[gobrdgo]

Hi everybody. I’m a newb to head porting and I was wondering how the ram air heads differ intake port floor wise to the d port. My noobie flow testing is showing the short turn radius in the d ports suck in a bad way. Are the port floors higher in the ram air 4 ? Almost wondering if you added material to the d port floor of it would improve flow.

[steve25]

If where talking about a high comp 2.11” valve D port head, and armed with the knowledge of how to rework it properly, and one can then get 290 cfm@28” without adding material, then why do they, as you say suck?

Especially in light of them flowing on average 205 cfm stock.

That’s a 70% flow gain by my math, so is that not substantial?

Not every D port head can be reworked that far due to factors of core shift in the casting , but 280 cfm can safely be had, and it can be had while still running a 30 degree intake valve seat, and even the low comp 5 and 6 series heads, other then 6H casting will go 280 cfm!

The fact is that the 1969 and 70 RA4 heads have a more narrow gap in between the push rod bulge and the opposite port wall then the D port heads do,

This is due to the bigger diameter push rods that where used in them.

If your porting a RA4 head to the max then you MUST grind back and brass sleeve the push rod hole otherwise that then becomes the choke point.

To answer your question, yes these RA4 heads do have a higher short turn due to the very shallow chamber they have and a higher roof path as well due to that higher short turn,

They also start of life with near a 1.80” valve bowl throat where as the 2.11” valve D port heads have a 1.60” throat.

This makes for a 12% gain in throat size right there .

You can rework a high comp D port head with a epoxy floor that needs to go all the way back to the push rod buldge and get 260 cfm , but you do then drop off some mid lift flow that you could have had, and this mid lift flow is more important to having larger average flow numbers and the power that can be made from that then the peak lift flow numbers matter!

[Half-Inch Stud]

Originally Posted by steve25

........

RA4 heads...also start of life with near a 1.80” valve bowl throat where as the 2.11” valve D port heads have a 1.60” throat.

This makes for a 12% gain in throat size right there ..........!

I did not know that. I go for 1.75" in the Intake Bowls using washers on a stick. Think RA2s were not 1.8"

[steve25]

Yes, the 1968 1/2 ( as in late year ) number 96 round exh port casting still had a stock D port intake size throat of 1.60”.

These heads had a near problematic high ratio of exh to intake flow, and the guys who raced them and did well with them new they had to make up for that!

Look at it from this perspective, the intake bowl throat in these 96 castings was 1.60” and the exh bowl throat was 1.650”!

I think that this fact is one of the reason’s that this 96 casting was so short lived, it was in a way a engineering experiment as was the short lived 061 casting in the previous year of 67.

The OP here has clearly stated that he is only talking about the RA4 heads, not any of the D port Based RA heads.

So my statement that the RA4 heads have a 1.80” throat is correct.

[steve25]

Here’s two shots of a high comp D port head flowing 290 cfm.

The valve bowl throat is 1.850” .

Note that to get the proper port shape and area that the roof has been raised to the point of very well exposing the rocker arm stud hole,

Also note that the push rod hole has been sleeved and ground back to expose that sleeve,

[1968GTO421]

Great info..............but all this is way beyond my pay grade.

[Stan Weiss]

Originally Posted by steve25

If where talking about a high comp 2.11” valve D port head, and armed with the knowledge of how to rework it properly, and one can then get 290 cfm@28” without adding material, then why do they, as you say suck?

Especially in light of them flowing on average 205 cfm stock.

That’s a 70% flow gain by my math, so is that not substantial?

Not every D port head can be reworked that far due to factors of core shift in the casting , but 280 cfm can safely be had, and it can be had while still running a 30 degree intake valve seat, and even the low comp 5 and 6 series heads, other then 6H casting will go 280 cfm!

The fact is that the 1969 and 70 RA4 heads have a more narrow gap in between the push rod bulge and the opposite port wall then the D port heads do,

This is due to the bigger diameter push rods that where used in them.

If your porting a RA4 head to the max then you MUST grind back and brass sleeve the push rod hole otherwise that then becomes the choke point.

To answer your question, yes these RA4 heads do have a higher short turn due to the very shallow chamber they have and a higher roof path as well due to that higher short turn,

They also start of life with near a 1.80” valve bowl throat where as the 2.11” valve D port heads have a 1.60” throat.

This makes for a 12% gain in throat size right there .

You can rework a high comp D port head with a epoxy floor that needs to go all the way back to the push rod buldge and get 260 cfm , but you do then drop off some mid lift flow that you could have had, and this mid lift flow is more important to having larger average flow numbers and the power that can be made from that then the peak lift flow numbers matter!

Steve,
You and I must be using different Math. I get about 41% increase.

Stan

[gobrdgo]

Good stuff I appreciate the sharing. Moved up floor with modeling clay and got skunked.

[steve25]

Your right Stan, my big flub!

Non the less a good amount of flow gain for a iron non high performance head.

Gogrbgo, it would seem now you can rest a little easier knowing that the stock short turn even in the low compression redesigned heads like the 5 and most 6 series castings are shaped very well to complement the way the rest of the port is shaped along with the port area it has been designed with.

This is what porting a head to higher levels of flow is all about, complementary shapes with the needed area to access greater levels of flow mass,

[Half-Inch Stud]

Steve, nice.

5C is my favorite low-compr head for having all the desired features, but those bowls do start out small.

I happen to widen the short-turn cheeks so the bowl washer or equiv CSA can pass thru. Really though, every effort to avoid eggshell bowl and short turn walls. Street/Strip for me means no epoxy, no wall flex failures. and bench-flow goal is least noise, no flow numbers.

Summary of my thoughts on Iron heads:
According to CSA; pushrod bulge is the primary flow choke, and widening is the quickest way to open the CSA, mitigate turbulent flow at .35" lift, and get into the 12s.
Bowl, guide boss, short-turn finishes the effort. Chamber Unshrouding makes me feel better and might provide a cleaner burn, reduced ping. Such port work yields 11s with 5250 rpm.

10s or less needs increased RPM, and weight loss.

[Cliff R]

A few years back I topped a 455 sitting here waiting for CNC ported heads from Dave at SD and one of his custom ground roller cams with a set of #46 heads from a 1969 428.

They had the small valves in them and 45 degree intake seats. I ground the valves, seats, installed better springs and tapped them for screw in studs.

Grabbed a used cam from the parts room, finished the 455 and installed it in a 1981 Firebird just in time to make it to the Pontiac race at Norwalk in August.

The #46 heads were completely stock, a grinder or sanding roll never touched them, not even a gasket match to the stock intake gaskets.

Right off the trailer the FB went high 11's over 112mph in the heat of August! I was expecting maybe mid to high 12's.......FWIW.......Cliff

[steve25]

You fully know the bottom line Cliff without question!
It’s the combination of things and how they compliment each other !
With those 46 castings you where fully utilizing all of the 180 plus intake cfm that they had to offer in stock form to make some 380 plus hp and getting it all hooked up to boot!

This is a flat out classic example of moving a limited amount of intake flow at a faster rate into the chamber and making for a higher average flow rate for that motors power band that the Cam provided.

[steve25]

Half inch stud, the Turbulence you speak of at .350” lift or so is 100% normal, and more then that will always show up to one degree or another in any port be it intake or exh in any head on the planet.

This turbulence you see on the vertical Manometer and hear at the entrance of the port is result of the air flow coming into the back side of the valve increasing to the point where that air mass can no longer take whatever the path of least resistance in that port to access the rear of the valve, but now instead must start to follow the contours and shape of the port itself!

This is why up to at least .300” lift bigger flow gains are Seen by improving the valve job , making more curtain area and unshrouding the chamber if need be then doing any other kind of grinding in the valve bowl down deeper then 3/4” or reworking any other part of the port.

All this being said if you talking about getting sheer taking place as low as .350” lift which is always accompanied by receding flow numbers when your porting a Pontiac Head, then you have the short turn shape all wrong .

I have never had sheer take place below .400” lift for example.
The proper porting procedure if your going for intake flow numbers above 230 cfm is to

1). enlarge the valve bowl throat to whatever percentage your shooting for.

2) if this percentage works out to a throat diameter of more then 1.70” then you must first size the throat and then re-arc the short turn with the needed template durived from that 1.70” throat template.
3) then you use the throat template once again, this time sitting on the short turn and grind out what’s needed to get that template up onto the new crown of the reworked short turn.

Remember that your throat template needs to have a flat on it’s perimeter equal to 94% of the diameter that your making the new throat to.
Also the transition of the template’s perimeter need to softened leading into that flat.

When running the throat template around the new short turn you want that flat side to be on the Intake vertical common wall side.

This means that once you get this template up onto the crown of the short turn, that port area will be 94 % of what the new throat area is in the valve bowl.
This procedure with the proper valve job should keep you clear from port sheer problems.

[Cliff R]

"You fully know the bottom line Cliff without question!
It’s the combination of things and how they compliment each other !"

Sometimes you just stumble on a combination that just works, even though it's not using main stream parts folks would typically choose if they had better options.

One key to success with that particular build was the camshaft. It was really tight LSA so narrowed up the power and yanked it down to where those heads would have been at their best in that size engine. STRONG mid-range power and one of the most responsive 455's I've ever built. Just "blip" the throttle and it was at 5000rpms before you could spit.

The cam was a Crower grind, 60213:

https://www.crower.com/searchresults...=60213&x=6&y=7

Pretty "hefty" for one of these engines but it worked pretty good for that particular set-up......

[steve25]

Is that where it liked to be shifted at, 5K?

[Cliff R]

I don't know where they shifted it at. I just prepared the engine, carb, distributor, transmission, and supplied a custom torque converter for it. Didn't go to the race or drive the car........

[Skip Fix]

In the old HPP magazine Pete McCarthy had some good article with really specific measurements on the RAIV heads even differences between castings.

[Jay S]

A friend has a RA 4 (614) that has a SR head on one bank and a OEM on the other. Rocky Rotella flowed both heads to compare them. The SR head had a little smaller diameter bowl throat, but the bowl was deeper and a little longer short turn. The OEM head flows topped out at .5”, but carried the flows to .6” lift. The SR head flowed a little more at .4” and .5” lift, but then lost flow after that. Lost quite a bit of flow on a couple ports. You could here the turbulence in the head. Rocky held a string into to port and slowly opened the intake valve on the SR head and the center of the port had a pretty big area that had bad turbulence beyond .5”. One port hit that point at .4” lift.

To get the SR and OEM head to flow more even the bowl was opened up on the SR head to match the OEM head, then the short turn was pulled back so they matched. After that, even though the OEM head had some work done to clean the bowl up some, the SR head out flowed the OEM head by 10 or more cfm. Hand written photo are the final numbers after the port work. So even some of the RA4’s benefit’s from some contouring on the short side and floor.

The short side and floor are almost always the last places I work on. That way you can adjust the short turn to keep the port from going turbulent and have decent flow gains thru the engines max valve lift.

[steve25]

What year casting number was this ?
I have seen the stock 70 casting out flow the 69 casting many times, if not at peak lift then by having fatter numbers at mid lift.

[Jay S]

They see both 614s. But IRC the SR head was cast in 72. Rocky probably recorded the casting dates.