Not really much difference. They both have the same valve size, the same runner size, the same cc chambers, and they both can be ported the same. It's been a looong time since I worked on a set of C8's, I forget if they have the emisions hump in them. That would be the only difference, and is easily removed from the head.
For all practical purposes, they're identical. All 385 heads, including the CJs, have the smog bumps. Block deck height was increased three times, but not enough to have any real meaning to compression ratio. Compression was lowered in '72 (8.5:1) and again in '73 (8.0:1) by going to larger cylinder head combustion chambers.
The deck height must not be much different thru the years, the same intake fits them all, so the spacing between the heads couldn't have changed much at all.
Compression was changed by the cc of the combustion chambers on the different heads.
There were 4 different cc's for the 385 engines.
72 76 92 97 are the 4 sizes I think.
72 and 92 are most popular.
A piston in an engine with 72cc heads will have 10.8 to 1. The same piston in an engine with 92cc heads will have 9.14 to 1 compression.
So figure that an 8.0 to 1 D3VE engine will have about 9.7 to 1 with D0VE or C8VE heads on it without changing the pistons.
Man, you guys really know your stuff. Several question here.
So, if the deck height was increased three times, the last increase would be the largest difference compared to the early blocks cast before the increase. What years were the increases made? I have a '75' truck with a 460. I assume the block was cast in '75' or perhaps '73' as are my heads. I haven't checked the casting date on the block yet.
How do you determine push rod length when installing D0VE heads on a '75' or maybe a '73' block? Is the deck height increase so little as it's not to be a concern? Can I use the same push rods from the '75' or if I to use the rods from a '70' block will they be too short because of the deck height increase? If I get new rods, what length, early or later model? If I use adjustable rocker arms, will it even matter?
I've heard someone mention at one time a tool called a Push Rod Checker. Where do I find one? Is it a speciality tool that I have to order from the factory or specialty parts house somewhere?
73- up blocks are pretty much the same.
If you use pre 73 heads on a 73-up block, you will need the early model pushrods and rocker arm assemblies.
The D3VE heads were used from 73 to the 80's sometime. So your heads are probably 75's as well.
You would have to find the actual casting date stamp. The D3VE number is a design number and will not change until the part is revised.
Sumitt and most of the other mail order houses sell push rod length checkers for under $25.
The deck height won't make enough diference to worry about. The push rod length issue is in the difference between the '72+ pedestal mounted valve train and pre-72 rail rocker valve train. You'd probably be fine using the early 8.70" pushrods, but for $25, I'd measure them. Your 27-year-old block might have been decked or the even older heads shaved to clean them up during a rebuild.
Don't forget the most important part of your project, using an early timing chain assembly to get rid of the retarded timing on the '76.
Originally posted by georgedavila 1.73 and 1972. It was for reduced emissions and changing it makes a big difference in any 429/460, especially with higher compression.
Maybe this has been addressed before, but I havn't seen it yet. Concering the retarded cam timing, wouldn't cam makers have changed cam lobe peaks to make up for this performance lag over the years?
So if a '73 cam begins opening the valves 4 degrees later, the aftermarket cam makers would eventually design their cams to open 4 degrees earlier to counter the retarded timing set.? Havn't they done this?? I have a aftermarket cam and would consider putting a straight up timing set on if I can resolve this question.
The retarded cam would also keep the exhaust valves open slightly longer, which could heat them up and contribute do detonation and knock. What was the original reason for changing it? I've heard that the early timing sets created an atmosphere where nitrogen began to burn creating no2. or nitrousoxide. This would seem to indicate a most compete burn which would reinforce the greater power and efficiency reported with the pre '72 timing sets.
Just trying to understand the how's and whys' of the situation.
Thanks for any comments and explainations.