[steve25]

This is only the second time I have had my hands on a pair of these heads.
The first time was before I had
My flow bench, but this set will not escape getting flow tested before and after my bowl porting work.

I also have the heavy as hell intake manifold that I want to flow test at least the 4 runners off the shallow side of the plenum.

Here are a few photos and a review of pertinent size info.

I will start with the intake port details, then the exh port and also make some comments on both.

INTAKE.

Intake bowl throat, very near exactly 1.70 x 1.59” as can be seen in one of the photos with the template sitting right on top of the valve guide.

This works out to 2.700” Sq in.

Intake seat
45 degree with a 2.075” OD.

Seat width .088”

1st bottom cut 60 degree, width .128”

2nd bottom cut 70 degree with a depth of .744” on the exh side of the bowl and .205” on the common wall side of the bowl.

What there is of a short turn arc is .996”, and there is not much overall short turn height, in fact the 6X castings have way more height then these heads.

Now I can see why these can not be ported into flow rates like the RA4 heads without building up the short turn.

Port window height at crown 1.925”.
This is quite tall and indeed breaks into the rocker stud hole.
Window width= 1.407” on the floor, 1.307” on the roof.

Note how squared off the floor is at the start of the windows.

This is a larger version of what the 6X heads have.

This ruffly works out to at best 2.67 Sq inches since I did not subtract for any corner radius.

Port height at flange = 2.265”.

Minimum Port width at center height of flange = 1.082”
Chamber depth on shallow side = .242”


EXHAUST


Valve bowl throat = 1.465”, 1.685” Sq inches.
This is only 67% of the massive area increase at the window as you will see in a photo.

Seat 45 degree.
Seat OD. 1.765”
Seat width .055”
Bottom cut 70 degree with a depth of .312”

This 70 degree bottom cut is a radical change from Pontiacs normal 90 degree cut in relation to the chamber floor.

The minimal amount of short turn arc these heads have looks like .992”.
With that said these exh ports have a good amount of overall short turn height for a deep chamber low compression head, that may exceed the good amount of what the 6X heads have going on.

Actually these SD heads may have more height then what the 6X heads have.

Window height = 1.565”

Window width = 1.505”.

Average width at flange = 1.735” or 2.364” Sq inches.
This amount of square inches and more importantly the amount at the window as compared to the bowl, if nothing else in my experience will make for a big velocity differential between the roof and floor of the exh runner, and that’s never good for reversion.

We will see when start flow testing later in the week.

I will also be making port molds .

There are two more photos I need to post separately after this.

[steve25]

More photos.
The first photo shows the area at the window as viewed from the flange.

The second photo shows how deep the 2nd bottom cut angle goes on the exh valve side of the bowl.

[Skip Fix]

When I flowed a 73 SD intake at about .300 on the ported #62 it actually picked up the airflow! But you ar right a heavy sucker. I tried it on my RAIV motor in NMCA as a cast iron intake did not get a HP factoring hit like even a factory aluminum so I could pull weight out vs the HO intake-ran the same.

[soupman]

Hey Steve, you flowed my intake that was ported by SD using the Ruggles template. Curious what the flow of the one you have vs. my d port modified intake?

[steve25]

I will be flow testing the intake over the weekend, or next week.

I have to reinforce my head adapter I will use to make that flow test since the last time I flow tested a very heavy Ford iron intake for a 390 FE motor it ripped the top plexiglass plate off that particular adapter of mine.

Skip that’s interesting!
It’s too bad the EGR valve had to be on the shallow side plenum.

If they could have put it on the deep side and yet cleared the carbs throttle linkage then those 4 runners would have had a better flow balance with the other 4 runners.

[mgarblik]

Interesting and timely information. I have a pair of first run SD-455 heads here as well. I need to get the short block finished first, Then I will take these heads apart and see how they compare to your set. I have no idea if any significant work was ever done to them. They are still assembled. I don't see any evidence of port matching or anything in the chambers. May have had a valve job though.

[johnta1]

Steve, what are the intake and exhaust port lengths? And the volume of each?


Will be interesting to see what they can flow.

[Skip Fix]

I think when I sold the SD intake and weighed it it was 44 lbs! about the same as an Olympic 20 KG plate! Had those giant EGR bosses on the bottom.

[steve25]

John I will get that info later in the week., I am also going only a bowl porting job on these heads so in terms of what they can be maxed out to I can only extrapolate.

I will add some clay on the short turn of the intake ports and see where those flow numbers head.


I recall reading decades ago somewhere that there where two versions of these heads in terms of the exh valve job done by the factory , like maybe the 74 heads had a 3 angle valve job or something?

Anyone recall such?

[Half-Inch Stud]

I agree that a Bowl job is all those ought get. Exhaust path doesn't need anything else.

Intake path will have the highest gain in the Bowl, while a touch to the rest of the runner would drop value vs a tiny improvement.

Intake valvestem roof grind on CYL-side to swirl the flow into the chamber; curved flow in CYL. Would also help to keep flow attached to chamber then blend to CYL wall. Proper head gasket hole would make a good stencil, for minimal grind.

[Joe's Garage]

Originally Posted by steve25

I recall reading decades ago somewhere that there where two versions of these heads in terms of the exh valve job done by the factory , like maybe the 74 heads had a 3 angle valve job or something?

Anyone recall such?

I think it was from one of the H.O. Racing articles where they pointed out that the earlier heads had a 3-angle exhaust seat while the later heads had a 2-angle exhaust seat.

[steve25]

Thanks Joe.

I think I still have that HO info.
I will dig it out later and report back.

[mgarblik]

Originally Posted by Joe's Garage

I think it was from one of the H.O. Racing articles where they pointed out that the earlier heads had a 3-angle exhaust seat while the later heads had a 2-angle exhaust seat.

Now I can't wait to see what my early heads have on them. Also interesting that they reduced the cuts and found something? I have an assortment of radius cutters from the Mondello collection that have improved every head I have ever used them on. Any thoughts? (Exhaust only)

[steve25]

I can’t say or recommend anything to you until I flow test one exh port on these SD heads.

I will make time to do that in the late afternoon and post up what I find.

The problem I find with getting big improvements when starting out with a head that all ready has a 1.77” valve and the typical factory 90 degree top throat cut ( which these SD don’t have ) is the time consuming screwing around valve job wise to find what works best for the motor your dealing with, as in for example do you go with a 3 angle valve job that helps out low lift flow a nice amount, or shoot for higher lift flow which will always take reworking of the runners for more area.

In terms of 1967 and up iron heads I love to start off with the small valve heads , port them up and apply a 3 angle valve job to get a 1.77” valve in there.


For example here are the flow numbers for a stock 6X center exh port in column 1, then ported in column 2 with a valve with a 30 degree back cut, and then column 3 that same port with a 3 angle job and a back cut 1.77” valve.


.050”//// 20.6///// 26.2/////32.9

.100”//// 43///// 52.6///// 67.3

.200”//// 93///// 105.8///// 127

.300”//// 125///// 138.6///// 157.5

.400”//// 135.7///// 160.4////// 172.3

.450”//// 138.7///// 166.4///// 179.3

.500”//// 140.2///// 171.8//// 185.7

.550”///// 141.7///// 175.8///// 191.6

.600”//// 141.7///// 180.7///// 193.6

.650”//// 141.7///// 181.7///// 207.5

.700”//// 141.7///// 174.7///// 211.4

With the 1.77” valve there was some light turbulence I could hear starting off at .500” up to .650” and polishing / blending in the 60 degree bottom cut around the short turn got rid of it.

The flow numbers in column 2 and 3 where achieved with what I call the sub throat (. Real throat size) of 1.494” which is not much bigger then the stock 1.360” throat.

Yes, I know I have taken my own post off the rails here with this talk of 6X heads, but it makes a good point in regards to what a 3 valve job can do along with a 6.5% bigger valve.

[sdbob]

Interesting. I have an 73 SD intake that I got from John Herslow. The bottom cast iron is ground off. Why ? He said NHRA allowed removal egr!

[steve25]

Well here’s the flow numbers for a stock exh port, and all I can say is I for sure got my work cut out for me!

I am so shocked and sad to say that I have never flow tested a exh port that had so much turbulence across a large range of valve lifts.

So here’s the details.

The exh port I just tested was the center one that has no exh heat passage.

I did a 3 second long valve job clean up just to get a good seal on the intake and exh valve.

The 1,77” valve I used was a stock one with no back cut.
Air temp was 60.
Bor 30.1
Humidity 88% / light rain.

With what I post here the T after the flow number is where there was turbulence, a plus sign means that lift point had more turbulence then the other lift points.

Flow@ 28”

.050”/////25.2

.100”///// 56

.150”///// 84.7

.200”///// 112 T

.250”///// 134.2 T

.300”///// 144 T+

.350”///// 154.5 T

.400”///// 160.4 T

.450”///// 165.4 T

.500”///// 167.4

.550”///// 169.9

.600”///// 173.8

.650”///// 179

.700”///// 181

I did not have the time to test the velocity gradient between the floor and the roof, nor do a flow test with a pipe, so I don’t know maybe a pipe on the end of the port will help with the turbulence.
We will see!

[sdbob]

I'm going look back at HPP mag where Pete flowed stock heads esp I'm going to look at the SD heads he did.

[steve25]

Bob just keep in mind that those flow numbers from the HPP shoot out article that Pete did where not done at 28”.

To flat out compare them to a test done at the normal 28” you will have to multiply them by anywhere from 22 to 24%.
And to add to the fun that flow bench was not calibrated well, so take all of those flow numbers with a grain of salt.

[Stan Weiss]

Originally Posted by steve25

Bob just keep in mind that those flow numbers from the HPP shoot out article that Pete did where not done at 28”.

To flat out compare them to a test done at the normal 28” you will have to multiply them by 24%.

Steve,
What depression did Pete use?

Stan

[mgarblik]

All of Pete's work I am aware of was done at 25" of water which was commoin in those days. Not sure when the standard became 28":. Thinking mid 1990's?.