Need Help- Porting Heads for beginners

Okay! That makes sense. And no problem, I just like having a visual of the ported heads.

And okay I'm lookin forward to your results.

 

Here is the flow test results from the bigger valve and more valve guide work , only a 2.08" valve at this point with no back cut.
If the valve had a 30 degree back cut on it then the low lift flow numbers from .250" on down would even be greater.

Flow @28"
.050"--.100"---.200"---.300"---.400"---.450"---.500"
34------67.5-----138.7---192-----224.4---227.9---232.5

The head is now flowing at .350" lift what the stock head did at .550" lift!, and since the port volume is still very close to stock the port velocity is higher which will make for more throttle response.
With a well built street motor of 430 cid you should be able to make 1 hp per cylinder for every 4.2 Intake cfm of flow at 28".
If you ran a Cam of .500" lift you should make 54 hp per cylinder, or some 432 hp
Assuming the Exh side can do 75% of what the Intake side can do air flow wise.

Note that this test was done with a valve that still had the large stock stem size of 3/8", if you change to valves and new guides for 11/32" stem valves you will pick up even a bit more flow then this .

 

Wow that's awesome. I'm really excited to start working on these heads! Awesome information Steve!

 

If you don't have a dust collector system to suck iron dust away as you grind, put a box fan behind you to keep from snorting all that iron dust into your nose & lungs.

 

I started putting a porting pdf based on what I was reading here. I’d like to get some thoughts and comments on it.

 

Love it Matt. Have you started? I have quite a few 1971 heads so I'm getting ready. What does unshroud the valves mean? Later, Mike

 

Here are some Exh flow numbers and rework details on these 1237661 castings.
One thing to note on this casting Exh wise is that the Exh ports flow very well for there Throat size , and while you can pick up the numbers some going for big flow gains without having a flow bench to guide you and a Mule head to sacrifice can get into trouble in regards to ending up with less flow then what you started with!

Stock flow@ 28" with stock 1.63" valve.

.050"--.100"--.200"---.300"---.400"---.450"---.500"---.550"
21.1-----47.3---97.4-----126-----142.6---146.6---149.5---151.5
Here is the changes in flow of the same port with just a normal , but wrong Boat tailing / taper of the valve guide.
+.5-----+1.3---+2.4-----+.9-----(-) 1.7----(-) 2.3--=------=
The guide at this stock flow level is just simply not a restriction.
If the valve guide Boss in this test where not layed back and tapered on the Intake valve bowl side of the guide then no flow loss would have been seen, but the minor flow gains would have still taken place.

Here is the gain in flow from going up to a 1.71" valve with a smaller 11/32" stem
A 3 angle valve job was done.
The valve was back cut at 30 degrees.
The margin of the valve was rolled over to its face.
The short turn arc was tightened up and the floor of the short turn was flattened out from 1/4" below the seat up to the apex/ crown of the short turn.
The bowl blended and the this center Exh port the head bolt boss was blended out.
Exh flow @ 28" with over size 1.71" valve.
.050"--.100"--.200"---.300"---.400"---.450"---.500"---.550"---.600"---.650"
23.5---59.6----109.2---141.6----166.2---170.2---171.2----174-----176------177
Flow gain over stock port with 1.63" valve.
.1------12.3-----11.8-----15.6-----23.6----22.6----22.7-----22.5----21.5----25.5
The addition of a 1 3/4" Exh tube on this port picked up another 5 to 7% more flow above .300" lift!!
With Exh flow numbers like this along with Intake flow numbers of 223 @.500" lift there is no need to run a duel pattern Cam and suffer the consequences of a crappy idle due to added overlap!

 

I haven’t started yet, spent most this year fixing some electrical messes that could have started a fire.

This explains unshrouding best. I’m thibking a person could wreck it if they don’t know what they are doing. You also increase combustion chamber and may decrease compression by unshrouding. I leave the rest to the experts.

http://www.diyporting.com/Shrouding.html

 

Good article, but instead of using a head gasket to scribe the circle where to unshroud, mount the head on the block and use the cylinder to scribe the "circle"(actually only need a semi-circle on both sides where the valves are).

Using the cylinder will give you that margin of safety that they spoke of in the article because usually the cylinder is a smaller diameter than the head gasket. Plus you don't want to unshroud to a dead end, aka the smaller cylinder diameter than the head gasket diameter will take it to dead end onto the deck surface.

Unshrouding to the cylinder aims the flow into the cylinder instead of aiming it to the deck surface if it is unshrouded to the head gasket.

 

Over the weekend im going to start working on my heads.

Before I start I want to hear what the consensuses is about taking material of the port floor, I see people gasket match and do all four sides or some people dont touch the floor and say to focus on the port roof. I want to hear from you guys and tell me what action you guys took and outcome.

This is was a good article, I never heard of unshrouding the valve during my research. Its amazing how many things you can do to our heads.

Im going to:
Intake and Exhaust Port Gasket Match(im still deciding actually on the intake side)
Take the Valve Guides as far down as im comfortable with
Lightly take off material from the bowl to right under the valve seat to smooth everything out
At a later date ill start doing some unshrouding

One thing im still confused about is what exact work needs to be done with the short turn radius? Are you taking the material off from the throat to the short turn radius or are we trying to focus on the 90 degree part and make the turn smoother ?If someone could explain the process Id appreciate it.

 

When more cfm is wanted out of a cast iron head because that's all that's available a skilled porter will epoxy the floor to make it higher and raise the roof as high as possible. The idea behind this is that the straighter you can make the port, the more air you will flow and it works. That's why you don't want to lower the floor because it doesn't help the port flow more air/time is $.

You don't want to lower the intake manifold port lower either if you port that.

Gasket matching is a waste of time that if you're lucky won't hurt flow if you do it but probably will. Opening up the first inch or so of the intake port in the head puts a bulge in the intake tract.(you don't want that) The port will only flow as much as the smallest section of the port will allow, (the pinch point). The pinch point is more than likely going to be further in than where the "gasket match" area is.

Grinding cast iron sucks, you don't want to grind more than you have to. If you have a practice head to work on, have 2 unported ports flowed to get your initial unported flow for both ports(because they will more than likely not be the same). Then do a "gasket match" on one port and have that port flowed without anything else done and port the bowl on the other one without any other work and have that one flowed.

If you did the work right you will see that the bowl port flows better, but do see for yourself so you can say you know for sure, don't just take my word for it.

Now, do the bowl work on the port with the gasket match and use the directions in Matt's pdf to port the one with the bowl work done already. When those 2 are done have both of them flowed again to see what you get. Make sure you keep a log of what you have done to each port, write it all down, every detail. Its going to cost a few $$ for all the flow bench testing but think of it as schooling yourself.

There's a lot of voodoo in the short turn that you should look up Visner's book I think his name is or some other references for you test head. Apply what you learn to both ports. Its to hard for me to explain how to grind the short turn without being there with a head or a pic of one pointing and such. Just remember less is more in that area because if it is done wrong you can lose the gains that you have already made.

After you think you have figured out the short turn, apply what you have learned to the 2 ports and then have them flowed again and record that.

Then do some unshrouding work, sometimes there is 12-20 cfm right here! Have your heads flowed and write down your finding in your log book.

Last but not least see what you can pick up with a valve job, three angle and maybe a 5 angle and you can play with back cut valves as well to see what you end up with after the valves.

After you do all this you will be well on your way to knowing what basics works and if your gains are good the shop you find to do you flow bench work might even try to hire you? Have fun with it.

 

That was detailed, thank you. Okay I understand not touching the port floor now, but why is gasket matching a waste of time? The more material you can take off will increase flow right? If not, you recommend me find the pinch point and open it up to the biggest point of the port?

 

Ideally if you could open the sides of the ports as big as the sides of the gasket hole all the way to the throat would probably help flow BUT you will likely hit water before you can open the port that big all the way. That's why you need to find the pinch point and start grinding there.

Using these inexpensive simple tools;

https://www.ebay.com/itm/Yankee-Spr...l1311.R4.TR4.TRC0.A0.H1.Xinside+calipers.TRS0

https://www.ebay.com/itm/Digital-Ca...acat=0&_nkw=6+digital+caliper&_from=R40&rt=nc

you can find the pinch point of the port. To make all ports the same, find the smallest pinch point of all 8 ports with the first tool listed. Then measure that with the second tool listed, then open the second tool up the amount you want to remove and lock it. Now open the 1st tool to that size and start by grinding the push rod side of the port first to the size of the 1st tool using it as a reference. If areas of the port is larger than what the tool is set at already, those areas don't need to be touched because they are already wider than the ported pinch point will be.

After all the push rod sides of the ports are done, open the 2nd tool the amount you want to remove from the other side and lock it. Now reset the 1st tool to this measurement and grind the other side to that size on all the ports and done with the sides.

To figure out how much you can remove, a sonic tester would be a good tool to use for that. Try to leave the thickness at least .100" thick at the thinnest point after grinding.(which would be the pinch point) From looking at sbb 350 head sections, the walls were around 3/16" thick, so around .080" would be the most I would take off the wall if it sonic tested that thick, but .060" at the most would probably be safer for most cast iron heads without sonic testing.

With the above tools and now knowing there is a pinch point in the port and knowing that there is water under where you'll be grinding, having a strategy will save you a whole lot of work and heart ache. I hope this shines a light on why "gasket matching" is a waste of time.

Using those 2 simple cheap tools will help you manually make your results very close to the same as you can get them without a CNC doing the work! The first tool would be good to use to make all the bowls/throats very close to the same as well.

 

Yes I understand now much better, but what do you mean by there's water under where you'll be grinding?

And I have both those tools plus more. I was going to use a telescoping gauge and electric caliper.

 

Not really under there when you're grinding, but the coolant passages are underneath the ports and if you grind through and try to run them anyway, coolant will flow into the combustion chamber(s). The heads aren't solid or they would run to hot! Coolant flows through the heads to cool down the combustion chambers or the heat would just keep building causing all sorts of problems.

 

Okay that's what I thought. I was thinking also maybe there was a manufacturer defect causing like random water pockets or something haha

 

The average wall thickness on GM made heads is .180" if no major rust has taken place, this is over 11/64 of a inch.
A novist porter should be grinding away anything thing more than 5/64 of a inch or some .080 and this leaves a very safe .060 to .100 cushion " from blowing thru a port wall that has water behind it.
Another thing to mention here in regards to a novist porter who without access to a flow bench is that if your removing close to 5/64" your very likely to be shotting yourself in the Foot and accutally loosing air flow , not gaining it!

One thing also not note about Buick heads, or any heads for that matter is the depth of the valve bowl in regards to porting work.

The deeper they are like the Intakes on Bucks in comparison to Buick Exh ( non nail heads) the safer you are from doing grinding work and loosing air flow, where as the Buick Exh valve bowls are on the shallow side even for a non HP passenger head.

What I mean by this is that in regards to these Buick heads with shallow Exh valve bowls when you know where to grind and how to reshape things you can pick up a good bunch of air flow fast, but if you do not know where to grind and how to shape things you can drop off a good chunk of flow fast also!

In regards to chamber shrouding it basically means this , when any valve is off the seat a given amount if the chamber is closer to the edge of the valve then the amount the valve is lifted off the seat then there is the potential for this shrouding to limit the air flow that could be taking place.
Note here that I posted there is a POTENTIAL, as air does not exit evenly around the circumference of the valve be it a Intake valve , or enter the Exh bowl evenly around Exh valve from the chamber side.

Rule of Thumb here is for example if the valve is open to .400" lift , but the clearance between the chamber wall to the edge of the valve is only.350" then there lie's the potential for that shrouding cutting into possible air flow numbers!

 

What do you do to limit mistakes when grinding the exhaust bowl? where are you concentrating when grinding the exhaust bowl?
So if the valve edge is .350'' or less to the wall you should grind it to what measurement, .400''?
Why would a novice porter maybe lose flow if grinding the 5/64''? Because they hit water?
Lets say I go to my machine shop constantly and get them flow tested every time I take a small amount off, What would be the ideal amount of material to take off between flow testing?
When your grinding material off when is it too much that flow goes down? I guess it was my understanding the material you take off the better the flow as long as you don't hit water.

 

Ok, there's a example of what I mean but first a question, do you know which part of the Exh port bowl is the most active in terms of flow leaving the cylinder and negotiating its way around the valve and thru the bowl and on out?
Even if you don't you should be thinking along the lines that it would be best to rework this most active part of the Exh or Intake bowl because these areas are the most likley to give good flow gains with the least amount of metal removal and in turn time input, no?
If you where to place a openeded big Coffee can on the chamber with the Exh valve open to let's say .400" you will clearly see that most of the cylinder area is from the center of the can ( left to right) on over to the Intake valve side of the chamber.
What this in turn means is that the bulk of the air flow from .200" on up in lift enters , or makes it way around the Exh valve from the Intake valve side of the Exh valve seat area, not the shrouded cylinder wall side.
Take a look at this drawing of a Exh port bowl as viewed when looking up the Exh runner.
This is not a Buick head , but it will serve our purpose!
In this view a lot of the air flow mass would end up on the roof of the valve bowl from the left side of the valve stem on over to the right side of the valve bowl roof.
So reworking the port wall on the cylinder wall side of the Exh port straight down from the seat,( or bottom cut ofthe valve job if there such ) and then kicking that wall out more ( tapering) as it gets down to the restriction of the valve guide boss is the way to go.
Place a flat wood ruler in the Exh bowl such that it sits on the Exh seat on its Intake valve side and the other end of the ruler rest on the roof of the bowl on the cylinder wall side of the valve guide.
This is the direction that a large part of the Exh air flow mass takes to get out of the motor!
This in turn means the there is more flow trying to get around the cylinder wall side of the short turn then the Intake valve side of the Exh short turn.
This roof area around the short turn can be raised and blended back over to the center line of the short turn.

Always keep this major fact in mind especially when reworking Exh ports no less Intake ports, that being that high velocity air will not freely follow any thing tighter than a 15 degree turn without just sheering away!!!

So like I posted since these non number 2 style heads have such a shallow Exh bowl you may now see why keeping in mind that 15 degree rule that any thing you can do to allow the flow to change direction slowly and allow it to go where it wants to go as best you can will provide the best flow gains!

If the shop you take your heads to for flow testing has a Pitot tube I would more then gladly pay them to probe a Exh port at the apex of the short turn from the Exh flange side as this will give a very clear picture where the most flow concentrated parts are , and its these locations where providing more area to will pick up the most flow!
Meat removal wise I have seen uninformed novist porters totally grind away the bottom cut to the valve job and unknowingly loose a total of near 45 cfm between .050" lift and .250" lift.
This 45 cfm drop means they worked hard at giving up a potential 70 to 80 hp especially if good tuned Hearders where to be employed for a gain in VE!

For a street or street strip head where you basically staying with the same amount of cid , you always want to produce a greater percentage of flow gain then the percentage of metal you grind off!

Here's a example of a set of heads I am working on now.
This head started life with a 1.96" Intake valve and now has a 2.11" valve , its stock port volume was 148.5 CCs, now its at 176 CCs.
In stock form the head flowed 185 cfm@28", now the head flows 261 cfm @28".
So what we are looking at here is that for a 18% gain in port volume the head picked up over 42% more flow!
These Heads will make a rocket out of the 400 cid motor they are going on!

 

Thank you for your time to explain this, its more important than you think to learn all this for me and its much appreciated.

Okay so how it flows from intake side into the exhaust bowl makes total sense. So how you explained it with the ruler the valve guide boss is the first point of contact for air. I see in your last 2 pictures attached your valve guide boss is flush with the port floor, is that recommended? The only reason I didnt want to do that is because its less structure for the valve stem.

What tool do you use to measure the turn with to make sure its at or above 15 degrees? and I will ask them about the pitot tube

Your port work looks very good! Someone is gonna be very happy with that gain in flow!!