. Back in the day, people would mill heads from .030 - .060" to increase compression. But then valve interference becomes an issue. And the only true way of knowing if the head has been milled before is by cc-ing yourself. My friend used a 1cc syringe to find out the cc's of a used TFS head he bought. He said it took forever. But it was accurate.
-P.

 

Thanks for the reply. I am the kind of guy who will measure combustion chamber volume directlyusing a syringe.

 

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Scott,

Thanks for the advice. I picked up a sparehead from a '67 on Craigs List that I'm going to experiment with. I notplanning ona new cam or anything like that but may get the 1.6:1 rocker arms and try do some porting to improve the air flow. I'll probably mill some nominal amount off the head and some off the engine block when I get around to pulling the engine.

I had not really seriously considered a turbo before now. That might be the way to go with these flow-constrained inline six engines.

Your website is very good and I've bookmarked it. I'm interested in the experiences of those who have done a good job on the '68 Mustang.

 

Screw the one ml syringe if you have a good balance, weigh head add water to chamber new weight minus old weight is volume for SI unit anyway, or slightly less acurate, add water to chamber, remove water into beaker of known weightre weigh water mass= volumes assumingwater densityis unity atroom temp.

 

Another good idea, and thanks for weighing in. I had forgotten the relationship between water mass and volume sometime after high school.

Seems like I'm going to get an answer that may have more significant digits than I need. Something tells me that this engine has a lot of margin for error and that my engineering does not have to be this exact. But I could be wrong.