About time for the spintron
- Thread starter comnoz
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comnoz said:
It might be worthwhile taking a swag at what the hot clearance would be, set lash to that and see how it behaves. With the 750 USS with Steve Maney alloy barrels and chromoly pushrods we set lash cold at 0.002" for the Megacycle N480 knowing it would open up. I am reasonably sure the 0.015 cold lash is for cast iron barrels and aluminum pushrods.
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Assuming that the lash setting for the spintron testing is the actual running lash, i.e., if set at 0.010", it remains at 0.010" throughout the test, it would be interesting to see Spintron images of the D+ grind run with a lash of 0.005", so that valve seating occurs well into the closing ramp, not in the transition between flank and ramp. The D+ data I've seen suggests that with the D+ lashed at either 0.015" or 0.011" lash, valve seating occurs in the transition between the flank and ramp, rather than out in the middle of the closing ramp.comnoz said:
I realize that testing time is precious and in short supply, but it would nevertheless be informative for all if you could demonstrate that valve bouncing can be controlled through lash setting. Or to the contrary, it would be equally informative if it turned out that regardless of lash setting, D+ IN valve bounce could not be controlled. From the cam data I've seen, a lash setting of 0.005" would be appropriate for all the cams under discussion here (CDO and PW3) since this would locate the IN closing event near the center of the closing ramp. My $0.02.
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D+ is labeled for drag use only with a race level valve train required to make use of it. I alway like WZ-Kurt inputs and got me searching to find lash alone may not help push rods acting like a vaulter pole bending on valve opening then springs back on valve faster than cam profit and slapping it off seat. So besides WZ's list to do's, might also try a steel tube push rod. Don't know if comnoz viewing area of push rod could see bow spring action. Oh yeah seems maxing out builders also shooting for endurance engines shoot for below .015" bounce - as measured by laser bouncing detector not video. No id if the same number values relate. comnoz ya got Sir Eddie and son world class engine shooting for 10-11 grand so when ya going find out what valve life is like above the red Zone?
lcrken
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hobot said:
One of the good things about running at Bonneville is that you don't have to worry as much about long life in the engine. We're only at WOT for a couple minutes max per run. Of course, it's nice if the engine will survive that for more than a couple of runs.
Ken
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i'm confused on a number of factioids Ken. How did TC and other drag racers and desert races survive fairly long routines into 8000's + more on their delayed or missed shifts they definitely noted vs comnoz dyno tested rationale implying bore friction makes much over 7000 counter power productive. Compared to examples of spintron on modern engines showing the waves in springs wobbling the stem with push rod spring back giving significant multiple seat bouncing, so comnoz spintrons so far look pretty stable yet claimed to be significantly out of control with the best valve train components available now. The threshold I've searched so far says .015" seat bounce is acceptable limit to live with so best wishes keeping 2 big valves bounce down to that in our engines as they turn into elastic cartoon characters. Anywho until comnoz grits teeth into 8000+ rpm he's not yet tested what's possible before failure. I know one thing hanging on past redline in lower gears don't reveal any power fall off until valve suddenly really bouncing and clattering.
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A 4StHead simulation of a PW3 exhaust cam in a 750 Commando engine.
The comments on the picture should be self explanatory.
The results from a 4StHead simulation are virtually identical to the results obtained from a Spintron machine, but the picture herewith shows the opening lag of the valve when cylinder pressure is present in addition to the valve springs. This is something that the Spintron cannot show, because it is not a firing engine. The dynamic opening lag as shown is 10 degrees from the static design
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Snotzo said:
That is some pretty interesting predictive software.
I picked up a laser position sensor that I have not got set up yet. It will be interesting to see how close the prediction comes to what I measure.
Once I get a couple holes in my barrel and a mounting bracket done I will install a PW3 and see how it looks. Jim
Snotzo said:
The simulations are simultaneously fascinating and thought provoking, thank you for providing them. In general, the simulated lift curves bear some resemblance to curves obtained by manually measuring a lift profile using a very light spring (minimum force required to maintain mechanical contact) vs measuring the same valve train with 100+ lb of seat pressure, where lag occurs due to lack of rigidity of valve train components. But your simulation obviously shows much more than that.
Comnoz said he'd be comparing his results to your PW3 simulation to see if in fact "The results from a 4StHead simulation are virtually identical to the results obtained from a Spintron machine." So I'm eager to see his results.
I'm sure the simulation is very good, but my intuition is that the output is only as good as the input, and I struggle to envision how the input could possibly be accurate and complete enough to allow the program to factor in the relative rigidity of the system as well as all the natural excitation frequencies of the valve train components that change continuously as a function of testing frequency. For instance, do you have to specify the pushrod alloy, length, wall thickness, weight, etc, as well as all spring-related parameters, i.e., wire x-sectional area, length, helix angle, progression rate, etc? Even with the aforementioned parameters specified carefully, it does not address the more subtle variables like possible flex of the end-supported cam, rocker geometry/deformation that may induce valve stem flex, or other parts of the valve train subject to flexural deformation.
Maybe I'm making a mountain out of mole hill but IMHO to make a valve train operate at a very high rate, everything matters, and there is a lot more required to control them than first meets the eye. Per the citation Comnoz cited earlier it is possible to be out of control at a given frequency, yet come under control at even higher frequency.
http://tinyurl.com/ovc8ncx
In light of the above points and questions, what inputs are required and how detailed do they have to be to run a 4StHead simulation?
Would it be possible for you to simulate what Jim has already done, i.e., the stock system and the D+ system to see how the simulation compares?
It would also be interesting to see if you can somehow tame your 9500 rpm (or 8500 rpm or whatever rpm you feel like simulating) by substituting other parts, e.g., a Maney steel pushrod (45g) vs the stock alloy pushrod (33g), or an aluminum matrix composite (ceramic) pushrod for the alloy pushrod?
http://tinyurl.com/me6gev7
If you do something as simple as change the seat pressure or spring rate, does the simulation suggest that such changes can render an "out of control" system "under control" at a given frequency?
Thanks again for the simulation. I think it's really neat that we’ve got both the spintron man and the simulation man on the same forum. Looking forward to your comments and data.
One final tidbit relating to valve bounce.
http://www.tech.plymouth.ac.uk/sme/desnotes/valvebounce.htm
lcrken
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Actually, as I recall, Dr. Blair's program pretty much does require all the data you mentioned as inputs to his simulation. It's quite a detailed simulation.
FWIW, it is possible in 4stHead to run the simulation in either a running mode, with cylinder compression forces included, or in motoring mode, with no combustion pressure included. The motoring mode is intended to allow direct comparison to spintron data.
Ken
FWIW, it is possible in 4stHead to run the simulation in either a running mode, with cylinder compression forces included, or in motoring mode, with no combustion pressure included. The motoring mode is intended to allow direct comparison to spintron data.
Ken
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lcrken said:
Ken you are correct. The input data required is very detailed. The 4StHead output compares very closely to the output from a full blown Spintron of the type regularly used by the top Nascar teams and development shops. It is relatively easy within 4StHead to vary both dimensions and material for most if not all of the components, but in the simulation I have done, all data was measured direct from an engine that is being now used in classic racing in the UK. The PW3 cam was a new item, and the static valve lift profile was first measured using CamProPlus equipment, and then converted for export direct into 4StHead.
Jim, when you get to the stage where you are able to get measured output data from your spintron I would be happy help you to make comparisons with a set of data run through 4StHead . That way it should be possible to see how close you are getting to results that would have come from an industrial spintron
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WZ507 said:
Actually, 4StHead accounts for these parameters. Gordon Blair offered to do the simulation for our USS 500 Norton. Herb Becker conducted the measurements including pushrod profile, rocker arm stiffness, rocker arm rotational inertia, valve dimensions, valve head profile and material. I provided generalized cam dimensions and distance between support bearings for the simulation to factor in cam stiffness. The data collection methodology specified was rather pragmatic - no need for FEA. This ultimately resulted in a custom cam profile data file. The file was sent to Megacycle for fabrication of the custom cam.
I was impressed with the detailed inputs. It was an eye opener for Herb as he ran the rocker arm stiffness test on one of his alloy rockers to see how much deflection there was.
The whole exercise made me appreciate the fact that in some ways, the valve train system is a series of springs.
It was an honor having Prof. Gordon Blair assist us and pure pleasure knowing him. He was always willing to help.
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The point is hobot that everything flexes to a degree and as you proceed up in derivatives of displacement (velocity, acceleration, jerk, jounce...etc) the slight displacements as a result of varying forces becomes more significant.
If you think about loads on a Norton cam it can get interesting. We began breaking cams in part due to the 180 degree firing order, the two center lobes were loaded to a certain degree during the cycle and that is not how Norton intended. The solution was a middle support bearing to split the span of the cam shaft (thanks to Herb Becker). There are other challenges that I will not expound on here.
So even in a 360 degree firing order, the cam bending has an impact. Even the valve head deformation and loads under pressures of combustion has a bearing on valve motion
If you think about loads on a Norton cam it can get interesting. We began breaking cams in part due to the 180 degree firing order, the two center lobes were loaded to a certain degree during the cycle and that is not how Norton intended. The solution was a middle support bearing to split the span of the cam shaft (thanks to Herb Becker). There are other challenges that I will not expound on here.
So even in a 360 degree firing order, the cam bending has an impact. Even the valve head deformation and loads under pressures of combustion has a bearing on valve motion
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