[Will]

What is generally accepted as the maximum amount you can machine a spring seat on iron heads? Can the valve guide be reduced by a like height with no issues?

Thanks!

[steve25]

Which heads?
The 67 and up iron heads can go .100” deeper on the spring seats if no major porting has been done. If

[54nomore]

I went .150" on a pair of #62's once. There was no porting per se, only some bowl work. I have no way of knowing how thin things got, but I did not break through anywhere.

[Jay S]

There is a pretty big step to go from the valve boss down to the port ceiling. We have a set of 96 heads with stock valves that have a 1.95” spring installed height. Not sure what that is cutting in, probably around .25” with the retainers it runs. Wells are pretty deep on those heads, RA 4 port size 280 cfm head. Some else prepped those heads with the springs, and I later ported them. We usually run a longer valve and not cut down quite as far, and more pushrod clearance for bigger rockers.

[Will]

Thanks fellas!

A 250-260 cfm port job doesn't require raising the port roof so I wouldn't think that would affect things. I suppose a max effort port job could.

I'm mainly concerned with '67 and later heads, I don't have any of the earlier heads and wouldn't know what to do with them if I did.

Is the consensus then that .100" would be safe on all '67 and later, or are there some caveats?

Is 54nomore's example of .150" unusual or risky?

[Half-Inch Stud]

I always go for longer (RA IV length) valve stems.

Spring seat is a kiss cut when grinding the Cast valveguides for Positive Unbrellas. 2- cuts: inner spring, then unbrella. Sweet tool bit for drill.

[Will]

Originally Posted by Jay S

There is a pretty big step to go from the valve boss down to the port ceiling. We have a set of 96 heads with stock valves that have a 1.95” spring installed height. Not sure what that is cutting in, probably around .25” with the retainers it runs. Wells are pretty deep on those heads, RA 4 port size 280 cfm head. Some else prepped those heads with the springs, and I later ported them. We usually run a longer valve and not cut down quite as far, and more pushrod clearance for bigger rockers.

You responded while I was typing my previous reply.

Wow... That's a LOT. I wouldn't have expected you could cut that much. Is there no water jacket between the spring seat and port roof to worry about?

I haven't been able to find a picture of a cross-section of a Pontiac head to get a better idea of how much room there is to work with.

Looking at pictures of various heads that do show up when google image searching on "pontiac intake port cross section" it's pretty clear that some heads have lots of room and others very little.

[steve25]

Someone on this board once posted a cut away of what I think was a 670 head because we where talking about chamber mods.
So if you can find that post string it would help you, or maybe that person will read this and repost his pictures .

I know for sure that .100” is very safe and where you will find water is at the rear of the spring seat if your cutting the OD very large and or the head has a lot of meat removal going on from rust as I have seen in heads from the Deep South that where with mostly water.

[steve25]

I found something for you in the race section of this site.

Go to search.

Type in Valve spring seat thickness .

Up first will come a listing with a picture of a sectioned # 96 head.

The average minimum wall thickness most anywhere in a iron head is .180" , but I think
This picture shows a bit more in the rear spring pocket .


That said, as I look at this cut away it looks to me like the rear / Exh side seat section is as thick as what we see in the photo of the cut valve guide liner in the photo.

The valves are .341" in diameter so there well may be that much meat to that spring pocket area.

Anyway even if you cut for only .180" you could still run a very long over 5.200" valve .

Accually here you go, I took a picture of my IPad with my phone for ya!

[Jay S]

Looks like it would take quite a bit of grinding from both sides to become a problem. Porting up on the roof most the metal comes of the rocker stud side of the ceiling to match the short side turn when it is pulled back.

The 96 head I mentioned that I recalled has the deep cuts spring is out in the shop. I double checked it and instead of the 1.95” installed height it is 1.85 install height with stock springs and stock length valves. They are not as deep as I thought, the 10* retainers looked like they add some height too, probably about .050”. Cut is about .150”.

[Formulas]

There has been cross section cut head pictures on this site before in porting threads they would be of some use in this endeavor

[steve25]

You can get off set retainers that will add .050"of installed height yes, but with bigger than stock diameter springs and roller rockers you may run into retainer to rocker body clearance issues

[Will]

Originally Posted by steve25

I found something for you in the race section of this site.

Go to search.

Type in Valve spring seat thickness .

Up first will come a listing with a picture of a sectioned # 96 head.

The average minimum wall thickness most anywhere in a iron head is .180" , but I think
This picture shows a bit more in the rear spring pocket .


That said, as I look at this cut away it looks to me like the rear / Exh side seat section is as thick as what we see in the photo of the cut valve guide liner in the photo.

The valves are .341" in diameter so there well may be that much meat to that spring pocket area.

Anyway even if you cut for only .180" you could still run a very long over 5.200" valve .

Accually here you go, I took a picture of my IPad with my phone for ya!

Awesome, thanks Steve!

From that it definitely looks like a .150" cut shouldn't be a problem unless there's severe water jacket corrosion, and even then it's going to be a problem in the bowl before the spring pocket.

[Will]

Originally Posted by Jay S

Looks like it would take quite a bit of grinding from both sides to become a problem. Porting up on the roof most the metal comes of the rocker stud side of the ceiling to match the short side turn when it is pulled back.

The 96 head I mentioned that I recalled has the deep cuts spring is out in the shop. I double checked it and instead of the 1.95” installed height it is 1.85 install height with stock springs and stock length valves. They are not as deep as I thought, the 10* retainers looked like they add some height too, probably about .050”. Cut is about .150”.

Thanks for the info Jay!

I'm thinking of this from two different angles -

1st, as a cheaper alternative to longer valves if I want to run a high lift cam. Might be cheaper to just have the seats cut at the same time the guides get cut for positive seals than to buy new valves.

Second, as a possible weight-savings measure. Shorter valves = lighter. Use some beehive springs with titanium retainers and some LS-style lifters if going roller or solid flat tappets and you should have a combo that can really rev without massive spring pressures.

[steve25]

The retainers used on Beehive or conical type springs are so much smaller in diameter and as such way lighter that it does not pay to shell out the money for Titanium ones unless your buzzing the motor to over 8000 rpm.

Also breaking into the runner is not a issue as I have intentionally done that to gain the port area I was looking for.

The easy fix was a .010” spring shim gray silicone gasketed in place.

[lust4speed]

I've posted this photo before of a junk 670 head we cut up a long time ago to see how far we could go on lowering the spring seat. Ended up going .120" back in 1985 and the heads we did have survived and are currently on the blue GTO street car running .620" lift with 148 set pressure and about 380 over the nose. At one point in the 90's we were running a solid roller with 260 seat and 490 with .666 lift.

Have to admit that we now simply take the easy way out on cast iron heads and run the RAIV length valves for 1.80" seat height.