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Discussion Starter #1
Hi guys could i get some of your wisdom? whats the diff between open/closed chambered heads? my 70 has 2v heads open/closed? they need valve seal/guides as starting to smoke and couple of the plugs are real oily i was gonna take them to mach. shop. I've seen a pair of closed chambered 4v heads on ebay(off 1971), i've wanted to convert my car to 4bb would this be something i should be interested in they also need valve seal/guides replaced. I've heard 2v are better for low end? not sure if they would be worth it or just have mine built which is better? Thanks
 

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Contributing Sr Motorhead
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Cleveland heads

I can only assume you're talking about Cleveland heads here.

All domestic 351C-2Vs had open chamber heads. All 2V engines had flat top pistons. If you put closed chamber 4V heads on your engine, you'll end up with around 10.5 to 11:1 compression. Do you really want to go that high on a street engine? You'll have to run 93 octane or higher gas all of the time if you do. How is the rest of the engine? Will it take the added stress?

Also, if you go with the 4V heads, you should also get the matching 4V intake and exhaust manifolds since the 4Vs have much larger intake and exhaust ports, otherwise, you're really wasting your time. Well, they'll make more power than your current 2V heads, but 4V Clevelands really like to breathe!

You can get aftermarket 4-bbl intakes for your 2V heads if you really want a 4-bbl. They will still have 2V port sizes, which are really all you need, but you can bolt a small 4-bbl carb on it. I'd go no higher than a 650cfm vac sec carb on it. My 'Beta Cat' is a true 4V and I'm running a 600cfm vac sec on it and it does quite nicely, lots of torque, and still rips off 14.40 passes all day, every day throu the stock dual exhausts.
 

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these are a set of closed chamber heads. 351C ones of course, off of a 70 Mustang. basically, the closed chamber means that the combustion chamber is smaller. but there are differences between the 4v and the 2v heads on the Clevelands. the 2v ones have large valves in them. im not too sure on the sizes but they are a good size. the 4v heads on the other hand have HUGE valves in them ( for a small block anyway ) they are a 2.19 intake and a 1.73 ( i think ) exhaust. alot of guys think that these are too big for a street engine, but just see that stop me from using them he he he.
 

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oops, wrong pic, but that 4 denotes that they are 4v heads. heres the chamber pic
 

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Contributing Sr Motorhead
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4V head clarification

Not all 4V heads have the large valves (2.19/1.71) 73-74 4V heads have the smaller 2V valves (2.04/1.66). Not a real big difference, eh? The 70-72 4Vs do have the large valves, in both the open and closed chamber variety heads.

My reference book says otherwise. It says that all 4Vs had the large valve heads but I take exception to that. Alpha Cat was made in Dec 72 and had the small valve heads. My friend's 73 Mach, built July 73, also has small valve 4V heads. OK, so who do you believe, the book or two cars in the flesh (iron?)?
 

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Discussion Starter #6
Hey thanks guys mine is cleveland i wasn't sure about difference of performance between 2v/4v the reason i asked was my 2v heads need rebuilt i'm sure at least valve seals/guides wasn't sure if i should opt for 4v and get 4bb intake and carb, I've seen edelbrock 2v intake (I think) made for 4bb carb that was original plan, I did'nt know about compression gain with 4v heads, i'll prob save the money and stick it in my heads to be rebuilt and get matching 2v intake for 4bb carb any suggestionson on whats out there would be great. Thanks
 
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