How much swirl is too much swirl

[Gobrdgo]

New guy here. Thanks in advance. I’ve been working on porting some Pontiac D Ports. The un shrouding of the valves in the combustion chamber took the swirl numbers from 3000 up to 4000 rpm. Understanding that you can have TOO much swirl, how much is too much? I tested the sbc vortec 906 head and got 2500. Did GM figure out 2500 is a sweet spot? Was thinking swirl was a motivation in that head design which is why I tested it. I’m a newbie FYI just blessed with some killer equipment and help at my disposal for my Pontiac head project. Just wanted to make sure I’m not mistaken for an experienced head porter.

[Walter R. Malik]

New guy here. Thanks in advance. I’ve been working on porting some Pontiac D Ports. The un shrouding of the valves in the combustion chamber took the swirl numbers from 3000 up to 4000 rpm. Understanding that you can have TOO much swirl, how much is too much? I tested the sbc vortec 906 head and got 2500. Did GM figure out 2500 is a sweet spot? Was thinking swirl was a motivation in that head design which is why I tested it. I’m a newbie FYI just blessed with some killer equipment and help at my disposal for my Pontiac head project. Just wanted to make sure I’m not mistaken for an experienced head porter.

Swirl is great for economy and controlling detonation so, it all depends upon what the particular engine needs for that application.

[BLSTIC]

I can't give you the measurements, but i know at least on a hemi combustion chamber swirl is better than nothing, but not as good as tumble. Excessive swirl tends to lead to inefficient combustion at high rpm. Mitsubishi Astron engines are a good example. Big valves, hemi, moderate flow, must be great right? Not above 4500rpm

[Gobrdgo]

I thought tumble was a 4 valve only thing? Am I in correct on that?

[Mummert]

Swirl is typically based on stability of the short turn. If the short turn works properly the swirl gain very slowly as you open the valve every .050".

A typical swirl curve will go something like this. A 2 valve engine that has a "semi modern" port and chamber will see the swirl increase for the first few lift points, say up to .200" lift or so (1200-1500rpm very common here). At this point the valve is starting to get open enough to start unshrouding itself. The swirl will stabilize and possibly start dropping (600-1000 rpm common) and then stabilize from .250 to .450 lift or so until you get to .25 L/D ratio. Once you've reached this point the shorturn starts to show its true colors. As the port start becoming less efficient the swirl starts to go up.
The less cfm the port gains per .050" the more the swirl rises. This goes for pretty much every head. 4 valves included.

Tumble is very possible in 2 valve heads. Remember that you almost never have perfect swirl or tumble but usually have some sort of an off axis tilted vortices.

4000rpm is high and usually means your short turn is not working at all. The chamber and the valve are all a part of the port. Your chamber unshrouding has placed more demand on your port and the flaws are starting to show up. If you take a ball point pen and turn the flow bench on you can start probing around in the port, when you touch the right spot your flow will go up and the swirl will drop, and then all you have to do is fix it.

Unless the cylinder head is some sort of shallow bowl 50's or 60's oem iron head, you should be able to stay around 2500 rpm at your peak cam lift, and not seeing more than 1000 rpm of increase in the last 1/3rd of the lift curve gradually.. I'm sure your head is not 4000rpm from half lift on up. Your looking for smooth transitions.

Old school heads have a tenancy to gradually gain swirl from start to finish.

Swirl rpm is a product of vortices pitch and intensity. Anything under 1000 rpm of PEAK lift swirl would be considered a form of tumble, anything over 3000rpm PEAK lift swirl would be considered swirl.

1250 -2250rpm PEAK lift swirl is an off axis swumble.

[mag2555]

A parallel valve wedge chamber head like a PONTIAC ( and many others ) can not be compared to a true Hemi type head in the least!
All heads that produce some level of swirl will do so in two steps .

The first being where the air mass traveling through the port is taking the path of least resistance and having a fine and dandy day!

The second step starts off when the air mass is great enough to start to be forced to follow the contoure of the port.

Making note in a flow test of how long and up to what lift point swirl keeps going. And or when tumble starts to kick in when seen on a flow bench with a open cylinder
Can be flat out misleading since in a running motor as rpm goes up the cylinder is wide open for less and less time.

In terms of getting tumble to take place as seen on a flow bench with a 14 degree valve inclination angle head like in a Pontiac or Ford FE Head ( and others) all you need to do is get the potential flow level up to the point where not having the needed correct short turn arc and width to control the velocity over it and your there looking at receding flow numbers!

A phrase has been coined by us folks who port these types of heads to high levels of air flow and it goes like this, “ if I haven’t got the flow then I don’t have the tumble, and if I haven’t got the tumble then I don’t have the flow!”

That Mitstu motor leveling off HP wise could simple be to too high a velocity that’s being developed else where in the intake tract other then in the head, bends in runners of more then 30 degrees can do this at high velocities that you may not see unless your testing above the normal 28”.

The fact that most of us can not do flow test and testing for swirl rates and such while piston cycles are taking place leaves up in the empirical testing Black hole!

[Stan Weiss]

Around the 53 Minute area.

David Vizard's PowerTec 10 EP 28 The ultimate youtube head porting video

https://www.youtube.com/watch?v=FBpf9nYyu6g

Stan

The dark vertical line would be .25 D for the intake valve.

Swirl.jpg

[Bryan Maloney]

We had swirl, tumble, and wet flow test equipment available as part of Dodge's Nascar effort from 2000 to 2012.
We measured swirl as rotational torque with a honeycomb insert and a rotary strain gauge. Tumble was measured on another fixture with a perforated plate and three load cells. Data from the three load cells gave us total combined tumble torque, and more importantly, the force location defined as distance from the bore center and clocking in degrees.
We found that the swirl and tumble combined define the helix of the incoming air column in a two-valve chamber.
As Mummert stated, the swirl tends to jump up at low lift, lag behind in the mid-lift, and ramp up again at high lift. The tumble curve tends to do the same. The tumble force location (we called it "moment arm") moved closer to the bore center as the intake valve opened, and moved away from the bore center rapidly at high lift, when the swirl was spiking.
Our conclusion was we needed a smooth, linear increase in the swirl as the valve opened; not a set value.
To manage the swirl, we worked with chamber containment of the flow cone, runner trajectory, and some slight steering with the fin behind the guide. The flow must stay attached to the short-turn; swirl and tumble go out of control if there is separation. The modern steep seat and top angles really helped.
Reverse swirl fins behind the intake guides can improve burn uniformity, BSFC, and help prevent the swirl from spiking at high lift.
If you can do some wet flow testing on your cylinder head, you will be mesmerized by what you see. It will tie in with your swirl and tumble observations.

[hysteric]

If you can do some wet flow testing on your cylinder head, you will be mesmerized by what you see. It will tie in with your swirl and tumble observations.

Did you see a net gain in performance by improving swirl?

[Bryan Maloney]

If you can do some wet flow testing on your cylinder head, you will be mesmerized by what you see. It will tie in with your swirl and tumble observations.

Did you see a net gain in performance by improving swirl?

No, our goal was to prevent the swirl from ramping up so highly at high lift. When the goal is cylinder filling, we wanted the air column helix to chase the piston down the bore and not sling the fuel into the cylinder walls.
Street engines with low valve lift may benefit at low RPM from additional swirl; the valve L/D never gets high enough to where the swirl naturally spikes.
The often maligned reverse-swirl "Elkins fin" behind the intake guides can be beneficial in moderation. Some OEM's take this feature to the extreme.
A "Glidden fin" along the centerline of the floor of the intake port can add flow stability and help limit high lift swirl.

[maxracesoftware]

on a Chrysler ProStock Truck , Bowl Swirl Fin gains 15+ CFM @ 28" on Flowbench ,
absolutely no ET or MPH gains , no difference down Dragstrip ,
so that without Swirl Fin you loose 15 CFM , but runs exactly the same as Bowl Swirl Fin that gains 15+ CFM on Bench.
Basically , a Bowl Swirl Fin ends up as Flow Numbers "Bragging Rights" , but no HP or ET performance gains !

on ProAction 14deg SBC with Bowl Swirl Fin and Methanol .. it looses 90 HP @ 9400 RPM
centrifuges Methanol on Walls / Chambers .. kills HP and TQ

on my SuperStock #462 and #041X ... they always naturally have Clockwise and CounterClockwise Port Swirl rotation
they "Peg" my Digital Swirl Meter's Strain Gage
but then you compare this to my #308 or #596 Chrysler Ports .. these have hardly no Swirl at all,
yet , both the Chevy and Chrysler Record setting SuperStock Heads make Tq and HP and BSFC's
accordingly to their Flowbench numbers , CompRatio, and CID sizes ,
so Port Swirl or lack of Port Swirl on these type Engines makes no difference on the Dyno or Dragstrip !
These are relatively small Port Volume CC Heads that on are the edge of too fast CSA velocities . turning 5500 to 8300+ RPM

[Bryan Maloney]

on a Chrysler ProStock Truck , Bowl Swirl Fin gains 15+ CFM @ 28" on Flowbench ,
absolutely no ET or MPH gains , no difference down Dragstrip ,
so that without Swirl Fin you loose 15 CFM , but runs eaxctly the same as Bowl Swirl Fin that gains 15+ CFM on Bench.
Basically , a Bowl Swirl Fin ends up as Flow Numbers "Bragging Rights" , but no HP or ET performance gains !

I observed almost the same thing years ago after adding reverse swirl fins to a pair of 18 degree Chevy heads on an open ARCA engine. Picked up 8-13 cfm on the bench, but no power increase on the Dyno.

Mike Chapman added the reverse swirl fins to a set of 18 degree heads for one of our Cup restrictor plate engines back in the 425hp/7000 rpm era. They were 2-3 hp better than the non-finned plate heads we received from him. The piston and chamber coloring looked phenomenal after racing them.

With the Dodge program, we ended up putting our effort into optimizing the tumble characteristics over the swirl.

[hysteric]

If you can do some wet flow testing on your cylinder head, you will be mesmerized by what you see. It will tie in with your swirl and tumble observations.

Did you see a net gain in performance by improving swirl?

No, our goal was to prevent the swirl from ramping up so highly at high lift. When the goal is cylinder filling, we wanted the air column helix to chase the piston down the bore and not sling the fuel into the cylinder walls.
Street engines with low valve lift may benefit at low RPM from additional swirl; the valve L/D never gets high enough to where the swirl naturally spikes.
The often maligned reverse-swirl "Elkins fin" behind the intake guides can be beneficial in moderation. Some OEM's take this feature to the extreme.
A "Glidden fin" along the centerline of the floor of the intake port can add flow stability and help limit high lift swirl.

Thanks Bryan, did you experiment with different droplet sizes? Also at what L/D's was it evident that spiking occurred?

[maxracesoftware]

by Bryan Maloney » Sun Sep 19, 2021 2:53 pm
I observed almost the same thing years ago after adding reverse swirl fins to a pair of 18 degree Chevy heads on an open ARCA engine. Picked up 8-13 cfm on the bench, but no power increase on the Dyno.

was that on Race Gasoline ??
any Dyno Tests with Methanol w/Bowl Swirl Fin ??

here's Pics of ProAction 14 deg SBC Heads on 406cid
Looses 90+ HP @ 9400 RPM with Bowl-Swirl Fin only on "Methanol"
makes 1005 HP @ 9400 RPM "without" any Bowl Swirl Fins
and without anyother trick Fins
Runs quickest down the Dragstrip "without" any Trick Fins !

You can get away with "Trick Fins" with Gasoline
but Methanol is a different story !!!
On Year 2020 NHRA Comp Eliminator Champion Craig Bourgeois's A/ND 14deg=1024HP and B/ND 23deg=1005.2 HP Heads
( highest Tq and HP Curve is with 4.7 to 4.85:1 Air/Fuel Ratio on both 14deg and 23deg )
with Methanol ....there are no "Trick Fins" ... just straight forward Porting !

Note : the Chrysler ProStock Truck Heads Bowl Swirl-Fin were even a little more drastic than these Pics ... but were only run on Race Gas , no Methanol tests !

a Bowl Swirl-Fin is "worthless" on Methanol ,
also i always gain HP , as much as 40 HP so far ,
grinding away Swirl-Fins in various LS-type Heads + reworking Short turn Curve -to- Floor Apex area
to compliment me removing that Bowl-Fin !

pretty drastic when you see Piston's Gas-Port hole combustion so deep inside the Chamber
( on the Deck surface , yes, but so deep into the Chamber , no ! )
i doubt anyone seen anything like this before ???

"How to Lose 90+ HP on Methanol"

Hi_Vortex_Bowl_Fin_18.jpg

Hi_Vortex_Bowl_Fin_17.jpg

Hi_Vortex_Bowl_Fin_15.jpg

Hi_Vortex_Bowl_Fin_13.jpg

Hi_Vortex_Bowl_Fin_5.jpg

[Bryan Maloney]

Did you see a net gain in performance by improving swirl?

No, our goal was to prevent the swirl from ramping up so highly at high lift. When the goal is cylinder filling, we wanted the air column helix to chase the piston down the bore and not sling the fuel into the cylinder walls.
Street engines with low valve lift may benefit at low RPM from additional swirl; the valve L/D never gets high enough to where the swirl naturally spikes.
The often maligned reverse-swirl "Elkins fin" behind the intake guides can be beneficial in moderation. Some OEM's take this feature to the extreme.
A "Glidden fin" along the centerline of the floor of the intake port can add flow stability and help limit high lift swirl.

Thanks Bryan, did you experiment with different droplet sizes? Also at what L/D's was it evident that spiking occurred?

We did not vary droplet size. The fluid was a mist leaving the booster. The swirl ramped up after .500 lift using a 2.170 valve.

Note in the photo there are two vortices in the chamber; one above and to the left of the intake valve and one between the plug and the exhaust valve. Just as there can be tornadoes within a hurricane. Swirl testing rigs are only showing net swirl, wet flow shows the motion is much more complex.

This photo does not do justice to what you actually see in motion. Everyone that has seen this in action has been mesmerized.

Effect_20210921_091526.jpg