Flathead Flow Bench Testing - What is Your Method?

[wkuran]

There are many posts on the forum that talk about flathead flow bench testing. I have just staring using a flow bench to look at the affect on flow when making combustion chamber changes. The rest of the intake is not changed.

The posts that I read aren't clear about whether the testing is done with the head installed or not installed. I want to understand how only the combustion chamber influences flow. Not installing the head required making some type of transition piece to connect to the flow bench. Not coming up with any good ideas on how to do that I decided to make a head with a combustion chamber so large (chamber roof height of 3.75" ,with 8.5 sq in transfer area, gives a CR 2:1) that it would eliminate most its influence on flow (an almost zero pressure drop across the chamber and pistion bore).

I used the results of that test to estabish what I consider to be the upper limit of flow with the existing intake (inlet port area, short side radius, throat area, seat angle, valve diameter, valve lift, curtain area, etc.). The idea being that when a real chamber is tested, the amount that flow is reduced can be attributed to the chamber design.

There are two version of what I call the tall chamber. One with an 80% (according to information provided by David Vizard) deshrouded intake and one without deshrouding. Testing showed an average of 5% flow increase between 0.200” lift and 0.400” lift, with a maximum of 6.5% at 0.350” lift. At 0.500” lift the de-shrouding effect is gone and both chambers reach a maximum of 160 cfm.

All designs were first modeled and evaluated using CFD, 3D printed, then tested on a physical flow bench to validate the simulations. I consider this work to application specific and don't have a sense of how it would apply to other engine designs.

The 100 cc chamber gives 7.5:1 CR and is currently installed on the engine (10 psi maximum boost). My goal is to design a 75 cc (9.5:1) that flows as well as the 100 cc chamber. So far the best I have done is an 80 cc (9.0:1) chamber with the same flow as the 100 cc chamber.

The first chart below shows the result of the physical flow bench testing. The second chart show the simulation results. I don't have enough experience to comment about the amount of flow, only that I have a better understanding of how chamber design (deshrouding, roof height, transfer area, ramp angle, and several other chamber design attributes) affects the flow.

Flow Bench Test Results.png

Flow Testing - Simulated Results.png

[mag2555]

To me what these / heads / chambers need is to be shaped in such a way to get some better pressure recovery taking place and getting a valve job done on the block with 3 angles or even better yet 4, with each one transitioning no more then 15 degrees so to simulate a radius valve job while still shearing up any wet flow.

If the valve uses a 45 degree main seat then it needs a back cut to pick up flow down low.

I would also not go with anything more then a 87% valve to throat ratio.

You should atleast watch Darin Morgans part 1 video called de-atomization, which is a series of 3 videos.

You should use your flow bench to find out how much the Intake Manifold flows also, because reworking the chamber and the in block block Intake tract to flow anything more then 15 cfm over what the worst Manifold runner can will just be a waste of time and effort.

[PackardV8]

Your supercharged application will act very different than will a normally aspirated. Flowing it with 10 PSI in the intake manifold inlet might be more representative than 28" of vacuum in the cylinder.

FWIW, I've been told in a normally aspirated flathead, it is necessary to pull vacuum through the intake manifold, intake port, valve, transfer area, down and out of the bottom of the cylinder or the oil pan to accurately measure intake flow.

Also, FWIW, if you can make a 9:1 compression flathead flow as well as a 7.5, you'll be the first. I've mentioned previously, for forty years, the Harley-Davidson Racing Department and Dick O'Brien worked over the KR and always found flow made more horsepower than compression and settled on 6.8:1 as the best NA compromise.

[wkuran]

For this project, I am not looking to improve any part of the intake except the chamber. I am looking for the chamber design (given a specific volume) that has the lowest resistance to flow between the open valve and the cylinder bore.

To me what these / heads / chambers need is to be shaped in such a way to get some better pressure recovery taking place and getting a valve job done on the block with 3 angles or even better yet 4, with each one transitioning no more then 15 degrees so to simulate a radius valve job while still shearing up any wet flow.

If I were to share a photo of the chamber, you could see that care has been taken to recover pressure losses due to flow separation.
[/i]

If the valve uses a 45 degree main seat then it needs a back cut to pick up flow down low.

Valve seats are three angle.The valve has a 45 degree seat angle, 30 degree back-cut angle and 10 degree back angle.

I would also not go with anything more then a 87% valve to throat ratio.

The throat to valve ratio is 0.88.

You should atleast watch Darin Morgans part 1 video called de-atomization, which is a series of 3 videos.

Yes, good information.

You should use your flow bench to find out how much the Intake Manifold flows also, because reworking the chamber and the in block block Intake tract to flow anything more then 15 cfm over what the worst Manifold runner can will just be a waste of time and effort.

Manifold design is not part of the project, although there are gains to be had. The existing flow bench fixture uses fairly well optimized air horn to replace the intake manifold.

[panic]

The position and angle of the quench ledge and shape of the "roof" in the head significantly affect flow to the cylinder.
The highest practical static CR also varies with bore:stroke ratio, engines with small chamber area like high CR: KH CR is higher than K. With the same cylinder and head, more stroke increases ideal CR. Chief 80": 3-1/4" X 4-13/16", 6.75:1.

Some work with Ford V8 suggests that engines built for peak power (LSR) value flow over CR, "torque" engines (sprint car) the reverse.

[wkuran]

Your supercharged application will act very different than will a normally aspirated. Flowing it with 10 PSI in the intake manifold inlet might be more representative than 28" of vacuum in the cylinder.

I wasn't able to do that with physical testing but did look into it with the CFD simulation. With the simulation, I increased the inlet air pressure by 10 psi but again so no flow change because the results are based on the pressure drop between two points. I had higher inlet and outlet pressures but the loss remained the same.

I also increased the air density ratio to equal the 1.7 boost pressure rato and saw no difference in flow. My conclusion is that density has little to no effect. But I would expect to see an effect if I were simulate or do physical testing with two-phase flow. That is way beyond what I am try to do. I am simply lookng for a better chamber with better defined by increased flow.

FWIW, I've been told in a normally aspirated flathead, it is necessary to pull vacuum through the intake manifold, intake port, valve, transfer area, down and out of the bottom of the cylinder or the oil pan to accurately measure intake flow.

The block section used for testing is set up in a way that air is pulled out through the bottom of the bore.

Also, FWIW, if you can make a 9:1 compression flathead flow as well as a 7.5, you'll be the first. I've mentioned previously, for forty years, the Harley-Davidson Racing Department and Dick O'Brien worked over the KR and always found flow made more horsepower than compression and settled on 6.8:1 as the best NA compromise.

Part of what I am looking for help with is to define, or understand, what good flow looks like. The 100 cc head flows 140 cfm without the intake installed. I can only guess, but let's assume the intake maifold, throttle body and plumbing to the supercharges eats up 10 cfm. That leaves 130 cfm - is that good flow?

It is also difficult to keep things in perspective. I have concluded that a smaller volume chamber will never flow as well as a larger volume chamber. If I were to now apply what I have learned about chamber design to the original 100 cc chamber, flow through it may be increased 10 - 15 percent. Isn't there a point at which any increase to flow will not mater for a given engine design?

[wkuran]

The position and angle of the quench ledge and shape of the "roof" in the head significantly affect flow to the cylinder.

The chamber roof over the bore is flat, quench height is 0.041", quench area is equal to 37% of the bore, simulated squish velocity at 5000 rpm is 137 ft per minute.Ssquish velocity can be lowered by softening the chamber (angling the chamber roof above the bore). All good stuff but what I found to influence flow is the ramp angle and the upper and lower radius. When the air passes through the transfer area it is making a hard turn to get down the bore. This photo (simulated) shows tha the flow separates at the top back corner of the bore and there is little to be done about that. The challenge is to minimize separation (pressure drop) as the air flows off the ramp.

100 CC Standard Chamber - Pressure Plot at 500 Lift .png

The highest practical static CR also varies with bore:stroke ratio, engines with small chamber area like high CR: KH CR is higher than K. With the same cylinder and head, more stroke increases ideal CR. Chief 80": 3-1/4" X 4-13/16", 6.75:1.

For my engine, the highest static CR is just below the detonation threshhold and use fuel, timing and water-methanol injection to manage it. I also use a knock controller.

Some work with Ford V8 suggests that engines built for peak power (LSR) value flow over CR, "torque" engines (sprint car) the reverse.

[frnkeore]

Very interesting! I've never seen any work like that, for the Ford FH.

I've haven't built a FH, since I was 15 (1960) but, I've always thought that putting a radius of at least .25 (larger if you move the top ring down), on the cyl wall corner, across the chamber area and blend that radius to the valve seat, would increase flow. I haven't seen that done. Can you model that?

I also think lowering the roof, just over the valve area to a minimum and increasing area, as much as possible, around the near side and rear of the chamber, to keep from flowing over the top of valve, would also help flow.

[Tom68]

You'd have to pull from the sump I'd imagine, didn't Smokey used to flow some engines that way ?


Dunno about the flow but here's a picture from an alternative universe.
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309208303_10221744030366920_5011384209509226153_n.jpg

[Ks Fats]

It is easier to build an adaptor to fit the bottom of the bore and pull from there; a simple hardwood plug and some silicone will work. The valves on six cylinders are closer to the bore centerline than the v-8 which changes the flow dynamics some. I had some photos of work done by Paul Shalk for Motorcity Flathead years back but couldn't attach them, probably can still find them on the web. I have used a variation of that design with some success but (as Panic stated above) it is really application specific. At this stage of my life grinding cast iron is about as exciting as watching paint dry so there will be more "finish what you have started" than development work.

[PackardV8]

I also think lowering the roof, just over the valve area to a minimum and increasing area, as much as possible, around the near side and rear of the chamber, to keep from flowing over the top of valve, would also help flow.

One might think that. However, some of those who've flowed flatheads disagree; they find flow over the backside and top of the valve to be beneficial.

Having said that, sixty years ago, I bought a pair of aluminum heads from an old dirt track racer which had pockets matching the valves, so when at max lift, the valve head was completely flush into the cylinder head combustion chamber.

[panic]

This is Brian Miller's work on the Kohler flathead tractor engine, note the area behind the valve (labeled "air flow").

[Ks Fats]

Back when I was more serious about flatheads I sprayed dykem into the intake ports at various points on the lift curve and never saw any evidence of color on the head of the valve. On the relief side of the transfer area most of the flow was concentrated biased between the exhaust and bore side of the bowl. Perhaps the use of dykem was a poor attempt at replicating working fluid flow but it seemed a valid test at the time. A smoke test might be best but it isn't going to replicate the density gradients found in the bowl area. Kloth used a chamber similar to what Panic posted with good results at Bonneville; early racers used Arco milled and filled stock heads so I can imagine about everything between the two has been tried at least once.

[Tom68]

Smoke test and a glass head.

[wkuran]

The position and angle of the quench ledge and shape of the "roof" in the head significantly affect flow to the cylinder.

I understand how the chamber roof shape affects flow but . . .

What is a quench ledge and how does it affect flow into the cylinder.