I was told a "333 and 690 head provides virtually same compression ratio".

hrlykngt

hrlykngt

Well Known Member
Here is a side by side of 2 different 333 I have, one has large valves in it, havent measured but guy I got from did some work on them.

IMG_8229.JPG
 

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MRHP

MRHP

 
Supporting Member 1
The 8cc difference between the heads cant be all that much compression difference on these engines. Maybe .5-.6 of a point.
 
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427John

Well Known Member
1964SuperStocker said:
How about the valves? If the seats were cut down/modified then that would change volume up or down depending on how it was done and which valves were stuffed back in. Finding as cast factory parts is hard.
Click to expand...
A head that has had multiple valve jobs where the valve heads are lower in the seat will affect CC's especially on a big valve head like a 690. The more a valve head stands proud of the roof of the combustion chamber the more it intrudes into the combustion volume making it smaller. The design of the valve head (dished vs flat) can also affect it, for example a 333 head that has had the big flat valves installed with minimal material removed to cut the seat could have equal or even less CC's that a 690 head with dished valves that has had multiple valve jobs sinking the valve in the seat. This is why published numbers for chamber volume don't really mean much except when they are fresh off the assembly line and it is important to measure your actual volume when targeting a specific CR and ordering pistons. Add in the fact that after all these years there is a good possibility that the heads have been clean up milled during previous valve jobs. But assuming 2 heads that are virgin I would agree with Randy that the 333 head would give slightly lower CR since there is an ~8 cc difference.
 
1964SuperStocker

1964SuperStocker

Well Known Member
Supporting Member 3
427John said:
A head that has had multiple valve jobs where the valve heads are lower in the seat will affect CC's especially on a big valve head like a 690. The more a valve head stands proud of the roof of the combustion chamber the more it intrudes into the combustion volume making it smaller. The design of the valve head (dished vs flat) can also affect it, for example a 333 head that has had the big flat valves installed with minimal material removed to cut the seat could have equal or even less CC's that a 690 head with dished valves that has had multiple valve jobs sinking the valve in the seat. This is why published numbers for chamber volume don't really mean much except when they are fresh off the assembly line and it is important to measure your actual volume when targeting a specific CR and ordering pistons. Add in the fact that after all these years there is a good possibility that the heads have been clean up milled during previous valve jobs. But assuming 2 heads that are virgin I would agree with Randy that the 333 head would give slightly lower CR since there is an ~8 cc difference.
Click to expand...
I was hoping to get these heads I have measured before Tri-State race here in Iowa but the kids flag football schedule is digging into my play time. So many questions on this topic to keep the information/understanding consistent. Again, a big thank you to all of you contributing to the information/knowledge. Some of us young guys want as much as we can gather so we don't loose this information.
 
MRHP

MRHP

 
Supporting Member 1
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