351c- what heads do I have?

[cazsper]

Though my '73 Mach-1 us an H code (2v) heads, I was told the engine had been rebuild with an hydraulic roller cam and 4v heads. I ever paid attention to casting numbers before because I've mostly been into stroked Windsors and AFR heads.

The heads have (in one corner) the letter "A". In another corner is a "4" with what looks like a large dot or a raised period "."

I like to assume I have 4v open chamber heads but I would like to know for sure.

 

[MotoArts]

Info on "4 dot" heads:

http://351cleveland.wetpaint.com/page/4V+Cylinder+Head+Spreadsheet

Your casting number will be found on the underside of an intake runner. Yes, unfortunately, you will need to pull the intake and use a mirror to see it...

The date code is visible under the valve cover, on the topside of an intake runner.

edit: Same thing but different:

http://www.network54.com/Forum/119419/thread/1197685946/4V+Head+Repository

 

[cazsper]

Ok. Thanks.

 

[cobra3073]

To elaborate just a bit for those who may not have completely understood the response.

The "4" on the head indicates it is a 4V head. Once the casting number is submitted, we can tell EXACTLY which head (open or quench chambered) is the subject of this thread.

BT

 

[cazsper]

Ok, thanks. So I have 4v heads? But not sure which ones (open/closed chamber)?

 

[Tnfastbk]

Ok, thanks. So I have 4v heads? But not sure which ones (open/closed chamber)?

Yes if they have the 4 or dot in the corner. Could be open or closed depending on which you have

 

[MotoArts]

Short of pulling the heads, basically you can't be absolutely sure when they're on the block. Unless you have a borescope or something to feel/see the chamber, it'll not be a 100% certainty.

------------------------------------------------------

This is a copy/paste from the second link above:


Here's my take on the how this data is looking:

 


So far it looks like it can help identify 4V Closed Chamber vs. Open Chamber for many applications without having to pull the heads or intake to check. This is useful if your shopping a complete mystery engine or looking at e-bay photos.

 


Here's what I see:

 


Looks like heads with 4 only with no dot marking fall into the early closed chamber category. (Date codes are 1969 9*** up to early 1970 0F** manufacture dates which would be early to mid year 1970 models.)

 


So in this case if a guy is selling an engine with "4" on the heads, based on the date, you could gamble it's an early closed chamber head.

 


Getting into 4 with dot heads, it gets murkier. In that case it looks like 4 Dot heads with date codes up to mid 71 manufacture date will be closed chamber. So in this case if the mystery engine has 4 dot, you'll have to pull the valve cover to get a date code. If the date code starts with 1970 0*** date code or to mid year 1971 1F***, it looks like its a safe bet on closed chamber.

 


This seems to jive with how manufactures split production for model years. For example 1970 models start production mid-year 69 and go to mid year 1970 dates. It also goes with published info that says 1970 and 71 engines were closed chamber high compression engines.

 


Notice I don't mention casting numbers, because you have to pull the intake to see those and I was looking for a quick ID way to tell if it's worth looking further.

 


So to summarize:

 


4 no dot - data so far says "closed chamber 1970 model" - maybe very early 71


no need to look too much further.

 


4 dot - pull the valve cover and check the date code - if it says 1F** or earlier, data says it will be closed chamber.

 


4 dot - date code later than mid year 71 date code, you'll have to confirm the casting number to guarantee closed chamber vs. open.

 


4 dot - date code later than 1972 date code 2***, probably open chamber unless some rare service head is in the mix.

 


I hope this will stir some discussion and help get some more open chamber 4V head data and service head data to confirm my theory.

 

[Tnfastbk]

I read somewhere once that all the dot was, was a casting mark. Thats why some have them some don't. Need to look for that article.

 

[cazsper]

Even if they were closed chamber 4v heads, can I still make some good power?

 

[mustang7173]

cazsper,

Oh yea baby. The quenched chamber will add to the compression ratio thus a bit more power!

mustang7173

 

[cobra3073]

Even if they were closed chamber 4v heads, can I still make some good power?

For all PRACTICAL purposes (in the case of modifying), open versus quench (Closed) does not really matter as you would simply order the pistons to get the compression ratio that you want. For the longest time, the closed chambered heads were generally desired, especially when utilizing stock pistons.

The above is an "over simplification" as other factors can come into play.

BT

 

[Jeff73Mach1]

Closed chamber heads are often said to be the hot ticket because when used with a flat top piston and proper piston to deck height setup, they resist detonation. It is referred to as a quench chamber. Open chamber heads work fine too, but cost a bit of compression unless pop up pistons are used.

It is my general understanding that Iron headed Clevelands are not detonation prone engines in general, though you can f*** up anything with enough time and effort

 

[cazsper]

Ok. I'm cool with that. I was really wanting a 460 big block but that may have to wait. As long as I can get some good power from what I have... As for intake manifolds, it seems nobody makes a dual plane intake for the 4v head setup. Is this true?

 

[cobra3073]

Ok. I'm cool with that. I was really wanting a 460 big block but that may have to wait. As long as I can get some good power from what I have... As for intake manifolds, it seems nobody makes a dual plane intake for the 4v head setup. Is this true?

http://www.summitracing.com/parts/EDL-2665/

No.

BT

 

[marks73]

Ok. I'm cool with that. I was really wanting a 460 big block but that may have to wait. As long as I can get some good power from what I have... As for intake manifolds, it seems nobody makes a dual plane intake for the 4v head setup. Is this true?

How much horsepower are you looking to make?

 

[Don C]

Blue Thunder has dual plane 4v intakes - http://www.bluethunderauto.com/id24.html

 

[c9zx]

Blue Thunder dual plane intake with the plenum divider and small notch. Works very well. Try Carl's ford Parts. Chuck

 

[goodnigh]

My heads are 4 dot with a date code of om 16.

No way to tell if they are quench but you can smell

gas in the morning before the car warms up and it

is not the carb or tuning. The engine will idle smoothly

down to 300 rpm And pull a load. Has tons of torque and

pick up. The engine is very responsive. The pistons are

standard Cleveland cast hypereutectic 0.030 over.

mike

 

[droptop73]

On a somewhat irrelevant tangent. (not meaning to hijack the thread). I'd like a set of C/C 2v heads to play with sometime.

Because...

Current engine technology uses closed chamber (quench) heads and a very tight piston to head clearance and a reverse "dome" (read dish) on the piston that mirrors the shape of the head's chamber. The theory is the tight piston to head clearance causes "squish" and creates turbulence in the chamber which better homogenizes the fuel/air mix and reduces detonation. This allows more compression for a given fuel.

I hope that mkes sense.