Hi everyone,
Recently, I posted a topic here about the differences between all of the BBC
dimple rods. It was great to get so much feedback and information. I now
have a much better understanding about them. My thanks to all. This forum is
truly the best venue for this type of research.
As some of you may recall, the BBC dimple rod discussions got into early vs.
late and/or 1st vs. 2nd designs for these rods and at some point, the topic
migrated into closed vs. open chamber designs.
To that end, I would like to ask some questions relating to the 427 engine and
the use of closed vs. open chamber pistons.
When exactly did the open chamber design come into production? Was it for the
late 1969 L-88's and all ZL-1's? Was it first in aluminum BBC heads, then
cast iron later? Then, there is the really odd 3933148 cast iron head that
used an almost full open chamber design. This was used in the 1969 model year
on the 396-265hp ( 2-bbl Rochester ) full size cars.
Now, it gets a little more involved. My '69 L/89 used the 3919842 closed
chamber aluminum heads. Over the years, I have seen a few '842 heads that
look more open chamber-like than closed. My '842 heads have a combustion
chamber that is the standard bathtub shape. I have seen '842's with the
spark plug side layed-back at an angle more like the open chambers.
Would not that change require a different casting or part number? Or, could
these '842 heads have been owner modified to reduce compression sometime in
the past? Can this modification be performed on aluminum heads safely? Due
to core shift in the casting process, I remember reading that this type of
combustion chamber modification was risky. Do any members here remember
any '842 heads with these differences?
Lastly, I know that closed chamber pistons can be used with open chamber heads,
but the inverse does not apply without dire consequences. If I am trying to
build an L-88, what piston should I be looking for to match up with the '842
heads, assuming I was to start with stock items from 1969? Were the 3946074
aluminum heads used on late introduction L-88's? Or even early L-88's? What
piston would match with these heads? BTW, did the L-88's use the '842 heads
in 1969? What about '67 & '68?
I know there were probably a lot of BBC combinations from 1967-1972 as they
relate to this topic. I hope some of you can help me understand how this all
fit together.
Yes, another BBC history lesson in the making.
Thanks,
Steve
Recently, I posted a topic here about the differences between all of the BBC
dimple rods. It was great to get so much feedback and information. I now
have a much better understanding about them. My thanks to all. This forum is
truly the best venue for this type of research.
As some of you may recall, the BBC dimple rod discussions got into early vs.
late and/or 1st vs. 2nd designs for these rods and at some point, the topic
migrated into closed vs. open chamber designs.
To that end, I would like to ask some questions relating to the 427 engine and
the use of closed vs. open chamber pistons.
When exactly did the open chamber design come into production? Was it for the
late 1969 L-88's and all ZL-1's? Was it first in aluminum BBC heads, then
cast iron later? Then, there is the really odd 3933148 cast iron head that
used an almost full open chamber design. This was used in the 1969 model year
on the 396-265hp ( 2-bbl Rochester ) full size cars.
Now, it gets a little more involved. My '69 L/89 used the 3919842 closed
chamber aluminum heads. Over the years, I have seen a few '842 heads that
look more open chamber-like than closed. My '842 heads have a combustion
chamber that is the standard bathtub shape. I have seen '842's with the
spark plug side layed-back at an angle more like the open chambers.
Would not that change require a different casting or part number? Or, could
these '842 heads have been owner modified to reduce compression sometime in
the past? Can this modification be performed on aluminum heads safely? Due
to core shift in the casting process, I remember reading that this type of
combustion chamber modification was risky. Do any members here remember
any '842 heads with these differences?
Lastly, I know that closed chamber pistons can be used with open chamber heads,
but the inverse does not apply without dire consequences. If I am trying to
build an L-88, what piston should I be looking for to match up with the '842
heads, assuming I was to start with stock items from 1969? Were the 3946074
aluminum heads used on late introduction L-88's? Or even early L-88's? What
piston would match with these heads? BTW, did the L-88's use the '842 heads
in 1969? What about '67 & '68?
I know there were probably a lot of BBC combinations from 1967-1972 as they
relate to this topic. I hope some of you can help me understand how this all
fit together.
Yes, another BBC history lesson in the making.
Thanks,
Steve
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