Milwaukee Midget

[Interested Observer]

“At 90 degrees, any difference in rod angle with respect to piston travel is 0.”

Let’s hold on here a minute--who says this is so?
At any given crank position (except TDC and BDC) the short-rod piston will be below the long-rod piston  due to the increased angularity of the short rod.  Given that, and assuming we consider the effective compression ratio to be related to the remaining stroke to be traveled, the short-rod version would have the larger remaining stroke and, consequently, the marginally increased CR.  Right?

So, as I read it above, Chris has his long and short rod effects reversed.  Not that any of us think there is any significant benefit to be obtained via this variation.

Further, it seems a lot easier to calculate the piston positions than to spend all day horsing around with dial indicators.  Having done the former, at 67 degrees ABDC I got up strokes from BDC of 0.639” long rod and 0.634” short rod for a difference of 0.0047” which is close to the measured 0.003” but measuring two entities and then subtracting to get the difference to this degree of accuracy is a challenge.
At 102 ABDC, I get 1.3578” and 1.3524” with a difference of 0.0054”.  The strokes vary from what Chris reported but the difference is comparable.

Now, if we knew what the effective valve timing and exhaust plumbing dimensions were, we armchair tuners would really have something to chew on!

[fordboy628]

I have some thoughts about this current section of the thread, but I don't have time to gather all my thoughts and information today.    Unlikely for it to happen tomorrow as it is Easter.    Will get it put up sometime next week, probably after the service for Al Baurle.

Sorry for the delay.
 
Fordboy

[Milwaukee Midget]

Now, if we knew what the effective valve timing and exhaust plumbing dimensions were, we armchair tuners would really have something to chew on!

Which I JUST received this morning.  About a month ago, Mark and I were given run on an old Audie cam profiler - we tested three cams - but were unable to download the files.  Antiquated Windows system with floppys.

Mel's MicroMaven was able to retrieve them, and I'm sending it off to Mark with the Mail on Monday.


IO, I misspoke bringing rod angle into my statement.  I'm still learning - you're witnessing that process. 
 

I found the distance the piston moved up the bore at 90 degrees to be equal to the radius of the throw.  Variance occurs between 0 and 90, and 90 and 180, which is a function of radius and rod length.

All of this is calculable, but I found it quicker to just measure it.

And yes - in the end, it's probably insignificant - I'm just trying to wrap my head around the "why".  I'm still very new at this.

Let's assume a static situation in the checking of dynamic CR.  We will disallow ramcharging effect, velocity, any other dynamic attributes in an engine, and just focus on the valve closing event with respect to piston placement in the bore.  Assuming the closing event on a compression stroke to occur .634 above BDC with the longer rod, compared to .639 above BDC for the short rod, how can there not be additional A/F mixture captured in the cylinder, and thus, more CR?

What am I missing?   

 

[Seldom Seen Slim]

Query for FordBoy w/ref. to his earlier comments:

EGV?  Stands for . . . "European Garbage Vehicle"?  Or, by some remote chance, Elk Grove Village?

I have never driven the former but lived in the latter for a handful of years.  I knew where UOP was in Des Plaines -- but not that there was an engine shop/whatever it was in Elk Grove.  My handful of years was a while before you were there, from the sound of it but still -- hmm, didn't know there was such a place.

Back to our regularly-scheduled roamings.

[jacksoni]

"Let's assume a static situation in the checking of dynamic CR.  We will disallow ramcharging effect, velocity, any other dynamic attributes in an engine, and just focus on the valve closing event with respect to piston placement in the bore.  Assuming the closing event on a compression stroke to occur .634 above BDC with the longer rod, compared to .639 above BDC for the short rod, how can there not be additional A/F mixture captured in the cylinder, and thus, more CR?"
I think when you ignore these things you become the "effective CR" that Fordboy described in his treatise on CR's. The whole point of dynamic is just that, dynamic. And if there is reversion, residual exhaust, inappropriate IVO etc, you can end with LESS cylinder filling and therefore less, not more, A/F mixture to be compressed with your lower down piston. Although mean piston speed is not different with the two rod lengths, peak piston speeds are and this may have some effect. So, we are waiting for Fordboy to pipe in (or someone else) to help us out here.

[Milwaukee Midget]

"Let's assume a static situation in the checking of dynamic CR.  We will disallow ramcharging effect, velocity, any other dynamic attributes in an engine, and just focus on the valve closing event with respect to piston placement in the bore.  Assuming the closing event on a compression stroke to occur .634 above BDC with the longer rod, compared to .639 above BDC for the short rod, how can there not be additional A/F mixture captured in the cylinder, and thus, more CR?"
I think when you ignore these things you become the "effective CR" that Fordboy described in his treatise on CR's. The whole point of dynamic is just that, dynamic. And if there is reversion, residual exhaust, inappropriate IVO etc, you can end with LESS cylinder filling and therefore less, not more, A/F mixture to be compressed with your lower down piston. Although mean piston speed is not different with the two rod lengths, peak piston speeds are and this may have some effect. So, we are waiting for Fordboy to pipe in (or someone else) to help us out here.

Coach IO, I think I got that bit of nomenclature right -

"Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder."

http://cochise.uia.net/pkelley2/DynamicCR.html

The dynamics being brought to bear on a dynamic CR - I'm ill equipped to argue against your insight.

 

[fordboy628]

Query for FordBoy w/ref. to his earlier comments:

EGV?  Stands for . . . "European Garbage Vehicle"?  Or, by some remote chance, Elk Grove Village?

I have never driven the former but lined in the latter for a handful of years.  I knew where UOP was in Des Plaines -- but not that there was an engine shop/whatever it was in Elk Grove.  My handful of years was a while before you were there, from the sound of it but still -- hmm, didn't know there was such a place.

Back to our regularly-scheduled roamings.

Slim,

Ahhh, another one time resident of NW Cook County . . . . . . . .

Yes indeed, EGV is NW Cook County-speak for ElK Grove Village.     HE = Hoffman Estates;   the burg = Schaumburg;   Strolling Ghettoes = Rolling Meadows;    Hangover Park = Hanover Park; etc, etc.

Not that anybody cares, but I resided on the NW side of Chicaga, 'till I was 5.   Was a resident of HE for 16 (gosh so wonderful years, mom & dad . . . . . NOT!!) whereupon I expanded my operational base to include the "collar counties", AKA, Greater Chicagaland, and of course, Walworth Co, WI, home of Lake Geneva and the blind (or nearly so) ID checkers at all/most of the watering holes . . . . . . .
 
Fordboy

[Seldom Seen Slim]

Wow.  If that's the case - that you lived on the NW side of the city -- you'll probably understand (maybe) that after I graduated from Forest View High School in Arlington Heights (you date yourself if you know that place -- it was disbanded after something like 15 years from when it was built for the baby boom) I spent two wonderful years commuting from EGV to UCLA (University of Chicago located on Austin (a/k/a Wright Junior).  But that was in another century, and when I was done there I headed north to the UP and have been here ever since.  Is there still anything down there?

[jacksoni]

"Let's assume a static situation in the checking of dynamic CR.  We will disallow ramcharging effect, velocity, any other dynamic attributes in an engine, and just focus on the valve closing event with respect to piston placement in the bore.  Assuming the closing event on a compression stroke to occur .634 above BDC with the longer rod, compared to .639 above BDC for the short rod, how can there not be additional A/F mixture captured in the cylinder, and thus, more CR?"
I think when you ignore these things you become the "effective CR" that Fordboy described in his treatise on CR's. The whole point of dynamic is just that, dynamic. And if there is reversion, residual exhaust, inappropriate IVO etc, you can end with LESS cylinder filling and therefore less, not more, A/F mixture to be compressed with your lower down piston. Although mean piston speed is not different with the two rod lengths, peak piston speeds are and this may have some effect. So, we are waiting for Fordboy to pipe in (or someone else) to help us out here.

Coach IO, I think I got that bit of nomenclature right -

"Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder."

http://cochise.uia.net/pkelley2/DynamicCR.html

The dynamics being brought to bear on a dynamic CR - I'm ill equipped to argue against your insight.

 

Fordboy points out the confusion, reversal or other controversies about what these events are called:
http://www.landracing.com/forum/index.php/topic,12353.0.html

[Interested Observer]

Chris,
The origin of the confusion is coming from the fact that you have the long/short rod positions crossed.  Should be 0.639 above BDC for the long and 0.634 for the short.  (The short rod is always lagging the long (on the compression stroke), except at TDC and BDC where they are equal.)

[landspeedrich]

Wow.  If that's the case - that you lived on the NW side of the city -- you'll probably understand (maybe) that after I graduated from Forest View High School in Arlington Heights (you date yourself if you know that place -- it was disbanded after something like 15 years from when it was built for the baby boom) I spent two wonderful years commuting from EGV to UCLA (University of Chicago located on Austin (a/k/a Wright Junior).  But that was in another century, and when I was done there I headed north to the UP and have been here ever since.  Is there still anything down there?

Seldom Seen,
      Did you go to Forest View with a Dave Klopfleisch ?Believed he graduated 66-67 if I am correct.I went to one of the Leyden HS.School of the Hooods back then.You know baggie greys,dago T's,cuban heels and the leather jackets.Ahh them were the days.

[Freud]

SSS......I'd suggest you insert Arlington Heights as the location for landspeedrich.

It may not be current but he seemed to enjoy his time there.

FREUD

[landspeedrich]

SSS......I'd suggest you insert Arlington Heights as the location for landspeedrich.

It may not be current but he seemed to enjoy his time there.

FREUD
[/quote
    Arlington Heights probably loaded with climbers back then.I was a happy GREASER over by Ohare with my 48 Chevy coupe.Don't mean sidetrack this thread.Did enjoy the mid 60's,what can I say

[Milwaukee Midget]

IO -

I've been humbled - but I have been made smarter for it.

http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm

And I owe you another beer. 

What bugs me is that I took painstaking efforts to accurately measure this.  I realized I had a rare opportunity to check the actual relationship of two different rod lengths side by side on a common axis to their relative piston travel.

And I see where one would think I inverted the numbers, and that the results would indicate that's what happened.  But man, I double checked them - I made a point to accurately assign the correct number with the correct cylinder.  So to that end, I don't know where the mistake is, and I'm having a difficult time accepting that there is one.

Maybe I should just go back to something simple.

Anybody want to give me a hand with my cold fusion project?

[krusty]

     My office was in EGV for a few years, then in Lincolnwood, and I lived in Roselle '75 - '85. My garage in Roselle was where I first started doing customer work on race cars as I terminated my job with Honeywell. In the first part of the eighties I rented some dyno time from ProMotor as I did some intake and exhaust development on a Porsche 924 race engine.

     Yes, Slim, the Don Nichols led Shadow CanAm operation ran out of what became the ProMotor shop.

     Mark, did you ever work with Bill Truesdale at Apex?

     vic