440 Mopar combustion chamber??
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440 Mopar combustion chamber??
What is the purpose of the flat divot cast into big block Mopar heads? Years ago a machine shop guy told me they were a reference for milling the head surface. What say you?
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Re: 440 Mopar combustion chamber??
Would doubt that very much. Since it is a casting, & not machined, how can accuracy of material removed be guaranteed?
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mag2555
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Re: 440 Mopar combustion chamber??
My best guess is that it’s a support pad for a machining operation, but not a reference point for such.
It looks like your using the Mopar performance porting temple kit?
If so that’s all well and good but be careful to not remove too much of the factory bottom cut, as it needs to be left at least ,060” tall, especially if that’s a cast with the very shallow short turn that has the so called Hubber hump cast into its short turn area.
I have ported many heads who’s owners have used that porting kit and removed too much and then even when stepping up to the 2.14” intake valve did not have enough bottom cut left for my liking even when making out the OD of that new bigger 2.14” valve!
Also note that if your fighting for compression do not unshroud the exh side of the chamber like you have it marked out for.
There’s a lot less flow on the cylinder wall side trying to get into the valve bowl then the area presented to the valve by the rest of the cylinders area, especially on the intake valve side of the exh bowl.
A much bigger flow gain can be had by adding a back cut to the exh valve itself!
It looks like your using the Mopar performance porting temple kit?
If so that’s all well and good but be careful to not remove too much of the factory bottom cut, as it needs to be left at least ,060” tall, especially if that’s a cast with the very shallow short turn that has the so called Hubber hump cast into its short turn area.
I have ported many heads who’s owners have used that porting kit and removed too much and then even when stepping up to the 2.14” intake valve did not have enough bottom cut left for my liking even when making out the OD of that new bigger 2.14” valve!
Also note that if your fighting for compression do not unshroud the exh side of the chamber like you have it marked out for.
There’s a lot less flow on the cylinder wall side trying to get into the valve bowl then the area presented to the valve by the rest of the cylinders area, especially on the intake valve side of the exh bowl.
A much bigger flow gain can be had by adding a back cut to the exh valve itself!
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
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rebelrouser
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Re: 440 Mopar combustion chamber??
My experience is that you are correct. Several years ago I built an engine with some KB pistons that had a pad on them to provide a Quench to the BBM mopar open chamber heads. The flat area of the chamber in the cast combustion chamber varied .015 from chamber to chamber and head to head, I had to set them up in a mill and make them all the same to use the pistons.
Re: 440 Mopar combustion chamber??
That’s actually a photo I grabbed quick off the interweb. You’re right as a casting is not a good reference point. Even when told that in my impressionable youth I doubted it but still respected my elders.
As for the mopar porting templates I always have stayed a little shy of what they want. I’ve seen guys go a little more and it actually slowed them down.
Just curious on the dimples. It’s always been a question in my mind and just happened to think of it again. Thanks for the responses.
As for the mopar porting templates I always have stayed a little shy of what they want. I’ve seen guys go a little more and it actually slowed them down.
Just curious on the dimples. It’s always been a question in my mind and just happened to think of it again. Thanks for the responses.
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Ken_Parkman
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Re: 440 Mopar combustion chamber??
That's a casting target point. Used for setting up the casting location relative to the machining operations. Since the machined deck is critical to the cast chamber location for volume you want the target point in the chamber.
Re: 440 Mopar combustion chamber??
This is just my theory on it....... nothing I’ve read anywhere confirms it.
I believe it is a “touch off” point for referencing how deep the seats are cut.
How I came to this conclusion is from seeing the correlation between the pad depths and seat depths on a decent sampling of what were probably the most inconsistent castings I’ve ever worked with....... Mopar Stage VI heads.
It was not at all uncommon to have the seat depth between two heads be .060” different.
And sometimes that would be on only one head.
The thing was...... if you just moved the valve from hole to hole....... it wasn't like the valves sat way proud in some chambers, and were sunk in others.
They all looked to be about the same...... relative to what chamber they were in.
How is that possible? The whole chamber, and that little pad, varied that amount.
On one head, one whole chamber was sunken in about 1/8”!!
And yes, so were the valves.
That head was being used before it was sent to me!!
I guess no one noticed the tip heights being .125” higher, or the .125” taller installed height.
That head ended up getting replaced.
Anyway......... I’ve never looked into whether or not there was any correlation between the pad and valve depths on the oe heads, but there seemed to be a link on the stage vi’s.
In the MP engine manual, referring to the factory SB Mopar heads there is some mention of using the pad to determine the amount the heads have been milled prior to rocker stand machining.
Many OE SBC heads have that pad as well.
I believe it is a “touch off” point for referencing how deep the seats are cut.
How I came to this conclusion is from seeing the correlation between the pad depths and seat depths on a decent sampling of what were probably the most inconsistent castings I’ve ever worked with....... Mopar Stage VI heads.
It was not at all uncommon to have the seat depth between two heads be .060” different.
And sometimes that would be on only one head.
The thing was...... if you just moved the valve from hole to hole....... it wasn't like the valves sat way proud in some chambers, and were sunk in others.
They all looked to be about the same...... relative to what chamber they were in.
How is that possible? The whole chamber, and that little pad, varied that amount.
On one head, one whole chamber was sunken in about 1/8”!!
And yes, so were the valves.
That head was being used before it was sent to me!!
I guess no one noticed the tip heights being .125” higher, or the .125” taller installed height.
That head ended up getting replaced.
Anyway......... I’ve never looked into whether or not there was any correlation between the pad and valve depths on the oe heads, but there seemed to be a link on the stage vi’s.
In the MP engine manual, referring to the factory SB Mopar heads there is some mention of using the pad to determine the amount the heads have been milled prior to rocker stand machining.
Many OE SBC heads have that pad as well.
Somewhat handy with a die grinder.