Cylinder Head Porting and Power Production
- Thread starter RAMM
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My basic combo minus the domed slug
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Oogliboogli
jay27
Well-Known Member
Are you contributing or just going deflect everything off course?
Why does he only run 28 degrees of timing? Why , Why , Why? Please explain why , you do know the answer right? I would sure like to hear it and please be factual.
jay27
Well-Known Member
Those are impressive numbers and I am confident you have your Demon working really well, what track did you achieve your best times? Just curious.
I am going to go out on a limb and suggest any decent street engine in your car would result in some impressive #s as well compared to an average street car. Did you dyno your engines?
What a train wreck. Couldda been so much more.
RAMM
Well-Known Member
I'm going to attempt the impossible and try to get this thread back on track while addressing @Hysteric .
I started this thread with the focus on why certain cylinder heads seem to punch above their weight while others yet with much greater flow rates don't.
My understanding of how to make power is not at the novice level in my estimation either.
I really think you need to read and re-read your quotation about engines being more than air pumps because I already have a firm grasp about where that chemical into mechanical energy process comes from. It is the FUEL burning which heats the NITROGEN content in our atmosphere which EXPANDS which creates the force that acts on the PISTON.
Again I would ask you if you don't think it happens this way then please tell us what happens in the combustion process that provides the force to turn the crankshaft. I asked you for your thoughts last night in this very thread. J.Rob
K.O. SWINGER
Meeting in the alley since 1976
Although rumble and others bring up very good points I can't help but being impressed by the overall performance of a stock style la head, to me it does bring to light that a lot of people consider these heads to be nothing more than door stops and obsolete when in fact the overall performance capabilities are impressive for a 50+-year-old small block head design. I don't think there's any arguing that there are improved designs available and working with cast iron heads is a lot of work & heavy but I love the fact that you can still pump out (very) respectable numbers out of those old heads!
@K.O. SWINGER Thanks for the mention but I also see an overall package at work.
I also agree with RRR.
Apologies to RAMM and everyone else. I was stoked on so much more myself rather than a flag saver shoving crap around the thread.
I also agree with RRR.
Apologies to RAMM and everyone else. I was stoked on so much more myself rather than a flag saver shoving crap around the thread.
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Oogliboogli
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Oogliboogli
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Good question. IDK. I’ve asked this question to a few people and it seems some don’t care stating it doesn’t matter or flow is flow while others said they’ll stop the valve lifting that high since the head/port doesn’t like it.
Beats me! IDK!
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Oogliboogli
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Funny you mentioned a “Running engine with speed and sound pulse” since that is a factory I never seen considered when cylinder heads are flowed. The camshaft has a huge play in this. The cam controls when and where and then there is the exhaust pressure wave that can help or hinder cylinder filling.
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Oogliboogli
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yellow rose
Overnight Sensation
So I’ll throw in my .02 cents now that I understand what RAMM wants to discuss.
You see overachieving heads when the size and shape of the port matches the RPM, and especially when you get the cam events spot on.
When you get all that right, you get an engine that is spectacular in transient response, which can’t typically be measured with a water brake dyno. BUT...you can look at the numbers I’ve already posted...BSAC, BSFC, A/F ratio. The big thing (IMO) is when you hit all of that (forgot about header sizing...that’s a BIG deal) you make overlap a positive, not a negative.
When you get the header working with overlap instead of fighting it, you make beaucoup power, way above what the flow numbers say.
To that end, anything (and I mean anything) you can do to reduce reverse flow in both the intake and exhaust ports will also help at overlap. Any time you can use overlap to get the air/fuel column fuel moving sooner, with more authority and with less combustion residue will also help fill the cylinder AFTER BDC.
And that’s a big deal. As the piston is moving back up the bore, if you can get the air/fuel column moving sooner and faster, you can use that kinetic energy to fill the cylinder much longer than you can if you are off on overlap. You effectively make IVC “later” without making it physically change. That’s a bonus. I think way too many guys sacrifice overlap, searching for idle quality when poor idle is mostly carb tuning. EFI bears that out. The EFI guys get better idle quality because they know how to clean up the idle circuit. Carb guys just live with ****, because that’s what we’ve always done. And, we were always told that’s how it should be.
It’s not true. Giving up overlap to try and crutch the idle is the quickest way to piss away power and drivability everywhere.
Overlap and header tuning go together.
If we want to talk about why one casting is better than another (lest say why is a W2 better than about every 23 degree SBC head out there, with the exception of some stuff Chad Speier and others are doing) then we get into architecture and geometry.
Valve angle is a big deal, but equally as big is port angle.
Let’s compare the W2 to most 23 degree SBC heads.
The W2 heads (like all SBM’s) have an 18 degree valve angle. The SBC is 23. That’s HUGE. That angle is measured from the deck, forward towards the intake manifold. As you stand the valve up, you can make the combustion chamber shallower. That’s a big deal. Also, the Chrysler small block heads open the valves on the centerline of the bore. Another big deal. Opening on the centerline of the bore means you can run a bigger valve before you get into cylinder shrouding. And...it changes the way the cylinder fills. The biggest issue with a bigger valve is getting the port volume to feed it.
Next up, the elephant in the shop...the offset intake rocker. That dread, hated, bitched about offset rocker. I will say ANY serious effort engine should be using an offset intake rocker, and it doesn’t matter what name is on the rocker boxes. There is a reason why Chrysler engineers went that way, and it’s a big deal. You can’t have dimensional changes in the port and not have issues. I’ll get into that more next. It’s sad that Chrysler was YEARS ahead with this head, and it’s sad they made it cost prohibitive, but the GM do NOT ***** nearly as much when they have to spend money for more power. Dicking around with stock rocker stuff is an exercise in futility IF you don’t have to do it.
That’s why the TF head was a small let down. I get that Chrysler guys will ***** about an offset rocker, but it NEEDS an offset rocker. Making air not only change directions, but making it change SHAPE is always a flow loser and power killer. Guys underestimate how bad the pushrod pinch is. Half a century of development has made that pinch less of a loss, but it’s still there, and it’s still a problem. Offsetting the intake rocker allows the exhaust side wall to get straighter, with less dimensional cross section changes. You won’t find any serious cylinder head that has a pinch at the pushrod. That’s not a coincidence, it’s an engineered design.
So why is the pinch so bad? Any time you squeeze the air down, and then open it back up, you piss Bernoulii off. You are creating a venturi where you don’t want one, or even need it. That’s what the pinch is. It squeezes the air down, speeding it up, and it drops the pressure. Low speed air is high pressure air, and high speed air is low pressure air. Unlike a booster venturi, where you are adding fuel at the low pressure area, the pinch already has fuel in it, and dropping the pressure will cause the fuel to liquify and fall out of suspension. The same thing happens when you slam the throttle opens...the pressure drops in the intake manifold, and any fuel that is atomized is converted back to a liquid, which is why you need an accelerator pump. The pinch does the same thing.
So the offset rocker is a HUGE deal IF you think air flow (which includes fuel in it) management is more important than bulk flow (I do) then dealing with the pushrod pinch, or getting rid of the damn thing is a big deal. If you took the TF head and eliminated the PR pinch, just using the TA offset, the head would make more power, even at the same airflow, because less better air flow makes more power than shitty more air flow. Another reason the W2 is still better than most any 23 degree SBC head is the offset rocker. Even if you put an offset rocker on the SBC head, you still have the 23 degree valve angle.
Another issue that crops up with the PR pinch is the velocity gradient, pressure gradient...whatever other name they call it. The greater the velocity gradient in the port (which also changes the pressure gradient as I laid out above) the more fuel control issues you have. If you velocity map a port and the air speed on the floor is say...260 and the roof is say...330, then anything you can do to reduce the differential between the floor will make more power at the same air flow, because you are keeping the air and fuel together because et he pressure drop across the port is less. Ideally you want the air speed the same all through the port. WithOE architecture that’s near impossible but I’m sure some guys can get close. Another reason why shape matters more than size, and why shape matters more than bulk air flow.
Now, we need to see the next evolution in just the 18* Chrysler head...the W5. It’s not popular, hard to find, most castings are ****, but the W5 is a MASSIVE upgrade over the W2. It takes the same offset intake rocker, but the big improvement is that the intake runner is RAISED. The intake port is something like .750 further off the deck than a W2. Maybe Rumble can measure one for us if he is up to it, as I know he is sitting on some of them. Whatever it is, it he intake is much higher in the W5 than the W2. That is a HUGE deal. Not only do you have all the benefits of the W2, plus you raise the runner. That means the short turn, the short side radius...whatever you want to call it now has less angle to it, which means you can carry more air speed around the corner before it separates. And that means a better mixture hits the chamber. That means you burn more fuel and make more power.
Then you start getting into heads that are even further developed with flatter valve angles (15, 14, 10 degree angles) and higher ports and they always make more power even at the same airflow, because you can develop better port shapes, cleaning up the discharge coefficient and making all the Lift/diameter ratios happier.
That’s the least amount of words I can use to try an explain why more airflow isn’t always better, and why certain head architecture is better than others. You can’t have all the shape changes that OE casting have and expect to use the airflow you have to make the most power.
As a head porter your job is to identify where the weak spots are and eliminate or mitigate them as best you can. When you do that, the engine will use the same (or less) air to make the same (air more) power. It’s all about shape, Shape, SHAPE. It’s about manipulating the air to make it do what you want it to do, without compromising shape.
I didn’t even get into combustion chamber shape, or intake manifolds. That’s all part of the same discussion.
Ok, asbestos fire suit on and ready for the heat..................
You see overachieving heads when the size and shape of the port matches the RPM, and especially when you get the cam events spot on.
When you get all that right, you get an engine that is spectacular in transient response, which can’t typically be measured with a water brake dyno. BUT...you can look at the numbers I’ve already posted...BSAC, BSFC, A/F ratio. The big thing (IMO) is when you hit all of that (forgot about header sizing...that’s a BIG deal) you make overlap a positive, not a negative.
When you get the header working with overlap instead of fighting it, you make beaucoup power, way above what the flow numbers say.
To that end, anything (and I mean anything) you can do to reduce reverse flow in both the intake and exhaust ports will also help at overlap. Any time you can use overlap to get the air/fuel column fuel moving sooner, with more authority and with less combustion residue will also help fill the cylinder AFTER BDC.
And that’s a big deal. As the piston is moving back up the bore, if you can get the air/fuel column moving sooner and faster, you can use that kinetic energy to fill the cylinder much longer than you can if you are off on overlap. You effectively make IVC “later” without making it physically change. That’s a bonus. I think way too many guys sacrifice overlap, searching for idle quality when poor idle is mostly carb tuning. EFI bears that out. The EFI guys get better idle quality because they know how to clean up the idle circuit. Carb guys just live with ****, because that’s what we’ve always done. And, we were always told that’s how it should be.
It’s not true. Giving up overlap to try and crutch the idle is the quickest way to piss away power and drivability everywhere.
Overlap and header tuning go together.
If we want to talk about why one casting is better than another (lest say why is a W2 better than about every 23 degree SBC head out there, with the exception of some stuff Chad Speier and others are doing) then we get into architecture and geometry.
Valve angle is a big deal, but equally as big is port angle.
Let’s compare the W2 to most 23 degree SBC heads.
The W2 heads (like all SBM’s) have an 18 degree valve angle. The SBC is 23. That’s HUGE. That angle is measured from the deck, forward towards the intake manifold. As you stand the valve up, you can make the combustion chamber shallower. That’s a big deal. Also, the Chrysler small block heads open the valves on the centerline of the bore. Another big deal. Opening on the centerline of the bore means you can run a bigger valve before you get into cylinder shrouding. And...it changes the way the cylinder fills. The biggest issue with a bigger valve is getting the port volume to feed it.
Next up, the elephant in the shop...the offset intake rocker. That dread, hated, bitched about offset rocker. I will say ANY serious effort engine should be using an offset intake rocker, and it doesn’t matter what name is on the rocker boxes. There is a reason why Chrysler engineers went that way, and it’s a big deal. You can’t have dimensional changes in the port and not have issues. I’ll get into that more next. It’s sad that Chrysler was YEARS ahead with this head, and it’s sad they made it cost prohibitive, but the GM do NOT ***** nearly as much when they have to spend money for more power. Dicking around with stock rocker stuff is an exercise in futility IF you don’t have to do it.
That’s why the TF head was a small let down. I get that Chrysler guys will ***** about an offset rocker, but it NEEDS an offset rocker. Making air not only change directions, but making it change SHAPE is always a flow loser and power killer. Guys underestimate how bad the pushrod pinch is. Half a century of development has made that pinch less of a loss, but it’s still there, and it’s still a problem. Offsetting the intake rocker allows the exhaust side wall to get straighter, with less dimensional cross section changes. You won’t find any serious cylinder head that has a pinch at the pushrod. That’s not a coincidence, it’s an engineered design.
So why is the pinch so bad? Any time you squeeze the air down, and then open it back up, you piss Bernoulii off. You are creating a venturi where you don’t want one, or even need it. That’s what the pinch is. It squeezes the air down, speeding it up, and it drops the pressure. Low speed air is high pressure air, and high speed air is low pressure air. Unlike a booster venturi, where you are adding fuel at the low pressure area, the pinch already has fuel in it, and dropping the pressure will cause the fuel to liquify and fall out of suspension. The same thing happens when you slam the throttle opens...the pressure drops in the intake manifold, and any fuel that is atomized is converted back to a liquid, which is why you need an accelerator pump. The pinch does the same thing.
So the offset rocker is a HUGE deal IF you think air flow (which includes fuel in it) management is more important than bulk flow (I do) then dealing with the pushrod pinch, or getting rid of the damn thing is a big deal. If you took the TF head and eliminated the PR pinch, just using the TA offset, the head would make more power, even at the same airflow, because less better air flow makes more power than shitty more air flow. Another reason the W2 is still better than most any 23 degree SBC head is the offset rocker. Even if you put an offset rocker on the SBC head, you still have the 23 degree valve angle.
Another issue that crops up with the PR pinch is the velocity gradient, pressure gradient...whatever other name they call it. The greater the velocity gradient in the port (which also changes the pressure gradient as I laid out above) the more fuel control issues you have. If you velocity map a port and the air speed on the floor is say...260 and the roof is say...330, then anything you can do to reduce the differential between the floor will make more power at the same air flow, because you are keeping the air and fuel together because et he pressure drop across the port is less. Ideally you want the air speed the same all through the port. WithOE architecture that’s near impossible but I’m sure some guys can get close. Another reason why shape matters more than size, and why shape matters more than bulk air flow.
Now, we need to see the next evolution in just the 18* Chrysler head...the W5. It’s not popular, hard to find, most castings are ****, but the W5 is a MASSIVE upgrade over the W2. It takes the same offset intake rocker, but the big improvement is that the intake runner is RAISED. The intake port is something like .750 further off the deck than a W2. Maybe Rumble can measure one for us if he is up to it, as I know he is sitting on some of them. Whatever it is, it he intake is much higher in the W5 than the W2. That is a HUGE deal. Not only do you have all the benefits of the W2, plus you raise the runner. That means the short turn, the short side radius...whatever you want to call it now has less angle to it, which means you can carry more air speed around the corner before it separates. And that means a better mixture hits the chamber. That means you burn more fuel and make more power.
Then you start getting into heads that are even further developed with flatter valve angles (15, 14, 10 degree angles) and higher ports and they always make more power even at the same airflow, because you can develop better port shapes, cleaning up the discharge coefficient and making all the Lift/diameter ratios happier.
That’s the least amount of words I can use to try an explain why more airflow isn’t always better, and why certain head architecture is better than others. You can’t have all the shape changes that OE casting have and expect to use the airflow you have to make the most power.
As a head porter your job is to identify where the weak spots are and eliminate or mitigate them as best you can. When you do that, the engine will use the same (or less) air to make the same (air more) power. It’s all about shape, Shape, SHAPE. It’s about manipulating the air to make it do what you want it to do, without compromising shape.
I didn’t even get into combustion chamber shape, or intake manifolds. That’s all part of the same discussion.
Ok, asbestos fire suit on and ready for the heat..................
yellow rose
Overnight Sensation
I think an often missed opportunity to fix port issues with turbulence and such, is the intake manifold.
I’ve seen some intakes just kill a head, some do nothing and some do the most important thing I’ve found...a good intake manifold, properly prepped can correct what looks like a break over or backing up issue. You may not see an increase in flow, or maybe even lose some air flow.
But a good intake will settle down the port. You can see it on the manometer. And I’ve seen it (mostly with tunnel rams but I’ve had a couple of single 4’s do it...but they took a bunch of welding and grinding) eliminate the break over. Even testing at pressure drops above 28 inches.
That’s why I never base lift on what the port does as far as backing up or breaking over. A good intake will fix that, or make it so minute that cutting back lift is just a power loser.
Along that line, seat angles matter. As I’ve said before, I really don’t see a need to do any real performance heads with a 45 any more. Yes, low lift flow will be less. But the SHAPE of the seat and valve will be much more beneficial than getting more curtain area. It’s about shape and air speed.
@yellow rose
Sorry, measure what again?
I’ll get to it in a bit as I just set up a cylinder head for work/tubing pushrod holes.
Sorry, measure what again?
I’ll get to it in a bit as I just set up a cylinder head for work/tubing pushrod holes.
yellow rose
Overnight Sensation
Measure from the deck to the bottom of the intake port. I used to know that number off the top of my head, but I’m not sure that .750 off the deck is right. If you don’t mind...while you are measuring can you measure the port height from the deck to the bottom of the port on a W2 so we can see the two together??
Thanks Rob.
OK, give me a few minutes as the heads are on total opposite sides of the house....
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Oogliboogli
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K.O. SWINGER
Meeting in the alley since 1976
Crap I got to get back to work 
you guys got me sucked in big time, thanks
you guys got me sucked in big time, thanks
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Oogliboogli
Brick wall.
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