Head flow testing.

All interesting stuff up to the point of the Antelope headers comment - time for the tinfoil hat again.

Still questioning the obvious - why have such things such as the dimples or NACA port floor configuration not been adopted across the IC engine industry? What are we missing here?

I have yet to see these concepts in anything but conceptual forms barring a few experiments.

Was I teasing about the headers? As to why, well do you own search on just how common various textures and flow trippers are used in OEM manifoilds and ports. On other hand, if a particular port don't need band aids then why bother. Thank goodness they are so pretty or would be bounty on them for all the faults & quirks...

These dimples, or steps or boundary trips (ie steps) are usually implemented to keep the airflow attached to the body. A little bit of background, a laminar boundary layer cannot sustain a large pressure differential across itself and the flow becomes detached with a very large boundary layer which effectively reduces the cross sectional area. Now although a laminar boundary layer is thinner than a turbulent boundary layer when it detaches it becomes much bigger, in terms of an engine it is also debatable as to whether you can actual get a laminar boundary layer developing with the unsteady flow... The turbulent boundary layer can sustain a much bigger pressure differential while remaining attached, ie the short radius of and inlet port. For any of these dimples or trips to be useful Im guessing they should be just before the short radius on the bottom surface of the port only. It is also likely that vortex generators may be even more effective here, possibly in the form of small hacksaw cuts, or deep scribe marks in the port floor, again I have never tried this but there is a little bit of theory behind it.

Vortex generators must stick up most the way ~2/3 into the thickness of the boundary layer where they are placed. Higher just adds drag. Boundary layer in ports is rather thin, till a bit after the short bend, so -1/32-1/16" might be plenty in the right spots. VG's work by throwing up some of the boundary layer into faster stream layers to lessen the flow shear differences, aka, re-energizes boundary layer to thin and flow faster.

A Harley shop's special little head helpers?
http://speedsperformanceplus.com/Press/ ... e-0806.htm

The problem with most heads is that the intake port has a long arc radius at the top but a short bend (almost straight) at the bottom. That short bend at the bottom is such a tight radius that it ‘s difficult for the incoming air to bend around it, so the air ends up separating and ricocheting around, losing its velocity and ability to flow the entire valve. To solve this problem, most people will run larger valves to catch more air around the part of the valve that ‘s flowing, but that still doesn ‘t solve the problem of that short bend.

R&R ‘s solution to the problem is the Vortex Generator, which has been around since the ‘90s. The Vortex Generator is a raised section of the port floor that splits the air and bends it around the short bend. The Vortex Generator is able to do this because its design creates a longer short-turn radius, making it easier for the air to flow around the bend, thus increasing velocity and flowing the entire valve. Because this head design is so efficient and flows the entire valve, not just part of it,

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Lots of Brit head trix history in here
http://www.bmw-m.net/techdata/cylinder.htm

Jerry has discovered that some ports flow better if he cuts tiny slots across the floor of the bend upstream from the valve. The slots apparently act as turbulence generators that energize the air and make it stick to the port floor, following the bend more closely. That's the theory anyway, though like so much we believe about port air flow, it's arguable because air hides is secrets behind a cloak if invisibility.

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Some good explanation from Cheesy and good references from hobot. Does a nice job of explaining the case for higher port velocities.

I've understood the theory behind boundary layer flow enhancements. Not challenging the port manifold mismatch theory.

Taking the 30,000 ft elevation view and asking the question why dimples have not been generally adapted to port designs. I suspect the answer may be as follows:

hobot said:

if a particular port don't need band aids then why bother.

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From the BWM article:

"Maybe one day soon we'll learn why the things a century of experience has taught us actually do work, and why others do not."

Ugh Dances, too pleasant now, back off the chemistry a dash so I can raise your fur for mo fun. To keep the brain juices flowing here's some Harley Davidson insight articles that over laps with Nortons.

Even though the conditions in a running engine are constantly changing throughout each intake and exhaust cycle, steady flow on a flow bench can give a good representation of the power available from the engine by approximating the average conditions in the engine. Tests done at 25″ of water test pressure seem to closely approximate the average conditions that exist in an engine.

As I mentioned earlier, there is a trend to testing at much higher pressures. Peak velocities in a port can be over 600 ft/sec, but testing an intake port sized for high rpm power at 25″ of water may only have 200 ft/sec on the flow bench. It may be very efficient at that velocity, but have high levels of turbulence at twice that velocity. The only way to determine the worth of a port at the higher velocities is to test it at those velocities, requiring higher test pressures.

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Horsepower per cylinder = .43 x airflow @ 10″ of Water, .275 x airflow @ 25″ of water, or .26 x airflow at 28″ of Water. To find required airflow for a given horsepower, divide the horsepower per cylinder by .43, .275, or .26 respectively.

RPM at peak horsepower will be 2000 divided by the displacement of one cylinder x airflow @ 10″ water. Use 1267 @ 25″ of water, or 1196 @ 28″ water. The more airflow available to the cylinder, the higher the rpm required to reach peak horsepower.

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http://10litre.com/cylinder-head-mods/

If I’m to do a full porting Job, I make a rubber mold of the port and slice the mold into segments ½ to ¾ inch wide. I lay each segment on graph paper, draw around the circumference, and count the squares in the outline of each segment to obtain its cross sectional area. This gives me a diagram of the shape of the port. The silicone rubber I use is Dow Corning Silastic V base and curing agent. You can find a distributor near you at dowcorning.com. I have tried the Silastic M, but it is too hard, which makes it difficult to get out of the port once it cures. I have also used Blue Sil type G, from Perma Flex, 1919 Livingston Ave, Columbus Ohio. Expect to pay close to $150 for a gallon of it.

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hobot said:

Ugh Dances, too pleasant now, back off the chemistry a dash so I can raise your fur for mo fun.

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OK.

I must say it was refreshing this morning to read your post over coffee and seeing the slow but positive transition from random neural firings to composing a thought, although crude, rudimentary and certainly delusional but completely in character.

Thank you sir, may I have another?

Feel better?

One of your quotes is spot on in my book regarding a more complete port flow analysis through different pressure differentials. I don't recall what reference brought this to my attention first (Heywood, Graham Bell, Charles Fayette Taylor, Prof. Gordon Blair or???). I remember reading in one of the texts where AMC (Kenosha, WI) did extensive port flow testing using considerably high port differential pressure. There was a picture of a roots type blower through a large air receiver.

To me, Prof. Gordon Blair's last book on four strokes brought it all together as he presented the case for developing maps of port flow coefficients (cv) for a variety of pressure differentials. This mapping was done for the intake and exhaust ports, both forward and reverse flow. This illustrated the complexity of the IC engine.

Ultimately this mapping would be a base of data for engine simulations.

Good stuff.

I must say it was refreshing this morning to read your post over coffee and seeing the slow but positive transition from random neural firings to composing a thought, although crude, rudimentary and certainly delusional but completely in character.

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hehe, which one of us is this describing : )
Lead the way on more head development and I'll tag along in the wake.

Well I got the first big valve conversion done on a Fullauto head. 3mm oversized intake valve with a re-angled guide. I enlarged and blended the bowl to the new seat and widened the port a little at the guide. Looked great.

Then I put it on the flowbench and got a surprise. It flowed slightly more than the stock valve up to .2 lift - the same from .2 to .3 - and less flow above .3- a lot less....

Back to the drawing board. Jim

comnoz said:

Well I got the first big valve conversion done on a Fullauto head. 3mm oversized intake valve with a re-angled guide. I enlarged and blended the bowl to the new seat and widened the port a little at the guide. Looked great.

Then I put it on the flowbench and got a surprise. It flowed slightly more than the stock valve up to .2 lift - the same from .2 to .3 - and less flow above .3- a lot less....

Back to the drawing board. Jim

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Needs dimples.

Kenny already has dimples

Actually all I had to do was find the cause for the major turbulence and fix it. It turned out to be the curve on the short side of the port started too late and the air was separating. A little work there and I think we have success.

The bottom line is Kenny's head as I got it.
The next line up is a Maney stage two head.
The blue line is the big-valve Fullauto with a 3mm oversize valve, re-angled guide and a standard size port.



Here is the cool part. This is the velocity comparison between the Maney head and the Fullauto head.

Good stuff. Looking forward to seeing the resultant power and torque characteristics.

Here is some pictures of the big valve conversion on Kenny's head.

First I set the head up in a jig on the mill with the new valve and guide angle set. Then I bored the guide hole and roughed in the seat cups. The seats and guides in these pictures are for testing only. I have several with differend IDs and angles to choose from. Here it is with the port roughed in to match the seat and ready for the first flow tests. The results were pretty bad but it was not too hard to find what was causing the problem.





After a day and a few dozen trips between the flowbench and the grinding bench I ended up with a pair of ports that flow what I was looking for.







Then a couple more hours on the exhaust so it can keep up.





Now what is left is installing the real guides and making a final choice for the seat profile. Then I will set up on the guide hole and make the final cut for the new seats. I have been able to get the flow above .3" up a bit better than the chart above and I am expecting some more low lift flow with different seats.
I am really happy with how well this is working out.
I have a batch of four of them to do so maybe the next three will go a little faster. I wrote the machine work into the CNC as I went so next time I will just need to push the go button and I will get a duplicate but it will still need several hours by hand with the carbide bur to finish the port. Jim

There are a lot more pictures here for anybody who wants a closer look.
http://s658.photobucket.com/albums/uu31 ... /Projects/

Duh, what are the colored bands around the bores?

hobot said:

Duh, what are the colored bands around the bores?

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They are bronze rings to bring the 850 head size down to the 750 bore. I use 850 heads and barrels because the wider bolt spacing means the bore does not distort so much when the head bolts are torqued. Jim

Oh, cool another new innovation for me.

Oh yeah, how did you detect/determine what was stifling the flow with the bigger valves? I read you said you knew it was the too late a bend radius, ok how so?
I'm academically interested in ways to visualize flow and shock fronts. Oh and dimples of course : (

I may not like the Drouin in real life for various reasons, weight and handling and temptation wise, so wonder what ya might do with a 750 CHO head already fixed to fit a Maney 920 to flow w/o help.

hobot said:

Oh, cool another new innovation for me.

Oh yeah, how did you detect/determine what was stifling the flow with the bigger valves? I read you said you knew it was the too late a bend radius, ok how so?
I'm academically interested in ways to visualize flow and shock fronts. Oh and dimples of course : (

I may not like the Drouin in real life for various reasons, weight and handling and temptation wise, so wonder what ya might do with a 750 CHO head already fixed to fit a Maney 920 to flow w/o help.

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I use a velocity probe connected to a computer. It will paint a grayscale picture of the port showing where the air moves fast or slow and where there is turbulence. Plus I had a pretty good idea where to look from previous jobs. Jim

Ok another thing I didn't know - you have a pressure probe.

I guess you ain't working tonight, so how do valve seats vary in style to effect flow?

hobot said:

Ok another thing I didn't know - you have a pressure probe.

I guess you ain't working tonight, so how do valve seats vary in style to effect flow?

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The valve seat can change the flow in lots of ways- sometimes not very predictable. Most of the time a valve seat with a smaller ID and a longer angle up to the seat will flow better at low lift and worse at high lift. A seat with an ID that is the same size as the ID of the seat will usually flow more at high lifts but it may make the low lift flow suffer.
Then there are lots of other variables such as a radius cut leading up to the seat or sometimes a small step will help the flow make the turn through the seat.
What works best with one head may not work the same on another head with different bowl angles and dimensions. Jim

Ok these seat details help fill me in on your artwork trial error choices and chances. Interesting about a step sometimes helping in tight quarters.