2V vs 4V Pistons
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2V vs 4V Pistons
In a 289 engine the pistons are dished for less compression in a 2V engine as opposed to a 4V which has flat tops (except in D engines) does this apply to Clevelands? I have not had a 2V engine down to verify.. Thanks Gordon
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the 4V's got different pistons depending upon the heads, the year, and if it was a Boss, HO, CJ or base 4V. lots of different pistons, forged, cast, F/T, dome...
not sure if the 2V's had a small dish or not? i have talked to a couple guys that refer to the early(up to about 71 or 72) 2V's being higher compression than the later smog model years. not much of a difference as i recall and with the same chamber, so could've been a piston dish? none of my reference material supports this though...
not sure if the 2V's had a small dish or not? i have talked to a couple guys that refer to the early(up to about 71 or 72) 2V's being higher compression than the later smog model years. not much of a difference as i recall and with the same chamber, so could've been a piston dish? none of my reference material supports this though...
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Re:2V vs 4V Pistons
Thanks My 4V is a base 71 Torino, I knew that the later heads were bigger chamber I would guess that these heads are around 60cc. I need to look at a 70-71 2V motor and see what the pistons look like as mine are dead flat with small valve relief at the edge. Gordon
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According to Tom Monroe's book, the '70 to '74 351C-2V heads had 76.2cc open combustion chamber. The later 351C-CJ and H.O. had the 4V ports, but open 75.4cc heads. The '70 and '71 351C-4V had the 62.8cc closed chamber heads and the large ports. The '71 351C Boss had 66.1cc heads with a dome piston, which gave it 11:1.
It appears that the piston was the same between the 351C-4V and the 351C-2V in the early motors. It is the head that makes the difference, but the compression ratios published in the book do not agree with the calculated CRs for either case. I believe that the book has some errors.
The '71 351C-4V has flattop pistons with valve relief. All of those early pistons were flattops, except for the Boss. They did change the Compression Height on some.
It appears that the piston was the same between the 351C-4V and the 351C-2V in the early motors. It is the head that makes the difference, but the compression ratios published in the book do not agree with the calculated CRs for either case. I believe that the book has some errors.
The '71 351C-4V has flattop pistons with valve relief. All of those early pistons were flattops, except for the Boss. They did change the Compression Height on some.
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Thank You Gentlemen, I need to get that book, I have learned that the CJ engine had the cam degreed in slightly retarded in the later year and that would affect the compression ratio. The Aussie heads (Ihave a set) are 58-59cc and yield a 10.1-10.5 compression.These heads were manufactured for 302's and will bolt on 351's(same basic block down there) however the increase in stroke raises the compression up to the aforementioned compression ratio. I am building a street motor looking for power at the bottom and the ability to use pump gas. Aus Ford parts claim their heads simply need premium fuel and will operate fine, I do not know what advance they are able to run timing wise.Do any of you have experience with the newer Edelbrock aluminum heads? Regards Gordon
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What motor do you have?
If it is a '71 Torino 351C-4V, it should have the closed chamber heads. You should keep those heads. If you have the CJ heads, then a good set of Aussies or alloy heads will help.
Retarding the cam reduces the Dynamic Compression Ratio, by reducing the swept volume of the cylinder after the intake valve has closed. A cam with a late Intake Valve Closing angle will have the same affect. You should use a cam with an IVC no earlier than 66 degrees ABDC with 58cc heads. With 64cc alloy heads you can have a cam with an IVC of 58 degrees ABDC. The early valve closing improves the torque at low RPM. This is better for a street motor.
What cam are you planning to use?
Alloy heads will allow you to have at least 0.5 points higher compression ratio without detonation. The Edelbrock heads are OK, but the best are the Cilinder Head Innovations heads. Check out this site.
http://www.tmeyerinc.com/351Caluminumheads.htm
These heads flow so good, that you can use a shorter duration cam and still get great power at high RPM.
If it is a '71 Torino 351C-4V, it should have the closed chamber heads. You should keep those heads. If you have the CJ heads, then a good set of Aussies or alloy heads will help.
Retarding the cam reduces the Dynamic Compression Ratio, by reducing the swept volume of the cylinder after the intake valve has closed. A cam with a late Intake Valve Closing angle will have the same affect. You should use a cam with an IVC no earlier than 66 degrees ABDC with 58cc heads. With 64cc alloy heads you can have a cam with an IVC of 58 degrees ABDC. The early valve closing improves the torque at low RPM. This is better for a street motor.
What cam are you planning to use?
Alloy heads will allow you to have at least 0.5 points higher compression ratio without detonation. The Edelbrock heads are OK, but the best are the Cilinder Head Innovations heads. Check out this site.
http://www.tmeyerinc.com/351Caluminumheads.htm
These heads flow so good, that you can use a shorter duration cam and still get great power at high RPM.
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Originally Posted by sabre62
Interesting. My cam would probably be the Comp extreme energy 270H.I think that is the number. I have this in 5.0 and it is great for the street motor I have in 66 Mustang Conv. with AOD. Gordon
With a 58cc head and a 61 degree IVC, the Dynamic CR will be 8.78:1. That is too high for pump fuel. Even with 63.5 degree IVC, the Dynamic CR is still 8.62:1, also too high for pump fuel.
With a 64cc head, and a 63.5 degree IVC, the DCR is 8.05:1, and with a 61 degree IVC, it is 8.2:1. This should run with 93 Octane fuel. With the 64cc alloy heads you could even run the 265DEH cam and 58.5 degree IVC. The DCR is 8.34:1.
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Excellant, This is the info I needed, I am thinking the Aussie heads would make a good clevor 302-289 hi-po type for a play car ..not everyday use as I planned for this Ranchero. Thanks for the good insight. Gordon
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"the B&A manifolds might be the only option for a baby boss?"
Check with the latest Edelbrock catalog. http://www.edelbrock.com/images/home/new_products.pdf
I saw a couple new intake manifold descriptions for a 302 or 351W application using 2V/4V Cleveland heads. 1500-6500rpm, no pics available yet.
Check with the latest Edelbrock catalog. http://www.edelbrock.com/images/home/new_products.pdf
I saw a couple new intake manifold descriptions for a 302 or 351W application using 2V/4V Cleveland heads. 1500-6500rpm, no pics available yet.
Last edited by Brian S; Nov 30, 2006 at 02:59 AM.
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