Continuing the Rod/Strike Ratio Saga
Incidentially, for any one interested, my name is Larry Mayfield and I live
in Madison, Al. As I indicated before, I am now retired after spending 31
years with The Boeing Co. I was a test engineer and the manager of Systems
Testing. My last assignment was as the International Space Station Test
Program Manager here in Huntsville, Al. I had test responsiblilty for all
pressurized volumes; living spaces and labs. This included everything to make
it run, life support, working conditions, experiments, etc. Was fun for a
long time, then I just got tired of it all.
Since I last posted my analysis information, I have added two additional data
sets for Piston Displacement from TDC and Piston Velocity based on 2200 RPM
(max torque for 260 cubic inch motor and BMEP of 124 psi at that max torque).
As a check on my calculations, I summed the torques for each cylinder
overlapping each by 90 degrees. The peak torque was 263.6 ft-lbs vs
advertised 258 ft-lbs. This gives me some confidence in the method.
As I stated before, the rod length was the only parameter changed in this
analysis. If rod length and consequently piston pin location in the piston
were to be changed to get more out of the motor, it simply would not be worth
it! Of course you can change cams, valves, ported heads, etc. to get more
torque and HP. The point was to determine the effectiveness of changing to a
longer rod. Period. It really does not matter, if that is all that is changed
- all data points could be covered by an eyelash. I reiterate, I'll be
happier than a pig on poop to send you my Excel spreadsheet and charts. If
necessary, I'll even do the math analysis in some graphical format such as
*.BMP or GIF or JPG so you can have it for your very own personal pleasure
(Moohahahaha....).
I also have a couple or three engine analysis software packages as well as a
dyno package and a very good package for drag racing analyses. If some of you
would like to predict what changes to you particular vehicle could do for
you, let me know. Pending the amount of requests, data, etc. I'd be happy to
do it...
Specific replies
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Spook37211 (Ray)
You mentioned getting more power from a truck block with a taller deck. That
changed the basic parameters of the analysis. Had the boat folk stuck with
their original block, used the truck rods and modified pistons, then the
results would be generally as I predict (I think): not much change. But in
going to a taller deck, I suspect that the intake manifold had to be changed
because the spacing between cylinder banks is farther. If so, then this adds
length to the port runners which
will have a tunning effect, I suspect. I know it did when I ran velocity
stacks on my preped 289: the stacks were tuned for 7800 rpm peak horsepower
and the motor would not pull well until in the vicinity of this rpm. Because
the deck was taller, I suspect that the cam geometry is also altered a
smidge. To keep the valve train in the same relative position the cam would
have to have been moved up in the block. Maybe the cam timing in relation to
crank/piston displacements also changed some. So yes, I can see that
additional horsepower and torque could be obtained this way.
What is a GP Boat? Is this the cigarette boat racing that I occasionally see
on TV? A few years ago, I snagged an old boat. It is a Hydroflight vintage
1966. It is a 3 point drag racing hydro with a water coled "Thorughbred"
V-Drive (20% overdrive), water shaft bearings. The original motor was an FE
427 side oiler, but it had long since disappeared, so it now has a
superstocked 390 in it. I built this motor from components using the 427
Lemans cam, 10.5 forged pistons, aligned bored, decked, honed for each
piston, solid lifters, adjustable rockers, plugged lifter oil galleries,
fully baffled 14 qt oil pan, water cooled exhaust (we have noise police here
- no zoomies!). The boat has a 3 cup Italian racing propeller 12 diameter, 14
inch pitch. Only two controls, steering and gas. I have had it to 80 mph at
only 4000 rpm. I run out of gas before it does. Figure 100+ is a possibility.
No, I do not drag race it. It just sits in my yard now covered. The wife is
scared spitless of it and the boys do not like to ski behind it - too noisy
and fast.
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wickland@eng.adaptec.com
Steve Wickland
Steve,
as a result of your question about how long does the piston dwell at TDC with
longer rods, I added that parameter to my analysis. The results are
discouraging. In all the cases I tried, from rod lengths between 4.5 and 6.0
inches (crank throw of 2.87 inches), the amount of crank rotation for about a
hundred thousandths of an inch was all within a degree. The range was from 19
degrees to 21 degrees. What was interesting is that the dwell at BDC is not
symetrical with TDC. The dwell for a similar displacement was 25 to 27
degrees. Jeeze, I said ( actually it was what the hell...). So I demonstrated
this graphically. Heres how...
1) Take a compass (no not that kind, the kind you draw a circle with) and
draw a circle with a diameter of about 2 inches. If you have a way, larger is
better for best accuracy, but this works to prove it to your self.
2) Draw a line through the center of the circle and extend it for 4 or 5
inches. This is the centerline of your "piston".
3) Set your compass to say 3.6 inches (hmm...this is about the same rod ratio
as our Tigers). Put the compass point on the circle where the line crosses
it. Make a mark on the extended line. This should be your TDC if you used the
circle point next to the extended line. Do the same for the other side of the
circle. Now you have both TDC and BDC. Use something to mark points along the
circle (you can reset the compass).
4) Now with the compass reset to the "rod" length you used to mark TDC,
sequentially move the compass to each point on the circle and make a mark
along the extended line. It is only necessary to do one half of the circle.
5) Now you should have a line going through the circle with a lot of little
lines on it. If you compare similar crank rotations from TDC and BDC, you
will see that dwell is longer at the BDC position.
If you followed all the above, you can repeat it for a longer or shorter rod.
The results are still about the same. Not much measureable difference between
varying rods at either end, just BDC has a longer dwell.
Hope this helps.
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