Milled Head & a 250...Opinons?

[Javabean]

Hey All,

I've been searchin for a new head to replace my original '66 200 as cracked threads on the original head is causing an exhaust leak from the last cylinder. I had some luck in my area and found someone looking to gut their '70 Ranchero with a 250 in favor of a V8. So I'm taking everything (radiator to tranny) with the thought of eventually swapping out my 200 with the 250, but that's still a few years out. In the mean time I want to start working on the head to adapt it to my 200.

I don't yet know if the 250 head has been milled in the past, so let's assume it's stock and my 200 is stock (with headers & single 2.25" exhaust). Anyhow, knowing that the stock 200 & 250 have different chamber sizes, if I milled the head to fit my 200, I'd kill CR when I put it back on the 250. Would it be possible to adapt the 250 head to work good on both engines? The 250 block will be rebuilt w/performance in mind, so a higher CR may not be all bad. If you had 1 head to work on both engines, what would you do? Just trying to weigh out my options.

Thanks,
Jay

 

[CobraSix]

You shouldn't have to do much of anything to the head.

Yes, the CR is lower on the 250 head I believe, but that's due to the year of manufacture, not the CI of the engine. They ran lower CR for emissions and other reasons. What ever you do to the head for the 200 will work just the same on the 250. The CR may be a little different on the 250...but still basically the same effect.

Someone correct me if I'm wrong.

Slade

 

[Anonymous]

If I were you I would replace the head gasket on the current 200 with a thin composite or metal gasket and just install the 250 head. Run that until you're ready to swap in the 250. This current configuration, assuming the 250 head's combustion chamber is 58cc's, is 8.3:1.

The same head(58cc) with the thicker Fel-Pro head gasket, longer rods(HSC) w/stock pistons and a deck height of ~.030 will yield 9.6:1 CR. Combine that with a somewhat lumpy cam and you'd be awright.

DB

 

[CZLN6]

Howdy Jay and All:

The question is what do you plan to do in rebuilding the 250 Block? If you are planning to deal with the perfromance KILLING deck height of the 250 you will be limited as to what you can do with the head.

The differences are several. Your '66 head has a a CR of 9:1 with a .025" deck height and a chamber volume of about 52 cc. The '70 250 has a CR of 8.2:1 and will have about .150" deck height and a chamber size of about 62 cc.

If you are planning a block with a zero deck height, you must plan to use dished pistons and a chamber size of about 60cc and a composite type head gasket or CR will get too high. Click on the website link below my signature. It will take you to our Web page and the CR calculator. You can ass any input numbers you want and it will figure the CR for you.

If you are not planning to fix the deck height problem, you can do whatever you want with the 250 head.

Ideally, you will design the block first and then do your final mill cut to the head to get your goal CR.

What you need to do the the head, other then milling to achieve final CR will be the same for both engines.

No easy answer here, sorry.

Adios, David

 

[Javabean]

Thank you all for the responses & info!

David, you raise a good point about the deck height. I had seen someone on here from Holland who had motor mounts made to address this problem, I believe it was The66Mustang. I was hoping to use them.....anyone have experience with em?

So in theory, should those mounts fit & I leave deck height unchanged on the 250, milling the head to account for the thicker gasket and to reduce the chamber size to 52cc (for use on my 200) would ultimately increase the CR on the 250 when I make the swap. Obviously, I need to play around with the CR calculator, but increased CR on the 250 seems like it would be ideal, just as long as I don't create too much by milling too much off the head. Am I off track with that reasoning?

Thanks again!
Jay

 

[Anonymous]

Hi Jay,

The deck height I believe is the area from the top of the piston to the top of your block. In the 250's it's .150 as David(CZLN6) has mentioned. XTAXI has mentioned replacing the stock 250 rods with ones from a 2.5L HSC motor which is 6" or .120 longer. Then use stock dished pistons and the thicker Fel-Pro head gasket. Of course this is all just my humblest of opinions .

DB

 

[Javabean]

Right you are DB.....thanks for clarifying. Too many things going through my mind at once.....I had just finished reading up on ways to address the taller block issue. I'm sure to get fired over all the fordsix time logged today! You know, people just don't understand how tough it is to fit in work around a Fordsix.com habit. TGIF!

Anyhow, playing with the CR calculator, if I machined the head for use on my 200 (for the 52cc chamber & fel pro gasket), leave the deck height alone on the 250, and use flat top pistons and stock rods, I come up with a CR of 9.2:1. and about 154 estimated hp. Right about where I want to be when I do the swap.

This seems to work in theory. Unless someone see fault with it, I think my direction is clear to me now....the one to the machine shop that is.

Gracias,
Jay