Advantages of longer rods in Nortons
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Matt Spencer said:
See Phil Irving on this. The crank angle at which maximum piston velocity occurs (thus maximum piston kinetic energy) is around 72-73 degrees. The precise angle is a function of rod to stroke length. Piston kinetic energy is zero (0) at TDC and BDC as there is no velocity.
I have a hunch that maximum flywheel velocity may coincide with maximum piston speed during each stroke.
Why do you ask?
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Just Found This . Light Blue is pressure 2 intake Valve , Red is 2 Exhaust valve . Dark Blue is in Cyl. Not particularly clear as less than 720 deg. shown .
http://www.epi-eng.com/piston_engine_te ... nology.htm is specific case , obviously .
What Im wondering is When piston is at its maximum specific energy , so I know when not to stick my finger in it . :wink:
another headache . Viewed from the pollutants point of view , but corrolates burn time etc . http://authors.library.caltech.edu/2506 ... 88-Ch4.pdf
http://www.epi-eng.com/piston_engine_te ... nology.htm is specific case , obviously .
What Im wondering is When piston is at its maximum specific energy , so I know when not to stick my finger in it . :wink:
another headache . Viewed from the pollutants point of view , but corrolates burn time etc . http://authors.library.caltech.edu/2506 ... 88-Ch4.pdf
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Oh! Maximum specific energy. Why didn't you say so. :roll:
jseng1 said:
Dan does have a shortrodded Vincent.
Standard Vincent rod ratio is 2.1, Dan reduced that to approximately the same as the DBD Gold star at 1.86 .
Here is a bit from Roland Pike on the rod ratios of Goldstars as they developed. As he mentions, as the motor was developed for more power, the rod ratio got shorter, other than the one off ultrashort stroke race motor which was a different kettle of fish due to very high rpm.
Roland Pike, BSA experimental division- The length of the connecting rod in relation to piston stroke has an important bearing on performance. For many years a ratio of stroke to -con rod length of 2: 1 was thought to be a good compromise. Some exhaustive testing along these lines was done and we found that for the standard 88 mm stroke 1.86:1 seemed best all round ratio. However, when it came to ultra short stroke engines a ratio of 2.2:1 became desirable to reduce piston acceleration at around TDC.
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A lot depends on what gearbox you have behind the motor. Long rods are OK if you have cams which require a lot of revs to give power, in a short stroke motor- provided you have enough close ratio gears to play the motor around a race circuit without bombing out at any point. Many 60s racers had 8 gears, the Suzuki miniature two strokes had a lot more to keep them within the power band. My 500cc Triumph was fantastic with the long rods, however the gearbox always let it down. You could choose where you wanted to lose a race by gearing it high or low. On a big circuit with very high gearing, it was scary - would lead you into real braking problems.
With a commando engine you don't really go top end, it is more a matter or torque characteristics.
About 'maximum kinetic energy' - maximum velocity is somewhere near mid stroke and depends a bit on cam timing. You get thrust until a bit after the exhaust valve opens, and the rest is noise. fast motors are not usually very loud compared with others.
With a commando engine you don't really go top end, it is more a matter or torque characteristics.
About 'maximum kinetic energy' - maximum velocity is somewhere near mid stroke and depends a bit on cam timing. You get thrust until a bit after the exhaust valve opens, and the rest is noise. fast motors are not usually very loud compared with others.
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acotrel said:
Maximum piston velocity has nothing whatsoever to do with cam timing.
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If the exhaust valve opens before 90 deg. BBDC, you often lose power and make more noise. The thrust on the piston finishes before mid stroke. So the potential max velocity is not reached. If you are talking about simply spinning the engine without firing it, max velocity of the piston probably occurs earlier than mid stroke. The calculation is easy , I'm just too lazy to do it. Similar to calculating port height from crankshaft rotation on a two stroke. I'll be home tomorrow, and I'll see if I can run BasicA and do the calculation. What is the rod length in the standard commando engine ?
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You are mixing up all sorts of dimensions here. You are talking force and power when Matt Spencer asked about Energy (kinetic).
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The real hot rods open exhaust early to take advantage of the heat-pressure energy to evacuate the chamber faster than pure piston pumping out drag so inlet can open earlier to pack more mix in. By far most the 4 stroke engine power is made 15-ish to 80-ish degrees ATDC. On the other hand the long-ish stroke garden tractor puller guys run 112 octane and hurt their ears grinning telling ya about the torque of burning fuel all the way to BDC.
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What I was after is where its at its maximum inetia , but its NOT inertia entirely . The KINETIC came in due to Brain Fade at 1:30 A.M. here . 
As the Combustion is a controled explosion , rather than instantaeneous ' explosion ' of the entire charge in the chamber - see ' Burn Rate ' , The Combustion starts about T.D.C. ,
and extends for ' X ' nanoseconds , or suchlike .
Not Entirely disimilar to a Steam train , which would exert a Continuous Rate of Pressure on the Piston Crown . / The CONTINUED Combustion of the Charge through some portion of the Stoke ,
sees a pressure applied to the Piston Crown , as the mixture ignites , then ' burns ' . Presumeably :wink: at the exhaustion of the favourable ratio ( 16:1 odd / Contamination of combustability )
the things achieved its optimum speed / inertia ( mechanically ) . Thus ' the end of the power pulse ; Thereafter its coasting , etc .
SO the contiuos exerted force through a portion of the stroke is accelerateing the piston . Assumeing the Combustion Pressure to be the maximum force , there must be some point at which it peaks ,
or some portion between tdc & bdc where its achieved maximum effort .
ASIDE from that , and further to that , the evacuation IF combustion is achieved IN the Exhaust can induce further negative pressure / vacum , enhanceing the scavengeing and thus Neg. pressure in the Chamber ( cylinder )
this combined with the induction pulse , which is greater therefore also , etc . Hence Setwrights term ' Thermo etc ( something that slips the mind at the moment ) ENGINE . As in the pressure temperature density Engine .
The mechanical pieces constructing & containing ( we hope :lol: ) this . But being secondary to this thermodynamic action , though constructing and trasmitting it .
Therefore that pistons going like stink , at a certain part of the cycle .
Digessing Further , a closed chamber crankcase the compression of the crankcase atmosphere cushions the piston descent at its lower extreme . Though this would be less so with a well ventilated crankcase . THEREFORE ' we '
would not expect exactly similar ' figures ' in these two differant cases .
8) :x :lol: .
vauge approximation might be the old large wooden mallet ( = combustion ) & the thingo that rings the bell ( = piston ) at the Circus . Though theres a few other bits in there too .
something vaugely relevant . http://www.youtube.com/watch?v=WuCUGcqO5SE
As the Combustion is a controled explosion , rather than instantaeneous ' explosion ' of the entire charge in the chamber - see ' Burn Rate ' , The Combustion starts about T.D.C. ,
and extends for ' X ' nanoseconds , or suchlike .
Not Entirely disimilar to a Steam train , which would exert a Continuous Rate of Pressure on the Piston Crown . / The CONTINUED Combustion of the Charge through some portion of the Stoke ,
sees a pressure applied to the Piston Crown , as the mixture ignites , then ' burns ' . Presumeably :wink: at the exhaustion of the favourable ratio ( 16:1 odd / Contamination of combustability )
the things achieved its optimum speed / inertia ( mechanically ) . Thus ' the end of the power pulse ; Thereafter its coasting , etc .
SO the contiuos exerted force through a portion of the stroke is accelerateing the piston . Assumeing the Combustion Pressure to be the maximum force , there must be some point at which it peaks ,
or some portion between tdc & bdc where its achieved maximum effort .
ASIDE from that , and further to that , the evacuation IF combustion is achieved IN the Exhaust can induce further negative pressure / vacum , enhanceing the scavengeing and thus Neg. pressure in the Chamber ( cylinder )
this combined with the induction pulse , which is greater therefore also , etc . Hence Setwrights term ' Thermo etc ( something that slips the mind at the moment ) ENGINE . As in the pressure temperature density Engine .
The mechanical pieces constructing & containing ( we hope :lol: ) this . But being secondary to this thermodynamic action , though constructing and trasmitting it .
Therefore that pistons going like stink , at a certain part of the cycle .
Digessing Further , a closed chamber crankcase the compression of the crankcase atmosphere cushions the piston descent at its lower extreme . Though this would be less so with a well ventilated crankcase . THEREFORE ' we '
would not expect exactly similar ' figures ' in these two differant cases .
8) :x :lol: .vauge approximation might be the old large wooden mallet ( = combustion ) & the thingo that rings the bell ( = piston ) at the Circus . Though theres a few other bits in there too .
something vaugely relevant . http://www.youtube.com/watch?v=WuCUGcqO5SE
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Steam piston engines only induce pressure ATDC while spark engines begins compression towards TDC and spark starts pressure rise a couple to 3 dozen degree's BTDC so pressure rising fast by TDC, which can get so dense its in a viscous liquid phase not gaseous so energizing Nitrogen gives most effective heat expansion into piston kinetic thrust to occurs about 15' ATDC. When we diddle spark time for maximum torque its basically to get max pressure about 15" ATDC, depending on CR, octane, temperature, humidity, carbon deposits, rpm and phase of our moon periods. Jim Comnoz long suffering touring engine got a bit on the wrong side of this splashing together. One thing that limits diesel engines rpm is they can not or should not combust-detonate before TDC so can't get a head start on maxing out pressure by 15' ATDC. VarrRRROOOM can lead to BLATTT! can lead to BANg.
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Matt Spencer said:What I was after is where its at its maximum inetia , but its NOT inertia entirely . The KINETIC came in due to Brain Fade at 1:30 A.M. here .
As the Combustion is a controled explosion , rather than instantaeneous ' explosion ' of the entire charge in the chamber - see ' Burn Rate ' , The Combustion starts about T.D.C. ,
and extends for ' X ' nanoseconds , or suchlike .
Not Entirely disimilar to a Steam train , which would exert a Continuous Rate of Pressure on the Piston Crown . / The CONTINUED Combustion of the Charge through some portion of the Stoke ,
sees a pressure applied to the Piston Crown , as the mixture ignites , then ' burns ' . Presumeably :wink: at the exhaustion of the favourable ratio ( 16:1 odd / Contamination of combustability )
the things achieved its optimum speed / inertia ( mechanically ) . Thus ' the end of the power pulse ; Thereafter its coasting , etc .
SO the contiuos exerted force through a portion of the stroke is accelerateing the piston . Assumeing the Combustion Pressure to be the maximum force , there must be some point at which it peaks ,
or some portion between tdc & bdc where its achieved maximum effort .
ASIDE from that , and further to that , the evacuation IF combustion is achieved IN the Exhaust can induce further negative pressure / vacum , enhanceing the scavengeing and thus Neg. pressure in the Chamber ( cylinder )
this combined with the induction pulse , which is greater therefore also , etc . Hence Setwrights term ' Thermo etc ( something that slips the mind at the moment ) ENGINE . As in the pressure temperature density Engine .
The mechanical pieces constructing & containing ( we hope :lol: ) this . But being secondary to this thermodynamic action , though constructing and trasmitting it .
Therefore that pistons going like stink , at a certain part of the cycle .
Digessing Further , a closed chamber crankcase the compression of the crankcase atmosphere cushions the piston descent at its lower extreme . Though this would be less so with a well ventilated crankcase . THEREFORE ' we '
would not expect exactly similar ' figures ' in these two differant cases .
vauge approximation might be the old large wooden mallet ( = combustion ) & the thingo that rings the bell ( = piston ) at the Circus . Though theres a few other bits in there too .
something vaugely relevant . http://www.youtube.com/watch?v=WuCUGcqO5SE
Ah, I see. So I can say with the least bit of uncertainty that the answer to your initial question (within the context of your brain fade) is "it depends". Someone on this thread offered to see if they could do the calculations for you. :lol:
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A infinate no of monkeys with a infinate no of typewriters would eventually come up with the complete works of Shakespear . :wink: so we're told . :?
A Kind thought Indeed , must be possable to establish some sort of parameters or trends , my thoughts my bikes were so fast as the combustion continued through the power stroke ! . :shock: :wink:
If the sucker was entirely instantaeneous , and it fired at 30 B T D C it would have to be Italian . Four reverse gears . :?
Tripped over this Today ; QUOTE .
" Vic Willoughby fills the tank of his 1960 Norton 99 Deluxe .
During the Thirties , three brands of petrol had the sporting market between them :
Pratts' Ethyl with added tetra ethyl lead ,
Cleavland Discol useing Ethanol , and
National Benzol with perhaps 15 % benzol .
In each case , the aditive was used to raise the Octane Rateing significantly .
By Product of the Gas Industry , benzole came into use as a substitute for petrol during and after WW1 , and from 1926 to 1939 was the only ' dope ' allowed to racers at the Isle of Man TT . Up to 50 % was permitted as a mixture with Number One petrol . "
unquote . ! some development was done Via rolls royce on octane & anti detonation for R R Merlins in service with the VVVS ( damn commies )
and the pre war Macchi Mc 72 dual inline engined supercharged world speed record holder pre war .
The nasty germans were stuck with 86 octane ( like the Commies ) where the poms ran 130/150 in tuned Griffon Spitfires intercepting the nasty doodlebugs ,
around 1944 . Yankee 130/150 of corse .
5 star pump gas , a true 100 + R.O.N. Octane , with Chryslers running as much as 12.5:1 C.R. along with the odd Ford , Early 70s fuel crisis
put paid to such decadance and ended that era of the ' Muscle Car ' . Noteably our nasty Nortons were of said Era . Particularly the Renowned COMBAT .
Just watch what juice you put in her .
A Kind thought Indeed , must be possable to establish some sort of parameters or trends , my thoughts my bikes were so fast as the combustion continued through the power stroke ! .
:shock: :wink: If the sucker was entirely instantaeneous , and it fired at 30 B T D C it would have to be Italian . Four reverse gears . :?
Tripped over this Today ; QUOTE .
" Vic Willoughby fills the tank of his 1960 Norton 99 Deluxe .
During the Thirties , three brands of petrol had the sporting market between them :
Pratts' Ethyl with added tetra ethyl lead ,
Cleavland Discol useing Ethanol , and
National Benzol with perhaps 15 % benzol .
In each case , the aditive was used to raise the Octane Rateing significantly .
By Product of the Gas Industry , benzole came into use as a substitute for petrol during and after WW1 , and from 1926 to 1939 was the only ' dope ' allowed to racers at the Isle of Man TT . Up to 50 % was permitted as a mixture with Number One petrol . "
unquote . ! some development was done Via rolls royce on octane & anti detonation for R R Merlins in service with the VVVS ( damn commies )
and the pre war Macchi Mc 72 dual inline engined supercharged world speed record holder pre war .
The nasty germans were stuck with 86 octane ( like the Commies ) where the poms ran 130/150 in tuned Griffon Spitfires intercepting the nasty doodlebugs ,
around 1944 . Yankee 130/150 of corse .
5 star pump gas , a true 100 + R.O.N. Octane , with Chryslers running as much as 12.5:1 C.R. along with the odd Ford , Early 70s fuel crisis
put paid to such decadance and ended that era of the ' Muscle Car ' . Noteably our nasty Nortons were of said Era . Particularly the Renowned COMBAT .
Just watch what juice you put in her .
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PS I will be running a 84 stroke @ 7500 . will endevour to re find :x the rod Length . Thanks .
145mm or 5.708in
Quote " With the assistance of Rod Banks " this is the Chap , apparently wrote a paper on detonation & suchlike .
foremost expert scientist on high performance fuels , back then .
The Point , though it may not be obvious , is we get back to the RODS , presumeably when at a tangent to the crank throw ,
theyre at there maximum mechanical advantage .
now if this were to occur symultaeneously with the maximum combustion pressure , we'd all go like T. C. :?
Thanks . 145mm or 5.708in
Quote " With the assistance of Rod Banks " this is the Chap , apparently wrote a paper on detonation & suchlike .
foremost expert scientist on high performance fuels , back then .
The Point , though it may not be obvious , is we get back to the RODS , presumeably when at a tangent to the crank throw ,
theyre at there maximum mechanical advantage .
now if this were to occur symultaeneously with the maximum combustion pressure , we'd all go like T. C. :?
There was some question/discussion above about where piston velocity maximizes in the Norton rotation cycle as well as some queries about piston inertia (which I didn't really understand anyway). The plot below provides both piston velocity and acceleration for an 850 CDO at 7000 rpm. If one wants to know something about the inertial force of the piston, it is simply the product of acceleration and piston mass. Bear in mind that an inertial force calculation of this nature is for a motored engine (operated with no combustion/compression event), thus excludes any forces other than those provided by the connecting rod driving the piston. Including those other forces is beyond anything I know how to do.
To the fact checkers in the crowd, please look over the math to assure I didn't have a short circuit, but seem to recall that "Dances" provided some calc in the past few months (forces on connected rods?) where he came up with acceleration numbers in the same general ballpark.
To the fact checkers in the crowd, please look over the math to assure I didn't have a short circuit, but seem to recall that "Dances" provided some calc in the past few months (forces on connected rods?) where he came up with acceleration numbers in the same general ballpark.
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worntorn said:
Note the rod specs quoted above and compared to the JS long rod below.
"Standard Vincent rod ratio is 2.1, Dan reduced that to approximately the same as the DBD Gold star at 1.86 ."
"we found that for the standard 88 mm stroke 1.86:1 seemed best all round ratio [BSA Goldsar]. However, when it came to ultra short stroke engines a ratio of 2.2:1 became desirable to reduce piston acceleration at around TDC"
Note that the 6.4" JS long rod ratio of 1.83 to 1 for Commando 89mm stroke nearly matches the figures above and the JS 6.57" long rod for shortstroke (80.4mm) comes out to a 2.1 to 1 rod ratio which nearly matches the short stroke ratio mentioned above.
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Matt Spencer touches on an important factor which is rod angularity versus cylinder pressure. The relatively short rod to stroke ratio is one element that helps the Commando engine in giving that extra grunt.
The Commando big twin is what I like to call a very angry motor due to the relatively high max mean piston speed and the relatively short rod to stroke ratio.
Rather than thinking about the rod angle and cylinder pressure (force on piston) as one point you need to look at the series of rod angles and corresponding cylinder pressures (forces on piston) to get a snap shot of work done (force X distance) throughout the power stroke. How fast you perform the work (piston speed or rotational speed) is power. Taking it one step further, one would need to step through the rpm range and do this set of calculations (or measurements) many times as cylinder filling varies with speed. This would ultimately render a torque curve and with engine speed you can calculate horsepower.........................
Or, you could put it on a dyno. Good stuff.
The Commando big twin is what I like to call a very angry motor due to the relatively high max mean piston speed and the relatively short rod to stroke ratio.
Rather than thinking about the rod angle and cylinder pressure (force on piston) as one point you need to look at the series of rod angles and corresponding cylinder pressures (forces on piston) to get a snap shot of work done (force X distance) throughout the power stroke. How fast you perform the work (piston speed or rotational speed) is power. Taking it one step further, one would need to step through the rpm range and do this set of calculations (or measurements) many times as cylinder filling varies with speed. This would ultimately render a torque curve and with engine speed you can calculate horsepower.........................
Or, you could put it on a dyno. Good stuff.
Jim, just to avoid confusion, note that your earlier information for BSA Goldstar ratios etc. is incorrect, the lower number is 1.86 for DB on bikes, not 1.99.
"When you're talking about BSA 500 Goldstars your talking about a very long rod - 7-3/8" (187mm) or 6-7/8" (175mm) depending on year. With a stroke of 88m that gives you a rod stroke ratio of about 2.1 to 1 or 1.99 to 1 depending on year. Thats a lot longer than the 1.86 to 1 JS rod stroke ratio with the 6.4" long rods. So if your friend Dan Smith is copying a Goldstar on this Vincent then he does not have a short rod motor but a (very) long rod motor. By comparison, a Commando with JS long rods would be a short rod motor."
By comparison, a Commando with JS long rods is the exactly the same as the modified Vincent, 1.86. The Vincent is shortrodded, the Commando long rodded, both end up at the same ratio as the DB on Goldstars.
"When you're talking about BSA 500 Goldstars your talking about a very long rod - 7-3/8" (187mm) or 6-7/8" (175mm) depending on year. With a stroke of 88m that gives you a rod stroke ratio of about 2.1 to 1 or 1.99 to 1 depending on year. Thats a lot longer than the 1.86 to 1 JS rod stroke ratio with the 6.4" long rods. So if your friend Dan Smith is copying a Goldstar on this Vincent then he does not have a short rod motor but a (very) long rod motor. By comparison, a Commando with JS long rods would be a short rod motor."
By comparison, a Commando with JS long rods is the exactly the same as the modified Vincent, 1.86. The Vincent is shortrodded, the Commando long rodded, both end up at the same ratio as the DB on Goldstars.
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I did my search on the web and that's the best info I could find at the time -those Goldstar specs probably refereed to earlier models because they were changing rod lengths. In either case - The correct specs are in my last post and are repeated below.
"Standard Vincent rod ratio is 2.1, Dan reduced that to approximately the same as the DBD Gold star at 1.86 ."
"we found that for the standard 88 mm stroke 1.86:1 seemed best all round ratio [BSA Goldsar]. However, when it came to ultra short stroke engines a ratio of 2.2:1 became desirable to reduce piston acceleration at around TDC"
Note that the 6.4" JS long rod ratio of 1.86 to 1 for Commando 89mm stroke matches the figures above and the JS 6.57" long rod for shortstroke (80.4mm) comes out to a 2.1 to 1 rod ratio which nearly matches the short stroke ratio mentioned above.
Also - in response to earlier posts:
The long rods have not made any difference in low end grunt that I can tell and of the many Norton owners who are using the longer rods - no one has reported a change in low end torque. You can still use the Norton with long rods to pull a plow through a field and leave your tractor in the barn.
"Standard Vincent rod ratio is 2.1, Dan reduced that to approximately the same as the DBD Gold star at 1.86 ."
"we found that for the standard 88 mm stroke 1.86:1 seemed best all round ratio [BSA Goldsar]. However, when it came to ultra short stroke engines a ratio of 2.2:1 became desirable to reduce piston acceleration at around TDC"
Note that the 6.4" JS long rod ratio of 1.86 to 1 for Commando 89mm stroke matches the figures above and the JS 6.57" long rod for shortstroke (80.4mm) comes out to a 2.1 to 1 rod ratio which nearly matches the short stroke ratio mentioned above.
Also - in response to earlier posts:
The long rods have not made any difference in low end grunt that I can tell and of the many Norton owners who are using the longer rods - no one has reported a change in low end torque. You can still use the Norton with long rods to pull a plow through a field and leave your tractor in the barn.
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