Beginner 300 head porting job

buckingbronco

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We are doing a rebuild of our 1980 Bronco with the 4.9l.
The build plan is for Holley 8007, Offy DP, EFI manifolds , cam upgrade, and some mild porting.

I have never done porting but we would like to do some on this 300 head to improve performance a little, but we are not building a race car engine either. So we intend to be conservative.

I have read as much as I can on porting and I have created some diagrams with rough (emphasis on rough) measurements to help make sure I understand the guidance correctly before I start. It sounds like the restriction is mostly below the valve and around the valve stem guide hole before it goes out to the port. At least this is where you get the biggest benefit.

I plan to do the following grinding/polishing steps:
1. grind down the valve guide boss or bump for the exhaust to be flat with bottom (really the top of the port exhaust when installed)
2. grind out the indent on the one side of the throat area just below the valve seat.... but dont take too much off.. just try to get the throat to be a near circle... this should be about 0.1 ish on that side
3. grind down the valve guide on the intake but not down to the bottom of the intake.. The intake guide sticks up about 0.42 inches so remove maybe 0.1ish from top and then narrow the guide width (its about 0.6 in wide so narrow to 0.4 but leave some side wall to guide the valve stem)
4. smooth out both of the bowl area below the seat down to the valve guide boss area do not take material off the inside radius of the turn since that area is apparently thin... so do most on the outside radius .. see diagram.. most of the constraint is where it turns by the valve guide boss (it narrows down to 0.9-0.97in vs1.2to 1.47)... so grinding that down will open up the flow..
5. smooth the outlet/inlets areas to the manifolds but just to smooth ... dont take much material off. There was guidance to not grind on the floor so I am thinking that is the bottom of the bowl area but it could include the bottom (or really top if installed) of the port inlet/outlet.
6. for exhaust port smooth out the bump on the bottom ( I am not sure what this is for??? ) but leave the indent.
7. I am not sure what should be done to the combustion chamber for a 1980 carb head... it sounds like just polish it up... I am not sure what that does for a benefit.. you do not want to grind on it to increase volume which would hurt compression ratio ... right? we do not touch the sharp edges around outside of the chamber...besides polishing is there anything needed?

Here are my pics and diagrams.. sorry for my crude diagrams... done in powerpoint not CAD... :D
After I port it I will get rough measurements again to see how much was really taken off.
I also had a recommendation that we flow test the head.. I assume this is to make sure that the cylinders all flow about the same.
For a mild build is this required? ... I can understand for a race engine... what is the cost for this test? and how close do the flows need to be? within 10% or tighter?

Thanks again for the guidance...
Brian

[image]https://i.imgur.com/3mWEPQU.jpg[/image]
[image]https://i.imgur.com/pASbK1V.jpg[/image]

[image]https://i.imgur.com/rFb2F3s.jpg[/image]
[image]https://i.imgur.com/QsqG119.jpg[/image]

[image]https://i.imgur.com/wq3hZO9.jpg[/image]
 

pmuller9

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Here are the 5 links from the previous post


3mWEPQU.jpg

pASbK1V.jpg

rFb2F3s.jpg

QsqG119.jpg

wq3hZO9.jpg


Looks good.
This is what a conservative intake looks like.

Back cut the valve seat angle at 30 degrees.

http://enthusiastnetwork.s3.amazonaws.com/uploads/sites/21/2007/08/116_0612_02_z-valve_angle-intake_valve_30_degree_back_cut.jpg?fit=around|29:16

Polishing the chamber and rounding off edges removes possible hot spots.
You won't remove enough material to make a significant change in the compression ratio with the H519P pistons.
Depending on which cam you choose you may want more volume in the combustion chambers

Don't worry about flow testing the head. There are too many other variables that will affect cylinder fill and air fuel ratio.
Do take the time to get the combustion chamber volumes close.

Have you decided on a cam?
 
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buckingbronco

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PMuller

thanks for guiding us through this...

Just to clarify, I should narrow the intake valve boss but do not remove it down to the bottom of the bowl?

But on the exhaust we can lower it down to bottom of the bowl but do not take off more material at the bottom of the bowl. Correct?

On your intake picture.. what is the tear drop dark shape that looks like it is dripping from the valve guide?
Its hard to see on the picture but it looks like the valve guide boss still pokes up.. do you have a rough guess of how high vs the 0.42 starting point?

on the combustion chamber we will round the edges slightly all around the perimeter of the D shaped chamber.
And we do not do anything near the spark plug...

Should we measure the volume of each chamber after done? I saw a video where you seal the valve in with some vasaline and plug spark plug hole and then fill with water from a syringe to up to a plexiglass top sheet... it looked like a reasonable way to do this.

my son is out fishing today so we have not had time to discuss the feedback on the cam ... but we will get back to you.
thanks again
Brian
 

pmuller9

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buckingbronco":3jzjitqz said:
Just to clarify, I should narrow the intake valve boss but do not remove it down to the bottom of the bowl?
But on the exhaust we can lower it down to bottom of the bowl but do not take off more material at the bottom of the bowl. Correct?
That is correct.

buckingbronco":3jzjitqz said:
On your intake picture.. what is the tear drop dark shape that looks like it is dripping from the valve guide?
Its hard to see on the picture but it looks like the valve guide boss still pokes up.. do you have a rough guess of how high vs the 0.42 starting point?
What you are seeing is the top of the valve guide boss at it's original height making a bridge back to the port wall.
It helps direct flow.

Yes measure each of the six chamber volumes.
Here is the economy measuring kit
https://www.summitracing.com/parts/cca-4975
Here is the more accurate and more expensive kit.
https://www.summitracing.com/parts/cca-4974

Since you are looking for just a 1 cc variation in chamber volume you can use the economy kit.
Food coloring in alcohol is easier to read than water. Less meniscus depth.
You will also want to check the piston dish volume when you get them.

Cam choice will determine the compression ratio.
 

buckingbronco

Active member
So we have started the porting work on the exhaust ports first. Here is the pic of the #1 port
[image]https://i.imgur.com/tIHjI7l.jpg[/image]
It looks like I may need to still take some more material off the bottom of the bowl area on the right side.
We should get perfectly flat on other side right?
Im just worried since this is the floor that we should avoid if possible..

Also I ground down the bump sticking up near the outlet. The bump has a big indent that you can see from the valve port and then a ridge that stuck up( that is what I ground down and then it dip again into the floor) I ground the ridge down so that it was close the the last dip before the exit. We do not need to grind the whole floor out smooth out the divit right?

We have ground off the bump on the one side of the bowl just below the valve seat.
[image]https://i.imgur.com/vJucEhr.jpg[/image]

How much do we widen the bowl? take 0.125 off? or less?

And to open up the constricted area where the bowl turns into the exhaust port should we take most of the material off the side walls or also off the floor where the bowl transitions into the port?

I have about 3hrs into doing 3 exhaust port rough ins using a drill and 1/4 inc bull nose carbide bit to do the gross rough in... I see why this is so expensive at a machine shop now.. :)
 

bubba22349

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For one thing there seams to be some confusion though you have the principles correct they are just in reseverse. Looking down the valve bowls the head is actually upside down so thats not the port floor your seeing it's the port roof when the head is bolted onto the engine. Yes the reason you don't spend much time on the port floor and very little to the short turn radius is there's not much of anything to be gained in flow from more than a very light cleanup of the port floor. Port flow gains are had first by working on the ports roof height and than to the widening the port sides looking at the head as its going to be bolted on the engine. Good luck on your porting (y) :nod: Edited
 

pmuller9

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The main goal was to get rid of the exhaust valve guide boss which you have done.
Don't worry about getting the ledge perfectly straight. A little bevel at the sides won't hurt.

Yes, straightening the side wall curve coming into the bowl helps but the walls are thin and you can hit water jacket very easily.

Don't widen the bowl. Keep the exhaust gas velocity high. The main restriction was the guide boss.

What you have now looks good.
Just make the surfaces smooth using sand paper rolls and call it good.

 
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buckingbronco

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Bubba
Thanks for pointing out the direction confusion. It was part of my confusion and hence my diagrams to help make sure I am grinding on the right places. Since I have the head on the bench upside down it looks like the bottom ( which is the top in real life when installed on the engine). So the places to avoid grinding is the short inside radius ( which is hard to get to anyhow) and the real floor of the port exit which is the top of the port when the head is upside down.

Another question is on the side walls... right now I am just polishing them since the restriction is up at the transition from the bowl to the exit port... or do I need to really dish them out for a moderate port job? Im trying to focus on the restriction area to get the most benefit a the rpm range that I am using eg <5000rpm...

Thanks
 

pmuller9

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The exhaust port operates under high pressure and the cylinder evacuates the majority of the exhaust gases just after BDC so you are looking for a smooth high velocity exit to produce a strong signal for scavenging in the exhaust system.
Removing material off the ceiling rather than the floor effectively decreases the port angle which decreases friction to flow.

The intake port is low pressure, 14.7 psi at sea level minus any drop in pressure due to carburetor and intake manifold.
It requires a lot more attention to airflow.
 

bubba22349

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buckingbronco":38or7ejf said:
Bubba

Another question is on the side walls... right now I am just polishing them since the restriction is up at the transition from the bowl to the exit port... or do I need to really dish them out for a moderate port job? Im trying to focus on the restriction area to get the most benefit a the rpm range that I am using eg <5000rpm...

Thanks

No you don't really need to hog out the ports unless you going with larger valves, just straighten them out and try to keep them the same from port to port. You need a way to guide you on the port shape and so the ports are somewhat equal, I use the machinist blue around the port openings some people use markers. Then if you still have your used intake / exhaust gasket, it's all ready crushed to installed size so it's better to use as a guide. If not get a new gasket but you won't want to scribe and grind the ports all the way out to that line as the gasket will be crushed and will intrude into the port some. Bolt the gasket on to the head and scribe a line around the gasket opening for your guide, but don't go any bigger than the scribe line or you could also rescribe lines a little inside that gasket line say a 1/32 or a 1/16 or find were largest as cast port is and clean it up first then try to match the others to that. As was said before the most befit you realize is directly under the valves in the bowl after blending into the port, next biggest improvement rasieing the top of the port and then the sides. If you want to also send the time there is benefit to polishing of the exhaust ports and valve bowls and combustion chamber but don't polish the intake ports. Hope that helps you and you have all ready been given very good advice from the others but if you have any others questions that I can help you with let me know, best of luck (y) :nod:
 

buckingbronco

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We have started to port the intakes now.
this is #1 roughed in with carbide bit.
I ground off about 1/2 of the width of the material around the valve guide and opened up the channel to the right
And opened up the bowl a little bit...~0.1 to smooth out imperfections.
Also smoothed out the intake port..

[image]https://i.imgur.com/pBLrTXs.jpg[/image]

So my questions are:
1. are we on the right track for the intakes?
2. should I thin down the valve guide more?
3. I left about the same curve from the top of the guide down to the port throat... I assume that is what I should do ?? or do I make the slope sharper eg grind down more on the bottom?
4. Do I widen the bowls more?
5. I also smoothed or rounded the sharp edge around the top of the combustion chamber... maybe a 1/16 to 1/8th... is that adequate to remove the sharp edge from a combustion standpoint? it is smooth to the touch..
6. The combustion chamber is surprisingly very rough.. from casting defects I guess... I would have thought the chamber would have been machined smooth from Ford??... am I supposed to smooth out those rough areas? and if so do I want to have them very smooth or polished or keep a 80 grit surface on them
7. I understand that the intake should not be polished to increase turbulent flow and thus mixing.. any guidance on that smoothness? eg 80 grit or 200 grit?

We are still polishing the exhausts... I will post a pic when we have one done.. to see if it is really done... :D
Thanks again
Brian
 

pmuller9

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pBLrTXs.jpg


You are on track for the intake.
Look at the example in post #2. Instead of a straight angle the valve guide should have more of a radius contour.
Take a little more off the valve guide as you make a radius and make the path a little wider on the side facing the exhaust port.
This is where the highest pressure of air flow is as it tries to make the turn towards the valve head.

The bowls should be wide enough but still leave room for a short 60 degree angle below the valve seat.
They look close as is.

The combustion chamber can be made smoother but it doesn't have to be perfect.
Remove what appears to be a ridge on the spark plug side of the chamber walls.

 
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THE FRENCHTOWN FLYER

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My "gut instinct" - not based on any A-B flow testing - is that the little remaining"fin" on the downstream side of the intake guide needs to be clocked more towards the center of the chamber, kinda almost facing the spark plug hole where you would want the preponderance of the charge to be headed. I've seen people place additional fin structures in the ports to do just that.
 

buckingbronco

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okay thanks for the additional guidance.

So the fin or top of the valve guide that comes out from the wall should be ground to be at about 4 or 5 oclock position vs at 6 oclock in my picture. this is to channel the fuel up towards the middle of the combustion chamber... vs the wall..makes sense
I will try to do that more on #2-#6

I had opened up the channel on the side towards the exhaust valve or in the middle.... but I will try to open it up more.

Just to be clear ... it sounds like I should still take off more of the valve guide... and maybe only leave 1/16 of the guide top around the valve guide hole.... correct? Im just worried that I will weaken the valve guide going too thin....but maybe there is not much lateral force here.

It sounds like the most benefit is from around the valve guide so I will put the time there vs trying to widen the inlet port side.
When I look in from the intake side it actually looks like the walls bow inwards maybe 1/16th or so.. I will try to take them flat to match tine inlet opening but not open the opening.... the gasket looks like it mates up pretty much directly to the original holes.

Thanks again
 

blprice74

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Buckingbronco,

To be honest I initially was going to do this process myself, and became concerned that I may do more harm than good. I get lost in terminology and quite frankly I just felt if I didn't have someone right beside me guiding me, I wouldn't be able to do it. You have asked all the questions I wanted to, plus more I wouldn't have thought of, and provided me the details I needed. Based on what you have managed to show here in this post, I know I can perform this process now.

FTF, it may be wise to make sure we save this information for folks like myself who honestly need that extra bit of information. This is a very good posting for a beginner like myself to help understand porting. Just a thought..

Brandon
 

buckingbronco

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Brandon
Thanks for the post. I had read a lot on porting before beginning and the experts on this forum have been very helpful even to novices like us. I think if you are doing a mild or moderate porting job that even a novice can do it without ruining the head if the focus is around the valve stem bosses where you get the most gain in flow. Good luck on your porting job!

PS if FTF or PMuller want to make this tread permanent for future reference that would be fine by me but I may need to find a more permanent place to post the pictures.

Brian
 

buckingbronco

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porting status: done?

here are the pics of the intake and exhaust ports in what I think is finished state for this mild porting job.
Any comment from the forum would be appreciated if I got it right or missed something

exhaust port polished
[image]https://i.imgur.com/GRyO9Qt.jpg[/image]

exhaust runner polished up to 600 grit. Note there still remain random pits.. Im not sure if these are in the base metal or from initial rough grinding. It was difficult to polish that divot so it will have to do. I lowered or flattened to small valve boss area ( the top or roof of the bowl even though it shows on the bottom in this picture). All of the exhausts are about the same 1.15 (vs ~0.9 to begin with)
[image]https://i.imgur.com/vMMWswc.jpg[/image]

intake port valve boss reshaped with the 'tail' of the boss directed towards the spark plug and an opening of the channel on each side of the valve guide. We did not polish or sand the intakes to increase gas turbulence and the mixing.

[image]https://i.imgur.com/09Wb0TP.jpg[/image]

intake runner showing the valve boss. I sloped it up from its original start of the valve boss slope up ... in other words the boss starts rising from the same spot but not its a more gradual slope up.

[image]https://i.imgur.com/XH0wBkr.jpg[/image]

combustion chamber; we only took off the sharp edges and did not polish it per sea.. so just the sharp edge around the top(or bottom corner where the head mates up to the block with the head installed) which was done with a small sanding drum on dremel. We also took sharp ridge on side of exhaust valves on all 6 cyl. Then just did a quick 'sanding' with a 120 grit dremel brillo type sanding wheel.
[image]https://i.imgur.com/8e2ZOt5.jpg[/image]

Any comments are welcome.
Thanks

ps Im not sure why the pics are not showing but I think if you click on the image wording it opens the link?
Thanks for the correct links on the pics... I must have done something wrong on the pic links initially
 

THE FRENCHTOWN FLYER

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You have done a very nice job.

Reach in to the short side radii with your finger to feel that they are very smooth with no abrupt ridges. You may need to get some strips of coarse grit sanding strips and "shoe shine" that area back-n-forth to even it out.

When you do the valve job smooth the transition of the 30 and 60 degree cuts into the chambers and bowls respectively. I use a fine curved radius jewelers' file to do this.

I do like to polish out the combustion chamber. A research paper I saw said power gains of 1% - 2% were possible.
 

pmuller9

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Porting looks good.
FTF's comments are sufficient.

buckingbronco:2hq9zd4j said:
ps Im not sure why the pics are not showing but I think if you click on the image wording it opens the link?

GRyO9Qt.jpg


vMMWswc.jpg



09Wb0TP.jpg

XH0wBkr.jpg


8e2ZOt5.jpg
 
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