[bluesmobile]

So I just realized that the heads I am planning to use on my 400 re-fresh have had the combustion chambers mucked with in a weird location. (engine is +0.030" 9.75:1 CR, Forged pistons & rods, 230/236/112 HR)

It appears that somebody ground away the sides of the combustion chambers in an effort to unshroud the valves. They ground away (between adjacent cylinders) enough material that a head gasket is line-to-line with the edge of the combustion chamber.

I have no other option but to use these heads, I'm not starting over now...

Since the combustion chamber is now wider than the cylinder bore, should I notch a small portion of the top of the cylinders (above the top ring) - so that the cylinder bore lines up with the edge of the combustion chamber? OR Should I just leave it alone, and live with the step from combustion chamber to cylinder?

thank you,
Jeremy

[72LuxuryLeMansLa.]

Originally Posted by bluesmobile

So I just realized that the heads I am planning to use on my 400 re-fresh have had the combustion chambers mucked with in a weird location. (engine is +0.030" 9.75:1 CR, Forged pistons & rods, 230/236/112 HR)

It appears that somebody ground away the sides of the combustion chambers in an effort to unshroud the valves. They ground away (between adjacent cylinders) enough material that a head gasket is line-to-line with the edge of the combustion chamber.

I have no other option but to use these heads, I'm not starting over now...

Since the combustion chamber is now wider than the cylinder bore, should I notch a small portion of the top of the cylinders (above the top ring) - so that the cylinder bore lines up with the edge of the combustion chamber? OR Should I just leave it alone, and live with the step from combustion chamber to cylinder?

thank you,
Jeremy

Pictures would help...........

[bluesmobile]

I searched around and found out one of the popular terms used is "Bore Notching".

I've attached a picture of what I'm contemplating doing to the bore, in order for the intake charge to flow smoothly out of the intake valve and into they cylinder, and not have a portion of the intake charge so rudely interrupted by the block surface (as the bore is smaller than the chamber).

Am I overthinking it?

Jeremy

[GRX]

Not sure which application and years, many of the blocks for 4-bbl heads had the intake relief at the top of the cylinders. Here is one of my personal '67 400 HO blocks which I pressed a sleeve into. After install I used a cone shaped sanding drum in my hand drill to reform the notch. That said, this is a 67 block with 670 heads. The notches on the later blocks were at different locations - at 3 and 9 o-clock.

[firechickenman]

Don't worry about it. Sounds like what someone did to my Wenzler heads. They have the chamber opened up to the same size as the fire ring of a Fel-pro 1016 gasket. Quite a bit larger than the 4.180" bore of the block I'm using them on. Yah, it might run a little better if the transition there was smooth, but it's not bothering me.

[pfilean]

Sounds like someone was trying to do what is suggested in some articles from a while back by Rocky Rotella. He was dong similar things but more machined and not as much hand grinding to get clearance for bigger valves.
And although some can explain when it was done and to what extent it was done better than I, in some of the early Super Duty engines the top of the block was cut to gain clearance when the heads with the bigger valves first came into use.

[android 211]

A lot of 350 Pontiacs were relieved that way.

[bluesmobile]

Originally Posted by GRX

Not sure which application and years, many of the blocks for 4-bbl heads had the intake relief at the top of the cylinders. Here is one of my personal '67 400 HO blocks which I pressed a sleeve into. After install I used a cone shaped sanding drum in my hand drill to reform the notch. That said, this is a 67 block with 670 heads. The notches on the later blocks were at different locations - at 3 and 9 o-clock.

Your relief is exactly what I am talking about!

Does anybody have any evidence that notching/relieving helps performance? I would guess that if the factory did it, then it had a benefit.

To clarify: The notch/relief, for me, is not for valve clearance (my valves are not large enough to hit the cylinder wall when open - I would guess maybe that's why the small-bore P350 had them), but to try and improve airflow from the intake charge.

Jeremy

[gtofreek]

The stock chambers are wider than the bore[4.300"]. That is why Pontiac notched them back in the performance days. Just depends on what heads you are running as to where they get notched.

What heads are you running?

[Ed Fitzgerald]

I have a 67 326 2bbl block that is notched and another I purchased from Toyswedo several years ago at Carlisle and it too was notched. I bought a 350 bored .060 over from gord (HO428) and it's also notched. FWIW. Ed

[72LuxuryLeMansLa.]

They did it to help relieve valve shrouding. There was no way the valves could hit the block without some extraordinary lift.......Or so I have been told.

[gtofreek]

Originally Posted by Ed Fitzgerald

I have a 67 326 2bbl block that is notched and another I purchased from Toyswedo several years ago at Carlisle and it too was notched. I bought a 350 bored .060 over from gord (HO428) and it's also notched. FWIW. Ed

All small bore engines were notched, as they needed to be, but the 400's in the mid 70's somewhere, lost the notches, as performance was not a priority anymore.

[GRX]

There was a whole long thread about cylinder notches a while back but can't find it. Since you're trying to match the modded combustion chambers you could go old school, clay the piston, drop the head on, and look at the impressions made.