https://www.enginebuilderma...m-numbers-need-know/

I always took CFM #'s with a bunch of salt, not a grain. Enjoy the article

I like engine builder mag articles.

Constant-flow bench testing looks easy to do, which would explain why it's commonly done.

For the Supernatural intake system, did you have a test setup other than a running engine?

quote Originally posted by pmbrunelle: Constant-flow bench testing looks easy to do, which would explain why it's commonly done. For the Supernatural intake system, did you have a test setup other than a running engine?

I first mathematically modeled it and for live testing I used my wife's hair blower (it has variable speeds), an air speed meter that can read CFM and air velocity (f/s, kph, mph) and my smoke machine.
The rod/stroke ratio and bore of the engine will determine the intake manifold designed and how the heads will be ported and if an upgrade in valve size is needed.
That's why if you compare the Supernatural 2.8 intake to the 3.4 intake they differ from one another in plenum size, runners length and shape.
These 2 engines have different geometries so they need different accessories to improve their volumetric efficiency.
Is that simple.

[This message has been edited by La fiera (edited 01-08-2020).]

Did you mathematically model a constant flow, or did you consider that the intake valve opens and closes (thus taking intermittent breaths of air, and the air slug has to start/stop).

How does the bore size relate to the porting? Are you trying to shoot the air such that it follows the cylinder wall in a circular path?

The bigger the bore, the further away it is from the valve and the more of the valve curtain area is effective and getting air through the port.

Assuming constant valve stem to cylinder wall distance:
Does an oversized valve that is shrouded by the bore flow less than a smaller valve that is more open on all sides?

Is maxing out the valve size not always a good thing? (power-wise)

La Fiera says that the bore size affects the porting job, so I am curious to know how the porting should be performed differently as a function of bore size.

quote Originally posted by pmbrunelle: Did you mathematically model a constant flow, or did you consider that the intake valve opens and closes (thus taking intermittent breaths of air, and the air slug has to start/stop).

Yes, I do. I put the blower sucking under the "cylinder" ( a pipe under the head with the diameter of the motor to be used) and I watch the smoke being sucked in first with the valve at full lift varying the speed of the blower. Then I use full speed on the blower and close and open the valve to see how the smoke changes shape and speed going in.
I also have the air speed meter at the entrance of the intake port taking a reading of the incoming air being sucked by the blower on the bottom.
I do this for two reasons:
1- To visualize how the air behaves at different speeds and at different valve opening and closing rates.
2- To get a speed reading of the incoming air to work on the mathematical model of the shape, volume and size of the plenum and the shape and length of the runners.
The bore will determine the valve sizes and Will explained the reason why.
The rod/stroke ratio will determine if the head porting and intake design will be a hi-pressure/hi-volume/low-velocity, a low-pressure/low-volume/hi-velocity or a mixture of both.
Then last is the camshaft. I come up with the camshaft specs to place the power curve where it would complement the entire system (intake, head & short block geometry) and also to regulate how that power is delivered (sudden burst, gradual increase or extended and smooth)


431WHP@5500RPM
497WTQ@3800RPM

Starts with 434WTQ@2000RPM

Take this dyno sheet for example. It's from a 1995 Camaro LT1 350 6 speed manual I built about 10 years ago.
The customer wanted a very fast off the line car with lots of pulling power from low to mid range and steady top end so he can chase some super cars if he wanted to; and a NASCAR-like idle lope. I predicted 400+WHP and 450-475WTQ but that power would be delibered very abruptly.
First thing I did was to stroke it to increase the displacement from 350 to 377CID.
I opted for the shorter 5.7 stock rods over the longer 6.0 rods to shorten the rod/stroke ratio to achieve the neck-snapping acceleration effect.
Since the shorter rod/stroke ratio also allows for more piston speed, this increase in piston speed has a direct effect on how fast the air is pumped in and out of it. The faster the air is digested the faster the engine accelerates.
The thuging or sucking effect of the piston dwell on the intake stroke was so drastic that I could shape the intake ports for hi-pressure, hi-volume and low-velocity by giving them a very large cross sectional area and get away with it. I didn't even bother to flowbench the heads.
The cam was tricky becasue I coundn't find an off the shelf cam with the specs I wanted for this engine, I ended up getting it custom ground like always.
It wasn't a big cam but it was very agressive. It was a roller. The stock intake (very good design) was port matched and a 1000CFM TB was installed with 36# injectors to start.
PCM FOR LESS made me the custom tune and it was ok and the above dyno is the result. Less than $3500 in parts and labor.
The car was sold to another friend of mine and he dynoed it last year. Oh, and this is the same dyno I use for my Fiero.
The original owner never dynoed it but I showed him these results and he was amazed!

I've been doing this approach for many years and it seems to work, Its a bit brute and unconventional but it works for me.

It is most interesting to learn about your working methods! Much more cool than an unexplained dyno sheet.

Do you use transparent plastic for prototypes to visualize the smoke? Is the cylinder pipe transparent?

When you do the low-pressure/low-volume/hi-velocity recipe, should the runner hold the volume needed to fill the cylinder, but not more? If the slug of air is too long/heavy, then it would be slow to accelerate into the cylinder when the intake valve opens?

You've been talking more about the intake than the exhaust; how much effort do you put in intake vs. exhaust?

The exhaust is driven by much greater pressure than the intake, so not as much effort is required to get it good enough. Basically, as long as it's not a disaster (see '00+ FWD Northstar exhaust ports...) then it's easy to come up with enough shape and flow to make it work.
The intake is only driven by atmospheric pressure, so it needs every little improvement possible to get more air into the engine.

The cam and port go hand-in-hand. The minimum cross sectional area of a port *should* be in the throat right upstream of the valve, when the valve is at full lift. As the valve lifts, the curtain area increases. If the curtain area exceeds the throat area at a low lift, then the rest of the lift is wasted. The higher the valve is lifted, the bigger the throat needs to be to provide enough flow area to keep air moving.

When the valve is just getting off the seat, the valve seat angles are critical for getting flow through the valve. This is the low lift flow regime. The valve transitions to the high lift flow regime as curtain area approaches throat area, and the curtain stops being the minimum cross-sectional area of the port.

Since optimum throat size is dependent on curtain area, reducing effective curtain area by shrouding the valve with the bore wall or chamber surface really hurts the effectiveness of port work.

quote Originally posted by pmbrunelle: When you do the low-pressure/low-volume/hi-velocity recipe, should the runner hold the volume needed to fill the cylinder, but not more? If the slug of air is too long/heavy, then it would be slow to accelerate into the cylinder when the intake valve opens?

That's when intake manifold runner length and shape come in to play.
In the mentioned LT1 example the runners have the same large cross sectional area to match the head intake port resulting in hi-pressure/hi-volume/low velocity set up.
The velocity needed to accelerate that slow moving air is generated by the fast hard suction of the piston drawing air in on the intake stroke and how hard the suction signal is, depends on the engine rod/stroke ratio, 1.52 in this specific case.
Now compare that to the 2.8 and 3.4 rod/stroke ratios which are 1.9 &1.72 respectively. As discussed before, the higher the rod/stroke ratio the slower the piston speed in comparison to short rod/stroke ratio.
This low piston speed will affect the piston dwell making it very slow weak at sucking air on the intake stroke. So, to help promote air velocity I play with the runner shape.
And the shape that works the best is the Funnel shape. This shape will give you a mix of hi-pressure/hi-volume/low-velocity at the top of the runner and a low-pressure/low-volume/hi-velocity at the bottom.
This type of runner combined with a properly sized plenum and TB can also creates a type of "natural supercharging", That's why I call it Supernatural.

As far as the exhaust side I use the camshaft to do most of the work. Of course, that is assuming that the engine has a good free flowing exhaust system that can be used in conjunction with exhaust cam lobe geometry to help even more the intake side on that "supercharging" effect.

quote Originally posted by Will: The cam and port go hand-in-hand. The minimum cross sectional area of a port *should* be in the throat right upstream of the valve, when the valve is at full lift. As the valve lifts, the curtain area increases. If the curtain area exceeds the throat area at a low lift, then the rest of the lift is wasted. The higher the valve is lifted, the bigger the throat needs to be to provide enough flow area to keep air moving.

Because there are limits on valve acceleration (and higher-order derivatives), it seems like the peak lift must exceed the "ideal" lift for a given throat size in order to have the duration you want.

That sounds like a good argument for a roller cam.

quote Originally posted by La fiera: This low piston speed will affect the piston dwell making it very slow weak at sucking air on the intake stroke. So, to help promote air velocity I play with the runner shape. And the shape that works the best is the Funnel shape. This shape will give you a mix of hi-pressure/hi-volume/low-velocity at the top of the runner and a low-pressure/low-volume/hi-velocity at the bottom.

It seems a benefit of the funnel shape would be insensitivity to small displacement changes, and manifold fabrication errors, since the "end" of the funnel is ill-defined.

quote Originally posted by pmbrunelle: It seems a benefit of the funnel shape would be insensitivity to small displacement changes, and manifold fabrication errors, since the "end" of the funnel is ill-defined.

Yes, despite the end of the funnel being ill-defined it works very good when properly sized regardless to engine displacement. Now, it takes experience to do so, and if you don't have the experience; trial and error is your best friend.