[tom s]

Steve,Dave had my 15s with a 2.05 intake at 260@600.FWIW,Tom

[steve25]

I don't doubt it at all Tom seing as my reworking of one port for Will on thus casting with a 1.96" valve hit 250 cfm at .600" and I still had more work to go to get to the needed port Area I was shotting for.

[steve25]

Here's the photos to go with the last flow test I posted last week.

Photo 1 is the 1.71" template sunk down sitting on top of the guide with the flat side on the common wall and the 3/16" shank sitting up on the short turn for a runner depth measurement.

Photo 2 shows how far down in the bowl the full 1.71" width of the template will sink before the sideways taper after that point stops it.

Photo 3 shows how deep the template goes into the runner now, the template is now some .030" away from sitting on the apex of the floor.

Photo 4 show the now 1.655" tall window at the apex .
This height was gained by a combination of laying back the short turn and widening it and also by raising the roof from just before the end of where the guide pops thru the roof on back to where the pinch of the push rod bulge ends.

[steve25]

Here's the last shot of that rework series.

This shows the stock window height of 1.580"

[steve25]

Here's my next installment on this thread since I got another 3 hours of work time in on the weekend.

First off I managed to repair my broken glass CC burette so I CCed a stock Intake port in this number 15 head, and I CCed the ported Intake I left off with in my last installment.

The stock port volume on these 1.96" valved heads check in at 148.5 , this is the result of 3 ports CCed and averaged out.
The ported Intake checked in at 167 CCs.
A way to look at this is that a 11% increase in port volume produced a 38% gain in air flow in conjunction with the bigger 2.11" valve.

Here are the flow numbers now with a rework from the 1.71" Throat size up to a 1.73" Throat size and the related work needed to get another nice flow increase.

This port is now at 175.5 CCs which is 8.5 CCs larger then in the last flow test done and posted last week.

.050"--.100"...200"--.300"---.400"---.450"---.500"---.550"---.600"---.650"---.700"
45.2---78.7---147.8--198.9--233.4---242.7--250.4---255----258.2----260----261.3

Flow gain over stock port with 1.96" valve.
9.3----5.3-----14.8----29.9---55.8----62.7----68------71.8----75------76.5----78

Notes on what's did from the last rework are as follows.
1) widen push rod pinch out to 1.11"
2) increase Throat to 1.735"
3) increase the roof height at the apex by .035" to 1.690"
4) blend out the back wall of the valve bowl from the cutting work done to get the Throat up to 1.735".
5) kick over the common wall more as seen in one of the photos here.
6) widen the floor over the short turn at the sides while keeping the same arc.
7 ) blend roof on Exh side in front of valve guide.

Now we have 18% more port volume 0ver stock and 42.5 % more flow over stock.

Note in photo 4 here how flat this common wall is , in other words wide.
Note much greater the width is on the roof from the valve guide over to the common wall in comparison to the valve guide and the Exh port side.
This is what I mean by kicking over the common wall.

At this point I will likely do one more increase in port size to get into 270 cfm of flow range and then move on to the Exh side of these Heads.

[steve25]

More shots here.
If you go back to my 3rd shot back in post 28 you can see how much wider the floor is now when looking at my 3rd photo here.
Another thing that is important to note between these 2 photos in regards to increased air flow is how much more the the roof of the port at the flange you can see in the last photo here.
This line of site is where big gains come from if you know how to control that air in guiding it over the short turn!

[steve25]

Here's the results from last nights little bit of rework that I had time for .

Manly this time around I layed back the upper half of the short turn more and spread out the floor wider on both sides around the short turn , but most of the width increase was on the Exh valve side of the floor .

Also the floor on the Exh valve side was intentionally lowered due to the grinding done to widen it.

This was needed as there was some light turbulence taking place at lifts above .540".
You can clearly see the width difference in the two short turn / floor photos here.
The roof was raised by .015" on the common wall side ( trapezoid shaped ) from just ahead of the valve guide on back to the push rod pinch point.
You can also see the difference in how the short turn rework as reduced the height of the tall 60 degree bottom cut .

The Throat is now 1.750".

I have not CC check the port from the last time, but I will and the next rework and test will be with a 1.80" Throat which will bring the Intake flow numbers easily into the low to mid 270 cfm range.
The next rework will also have the roof raised up to the RA4/ SD 455 height.

After that I am on to the Exh side for sure!

This first photo is the 1.750" template with the flat side of it on the common wall and a near perfect match of the arc of the template to the crown / apex of the floor.
The second photo is the short turn as it was in flow test #15, and the last photo is the short turn now in flow test 16.

Intake flow test #16 @ 28"

.050"--.100--.200---.300----.400---.450---.500---.550---.600---.650---.700
41.7---75.9--143.5--194.6--236----244.9---254---260---=------261.7--263.2

[455-4+1]

Thanks for the updates, much appreciated

[steve25]

Welcome!
The final installment if you in regards to the Intake will likley be on Sunday morning .
Even for me it's been very interesting doing this rework in many small steps and getting a clear example of how getting good overall numbers can't be done Willy nilly!

[steve25]

Sorry for being late in getting back to up dating this!
I had time to take the next porting step last night to bring the Intake flow into the low 270 cfm range, but first I need to make a correction , that being in my post number 45 I posted that the CCs at that point where 175.5, when they are not, the correct port volume was 172.5.

The flow results posted in #47 where at 175.5 CCs.

Here are the flow numbers for last nights work.

I did not have the time to CC the port , but tonight I will and I will post that up along with the dimensions the port is at now and pictures in the morning.

What I can tell you about the size is with this flow test I increased the roof height up to the RA4 size gasket and blended that on back into the runner with other changes done also.

Flow test #17 , intake @ 28".

.050--.100--.200---.300---.400---.450---.500---.550---.600---.650--.700
40.6--75----139.6--193.3--234.2--244.9-251---257-----261.7-266.3-269.6

[455-4+1]

Looks like the first thing most people do, is probably the last thing they should be doing lol 😎
( Enlarging the port at the intake flange )

[steve25]

Well yes and no!

Port Area wise the push rod pinch itself does not act as that much of a restriction until flow numbers in the 250 cfm range start to be had.

The problem it's presence does make is that is causes the air mass that passes thru it compress and also speed up then slow down, and in making the air mass compress it packs more flow on the common when it otherwise could have kept on going straight on it's way over the turn and into the valve bowl.

This speed up and slow down action acts like a port choke and in a perfect world the whole Intake tract would have only one port choke .

The compression of the air mass causes a slight reduction in the width of the motors power band and it has a bigger effect on the Intake ports who's outside runner meets up with the push rod budge.

Anytime a Intake Manifold runner makes a curve to meet up with the head a good deal more of the air mass passing thru it will ride on the more gentle bend of the outside wall of the Intake runner.

Once again just like flowing water the air mass wants to take the path of least resistance!

This means that the two outside Intake ports in each head see more of a compression effect then the two inside ports!

In short, even with stock flowing heads if I was doing even only valve bowl work I would cut back the push rod pinch!

[steve25]

Ok, here's where where at with the flow numbers from my post number 50.

At .700" lift the port is now flowing well over 83 cfm more that it did stock with the 1.96" valve.

Where now at 47% more flow with a 19% larger port so we have picked up port velocity big time!

The port volume is now up to 177CCs .

Size details.
The 1.83"round Throat stops at .175" down the bowl which is right at the bottom of the 60 degree bottom cut as seen in the photo.

From there on down to the roof of the bowl it tapers to 1.77" as can be seen in the photo.

The height of the roof at the crown of the short turn is now 1.70"

[455-4+1]

Thanks for the info. I was referring more to people "gasket matching" at the intake flange an nothing much else probably making the pushrod pinch issue worse. It seems more common on SBC stuff I see with a huge 1207 gasket matching and stock pushrod location. The port shap from intake face to pushrod pinch almost looks like a 45 degree reduction in Port direction.

[Squidward]

I love the updates, great thread!

[steve25]

Thanks much!
With that said here's the next to last installment on the Intake side as yesterday I had time to take a big jump into the 270 plus CFM range so I can get to the target and move on to the Exh side.
I will I post the flow numbers now and the rest of the details tomorrow.

If I had to take a guess on the port volume I will say 178.5, but I will pour it again later today and report tomorrow.

I still have some tweaking I could do with the valve job , but we'll see!

Flow test #18 @28"
Lift
.050--.100--.200---.300---.400---.450---.500---.550---.600
40----76.9--146.3--234.2--249.5--261.7-266.3--269---275.2

Flow test

[steve25]

Well things are a little different with the SBC Chevy !
For one it's runner in the head is a tad longer then a Pontiac, and 2 having a 23 degree valve inclination angle when porting it responds to increases in width fast then increases port height until a certain point in reworking if it's not a raised floor type head.

Take look a factory iron Head like the 906 casting and how tall that runner is and how tall the short turn is as compared to something like a 462 casting.

The 906 casting is very hard to do a bowl port job on and get better numbers then the factory number!
Sorry for getting off corse here with the SBC stuff for a minute!

[steve25]

Ok folks where on to the Exh side of the head now and here's some notes besides the flow test.

These test are on a center Exh port and I blocked the Exh crossover with clay , but made no attempt to shape the rear wall for better flow.
These center Exh ports flow anywhere from 5 to 10 cfm less then a end Exh port above .400" lift.

In this non emission era when Pontiac went with the smaller 1.66" Exh valve size for these Heads they left the rest of the port the same thank God, and this is great for flow numbers as you will see.

It's also interesting to note that this casting does not have the nasty casting nub that is usually on the crown of the short turn and makes for a flow loss.

Other then the smaller valve seat the runners are the same size as any other high comp large 1.77" valve heads!

The height of the Exh flange on these Heads is 1.758" and the height of the Exh flange on all the post 1972 heads is only 1.655".

This tenth of a inch difference shows up in some nice mid to high lift flow numbers for this stock head.

This combination of valve size and port area shows that it makes better use of this available port area then a stock high comp D port head with a 1.77" Exh valve.

The exception to this may be the Exh side of the # 48 casting that has more high lift flow then other heads.

Stock Exh flow with stock 1.66" valve @28"

.050--.100--.200---.300---.400---.450---.500---.550---.600---.650---.700
22.4---43.8--89.9--120.2--149.5--156.4-161.3--166.6--167.2

The high lift flow numbers on this head are as good as a 1.77" big valve head.
This head in stock form also tops the flow numbers of the post 1972 heads at only .450" lift!

For the next flow test all I did was to take a 80 grit polishing roll and remove all the carbon and the pimples of rust from the casting , No blending and No full on polish was done.

I also took a long strip of 120 grit , rapped it around the short turn and gave that a few strokes to knock the rust off of that area.

Flow test after a 5 minute long port clean up.
.050--.100--.200---.300---.400---.450---.500----.550---.600---.650
22.5---44.2--91.5--128.4--153.5--161.3--167.2--174---177-----180

Note that the air injection Boss is still in place!

[steve25]

I would like to go back to my post 58 about the Exh side for a moment and note how much flow was picked up in the second flow test just from removing the carbon and rust scale from the port.

The average gain here up from the 5 minute clean up job up to .600" lift was 5.2 cfm.

Now this 5.2 cfm gain was just in regards to a port who's length is a tad over 3 inches so imagine what Exh flow losses can take place in a Exh Manifold or worse yet long header tubes that are rusted and carboned up on the inside, especially around turns in the flow path!

I myself have seen a dyno test where a well tuned 10 second bracket race motor lost over 50 hp to such a headers and others have reported a greater loss with motors as the rpm power band of the motor went higher!

[ponjohn]

Wow..275 @ .600.

Are the middle runners typically better or worse than the ends?