[Wanton Pontan]

So I've been reading (and watching) a good deal about porting iron heads. And now have a decent understanding of the fluid dynamics, the porting theory etc... and of course I want to try my hand at it....

And as you'd expect from a 50 year old set of heads they look nothing like any tutorial--I can hardly make out the seat (maybe) from the rust. So I know this is the one area where flow really matters, and the one area where I can really eat it.

So, I'm a bit stuck..I was going thinking I'd have the valves shaved and re-seated after porting in case I did nick a seat, but with the photo attached I really don't know where to start with these.

Would you take them to the machine shop, have it all shot, square-decked, shaved, and then take it home do the porting and then go back to have them install new seats?

[Schurkey]

Decent drill motor, wire brush. Remove all loose carbon and rust. Will make the valve seats easier to see.

No sense putting ten cents of machine work into those heads until after you've played with the porting. You break-through into water, or the pushrod pinch, and you can just upend 'em into the recycle bin.

[J.C.you]

If you don’t know history of heads. Wire brush, take to machine shop have cleaned, check for excessive core shift, then magniflux before go any further

[steve25]

Do first what's posted in the above,that being getting them cleaned up, then glass beaded and then mag'ed.

You do not what to waste hours grinding only to later find out one or both may be cracked.

I don't know what on line videos you have been watching, but 99% of all the ones I have seen are a waste of of time, all to many of these literal shade tree grinding good old boys do not even have a flow bench to prove out before and after flow numbers.

Such a bunch of clowns only trying make some YouTube bucks off the video!

Here's and simple 100% carved in stone rule to keep in mind about porting any head, it's easy math.

It states Dx1.8 and relates to valve lift numbers vs flow.

D is the diameter of the valve your working with.

Example.
Pontiac 2.11 Intake

The math then produces a number of 379.

This tells us that up to . 379" Intake valve lift the profile / angles of the the valve seat ( especially with a multi angle valve job) will control the level of flow produced, not for example the much talked about push rod pinch area or the sharp edge left on the short turn from the factory machining or casting.


So if your running a Cam of let's say .500" lift then 67% of the air flow your getting is taking place up to that .379" lift, you don't want to unknowingly screw that up / demimish that unless you pick up enough higher lift flow to make up for the loss, especially in terms of Intake cfm numbers from .200" on up.

Next the max hp you can make is determined by the minimum port area , do you know where that is in a Pontiac head?

[Wanton Pontan]

Thanks. So I'm mostly relying on Ch, 7 of the Jim Hand book -- am making a few sizing coins. I was not sure if a wire wheel would damage the seats...

When I mentioned videos, I really meant more of the theory for instance:
https://www.youtube.com/watch?v=NlRX...THonde&index=1

Of course come across good ole boys, but trying to get beyond the basics and still marry with the practical application.

[steve25]

What casting number head is in your photo?

It’s hard to tell, but it looks like 6X-8, or maybe even a 6H casting off of a 455.

[Wanton Pontan]

Originally Posted by steve25

What casting number head is in your photo?

It’s hard to tell, but it looks like 6X-8, or maybe even a 6H casting off of a 455.

Thanks Steve,
They're 6x-4's. I was planning on following Jim Hand's book and then getting them shaved to about 84-85 cc. Although the book mentioned shaving upto 0.60" the machine shop I spoke to was already hesitant at taking 0.030" off.

[Dragncar]

I had .060 shaved off my 197 HOs and ran them for thirty years. Heads are still fine, never blew a head gasket.

[steve25]

I have had and used the 4 series, 5 and 6 series ( 6X) milled .060” and have had no issues.
But whenever you mill them all the holes on the deck surface should get treated to a slight chamfer with a chamfering bit as in my photo.
This especially needs to be done when milling has taken off more then .030” so as to deny a crack a place to start.

I would also suggest you check on machine shop prices for milling a head more then .040” because at that point the cost for the needed milling of the intake flange the same amount will need to be factored in .

[Wanton Pontan]

Originally Posted by steve25

I have had and used the 4 series, 5 and 6 series ( 6X) milled .060” and have had no issues.
But whenever you mill them all the holes on the deck surface should get treated to a slight chamfer with a chamfering bit as in my photo.
This especially needs to be done when milling has taken off more then .030” so as to deny a crack a place to start.

I would also suggest you check on machine shop prices for milling a head more then .040” because at that point the cost for the needed milling of the intake flange the same amount will need to be factored in .

This is great to hear. To you guys running milled 6x heads, did you go to 1.77" exhaust valves? As pointed out that was rate-limiting at a lower lift. I took apart the 670 heads an found the valves were 5.060" while the 1.66" ext valves were 4.960" in length. Then, if milling 0.030+ off the head I worry about interference issues. I was looking at flat-top pistons with the stock wrist pin height. Do you tend to get a stronger valve spring combo? Any issues with floating?

[steve25]

With a 455 if you’re not intending to have a need to make peak hp above 5400 rpm then you do not need to step up to a 1.77” exh valve.

Just get a set of new intake and exh valves in the stock length for your 6X heads.

If you mill your heads .045” or more you will need to check your valve train geometry to see if you need a different length push rods.

Note, with stock 6X heads, 9.5 compression, a comp cams P-286-AH8 cam, a Q-jet and headers you would have to work at not making at least 370 Hp and 480 ft lbs .

You need to run new valve springs and for this cam above you need the correct springs to handle the lift it produces.

Also if your heads have more then 30K miles on them you can’t rerun your heads and expect good results.
You need to at least having a shop freshen up the valve job.

After doing the porting work guided by Jim’s book I would assume you would much closer to producing 400 Hp.

[Wanton Pontan]

Originally Posted by steve25

I have had and used the 4 series, 5 and 6 series ( 6X) milled .060” and have had no issues.
But whenever you mill them all the holes on the deck surface should get treated to a slight chamfer with a chamfering bit as in my photo.
This especially needs to be done when milling has taken off more then .030” so as to deny a crack a place to start.

I would also suggest you check on machine shop prices for milling a head more then .040” because at that point the cost for the needed milling of the intake flange the same amount will need to be factored in .

Originally Posted by steve25

With a 455 if you’re not intending to have a need to make peak hp above 5400 rpm then you do not need to step up to a 1.77” exh valve.

Just get a set of new intake and exh valves in the stock length for your 6X heads.

If you mill your heads .045” or more you will need to check your valve train geometry to see if you need a different length push rods.

Note, with stock 6X heads, 9.5 compression, a comp cams P-286-AH8 cam, a Q-jet and headers you would have to work at not making at least 370 Hp and 480 ft lbs .

You need to run new valve springs and for this cam above you need the correct springs to handle the lift it produces.

Also if your heads have more then 30K miles on them you can’t rerun your heads and expect good results.
You need to at least having a shop freshen up the valve job.

After doing the porting work guided by Jim’s book I would assume you would much closer to producing 400 Hp.

So I had the following in mind:
It's a 400 (1976 557xxx block).
Hone+stud the caps.
Keep stock crank+rods
Bore +0.040 with a 6.7 cc flat top piston.
Melling SPC-7 (068) cam w/stock lift
6x-4 ported, valves re-cut etc (which was why I'm thinking I'd have them cut for 1.77" ex). Have heads shaved ~0.030" which hopefully will yield 85-87 cc chambers depending on what I read about casting tolerances, the valve job, and "deburing" the chamber.
Planned to use the stock 1.5:1 rockers, was planning to use factory replacement valve springs...but I'm continuing to learn
Use a 0.027" thin head gasket to get just north of 9:1 static CR.
Either Q-jet or a Holley 750 on top.

For now this will sit in front of a TH400 and a highway geared rear.
This seemed like a fairly straight forward recipe similar to many in the back of Jim's book.