Magnum head porting for the beginner
Recently, in one of my fits of boredom, I grabbed a spare test head.
A '97 Magnum off of a 5.9 with 1.92/1.62 valves. As I went through my normal process of grinding and testing, I discovered how this head responds to changes. I enjoy this sort of thing. Quirky.
I had fun with it. 255 cfm worth of fun with a stock 1.92 valve. It will go more but, not without a lot of nit-picking. I wasn't up to that this time around. Wasn't bored enough, I guess.
So my thought at this point was, with the growing migration to the Magnum series iron, why not do a How-To for the low buck – can't afford a port job – DIY sort of guy???
A guide to 30 cfm extra flow that even a newbie can replicate in the corner of their garage.
A fail-safe approach that won't turn your head into scrap. Complete with flowtests, so that you will have a good idea where you're at.
Again, this is for the newbie ! While I'm sure I'll draw the criticism of some of the other porters on FABO, this is not for them. But, help is always appreciated :)
With that, HERE WE GO !!
lt wouldn't be right to make a baseline test without touching up the Valve Job. Intake was short work, re-establish the seat and locate it with a top and bottom without upsetting the OE VJ.
The exhaust is going to take some effort. See how the Exh seat grows in width as it gets closer to the Int?
For basic info, let's CC it, as cast, shall we?
Any guesses ? 154.8 cc
Now comes the flow test.
I will be using this Radius Entry throughout the testing for consistency and to reduce any variables.
The radii I used here is capable of supplying 320 cfm without any restriction. Plenty for this head...
I will also be flowing every .050, it makes it easier to make an assessment.
OEM 1.920 valve. I added a 28° BC .050 wide: (easy to add)
.050 46.3 47.8
.100 75.8 80.3
.150 106.2 113.4
.200 132.5 141.4
.250 156.9 165.2
.300 179.7 186.4
.350 196.4 202.6
.400 206.4 213.1
.450 210.3 216.8
.500 211.2 218.0
.550 213.0 213.8
.600 212.6 210.3
Now lets measure the bowl ID and see what we get. The Superflow manual states it likes to see the bowl 80% of the valve diameter.
While this is a decent percentage to work with, I feel this is merely an entry level objective and should be limited to low lift applications.
While this head started it's life in this realm, we want to raise the bar. In fact, my testing over the years have shown percentages up to 85% does not limit low lift efficiency, that much, but does aid in lifts above .500 while 80% does not. 85% is our target.
Pushing the percentage to 88% is not uncommon for race applications, and a 50° seat is frequently used.
The 50 ° seat does hurt the bottom end but, when using cams that are >275° @ .050, so what.
The smallest cross sectional area (CSA) is about 1/2” below the seat and intersects with the port cast at the bottom of the counter bore. I get 1.564” here, that's 81.4% of the 1.92 valve. Way to go!
That is much better than some of the stuff turned out in the early years but, we'd like to be about 85% for this project. 85% of a 1.920 valve is 1.632. Well ! Thats just a hair over the exhaust valve diameter ! So lets do this, take your 1.620 exhaust valve and stick it in the intake port and scribe a mark, like this:
Your scribe mark should be visible like you see here. Yellow arrow.
We are going to grind up to this mark. Use the Exh valve as a template. Take your time, it's not a race..yet. Grind and check with the valve, so that you get it nice and concentric.
The red arrow is pointing out a low lift killer. All heads have them, we will fix this later. The green arrow is how it should look.
It should look something like below. Also blend into the short side radius (SSR) and Bowl.
Let's test it and see what we've got!
.050 47.8 Peak flow is .050” lower than the OE test with a BC valve.
.100 79.1 While flow was up, you can see a limitation from another
.150 112.5 part of the port, limiting the upper lifts
.200 140.3 We will look at that next.
.250 165.9
.300 187.0 Let's measure the CSA in the pushrod pinch. Red line below.
.350 205.5 width x height at the pinch is 1.629 sq. in.
.400 220.5 The area in the bowl is 2.08 (1.63 sq. x 3.14)
.450 227.1 There's our deficit. The pinch is 22% smaller than the bowl.
.500 226.4 Let's open that up.
.550 222.9
.600 211.5
Recently, in one of my fits of boredom, I grabbed a spare test head.
A '97 Magnum off of a 5.9 with 1.92/1.62 valves. As I went through my normal process of grinding and testing, I discovered how this head responds to changes. I enjoy this sort of thing. Quirky.
I had fun with it. 255 cfm worth of fun with a stock 1.92 valve. It will go more but, not without a lot of nit-picking. I wasn't up to that this time around. Wasn't bored enough, I guess.
So my thought at this point was, with the growing migration to the Magnum series iron, why not do a How-To for the low buck – can't afford a port job – DIY sort of guy???
A guide to 30 cfm extra flow that even a newbie can replicate in the corner of their garage.
A fail-safe approach that won't turn your head into scrap. Complete with flowtests, so that you will have a good idea where you're at.
Again, this is for the newbie ! While I'm sure I'll draw the criticism of some of the other porters on FABO, this is not for them. But, help is always appreciated :)
With that, HERE WE GO !!
lt wouldn't be right to make a baseline test without touching up the Valve Job. Intake was short work, re-establish the seat and locate it with a top and bottom without upsetting the OE VJ.
The exhaust is going to take some effort. See how the Exh seat grows in width as it gets closer to the Int?
For basic info, let's CC it, as cast, shall we?
Any guesses ? 154.8 cc
Now comes the flow test.
I will be using this Radius Entry throughout the testing for consistency and to reduce any variables.
The radii I used here is capable of supplying 320 cfm without any restriction. Plenty for this head...
I will also be flowing every .050, it makes it easier to make an assessment.
OEM 1.920 valve. I added a 28° BC .050 wide: (easy to add)
.050 46.3 47.8
.100 75.8 80.3
.150 106.2 113.4
.200 132.5 141.4
.250 156.9 165.2
.300 179.7 186.4
.350 196.4 202.6
.400 206.4 213.1
.450 210.3 216.8
.500 211.2 218.0
.550 213.0 213.8
.600 212.6 210.3
Now lets measure the bowl ID and see what we get. The Superflow manual states it likes to see the bowl 80% of the valve diameter.
While this is a decent percentage to work with, I feel this is merely an entry level objective and should be limited to low lift applications.
While this head started it's life in this realm, we want to raise the bar. In fact, my testing over the years have shown percentages up to 85% does not limit low lift efficiency, that much, but does aid in lifts above .500 while 80% does not. 85% is our target.
Pushing the percentage to 88% is not uncommon for race applications, and a 50° seat is frequently used.
The 50 ° seat does hurt the bottom end but, when using cams that are >275° @ .050, so what.
The smallest cross sectional area (CSA) is about 1/2” below the seat and intersects with the port cast at the bottom of the counter bore. I get 1.564” here, that's 81.4% of the 1.92 valve. Way to go!
That is much better than some of the stuff turned out in the early years but, we'd like to be about 85% for this project. 85% of a 1.920 valve is 1.632. Well ! Thats just a hair over the exhaust valve diameter ! So lets do this, take your 1.620 exhaust valve and stick it in the intake port and scribe a mark, like this:
Your scribe mark should be visible like you see here. Yellow arrow.
We are going to grind up to this mark. Use the Exh valve as a template. Take your time, it's not a race..yet. Grind and check with the valve, so that you get it nice and concentric.
The red arrow is pointing out a low lift killer. All heads have them, we will fix this later. The green arrow is how it should look.
It should look something like below. Also blend into the short side radius (SSR) and Bowl.
Let's test it and see what we've got!
.050 47.8 Peak flow is .050” lower than the OE test with a BC valve.
.100 79.1 While flow was up, you can see a limitation from another
.150 112.5 part of the port, limiting the upper lifts
.200 140.3 We will look at that next.
.250 165.9
.300 187.0 Let's measure the CSA in the pushrod pinch. Red line below.
.350 205.5 width x height at the pinch is 1.629 sq. in.
.400 220.5 The area in the bowl is 2.08 (1.63 sq. x 3.14)
.450 227.1 There's our deficit. The pinch is 22% smaller than the bowl.
.500 226.4 Let's open that up.
.550 222.9
.600 211.5
