Originally posted by Ron454:
Hello gang.

I'm going to use AFR 305 cc heads. I have noticed that the chamber at it's widest point is wider than the bore, which in my case is 4.32".
In the old days, GM used to notch the top of the bores...for valve clearance? Or was it for airflow?
I'm wondering if the overhang hinders airflow???
Years ago on a 427 we built, we used a die grinder to releive the tops of the bores to aid airflow. That engine ran damn hard for what it was.
Just thinking outloud, but I've often heard that bigger bore unshroud the valves and give better airflow.
Comment?
I plan to discuss this with my engine builder.....

Ron

=
Hi Ron,
Yes the relief helps airflow on the small bore stuff especially with those heads.
They were designed around the bigger bore & will pick up around 20cfm in some places on the larger bore so anything you can do to unshoroud the chamber will help.
Also use the 1017-1 gasket not the 1027.

 

Yes, just carefully contour the chambers out to the headgasket and down to just above the top rings closest measurement to the deck.. Say an 1/8" deep or maybe a schosh more?? (3/16"??)....

Usually a .060" overbore will remove stock reliefs anyway...

pdq67

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Sorry that I can't seem to type in english! Gads, I are a college graduate and I no plenty!

Anyway, I'll haul a head out to the machins shop and scribe the chamber size on the top of the bore and we can go from there. It's a bit tricky, but with the block empty......it works ok.
I'm not going to mod the chamber out to the gasket, I figure AFR knew what they were doing when they CNC'd them.

BTW...I will buy the 1017-1 gaskets and hopefully someone can use the 1027's that I already have!

Thanks Mike and PDQ (Real name?)

 

Paul, (aka, pdq67)

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You definitely don't want to mess with the chamber & the reason for the large bore gasket is the 1027 will hang into the chamber the way the heads are CNC'd

And before someone tells me what gasket they tell you to use in the AFR catalog or their site for the 4.250xxx bore,,, it is wrong.

 

wouldnt it be a better idea to use the head gasket as a template ? It would make for a smoother transition into the cylinder.

Where if going by the chamber shape there will be a gap between the head and the block ....

After all .. your just going to releive the valve areas ... correct ??

 

Originally posted by BLK64SS:
wouldnt it be a better idea to use the head gasket as a template ? It would make for a smoother transition into the cylinder.

Where if going by the chamber shape there will be a gap between the head and the block ....

After all .. your just going to releive the valve areas ... correct ??

Yes & a lot simpler
And you will find the chamber follows the gasket pretty close around the valves

 

Hello Fellas,

This is sort of a side note but my question is:

If you have a 1.25 bored out 454 that has a 4.375 bore size can a 781# combustion chamber be too small?

 

Not really.
A stock closed chamber BBC head will actually overhang the bore on a .100" over 454, meaning the chamber is wider than the bore...