Why multi-angled valve jobs?Why not just rounded over seats?

[Donnie1126]

It seems to me that in doing something like 5 angled valve jobs on seats that it's just an attempt perhaps unknowingly to create the Coanda affect.Is it possible that rounded over valve seats could do just as well as multi-angled valve jobs?Has anyone ever tried it?

[maxracesoftware]

It seems to me that in doing something like 5 angled valve jobs on seats that it's just an attempt perhaps unknowingly to create the Coanda affect.Is it possible that rounded over valve seats could do just as well as multi-angled valve jobs?Has anyone ever tried it?

in the Dyno research tests i've done so far, there is a definite "Trend"
developing that shows most Engines will make a slightly "wider" Power Curve with sharp multi-angle valve jobs on the Intake side -vs- radius valve job on same castings.

on some Cyl Heads , the Short Turn radius and shape needs a
very sharp bottom cut to help turn the mixture and helps in overall Flow Curve. in those situations, a sharp edged bottom cut will make much more HP/TQ than a Radius seat valve job.

you can use 10 to up to 15 degree angle segments to turn airflow.

Darin Morgan or others might have to more to say or reveal in their Dyno and Track testing??

[bill jones]

-The intake seat affects the air AFTER it has come thru the inlet port and the multi angle demarcations help to move the air, maybe the coanda affect, as the air has to exit the port into the chamber.
-I have never seen where a smooth intake seat ever makes better flow numbers, always hurts my flow numbers.
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-Whatever you do at the exhaust seat is preparing the flow that is entering to go INTO the exhaust port rather than manipulating the exit as in the intake.
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-The exhaust seats that I have the best results with are a full round polished smooth seat area with only a narrow seat flat area.
-I THINK that as the exhaust flow passes over the rounded and polished exhaust seat, that the air tends to stay in the center of the port rather than attach to the boundary layers of the exhaust port walls.
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-I feel the coanda affect of using the multi angles and the nice defined demarcation lines of the seats (and the valve backcuts) can be visually seen by spraying water with a garden hose and sticking your finger just barely into the outer edge of the water stream, and you will see a nice stream of water will deflect and and come outward behind the entry point of your finger.
-If you do that to that little deflected stream 3 or 4 times the liquid will change directions pretty radically.

[Mouse]

I too have never found any air with rounded angles. It has been my theory that the sharp edges cause the air to cleanly separate from the valve or seat rather than cling to and tend to follow the surface, wasting energy and direction. Each angle promoting separation through the valve lift height.

[SWB]

I think:

If you guys are using a single radius with a seat on it you are not going to have good results at all on an intake. (it never has worked for me, but can make a pretty good exhaust profile)

When you cut multiple bottom cuts you are defining a shape and that shape will not simulate a perfect radius but instead something more like an exponetial curve.

If that curve were perfectly smooth and did not have any steps, would it flow the same? Better? Worse?

One thing that's been mentioned previously, is that steps and roughness in the vacinity of the seat area can increase the "boundry layer" turbulance and cause the throat area to seem smaller to the air. Thus your smooth curve may have to be different than your stepped angle simulation...

Just some thoughts I had..

SWB

[Jginger]

Just thinking,( usally gets me in trouble) that the best way to get around
the SS may not be a smooth radius at all but sharp edged steps, anybody
tried this,
Just thinking

[cboggs]

Just thinking,( usally gets me in trouble) that the best way to get around
the SS may not be a smooth radius at all but sharp edged steps, anybody
tried this,
Just thinking

Yes, .. I use "steps" and some sharp edges on short turns in a few
heads. It doesn't work where you have the port to use a nice radius,
but in "short turn limited" head sharp steps can be a blessing.

Curtis

[lil289]

Larry Widmer, the guy rumored to be behind the 80's success of Bill Elliot and Bob Glidden, advocates radiused valve seats. There is a bunch of interesting reading on his website:

http://www.theoldone.com/articles/

From what I have been able to gather is that he uses a full radius cutter on the exhaust and grinds a 45 degree seat on that so that there is a radius above and below the seat, just as some have mentioned here. However, on the intake he has a 45 degree seat at the top. No 30 degree top cut or anything. Then he cuts the bottom angle to define the lower edge of the seat but then he radiuses and blends the lower edges of this angle all the way up the the lower edge of the 45 degree seat. The blending is done in an assymetrical manner too. I think he means that the blending is not concentric to the seat/guide but just blends smoothly into the adjacent bowl area. He says that this kills low lift flow but he says that the engine is hardly drawing any air at low lift anyway. This seat configuration is supposed to be anti-reversionary. He says that any head that flows well at low lift also flows well backward and is susceptible to reversion. He has a lot of other interesting theories about small, high velocity ports, extreme compression, "soft" chamber shapes to prevent detonation and reduce the pressure spike on the power stroke, etc. I always thought it would be interesting to experiment with this but it seems that it would require custom domed pistons to bias the dome to the intake side of the chamber. Apparantly, at TDC, he likes the volume of the chamber to be over the exhaust valve. Some here have experimented with radiused intake seats and found that they lost power. Could it be that radiused intake seats require altered valve timing to compensate for the effective shorter duration that the engine sees due to the loss of low lift flow? Perhaps a little more overlap, more intake duration, and a much later closing of the intake valve due to both the duration loss and the anti-reversionary intake port? I have no idea. Just throwing out some ideas.

[SWB]

I think the reason most people see a reduction in power is because the full radius inlet seat doesn't flow well in the forward direction and does in the reverse.

What Widmer is describing is not what I believe most people are making with thier single cutter seat and guide machines. It requires either lots of hand work or offset grinding/cutting (or both) to achieve the assymetrical seat profiles he describes.

There is a lot to getting a really effective seat in some situations and a single profile (multi-angle or otherwise) cutter is never going to be it. That doesn't mean you can't get close to ideal that way, but it will never be perfect.

[Ape]

SWB, larry, bill!
Ok now wouldnt it also work to make rounded up multiangle bottomcut seats and finish the lower(throat, bowl) angles with a somewhat course grind in order to get the flow sticking to the seat area?
i know it could make seating for backblow residues easier, but taking that not in consideration, wouldnt it make sense??
since i read that article on the us cup yacht(and glider plane wings) and the 3m foil they used i try to grind all my ports with coarse paper on the short turn for that reason, maybe a lil esoteric(??) but who knows, my bench couldnt tell me the difference yet.

Bill: i really liked the thing with the fingers in the stream of the water very visual, so how about lotsa little scratches from a sandpaper roll?

cheers
christian

[Ron E]

Many ways to read the results of radiused intake VJs. What we've observed is the radiused seat does flow hard. But, as the lift increases it does so at the expense of the flow normally "hugging" the valve head. In other words it can pull flow away from the valve-head. And, the result is a mess at higher lifts. Add to that, it low flows great in both directions. Reversion is bad, and due to the bad hi-flow the port velocity is slower, all lending their part to poor output.
Which ever theory is more correct, what's common is they don't seem to work very well.

[Darin Morgan]

I have yet to see an instance where a full radius seat made more power than sharp angles or one sharp angle at least. I use a semi radius seat but I leave at least one sharp definition angle under the seat and sometimes two. If you ask Flotz, Myself, Warren, Ikie, Chapman, Bill Jones, and anyone from Dart or Brodix, you will find the general consensus is that radius seats do not work in a high performance engine. I have never seen a case where a full Radius has worked better than a "correct" sharp angle. On the wet flow bench a Radius seat will not form what we are now calling a shear ridge. There are a couple of places within the intake port and chamber that help shear the wet fuel as it enters the chamber. Without them, you get a puddled mess of wet fuel that wont burn very well. The last portion of Bill Jones post touches on this.

The exhaust however is different. The correct radius seat has always proven to be better.

I even tried a radius seat again last year on one of our test engines. It lost 15lbs/hr of fuel flow and killed the engine 12ft/lbs and about 23hp.

[SchmidtMotorWorks]

Just thinking,( usally gets me in trouble) that the best way to get around
the SS may not be a smooth radius at all but sharp edged steps, anybody
tried this,
Just thinking

Maybe dimples like a golf ball? I know golf ball manufacturers employ aerodynamics engineers to design and test dimple shapes and patterns and regularly find improvements even within rules about dimples that they must comform to. As I recall some years ago there was a ball that wasn't legal for use in tournaments that had diamond shaped dimples that was supposed to go real far on drives.

[bill jones]

-here's one for ya,,,
-I was doing an inline 6 cylinder Ford head one time and I got the dreaded water hole at the corner crest of the SSR.
-I drilled in from the roof---across and down to that corner and installed a cast iron taper pin plug that is usually used for crack repairs.
-The pin goes in nice and tight and then breaks off leaving like a nearly flat 3/8" diameter end to that pin sticking up just slightly.
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-I learned long ago (from Fred Joehnck) that usually the best gains we FIND come from testing----EVERYTHING---and more often that not we find good that comes from mistakes and screwups.
-So I flowtested this port with that flat edged pin sitting right there in the sweet spot and it was like magic something---like 30 big CFM over my best ported port of that head.
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-So then I got to talking about this with another guy who was familiar with these engines on dirt ovals in the midwest and he showed me a photo of one of his heads that was done on every intake port exactly like I had done---that was supposedly the "hot head" of that era.
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-Our big daddy Don Terrill mentions using a different method of finger sanding from the crest down to close to the seat so that the lines run in-line with the flow.
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-I've tried a lot of ideas but what I have come to the conclusion of is this--
-We all have to make some money and keep the customer happy and tho we might be able to get one port or one head or maybe even one full set of ports to respond to the onsey twosy %---it usually becomes too time consuming and too expensive unless we can duplicate it EVERY time.
-So if we find something that does us pretty darn good and we can get that same good every time then we incorporate that into our daily program and get on with out lives.
-But when we work our as-es off and work out that special set of heads we tend to save those for the chosen few that can really show us what it's worth on the race track.
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-One other thing that I can't say if it works but any of you guys who have used Chapmans heads might have noticed Mikeys method of CNC'ing the intake chamber shrouds outwards in a radial fashion
-That was one thing that I felt was well worth looking at when Mikey first got started in CNC'ing and I see where he has been doing that radial thing now for some years, but I don't know of any positive proof that it is good bad or indifferent.

[hotrod]

Talking about the effect of stepped seats and golf ball dimples brings to mind a web page I stumbled upon some time ago by accident. It was part of a students thesis or similar presentation, and discussed the nature of the air flow through an intake and exhaust valve in an internal combustion engine. As part of the presentation he had a simple little animated GIF showing how the air flow changes as the valve lifts.

He showed that there are basically 3 forms of flow through/past the valve head and seat. (in his idealzed case)

On the intake valve at low lift with a normal single 45 deg valve cut, and a single cut 45 deg seat. At low lift the valve forms a simple nozzle with a significant reduction in flow area due to the vena contracta that forms just past the sharp edge of the entry angles of the valve seat and valve head cuts.

As the valve head lift further off the seat the flow separates cleanly from the valve head at the upper edge (entry) angle of the valve head but still forms a detached flow on the entry angle of the valve seat, re-attaching (or attempting to re-attach) as it clears the lower edge of the valve seat. (there should also be some flow turning here due to the coanda effect.

Then at higher lift, the flow separates cleanly at the upper edge of both the valve head cut and the valve seat cut.


Now this is not really news, and his discriptions are only applicable to a very simple idealized case -- but his diagrams suddenly made it inuitively clear how much the flow changes on a small local level as the valve lifts off the seat. As mentioned above by making small changes in how sharp those edges and angle cuts are you can strongly influence the flow at one specific lift.

I recall also that "the oldone" Larry Widmer has used dimples on the intake port to promote fuel re-atomization just below the fuel injector, and Jim Macfarland mentions use of dimples on piston heads to effect flow in the cylinder. As well as some on this forum have discussed modifying the surface texture with burrs and sanding to change when and how the flow separates.

As Bill points out above, you could spend a life time learning just a very small fraction of what is possible with a single head design (not to mention a good fraction of a fortune). The biggest issue is the problem of coming up with a cost effective way to get there from here once you find a magic spot in a port that needs some special attention.
Maybe some day we will have high energy lasers on a 5 axis rig that can quickly with precision dimble the SSR of a port.

Discussion of how flow separation is influenced by very small changes in the surface it flows over, lead me to look at what the glider pilots do with "turbulator tape" to control flow separation on the wings of their gliders.
And the "oil tests" they run to see what the flow is doing.

They paint a section of the gliders wing with old engine oil and go for a 30 minute flight at mostly a specific speed of interest. When they land you can clearly see the effects of local air flow in the boundary layer, as the oil moves with the boundary layer air.

http://ssa.org/Johnson/80-1996-06.pdf
http://www.standardcirrus.org/Turbulators.html

I have also done the same with a car to help visualize the air flow and air flow separation over the trunk and rear C posts to figure out some issues with spoiler placement.

On a car I found useful info is available at legal highway speeds and a 5-10 min run at 75 mph. A few lonely road tests to 120 mph demonstrated that in most cases auto body flow separtion shows up by the time you get to 60-75 mph, and only changes in magnitude as speeds go up from there.

Of course for the folks running at Bonneville the rules would be a bit different, and an oil test done at 150+ would probably be an eye opener to some car owners.

I'm wondering if any of you have put a few drops of old engine oil in an intake port and held the valve at a key lift point and then watched where the oil went. (you can make it more visible in thin layers by adding some of the florescent leak detector and using an UV light to examine the flow)

I suspect you would learn some intersting things about flow (especially wet flow) by doing that.

This may be an affordable way for the average joe to do wet flow testing.
Perhaps using a very small tube like a hypodermic needle to release the oil drop in free space, only after the flow has stabilized at the lift and flow of interest, you could also see where small dropplets would be carried by the flow.

Larry