Engine Masters rod ratio test results

[maxracesoftware]

48 years
my Marquette Distributor Machine ( purchased 1972 ) ... made my own Spark Plug load bar w/adjustable Plug Gaps
what i did was experiment with 5 or so Distributors that would start missing at certain RPMs
adjusted Plug Gaps until Distributor Machine should same RPM as Race Car or Dyno
and its worked great all these years with that Gap ... and correlates within +- 100 RPMs on Dyno
this Pic in 1980's
still works in 2020 ... moved it into Dyno Engine Room years ago .

Nice set up, looks somewhat similar to mine.

I have noticed a considerable difference in required firing voltage when firing plugs into a pressure
chamber compared to free air. As the pressure goes up, the voltage requirement does as well and the
spark duration diminishes until misfires occur.

Combining a scope with the distributor machine results in one of the most useful tools in the shop.

With a multi channel scope, various spark plug secondary wires can be tested as well. Some name brands
are not much (if at all) better than OEM wires.

Run the test bench with the shop lights turned off and watch the light show. All that is missing is a guitar.

i also had the Marquette Oscilloscope hooked a few times with Distributor Machine as well as a few times on the Dyno
i wish i would have not sold the Marquette Oscilloscope to a friend

i also back-to-back old Champion Spark Plug checker w/Air pressure Psi -vs- what i was seeing on Dyno + Distributor Machine
played around with modififying Plug ground straps to J-style and J-style pointed end-shapes in 1970's
modified many Distributor single point-plates to for 32oz ? Accel dual-points
used clear distributor caps for more testing
really cool at nite to turn lights off in the Shop and spin a Distributor hooked up to my Spark Plug Load-Board
and watch + hear MSD fire multiple sparks at low to mid RPM then change to lesser multiple sparks at highr RPMs
could spin a Magneto to 9500 RPM , and normal distributors to 11,000 RPMs easily , optional higher HP electric motor
... also cool was smell of Ozone from MSD sparks

i'll Post a Pic of my Marquette Oscilloscope later today or tonite

almost forgot to Post a Pic of my Marquette Oscilloscope ....
Sunnen Rod Heater in back , old bath tub converted to Parts cleaner, ideal Block cleaner
bunch of Crankshafts , Jack Stands , Rimac Spring Tester ,etc

[David Redszus]

Tonight i was studying all the data that was gathered from analyzing a camshaft on a Cam Pro Plus. I started out looking at the lifter rise/valve lift at .050" and then increasingly in .050" steps (ie) .050--.100--.150--.200--.250 and up to max. lifter rise. I was looking at the degrees ATDC at which these lifter rise points occurred mainly to see where the valve lift number was at in the area of 70 to 80 degrees ATDC. As i was pondering this that and the other a thought came to mind. The engine with a longer con-rod set up has more degrees of piston dwell in the TDC area. So the piston starts down the hole a little bit later, but while the piston was not yet moving the camshaft was still turning opening the valve giving it "more" of a head start in relation to the piston compared to a shorter rod set up. Does this make sense ? Mark H.

Using reasonable engine data, I can find no basis for the claim that a rod length makes a significant difference in
dwell at TDC; unlike the dwell at BDC. Nor in velocity or acceleration.
For a significant change in performance, there must be a very large difference in rod lengths.
If someone can show why this assumption has been made, I would very much appreciate seeing it.

Here is what we do know for an engine with a 3.75" stroke and rods of 5.70" and 6.0" at 8000 rpm.

5.7 rod
Piston position from TDC
6 deg...0.35mm
10 deg..0.96
14 deg..1.87
Velocity
6 deg.......5.54m/s
10 deg......9.19
14 deg.....12.77
74 deg.....42.03
Acceleration
6 deg....4484g
10 deg...4408
14 deg...4295

6.0 rod
Piston position from TDC
6 deg...0.34mm
10 deg..0.95
14 deg..1.85
Velocity
6 deg.......5.47m/s
10 deg......9.08
14 deg.....12.61
74 deg.....41.82
Acceleration
6 deg....4430g
10 deg...4356
14 deg...4246

A rod length change of 5 percent will result in a position motion change of about or less than 1 percent.

Nonetheless, given the opportunity, always run the longest rod that will fit.

[digger]

The key takeaway that I noticed, was that the short rod was more sensitive to changes in ignition timing than the longer rod, I attribute this in my mind to the shorter rod having less dwell at TDC, which to me implies that the engine with the longer rod will perform more consistently as outside parameters change IE: air temp, baro, humidity ect. I think I would prefer to run a longer rod due to that, but I'm not going to build my engine specifically around the connecting rod either.

didn't they say it was insensitive to timing over a range of about 4 degrees?

the takeaway on the ignition timing seems more like that it required more timing by like 4 degrees or whatever it was, gotta light the fire earlier so the pistons haven't moved down the bore too much to decay the pressure? when you look at the piston position differences 0-20 degrees ATDC (0.02mm or so) they are extremely small i'm skeptical that's the reason when the tolerance of parts, temperature of the parts is probably more variable than that

[swampbuggy]

Mr. Redszus; you made the statement above, (quote) when given the opportunity, always use the longest rod that will fit. Now please state the "reason (or) reasons" for saying this. If there is more than one reason, state the most important reason first and work down the list. Thanks, Mark H.

[David Redszus]

Mr. Redszus; you made the statement above, (quote) when given the opportunity, always use the longest rod that will fit. Now please state the "reason (or) reasons" for saying this. If there is more than one reason, state the most important reason first and work down the list. Thanks, Mark H.

The most important benefit to the use of long rods (at a given stroke) is that it substantially reduces
side thrust friction, especially at higher rpms.

The second important benefit is that the piston can be made significantly lighter which also contributes
to reduced friction and piston skirt wear. Remember that the piston skirt diameter expands (and contracts)
under firing load.

Please note the bold faced data below.

Engine RPM...........................................6000...............8000
3.48/5.7 = rod ratio 1.64
Axial peak inertial G force, tension .............2321...............4127
Axial peak inertial G force, compression.......-1256..............-2234
Axial resultant force, tension N...................8881.............15789
Axial resultant force, compression N..........-16130.............-28676
Inertial side Thrust friction N......................2217...............3942
Inertial side AntiThrust friction N................-2217..............-3942
Resultant side Thrust friction N.................3735...............5390
Resultant side AntiThrust friction N...........-3010..............-4735
Mean piston speed m/s............................17.48...............23.31
Max piston speed m/s..............................29.04...............38.72

3.48/6.285 = rod ratio 1.80
Axial peak inertial G force, tension .............2271...............4037
Axial peak inertial G force, compression.......-1288..............-2290
Axial resultant force, tension N...................9012.............16021
Axial resultant force, compression N..........-15780.............-28054
Inertial side Thrust friction N......................1948...............3464
Inertial side AntiThrust friction N................-1948..............-3464
Resultant side Thrust friction N.................3271...............4724
Resultant side AntiThrust friction N...........-2662..............-4177
Mean piston speed m/s............................17.48...............23.31
Max piston speed m/s..............................28.82...............38.42

It is interesting to note that both Formula One and Cup engines run very long rods
with ratios above 2.0.

They also run very similar mean and maximum piston speeds and very similar BMEP values.

[Stan Weiss]

David,
What would the numbers look like for a 3.555" with a 6.050" rod turning 11500 RPM. If it matters a bore of 4.73" (499.74 ci) This would be the old carb NHRA Pro Stocker engine. Remember have a min piston and rod weight rule.

Stan

Hemi_PS_Block.gif

[LSP]

It is interesting to note that both Formula One and Cup engines run very long rods
with ratios above 2.0.

No, they don't

[frnkeore]

While the Cup cars do run a little under 2.0 (1.908), the last V10 & V8, F1 cars, ran over 2.0 (2.564).

[David Redszus]

David,
What would the numbers look like for a 3.555" with a 6.050" rod turning 11500 RPM. If it matters a bore of 4.73" (499.74 ci) This would be the old carb NHRA Pro Stocker engine. Remember have a min piston and rod weight rule.

Stan

Hemi_PS_Block.gif

3.55/6.050 = rod ratio 1.70......................11500rpm
Axial peak inertial G force, tension .............8636
Axial peak inertial G force, compression.......-4756
Axial resultant force, tension N..................37760
Axial resultant force, compression N...........-59797
Inertial side Thrust friction N......................7906
Inertial side AntiThrust friction N................-7906
Resultant side Thrust friction N...................9343
Resultant side AntiThrust friction N.............-8729
Mean piston speed m/s............................34.23
Max piston speed m/s..............................56.68

For accurate side force values, we would need piston weights and
combustion gas pressure curves. The above are based on typical SBC.

Does anyone wonder why they change pistons quite frequently?

[Stan Weiss]

While the Cup cars do run a little under 2.0 (1.908), the last V10 & V8, F1 cars, ran over 2.0 (2.564).

I have added some numbers for an NHRA 500 ci Pro Stock engine to your chart.

Stan

[Stan Weiss]

David,
What would the numbers look like for a 3.555" with a 6.050" rod turning 11500 RPM. If it matters a bore of 4.73" (499.74 ci) This would be the old carb NHRA Pro Stocker engine. Remember have a min piston and rod weight rule.

Stan

Hemi_PS_Block.gif

3.55/6.050 = rod ratio 1.70......................11500rpm
Axial peak inertial G force, tension .............8636
Axial peak inertial G force, compression.......-4756
Axial resultant force, tension N..................37760
Axial resultant force, compression N...........-59797
Inertial side Thrust friction N......................7906
Inertial side AntiThrust friction N................-7906
Resultant side Thrust friction N...................9343
Resultant side AntiThrust friction N.............-8729
Mean piston speed m/s............................34.23
Max piston speed m/s..............................56.68

For accurate side force values, we would need piston weights and
combustion gas pressure curves. The above are based on typical SBC.

Does anyone wonder why they change pistons quite frequently?

David,
"Does anyone wonder why they change pistons quite frequently?"

Where did you hear this?

Stan

[Rick!]

It is interesting to note that both Formula One and Cup engines run very long rods
with ratios above 2.0.

No, they don't

Dale Carnegie would put it another way:
"Here's a conversation about F1 rod/stroke ratio that might be interesting and shows myriad combinations of which some are below 2:1."

https://www.f1technical.net/forum/viewt ... =4&t=22921
Our own local representative participates in the discussion.

See how easy that is?

[Stan Weiss]

Minimum weight requirements for the following engine components: Piston - 460 grams; Wrist pin - 135 grams; Connecting rod - 480 grams; Intake valve - 90 grams; Exhaust valve - 80 grams.

From the latest rule book I have.

Stan

[Stan Weiss]

Since my calculations are not exactly the same as the chart for the Loads I here is what I get and also the 500 ci Pro Stock. For the 500 ci engine I used the same ring and ros bearing weight as the NASCAR engine.

Stan

Bore_=_3.858268___Stroke_=_1.565748___Rod_Length_=_4.015748___RPM_=_20000
Piston_Weight_=_295.0___Rod_Weight_=_311.0
Small_End_Rod_Weight_=_85.0___Big_End_Rod_Weight_=_226.0
Rod_CG_/_Distance_from_Small_End_=_2.918196
Crankpin_/_Rod_Big_End_Acceleration_=_286172.4
Crankpin_/_Rod_Big_End_Rotational_Force_=_4431.643

____________Reciprocating____Total_____Piston_Side___Piston______Crank_Pin__Instantaneous
Crank_Angle____Force_________Force________Force__Inertia_Force__Tangent_Force__Torque
__Degree_______Pounds________Pounds_______Pounds______Pounds_______Pounds___FT-Pounds
___.000______8904.100_____13335.744_________.000____6912.394_________.000________.000

=======================

Bore_=_4.185___Stroke_=_3.25___Rod_Length_=_6.2___RPM_=_10000
Piston_Weight_=_500.0___Rod_Weight_=_564.0
Small_End_Rod_Weight_=_140.0___Big_End_Rod_Weight_=_424.0
Rod_CG_/_Distance_from_Small_End_=_4.660993
Crankpin_/_Rod_Big_End_Acceleration_=_148500.9
Crankpin_/_Rod_Big_End_Rotational_Force_=_4314.432

____________Reciprocating____Total_____Piston_Side___Piston______Crank_Pin__Instantaneous
Crank_Angle____Force_________Force________Force__Inertia_Force__Tangent_Force__Torque
__Degree_______Pounds________Pounds_______Pounds______Pounds_______Pounds___FT-Pounds
___.000______8219.218_____12533.651_________.000____6421.264_________.000________.000

=======================

Bore_=_4.73___Stroke_=_3.555___Rod_Length_=_6.05___RPM_=_11500
Piston_Weight_=_615.0___Rod_Weight_=_519.0
Small_End_Rod_Weight_=_160.0___Big_End_Rod_Weight_=_359.0
Rod_CG_/_Distance_from_Small_End_=_4.184875
Crankpin_/_Rod_Big_End_Acceleration_=_214823.2
Crankpin_/_Rod_Big_End_Rotational_Force_=_5284.504

____________Reciprocating____Total_____Piston_Side___Piston______Crank_Pin__Instantaneous
Crank_Angle____Force_________Force________Force__Inertia_Force__Tangent_Force__Torque
__Degree_______Pounds________Pounds_______Pounds______Pounds_______Pounds___FT-Pounds
___.000_____14759.757_____20044.261_________.000___11712.581_________.000________.000

[David Redszus]

David,
What would the numbers look like for a 3.555" with a 6.050" rod turning 11500 RPM. If it matters a bore of 4.73" (499.74 ci) This would be the old carb NHRA Pro Stocker engine. Remember have a min piston and rod weight rule.

Stan

Hemi_PS_Block.gif

3.55/6.050 = rod ratio 1.70......................11500rpm
Axial peak inertial G force, tension .............8636
Axial peak inertial G force, compression.......-4756
Axial resultant force, tension N..................37760
Axial resultant force, compression N...........-59797
Inertial side Thrust friction N......................7906
Inertial side AntiThrust friction N................-7906
Resultant side Thrust friction N...................9343
Resultant side AntiThrust friction N.............-8729
Mean piston speed m/s............................34.23
Max piston speed m/s..............................56.68

For accurate side force values, we would need piston weights and
combustion gas pressure curves. The above are based on typical SBC.

Does anyone wonder why they change pistons quite frequently?

David,
"Does anyone wonder why they change pistons quite frequently?"

Where did you hear this?

Stan

Most recently (20 minutes ago) from an engineer at Mahle Motorsports. Their recommendation
is for a mean piston speed limit of 25 m/s; as speed increases, piston life is shortened.
Typical ProStock piston life is about half of a season, sometimes less.