Cylinder head porting and the term gas flowing

[MIGHTY 8]

Hello all,

When one is having head porting work done is this generally also referred to as "gas flowing the head?"

I currently have 40 IDF's with 32MM mains, but the plan is to increase to the 44's and their respective 34MM mains.

I'm just learning as I follow along, but I was wondering if these numerical values are barometers used by engine builders to determine a head's performance potential. I've since been hit over the head with all this new theory but was curious what these numbers really mean. Is bigger naturally better? And if so, what were stock flow rates for our factory TC's? When doing performance mods, what would be considered standards in MM to shoot for? I realize all things have a max capacity, was just wondering that if ours is measured in MM, what are the low/high parameters.

Tried using the search function, but to no avail. Thanks to all for helping me wrap my head around this stuff.

[v6spider]

First question you have to ask yourself ... is this going to be driven on the street or track.. If the answer is street than I would only do some mild gasket matching style porting and leave the finish on the intake rough so that the fuel atomises better.. You can polish the exhaust ports.. In fact, that is preferred I think. If the engine is to be used only on the track. Then I would take it to someone that specializes in porting for race that has the proper equipment to flow test the head. Or CNC port it because you can actually make the head flow worse if you don't have the proper way to test the porting work that will be done. Size and shape are important, but numbers don't mean a thing of the engine runs like a dog after its been ported..Anyway, my two cents on the subject..

Cheers!
Rob

[So Cal Mark]

it's important to know not only the max flow but the flow at various valve openings, that way you'll know if the motor makes more power at low, mid and top end

[131]

I was wondering if these numerical values are barometers used by engine builders to determine a head's performance potential.

Those numbers are the throttleplate size in mm, 40 or 44 IDF and the main venturi size in mm, in this case 32 or 34 respectively. All about how much air you'll get through the carbs, not anything to do with what the head will flow.

[vandor]

Yes. If you decide on porting the head be sure to get it done by a Fiat specialist. This is not something that a shop can do on a one-off basis never having worked on Fiat engines before. The optimum port shape is arrived at after a lot of trial and error and a lot of testing on the flowbench.

[fiatfactory]

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[bradartigue]

On the question of size...
You can have too much or too little, but it depends on what you are doing. Cars are generally under carbureted for city driving, focusing more on smooth operation at lower and variable speeds. Performance cars are generally correctly or over carbureted to deliver more fuel during acceleration and top-end. Fuel injection much the same way; the FI Spiders are tuned lean for complete burning and emissions, the top end on them is a bit weak.

[TimpanogosSlim]

Polishing is probably a fool's errand. The physics don't support it rough surfaces are more slippery, it turns out.

Aircraft are even being coated with materials that leave a random pattern of surface imperfections these days. The general function is that the occlusions support the creation of high-pressure pockets, which act like air bearings.

Dimpled channels are where a lot of the new excitement is. Helps a lot to have flow simulation software and 5-axis CNC tho.

[fiatfactory]

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[azruss]

Years ago, as part of an Okuma sales team, I got to tour the Richard Childress facility in N.C. They had an Okuma PM600 (check out this seriously trick cnc mill on the web) machining prototype heads. This machine reduced the machining time by half from the previous cnc mill they were using with a far better finish. The Childress guys had to go in and rough up the finish at specific locations to get the flow they wanted.

[TimpanogosSlim]

The latest greatest bellmouths available have dimples allover the inner bell mouthed surface like a golfball, in quite specific patterns though, certainly not random dimples all over the place.

Look at world superbikes and they all have them... so there must be something to it, as those engines are certainly developed to the Nth degree...

SteveC

I've seen dyno numbers that, if true, are pretty impressive.

As for "random" - afaik they should be mostly regular in size and distribution, but both flow simulation and real world testing show that a strictly uniform checkerboard or honeycomb pattern is generally inferior to random layouts, and always inferior to what the computer suggests.

With the new coatings they are using on aircraft, what i read was that when they attempted to strictly control the size and position of their dimples, it didn't perform as well as the spray-on coatings that produce a random pattern with mostly the same size dimples.

Lots of pretty pictures of dimple ported heads out there to ogle, fwiw.

[fiatfactory]

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[MIGHTY 8]

"Porting"the head is the physical act of removing material to achieve higher flow figures.

"Gas flowing" the head is the physical act of measuring the amount of air that flows through the head ports, usually done before and after so the results can be quantified.

To measure the flow through the cylinder head requires the use of a flow bench, gross flow is measured traditionally in the units of CFM or cubic feet per minute. Most flow benches also have facility to measure air speed in the port in FPS or Feet per second. Other measurements usually taken on a flow bench include 'swirl' which is the rotation of the air as it travels past the valve and into the dummy cylinder, units are simply RPM and clockwise or anti clockwise in it's rotation. Another unit of measurement is 'tumble' which measures rotation as well, but in the vertical axis... swirl is in the horizontal axis.

Obviously to measure all this requires some fancy sensors, and most benches these days are computer controlled.

Gas flowing the head would also involve measuring exhaust flow, not just inlet flow. And part of the measurement is to also test the air flow/ air speed / swirl and tumble all at each valve lift value.

How do I know so much about all this...well I have owned my own personal flow bench for about five years now, and I only work on Fiat heads.

some raw figures from a Fiat cylinder head.

Intake
Lift CFM
0.05 45.7
0.10 64.6
0.15 87.9
0.20 106.6
0.25 124.2
0.30 135.2
0.35 143.7
0.40 148.0
0.45 149.7

Exhaust
Lift CFM
0.05 32.9
0.10 50.3
0.15 62.4
0.20 78.8
0.25 90.7
0.30 102.0
0.35 114.0
0.40 121.6
0.45 126.7

flow values are in CFM, lift values are in thousanths of an inch, the depression used for this test was 25 inches of water.

Gross flow figures are only half the story, equally as important is the value for port air speed.

Whatever you do, do NOT follow the advice in a certain well publicised book on Fiat engine building, and follow the authors recommendation of 'dropping the port floor' and 'welding up coolant galleries' ... this is just totally incorrect. As a general rule better flow figures will be achieved by removing material from the port roof,and raising the port centreline.

If your going to search this site on the subject, perhaps search posts authored by myself, or maybe check out my little corner of cyberspace, http://www.turbo124.com/forum/viewforum.php?f=13

here's a picture of my bench, an FMA400 ,capable of measuring up to 400CFM at 28 inches of water depression. The head stand is off to the left, standard supaflow 600issue,,next to the PC. It uses a "flow com" which is precisely the same hardware internally as a Supa-flow bench, and I use Flow analyser pro software, which again is the same as supplied with a supaflow bench.It automatically adjusts the readings for temperature /pressure and humidity.


click on the thumbnail for a full sized image.
SteveC

Are these figures for a stock head Steve?

[fiatfactory]

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[fiatfactory]

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