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Discussion Starter #1
You're probably getting sick of all these questions by now BUT, one more.

If I have an H code 351C and just switch the 2V heads with 4V heads, what octane of gas "could" be run in it with out any trouble?

Here I am thinking that I've got a full fledged 351C 4V when possibly all I have is just an H code with 4V heads.

If I can run 87 test gas in this motor then there may be more hope for it than I thought, unless my "oil in the coolant" problem IS related to a cracked head or water jacket.:uhoh:

Thanks, Paul
 

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Which 351C 4V cylinder heads?
Along with those 4V 351C heads, you will need the appropriate intake manifold and exhaust manifolds or headers.
 

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Discussion Starter #3
What I was under the assumption was this: A 351 that came WITH, from the factory, 4v heads, what makes that engine have the higher compression ratio? Do the heads, the 4V heads make the ratio or is it a combo of pistons and heads?

What I think the previous owner did to my Cougar was just take the 2V heads off and put 4V heads on. Would that alone make the compression high enough so I'd have to use the 90+ octane gas.

351C 2V Compression = 9.51:1

351C 4V Compression = 11.0:1

What makes the difference - the heads, heads and pistons, other parts and heads/pistons?

I guess I'd like to know, maybe even have someone hazard a guess at the compression ratio of a 1970 H code 351C with the 4V heads.

I have a possible HG leak/cracked head and or cracked water jacket. If it's one of the first two problems I can handle it BUT, I'd like to try to keep the costs down. If it's just HG then my cost is WAYYYYYY down. If the head is cracked I have a set of good 2V heads. If it's something in the block then I'm hosed.

Thanks,
Paul
 

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It is going to depend on the casting number on the heads. There were a few differant 4V heads cast, but if they are 70, then they were all the same. http://www.boss351registry.com/351_Cleveland.htm Look this over. The compression in 70 came from the heads, all Clevelands recieved the same piston. They should be flat tops with notched valve reliefs on the edges. If you put 2V heads on it, you will have 9.5:1, given that you have the factory pistons. The only way to tell what heads you have is to take the intake off and use a mirror to look at the casting number on the bottom side of the runners. Depending on the year, you may be able to tell what they are by the date code that is under the valve cover. I believe that 70 was the only year that an open chamber 4V was not used.
 

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Discussion Starter #5
The only way to tell what heads you have is to take the intake off and use a mirror to look at the casting number on the bottom side of the runners.
Annnd, you were a DENTIST in a prior life? LOL!!!

This is the answer I was looking for, the whole post is the answer. Good info here.

I was planning on putting 2V heads on anyways BUT, I thought if the compression came from the pistons then I might as well just do the gaskets and keep the 4V's on there.

Nice to know and hopefully I'll have an update on this in a week or 2.
 

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There is also a difference in 4V heads as well.
Didnt the 70-71 4V use quench heads, and after 71, open chamber?
 

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There is also a difference in 4V heads as well.
Didnt the 70-71 4V use quench heads, and after 71, open chamber?
70-71 4V heads were high compression 'quench' heads with 2.19/1.71 valves, 11.0:1 compression in factory form
72 4V heads were open chamber low compression heads also with 2.19/1.71 valves - 9.0:1
73-74 4V heads were open chamber low compression heads with the smaller 2.04/1.65 2V valves

73-4 4Vs also got dished pistons for a 8.7:1 compression. The use of those later dish pistons in combination with early quench heads will yield a 10.4:1 compression.
 

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The 2v and 4v engines generally have different pistons as well as chamber volume. This makes the difference. If your engine has been rebuilt, it'll be important to find which pistons they used and what the compression height is.
Part number from both the head and the piston are pretty crucial to be absolutely accurate.
Use this compression calculator to help with keeping the numbers straight.
http://kb-silvolite.com/calc.php?action=comp

Don't get ahead of yourself though. Read the plugs and pull the head that seems to have the problem cylinder(s). One problem at a time.
 

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70-71 4Vs from the factory have the same cast flat top pistons that a 2V has. Not sure about 72 4Vs, but 73-74 4Vs have the dished pistons. All 70-74 2Vs have flat-tops.
 

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Negative.
I've disassembled a number of 2 and 4v engines from 70-71 that had different pistons from Ford.
There's also the monkey wrench of rebuilder pistons over the course of 40 years. Could be any one or more of various part numbers with differing dimensional issues in there. And, it's always possible that a 70 will have a 71+ engine in it, as a matter of replacement due to catastrophic failure or wear.
Either way, the only way to be sure is to pull the head and get the part number off the piston.
 

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Discussion Starter #11
Well, after speaking with an authority figure on driving and gas prices and muscle cars, I have come to the conclusion that my project "Resuscitating A Cat" is going to go ahead with or without a head swap.

If my "Oil in coolant" issue IS a gasket, AWESOME news = no head swap. If not, oh well, just get my 2V heads reconditioned and use them and still use a 90+ gas rating, the usage of which wouldn't really matter. If I used lower the savings wouldn't be seen for QUITE a few years.
 

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70-71 4Vs from the factory have the same cast flat top pistons that a 2V has. Not sure about 72 4Vs, but 73-74 4Vs have the dished pistons. All 70-74 2Vs have flat-tops.
I must say my '73 XR7 Hdtp had a 351C 2V, I peeled the heads off and they were dished.
For sure!! 8.0:1 C.R. My '72 cat did have flat tops, in a 2V thoe. I think dished pistons were the rule on '73 & up, and even on the 2v's, the cam was indexed 4 degrees retarded. Easy to fix with a aftermarket Timing chain and gear set, roller, ajdustable 2degree increments. Yeah Ford did that just to pass E.C. and there was no low end snort any more!!
 

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Discussion Starter #13
Just a minor update. I've decided to EAT $8.99 plus tax to try the Bar's Leak "Bar's/18 oz. liquid copper block seal, intake and radiator stop leak".

I figure it can't hurt since it's mixed with just water instead of the 50/50 mix water and coolant. Plus, I believe my leak, or better yet, what's causing it, is acting like a one street . The cooling system pressure is only what, 13 - 15 lbs whereas the oil system is 70 psi. So, possibly, a small piece of HG metal is only opening one way = oil into the coolant. As soon as the car is turned off the oil pressure drops and now the coolant presses on the leak area and it closes shut.

If anyone has any experience with this stuff OR even friends/neighbor/co-workers I'd like to hear both sides, Good and Bad. I'm not doing it until Thursday so you may still have time to talk me out of it:lolani:


 

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Discussion Starter #15
Even before Cedar responded I decided to take it to the shop instead of using the Bar's on it.

As it so happens to be, the one mechanic almost bought the Cougar before we did. He was describing a Cougar that he looked at 3 years ago and I asked him the name of the place selling it. When he told me I pointed to MY Cougar and said "Here it is!!"

Plus, this guy has worked on Fords his whole life (Torino, T-Bird, 79 Capri, etc...)

In 5 minutes of brainstorming with the shop owner they had 6-12 ideas of why I have the oil in the coolant and they DO NOT involve a ton of money to fix.

More details coming. I'll update this JUST for the fact that I have a very unusual problem AND the fact that this is the beginning of my Cougar coming back to life, I HOPE (KNOCK ON WOOD)
 
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