[Gary H]

I'm restoring a 66' GTO and I've decided to go back with the original 093 heads. I'm going to be running a mild hydraulic roller cam and I want to convert the heads to screw in studs. Does the rocker stud boss need to be milled down first before tapping for the studs? I want to make sure that the rocker arm will clear the stud hex where you tighten it down. Secondly, what's the largest intake valve that I can run on that head? The exhaust valve will stay the stock diameter.

[b-man]

There’s not much room to go bigger with the intake valves, you might be able to fit a 1.96” valve and even then you may need to turn the valve head diameter down a little.

The stud bosses definitely need milling, something around .250” would be my estimation. A little more if you’re eliminating (drilling out) the factory guide slots in the heads and adding aftermarket adjustable guide plates.

When we did my 1964 #9770716 heads we ended up going 1.93” and 1.645” using whatever aftermarket valves that were close and then turning them down. Bigger may have worked but I wasn’t the one doing the work.

https://forums.maxperformanceinc.com...2&postcount=24

We used these valves:

8 ea. 6000SG S.I. Stainless Intake Valves - 1.960" x 4.970" - $128.00
8 ea. 6001SG S.I. Stainless Exhaust Valves - 1.660" x 4.970" - $128.00

[25stevem]

It’s flat out not worth the effort to put bigger valves in these heads unless you looking to pick up compression from having the bigger valves eat up chamber CCs.
For these heads to begin to make good usage of a bigger intake valve the throat needs to be opened up and the short turn precisely reworked so as to pick up high lift flow, yet not loose any flow below .300” lift.

The gain in flow on the intake side by just installing a bigger valve is minimal and if you where stepping up in intake valve size I would not go bigger then 1.90”.

Above 1.90” the chamber needs to be unshrouded to get all the added new high lift flow out of it.

On the exh size just stepping up to a bigger valve provides even a smaller percentage of gain then doing such on the intake side.

The most helpful easy thing you can do on the exh side is to simple put a 30 degree back cut on the back side of that valve.
On the intake side the right valve job even with using the stock size valve will pick up more air flow then then just stuffing in a hair bigger valve with the wrong valve job.

The stock intake throat size used in these heads is not too bad, in fact the valve to throat ratio is a bit bigger then that used on the later 14 degree 2.11” valve heads.

What flat out sucks on all of these heads is the pinch in horizontally of the exh port short turn in the valve bowl .
3 minutes spent with a grinder in each exh port will pick you up 8 to 12 cfm .

Here’s a picture of what I mean in a stock exh port bowl.

Note how the upside down U shape is badly pinched in on the intake valve side of the exh bowl.

The next picture shows the difference after not even 2 minutes of rework,

[25stevem]

Here’s another shot of the pinch in with it back lit.

[Gary H]

Originally Posted by 25stevem

Here’s another shot of the pinch in with it back lit.

Great information! Thanks for the pictures too. What's your thoughts on porting on the intake side. What areas would you concentrate on?

[25stevem]

I will post some pictures for you tomorrow.

[25stevem]

Gary, what do you have for porting tools?

[Gary H]

Originally Posted by 25stevem

Gary, what do you have for porting tools?

High speed 1/4" shank air grinder and a variety of carbide bits

[25stevem]

You will need to get some inside snap gauges, a cheap plastic dial caliper and some pan cake type grinding stones.

[77 TRASHCAN]

Steve,
What ca, be gained by smoothing the shap edges off, just below the valve seats. I'm aware the short turn radius CANNOT be improperly shaped.
Thanks!!!

[25stevem]

In terms of the intake ports there’s nothing to be gained by let’s say .005” to .010” removed just to as you say smooth things over, but there is a fuel droplet break up action that is lost by anything smoother then a 120 grit like finish .

On the exh side smooth blending of changes in shape and area will always help .