The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
johnny comelately
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The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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The status quo seems to be the use of Crank Angle for various particular engine analysis characteristics.
This fails in comaparative applications because it does not take into consideration the Bore Stroke ratios nor the Rod ratios and their effect on the very parameters that are being measured.
Before someone jumps in and says that some of those measurements are independent it would be prudent to see that a normalised factor that reflects all three parameters as a single encompassing new paradigm would be more indicative.
Not being particularly mathematical, any suggestions as to how this could be achieved?
The starting point would be the conversion of the stroke to a percentage.
Methinks this has been touched on before but I could not find it.
Last edited by johnny comelately on Wed Nov 23, 2022 10:03 am, edited 1 time in total.

Hoffman900
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Re: The Better Alternative to the Folly of CA in Comparative Analysis of IC engines.

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johnny comelately wrote:
Wed Nov 23, 2022 5:41 am
The status quo seems to be the use of Crank Angle for various particular engine analysis characteristics.
This fails in comaparative applications because it does not take into consideration the Bore Stroke ratios nor the Rod ratios and their effect on the very parameters that are being measured.
Before someone jumps in and says that some of those measurements are independent it would be prudent to see that a normalised factor that reflects all three parameters as a single encompassing new paradigm would be more indicative.
Not being particularly mathematical, any suggestions as to how this could be achieved?
The starting point would be the conversion of the stroke to a percentage.
Methinks this has been touched on before but I could not find it.
I think the math is going to take you back to crank angle being the thing. If you want to make it comparative, that's what BMEP is for. Otherwise, there is just too many "depends" for ratios. Bigger bores up to 100-110mm or so for good combustion on a naturally aspirated set-up. Smaller bores / longer stroke for a high tumble, turbo charged set up, etc.

Rod ratios are pretty much meaningless tbh. You set deck height, design a piston as light as the package will allow, and stick a rod in it. The stroke vs. bore is usually spec'ed by the rules and what your package can tolerate from a piston speed perspective.

At the end of the day, it comes down to make the most amount of torque (cylinder pressure) at an rpm that works for your rule set and then hold onto it the best you can with increasing revs.

johnny comelately
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Re: The Better Alternative to the Folly of CA in Comparative Analysis of IC engines.

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I'm glad you're not the decisionmaker Hoff
:wink:

Tommy Cookers
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Re: The Better Alternative to the Folly of CA in Comparative Analysis of IC engines.

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Hoffman900 wrote:
Wed Nov 23, 2022 7:16 am
johnny comelately wrote:
Wed Nov 23, 2022 5:41 am
The status quo seems to be the use of Crank Angle for various particular engine analysis characteristics.....
... At the end of the day, it comes down to make the most amount of torque (cylinder pressure) at an rpm that works for your rule set and then hold onto it the best you can with increasing revs.
I don't know what crank angle means
I do know that torque isn't equivalent to cylinder pressure unless the engines compared have equal bores

cylinder pressure flatters engines with small bore:stroke ratios (eg Setright the Bristol flatterer)
the Bristol 66 x 96 and 68 x 104 was descended from the Austin 7 via Dixi - the Himmler-pleaser bought by BMW

a small b:s engine can be run at higher piston speed (for a given piston acceleration/stress) and .....
its smaller piston/combustion chamber) area dumps less heat to coolant
but larger b:s ('short stroke') engines were seen as modern and so worthier

johnny comelately
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Re: The Better Alternative to the Folly of CA in Comparative Analysis of IC engines.

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Tommy Cookers wrote:
Wed Nov 23, 2022 1:25 pm
Hoffman900 wrote:
Wed Nov 23, 2022 7:16 am
johnny comelately wrote:
Wed Nov 23, 2022 5:41 am
The status quo seems to be the use of Crank Angle for various particular engine analysis characteristics.....
... At the end of the day, it comes down to make the most amount of torque (cylinder pressure) at an rpm that works for your rule set and then hold onto it the best you can with increasing revs.
I don't know what crank angle means
I do know that torque isn't equivalent to cylinder pressure unless the engines compared have equal bores

cylinder pressure flatters engines with small bore:stroke ratios (eg Setright the Bristol flatterer)
the Bristol 66 x 96 and 68 x 104 was descended from the Austin 7 via Dixi - the Himmler-pleaser bought by BMW

a small b:s engine can be run at higher piston speed (for a given piston acceleration/stress) and .....
its smaller piston/combustion chamber) area dumps less heat to coolant
but larger b:s ('short stroke') engines were seen as modern and so worthier
BS Tommy, you know full well what crank angle is.
And how it is used in this context.
Apart from that, how to normalise the piston position for comparative purposes across all B/S ratios for cylinder and chamber observations that are not governed by the PV association, and to account for rod ratios if you are doing crank related comparisons?
As I said maths is not my forte, so can the engineers help.

Hoffman900
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Re: The Better Alternative to the Folly of CA in Comparative Analysis of IC engines.

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johnny comelately wrote:
Wed Nov 23, 2022 9:57 am
I'm glad you're not the decisionmaker Hoff
:wink:
You want to create an index to do comparative analysis for something you can’t explain or know why you want to explain..

A bigger bore has more surface area for pressure to act on. A longer stroke had a longer lever arm.

There are too many “it depends” when you set the bottom end architecture; rules, rpm limits, engine height and length (which balance also plays a roll in this), lean burning / high knock resistance, naturally aspirated so valve is a driver, etc.

Greg Locock
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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I think you'll find that within the normal range of l/r ratio the plot of crank angle vs %age stroke is pretty much identical around TDC, and only changes significantly around +/-90. So it all depends where your interesting events occur. I can't say it ever crossed my mind to use anything other then CA, but to be honest we didn't get all reverse engineering with competitor engines' top ends. We optimised ours, not copied theirs. Block design was reverse engineered because at the time we knew it was important for NVH and were looking for ideas.
Last edited by Greg Locock on Thu Nov 24, 2022 1:25 am, edited 1 time in total.

johnny comelately
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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Greg Locock wrote:
Wed Nov 23, 2022 10:05 pm
I think you'll find that within the normal range of l/r ratio the plot of crank angle vs %age stroke is pretty much identical around TDC, and only changes significantly around BDC. So it all depends where your interesting events occur. I can't say it ever crossed my mind to use anything other then CA, but to be honest we didn't get all reverse engineering with competitor engines' top ends. We optimised ours, not copied theirs. Block design was reverse engineered because at the time we knew it was important for NVH and were looking for ideas.
Thanks Greg
Even near TDC the dwell changes significantly with different rod ratios (normalised for b/s) affecting combustion properties and hence crank effect. Of course rod ratios change piston acceleration significantly affecting both combustion characteristics and pressure profiles.
The point of this exercise is to normalise or compensate for the effect of piston position with other variations like stroke.

CMSMJ1
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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johnny comelately wrote:
Wed Nov 23, 2022 5:41 am
The status quo seems to be the use of Crank Angle for various particular engine analysis characteristics.
This fails in comaparative applications because it does not take into consideration the Bore Stroke ratios nor the Rod ratios and their effect on the very parameters that are being measured.
Before someone jumps in and says that some of those measurements are independent it would be prudent to see that a normalised factor that reflects all three parameters as a single encompassing new paradigm would be more indicative.
Not being particularly mathematical, any suggestions as to how this could be achieved?
The starting point would be the conversion of the stroke to a percentage.
Methinks this has been touched on before but I could not find it.
I think I understand what it is that you are wanting to do - but for the hard of thinknig (me) can we have some pretty pictures to really drive it home?

My only experience has been with looking at a stroked NC30 engine for my old race bike. This involved various options relating to a +.5mm over bore, or a 'stroker' rod or both.

it broke my head back then - and I was always up for more being better... In the end the clever people at G-Force in the US sorted the business but I missed the boat. (and some beautiful bespoke Cosworth pistons - link > https://mngforce.typepad.com/nc450vdev/ ... stons.html
IMPERATOR REX ANGLORUM

johnny comelately
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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CMSMJ1 wrote:
Wed Nov 23, 2022 10:14 pm
johnny comelately wrote:
Wed Nov 23, 2022 5:41 am
The status quo seems to be the use of Crank Angle for various particular engine analysis characteristics.
This fails in comaparative applications because it does not take into consideration the Bore Stroke ratios nor the Rod ratios and their effect on the very parameters that are being measured.
Before someone jumps in and says that some of those measurements are independent it would be prudent to see that a normalised factor that reflects all three parameters as a single encompassing new paradigm would be more indicative.
Not being particularly mathematical, any suggestions as to how this could be achieved?
The starting point would be the conversion of the stroke to a percentage.
Methinks this has been touched on before but I could not find it.
I think I understand what it is that you are wanting to do - but for the hard of thinknig (me) can we have some pretty pictures to really drive it home?

My only experience has been with looking at a stroked NC30 engine for my old race bike. This involved various options relating to a +.5mm over bore, or a 'stroker' rod or both.

it broke my head back then - and I was always up for more being better... In the end the clever people at G-Force in the US sorted the business but I missed the boat. (and some beautiful bespoke Cosworth pistons - link > https://mngforce.typepad.com/nc450vdev/ ... stons.html
Will do, but I have to do some work now.

It is also breaking my head as I have two deficits, one with maths and the other with complex logics.
The solution for your bike was to offset the bores towards the thrust side, something that was successful for me on one of #87's early CB900 based superbikes. Yes I am from the last century, the last millenia in fact :wink:
Last edited by johnny comelately on Thu Nov 24, 2022 1:28 am, edited 1 time in total.

Greg Locock
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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Here's a plot. A Scotch yoke has an infinite L/r, I don't know what the other one was, probably 3 or so.

https://en.wikipedia.org/wiki/Scotch_yoke

johnny comelately
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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To illustrate the challenge using a standard 266 point 6 cc cylinder.

The difference between an 80mm bore by 53mm stroke
and a 50mm bore by 135.6 stroke
Both at 20 degrees CA
The rod length was 116 mm for both (rightly or wrongly)

Produced piston heights of 2 point 234 and 6 point 43 respectively.
This translates into the different volumes of 11 point 229 cc and 12 point 625 cc respectively.
Image
So the solution is to use a function of CA modified to account for the B/S ratio and maybe the rod ratio or length.
Most research papers get around it by stating the engine config but that reduces the comparability.
When deconstructing BMEP finding the peak, which might be anywhere between say 8 degrees and 27 degrees, and the gradients.
It becomes more critical when looking at burn properties.

Hoffman900
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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johnny comelately wrote:
Thu Nov 24, 2022 11:18 pm
To illustrate the challenge using a standard 266 point 6 cc cylinder.

The difference between an 80mm bore by 53mm stroke
and a 50mm bore by 135.6 stroke
Both at 20 degrees CA
The rod length was 116 mm for both (rightly or wrongly)

Produced piston heights of 2 point 234 and 6 point 43 respectively.
This translates into the different volumes of 11 point 229 cc and 12 point 625 cc respectively.
https://images-wixmp-ed30a86b8c4ca88777 ... 4P86mdAQdU
So the solution is to use a function of CA modified to account for the B/S ratio and maybe the rod ratio or length.
Most research papers get around it by stating the engine config but that reduces the comparability.
When deconstructing BMEP finding the peak, which might be anywhere between say 8 degrees and 27 degrees, and the gradients.
It becomes more critical when looking at burn properties.
This ignores reality that there are no designs built to those extrems.

You are worried about the following when designing an engine:

Deck height: Going to dictate the physical dimensions / size of the engine / port alignment. With size there is an aero component.

Bore size: bigger bore for bigger valves for naturally aspirated engines. On boost unlimited engines, you go smaller as it is a more efficient chamber, tumble or swirl are easier to manage, and so is combustion. Bore size / combustion is going to dictate rpm ultimately. Either through valve area or by out running the combustion. There is also a size of the engine consideration as well. Bigger bore = longer engine.

Stroke: Manages piston speed and displacement and is a function of deck height.

Rod Length: Is what it is. You run the longest that can fit. Small changes in pin height don't change the peak that much. On a Chevrolet R07 changing rod length was worth 2hp on a 850bhp engine. It's negligible.

johnny comelately
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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Hoffman900 wrote:
Fri Nov 25, 2022 9:22 pm
johnny comelately wrote:
Thu Nov 24, 2022 11:18 pm
To illustrate the challenge using a standard 266 point 6 cc cylinder.

The difference between an 80mm bore by 53mm stroke
and a 50mm bore by 135.6 stroke
Both at 20 degrees CA
The rod length was 116 mm for both (rightly or wrongly)

Produced piston heights of 2 point 234 and 6 point 43 respectively.
This translates into the different volumes of 11 point 229 cc and 12 point 625 cc respectively.
https://images-wixmp-ed30a86b8c4ca88777 ... 4P86mdAQdU
So the solution is to use a function of CA modified to account for the B/S ratio and maybe the rod ratio or length.
Most research papers get around it by stating the engine config but that reduces the comparability.
When deconstructing BMEP finding the peak, which might be anywhere between say 8 degrees and 27 degrees, and the gradients.
It becomes more critical when looking at burn properties.
This ignores reality that there are no designs built to those extrems.

You are worried about the following when designing an engine:

Deck height: Going to dictate the physical dimensions / size of the engine / port alignment. With size there is an aero component.

Bore size: bigger bore for bigger valves for naturally aspirated engines. On boost unlimited engines, you go smaller as it is a more efficient chamber, tumble or swirl are easier to manage, and so is combustion. Bore size / combustion is going to dictate rpm ultimately. Either through valve area or by out running the combustion. There is also a size of the engine consideration as well. Bigger bore = longer engine.

Stroke: Manages piston speed and displacement and is a function of deck height.

Rod Length: Is what it is. You run the longest that can fit. Small changes in pin height don't change the peak that much. On a Chevrolet R07 changing rod length was worth 2hp on a 850bhp engine. It's negligible.
We are on two different paths here Hoff.
I understand what you are saying and it is right.
But my point is in the topic title. A different matter.
I will post some images later which may explain things better.

Hoffman900
Hoffman900
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Re: The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

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johnny comelately wrote:
Fri Nov 25, 2022 9:45 pm
Hoffman900 wrote:
Fri Nov 25, 2022 9:22 pm
johnny comelately wrote:
Thu Nov 24, 2022 11:18 pm
To illustrate the challenge using a standard 266 point 6 cc cylinder.

The difference between an 80mm bore by 53mm stroke
and a 50mm bore by 135.6 stroke
Both at 20 degrees CA
The rod length was 116 mm for both (rightly or wrongly)

Produced piston heights of 2 point 234 and 6 point 43 respectively.
This translates into the different volumes of 11 point 229 cc and 12 point 625 cc respectively.
https://images-wixmp-ed30a86b8c4ca88777 ... 4P86mdAQdU
So the solution is to use a function of CA modified to account for the B/S ratio and maybe the rod ratio or length.
Most research papers get around it by stating the engine config but that reduces the comparability.
When deconstructing BMEP finding the peak, which might be anywhere between say 8 degrees and 27 degrees, and the gradients.
It becomes more critical when looking at burn properties.
This ignores reality that there are no designs built to those extrems.

You are worried about the following when designing an engine:

Deck height: Going to dictate the physical dimensions / size of the engine / port alignment. With size there is an aero component.

Bore size: bigger bore for bigger valves for naturally aspirated engines. On boost unlimited engines, you go smaller as it is a more efficient chamber, tumble or swirl are easier to manage, and so is combustion. Bore size / combustion is going to dictate rpm ultimately. Either through valve area or by out running the combustion. There is also a size of the engine consideration as well. Bigger bore = longer engine.

Stroke: Manages piston speed and displacement and is a function of deck height.

Rod Length: Is what it is. You run the longest that can fit. Small changes in pin height don't change the peak that much. On a Chevrolet R07 changing rod length was worth 2hp on a 850bhp engine. It's negligible.
We are on two different paths here Hoff.
I understand what you are saying and it is right.
But my point is in the topic title. A different matter.
I will post some images later which may explain things better.
Yeah, definitely missing what you are trying to do here.