351 c 2v to 4v head swap?

black95gts5.0 · May 11, 2009

I have a running 351 cleveland 2bbl out of a 73 rideau 500 and was wondering if anyone knows what kind of compression that motor would have? (low I know) and if I put open chamber 4 bbl heads on this motor what would I have for compression? I would most likely cam it at the same time. would this be worth it or should I just build a proper bottom end? I am on a budget and a bit of a time crunch. thanks for taking the time.

70grande · May 11, 2009

I've got that same engine! I also have a stock 4V intake manifold lying around that I would sell to you real cheap if you want it. It will need to be resurfaced though, let me know if you want any pictures. Good luck with the swap and I can't wait to see how it works out.

96 DOHC Cobra · May 11, 2009

I think 73 was the first year 351Cs got a dished piston (both 4Vs and 2Vs) The compression ratio should be about 8.5:1 with either a 2V open chamber head or a 4V open chamber head.

Hack · May 12, 2009

96 DOHC Cobra said:
I think 73 was the first year 351Cs got a dished piston (both 4Vs and 2Vs) The compression ratio should be about 8.5:1 with either a 2V open chamber head or a 4V open chamber head.

That's right.

The 2V and 4V open chamber heads have the same size combustion chamber - that is if neither set of heads have ever been cut.

black95gts5.0 · May 12, 2009

so if i get the heads cut I will bump compression up some. Is that a bad way to up the compression? would it be better to put better pistons in than cut the heads?

71stangfreak · May 12, 2009

I read somewhere, a long time ago, that the open chamber heads were much less prone to detonation, even with a domed piston, and the comb chamber shape was better for a more complete fuel burn. I dont know how much it costs to get the heads milled but If there was ever a possibility of putting it back the way it was, you wont want to mill the heads, other wise it would be much easier if you weren't doing a complete rebuild to just pull the heads and take them to the shop. If you already have it apart, I might lean towards changing pistons. Just my worthless $.02.

dodgestang · May 12, 2009

71stangfreak said:
I read somewhere, a long time ago, that the open chamber heads were much less prone to detonation, even with a domed piston, and the comb chamber shape was better for a more complete fuel burn. I dont know how much it costs to get the heads milled but If there was ever a possibility of putting it back the way it was, you wont want to mill the heads, other wise it would be much easier if you weren't doing a complete rebuild to just pull the heads and take them to the shop. If you already have it apart, I might lean towards changing pistons. Just my worthless $.02.

Your memory is failing you. 4v closed chamber heads are more ping resistant because of the dove shape compression chamber in the cylinder head which means with the closed chamber you can get away with a little more compression all other things being equal.

The American 2v are all open chamber, you can get an Aussie 2v with the dove chamber which would bump the compression in the motor.

Regarding pistons versus head changing...the answer is "depends"

How much money you got, what you using the car for, and what is the performance goal you are trying to reach?

downwardspiral · May 12, 2009

dodgestang said:
Your memory is failing you. 4v closed chamber heads are more ping resistant because of the dove shape compression chamber in the cylinder head which means with the closed chamber you can get away with a little more compression all other things being equal.

The American 2v are all open chamber, you can get an Aussie 2v with the dove chamber which would bump the compression in the motor.

Regarding pistons versus head changing...the answer is "depends"

How much money you got, what you using the car for, and what is the performance goal you are trying to reach?

best steel cleveland heads for street use!

D.Hearne · May 13, 2009

71stangfreak said:
I read somewhere, a long time ago, that the open chamber heads were much less prone to detonation, even with a domed piston, and the comb chamber shape was better for a more complete fuel burn. I dont know how much it costs to get the heads milled but If there was ever a possibility of putting it back the way it was, you wont want to mill the heads, other wise it would be much easier if you weren't doing a complete rebuild to just pull the heads and take them to the shop. If you already have it apart, I might lean towards changing pistons. Just my worthless $.02.

+2 on your memory failing you. Quench heads are what you want for ping resistence. The quench portion of the head tends to put out the fires of detonation. I built a 400 with milled open chamber heads and with only a 9.7 to 1 comp ratio, it wanted only 93 octane fuel to control the ping where a quench headed 390 with a 10.25 to 1 ratio gladly accepted 89 octane fuel.

71stangfreak · May 13, 2009

I did say it was a long time ago, my memory fails me all the time. Either that or the info had came from an incorrect source.

351 c 2v to 4v head swap?

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