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Effective C:R #773587
05/13/19 6:15 pm
05/13/19 6:15 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Posts: 2,965
Comox BC Canada
To all the tuning experts out there I am asking what influence does valve profile and timing have on the effective compression ratio. Given that the theoretical C:R calculation is of a piston moving up a "closed" cylinder to squeeze the mixture into a combustion chamber, what happens to the C:R when you change the cams? For example on most engines as the piston starts up on the compression stroke the inlet valve is still open and the air/fuel mixture is still pouring in. The piston is not going up a "closed " cylinder of static air/fuel.

With the GS 2442 inlet cam the valve is open until the crankpin is 85 degrees past BDC. What is the end result of the mixture filling the cylinder as the piston compresses it? I would imagine that if the valve stayed open much longer the rising piston would start to push the mixture back out. Does the effective C:R change with the RPM?

Any ideas?

Gordo


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Re: Effective C:R [Re: Gordo in Comox] #773619
05/13/19 10:29 pm
05/13/19 10:29 pm
Joined: Aug 2010
Posts: 329
New Hampshire, USA
David Dunfey Offline
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New Hampshire, USA
Gordo,

It makes perfect sense, but it does not change with the RPMs. The "advertised" CR is what is on the box, say 9:1. But, that is measured with the intake closed for the entire travel of the piston. The intake valve may stay open for many degrees of piston movement after BDC. So, as long as the engine is rotating, the "dynamic" CR will usually be much less. There are dynamic CR calculators on line and a good one is at the Wallace Racing site:

http://www.wallaceracing.com/dynamic-cr.php

You need to know your bore, stroke and rod length. Put "0" in for boost. My engine has a stroke of 3.54", but the effective stroke is 2.46" because that is where the valve closes. The dynamic CR is important to check to see what fuel you can run. Premium pump gas may support up to 9.1:1 dynamic CR. When you see a bike manufacturer saying that the CR is 10:1 you know that if it is running on premium pump gas the dynamic CR has to be 9.1:1 or less. This is all done by the cam design and piston design.

The problem you talk about, keeping as much CR as you can that will work with all your other parts, is important. Dyno tuning is the only way to find out what is working best. However, what you are talking about also applies to ignition timing. The more advanced your ignition, the earlier you are setting off the charge. If you set the charge off early then the piston is not at or near TDC. If this happens, then the piston has not hit maximum compression and the combustion slows the piston before it hits max compression. This is why you want to adjust your timing for maximum retard at best torque. Thus, your cam and your ignition timing are really in control of your CR.

David

Re: Effective C:R [Re: Gordo in Comox] #773626
05/14/19 12:01 am
05/14/19 12:01 am
Joined: Nov 2011
Posts: 5,239
U.S.
Magnetoman Online content

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Originally Posted by David Dunfey
it does not change with the RPMs....There are dynamic CR calculators on line and a good one is at the Wallace Racing site:
David, I have to disagree. At 600 rpm the piston slowly descends so the air only acquires a low velocity. Because of this, air goes in on the downward stroke and some of it comes back out again until the valve finally closes on the upward stroke (e.g. 72-deg. ABDC for the 65-2446), leaving less to be compressed. However, at 6000 rpm everything happens 10x faster so the air develops a lot of momentum. Even after the piston has reached BDC that momentum continues to carry air in so more of it is trapped in the cylinder when the valve closes, so the pressure it reaches when compressed is higher, i.e. it has a higher effective CR at high rpm than at low rpm because of the dynamic effect of the moving air mass.

Valve overlap adds more complexity. When the intake valve first opens the exhaust valve is still open so some of the mixture goes straight out the exhaust pipe. However, on resonance at high rpm a positive pressure pulse from the exhaust outlet reaches the exhaust port and keeps some of that mixture inside the cylinder, thus increasing the amount that eventually gets compressed. This is an additional effect that gives a higher effective CR at high rpm than at low rpm.

There's even a third rpm-dependent effect that might not be negligible. When air is compressed it heats up, increasing the pressure even further than it would from a simple CR calculation. If it is compressed slowly there is time for some of that heat to be conducted away so the additional pressure rise due to the temperature is less. This effect would be smallest at low rpm, where heat has more time to escape, and highest at high rpm, where it doesn't, again increasing the effective CR at high rpm

Although that link you provided is to something labeled a "dynamic compression ratio calculator," it isn't. In fact, it only is partially valid for the low rpm situation where air momentum is small and geometry is all that matters. Even then the calculator assumes an on/off behavior for the valve closing, which even at low rpm is an oversimplification.

Gordo, what is behind your question? It wouldn't be all that hard to actually measure the dynamic CR vs. rpm. Ideally, you'd want this information for a twin-cylinder Gold Star, since in that case one cylinder could drive the engine while the other cylinder would be blanked off with a fast-responding pressure gauge.

Re: Effective C:R [Re: Gordo in Comox] #773651
05/14/19 3:44 am
05/14/19 3:44 am
Joined: Feb 2012
Posts: 1,322
Middle East,
Kerry W Online content
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Kerry W  Online Content
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Posts: 1,322
Middle East,
Like MM said.

Simplistically, adding GS cams to a B31 will make a change and seem like there's more power (this can be an illusion, based only on the power characteristics!), though practically, the compression reduces with the increased valve timing. This is one reason why even the old (period) books say that a change in compassion ration is needed to achieve the full effect i.e. to pick up the compression lost with the valve timing.

The exhaust resonance is also a big factor, depending on the exhaust timing - the 'stuffing' of the cylinder with hot exhaust gases has positive and negative effects. That trendy exhaust pipe wrapping can keep the top end of the p[ipe so hot that the hot gases being pumped back into the cylinder can be pushed into detonation...one reason why it's very rare to see wrapping of pipes on high performance two strokes, which live and die on the exhaust pipe effects.


No generalisation is wholly true, not even this one.
Oliver Wendell Holmes
Re: Effective C:R [Re: Gordo in Comox] #773695
05/14/19 3:23 pm
05/14/19 3:23 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Comox BC Canada
Thanks all for the inputs and differing opinions.

I am looking at this idea to see if it is possible to predict how changes to the basic engine setup will affect the performance/safety and effective C:R of the engine. Around here we can only get 94 octane fuel so that is a limiting factor over which I have no control without going to something other than pump fuel. In fact only one local brand carries 94, the rest are at 92.

I far as I can see the more aggressive cams are designed to get more air/fuel mixture into the cylinder at the right time to produce more power than a set of mild cams but what are the other consequences of making those changes. If one has an engine that runs well and does not suffer any detonation can one change the cams without changing the C:R or change the piston without changing the cams and still have a safe engine? Should one consider changing the piston anytime the cams are changed?

Seeing that this is a GS forum I will use the BSA cam numbers. If your engine had 2448/2450 touring cams what would happen to the effective C:R if a switch to 2442/2446 cams were to be made? The other extreme, though unlikely, would be a change to 2420/2420 trials cams. Would either of these changes benefit from a piston change or even demand such a change to keep the engine operating safely.

It would be nice to have a chart showing some piston/cam starting point then a plotting of how each change in either would affect the effective C:R of the engine.

Gordo


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773703
05/14/19 4:51 pm
05/14/19 4:51 pm
Joined: Nov 2011
Posts: 5,239
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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U.S.
Originally Posted by Gordo in Comox
I am looking at this idea to see if it is possible to predict how changes to the basic engine setup will affect the performance/safety and effective C:R of the engine.

If one has an engine that runs well and does not suffer any detonation can one change the cams without changing the C:R or change the piston without changing the cams and still have a safe engine? Should one consider changing the piston anytime the cams are changed?
Gordo, around 20 years ago I bought a program called Desktop Dyno, input the parameters for my 10:1 Competition engine, and the attached graph shows the results.

The red circles are the data from my engine's actual test at BSA and in yellow is the calculation. As can be seen, up to 6500 rpm the agreement is essentially perfect, with the calculation tailing off by 5% for the final 500 rpm. The version of the program I used was old enough that it no longer would run once Windows XP came out, although they've continued to update it.

I don't have any familiarity with any version later than mine, but I remember that way back when the inputs I was able to make were fairly crude (e.g. "sport" vs. "touring" cams, etc.). But, despite that, the simulation program did remarkably well. Modern versions, such as Engine Analyzer by Performance Trends, allow you to enter the actual cam profile (and many other parameters) and they claim to predict when knock will set in. So, it seems the answer to your question is, yes, it appears it is possible to simulate the effect of changes with some fair degree of accuracy.

Attached Files DesktopDyno.jpg
Re: Effective C:R [Re: Gordo in Comox] #773709
05/14/19 5:45 pm
05/14/19 5:45 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Gordo in Comox  Offline OP
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Comox BC Canada
Thanks MM. Nice graph. That Engine Analyzer link is very interesting but I think one of their programs is way more than I need.

I was hoping that someone had some first hand experience with the GS engine from making some of the possible changes. Some basic proven rules of thumb would give me things to expect or to watch out for. Maybe changes have no real impact on some of the issues I would be concerned about.

What is the experience out there? Does the risk of detonation increase or decrease with changes? Should the ignition timing be changed with a different set up? How does the power band change? If the expected normal max cruising RPM is say 4000 (for example only), which cams and piston should be used?

Gordo


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773721
05/14/19 7:40 pm
05/14/19 7:40 pm
Joined: Nov 2011
Posts: 5,239
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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Originally Posted by Gordo in Comox
That Engine Analyzer link is very interesting but I think one of their programs is way more than I need.
Does the risk of detonation increase or decrease with changes? Should the ignition timing be changed with a different set up? How does the power band change?
I'll make an offer. If ten people step up with $10 ea. ($100 total) I'll buy 'Engine Analyzer Plus' ($199) and run simulations with trials, road, scrambles and clubmans cams, CR from 7 to 10, octane (R+M/2) from 89 to 94 plus aviation, and whatever else seems reasonable. I'll post the plots of h.p., suggested timing, onset of knock, and whatever else seems reasonable. For those who buy into this offer I'll run a couple of special simulations each if requested, should the program have relevant parameters I can change (e.g. smaller carburetor, worse-flowing head such as on a ZB, straight-through pipe such as on a Catalina, etc.).

The premise is that, rather than hoping anecdotal results are valid, the simulations should allow anyone building a 500 Gold Star or B33/34 to mix and match cams, pistons and carburetors and have a pretty good idea ahead of time what the final results will be. Including what timing to use to keep the CR from becoming 1:1 with the 89 octane that they insist on using.

I downloaded the 323-page manual but since I've only skimmed it so far I reserve the right to withdraw this offer should I realize it will be way too time consuming. If genuinely interested, PM me to say you are committed to coughing up $10. If I get ten commitments I'll then email each of you my Paypal information. If I don't get ten responses the offer will just die a quiet death. Please, please don't say you are interested and then not follow through later because I don't need the headache of refunding money to those who did pay up.

Re: Effective C:R [Re: Gordo in Comox] #773728
05/14/19 8:26 pm
05/14/19 8:26 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Gordo in Comox  Offline OP
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Posts: 2,965
Comox BC Canada
MM: Great offer! Much better than guessing or relying on unscientific "seat of the pants" data.

Gordo


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773755
05/15/19 2:53 am
05/15/19 2:53 am
Joined: Feb 2012
Posts: 1,322
Middle East,
Kerry W Online content
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Kerry W  Online Content
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Joined: Feb 2012
Posts: 1,322
Middle East,
I don't even have a bike at the moment, but would very much like to see the results...where do I sign-up?


No generalisation is wholly true, not even this one.
Oliver Wendell Holmes
Re: Effective C:R [Re: Gordo in Comox] #773778
05/15/19 10:56 am
05/15/19 10:56 am
Joined: Sep 2010
Posts: 58
Denmark
O
Ole K Offline
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Ole K  Offline
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O

Joined: Sep 2010
Posts: 58
Denmark
Originally Posted by Gordo in Comox

What is the experience out there? Does the risk of detonation increase or decrease with changes? Should the ignition timing be changed with a different set up? How does the power band change? If the expected normal max cruising RPM is say 4000 (for example only), which cams and piston should be used?
Gordo


My setup is standard Clubmans except that I have changed the inlet cam to a scrambler cam.

It gives more torque at 4000-5000 RPM, which is what I wanted as I seldom go higher than 6000 RPM.

Re: Effective C:R [Re: Gordo in Comox] #773786
05/15/19 1:08 pm
05/15/19 1:08 pm
Joined: May 2014
Posts: 51
UK Carnforth
M
Mal Marsden Offline
BritBike Forum member
Mal Marsden  Offline
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M

Joined: May 2014
Posts: 51
UK Carnforth
Gordo
Why not try a different approach to the petrol problem? I needed aviation fuel to run my Aermacchi racer, CR 11:1, but it is more than difficult to buy so I have bought a tetra ethyl lead booster called Tetraboost here in the UK. Using sufficient quantities you can get 105 octane from our four star, supposedly at about 98 octane. It is also meant to combat some of the problems with the alcohol in the petrol and I guess you get that in the States too. Search for tetraboost.com, can’t believe there isn’t something similar over there.

Mal


Daytona Gold Star replica
DBD34/Norton
996 Ducati Boposta
350 MV Augusta
Aermacchi racer
Re: Effective C:R [Re: Gordo in Comox] #773815
05/15/19 5:00 pm
05/15/19 5:00 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Gordo in Comox  Offline OP
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Comox BC Canada
Mal: Here in Canada Chevron has the 94 octane fuel with its own hose and it contains no alcohol. Their lower grades are selected through a common hose and 'may' contain alcohol. Most if not all other brands have alcohol in all their grades.

It would be nice to have actual data for comparison given all of the possible combinations. The BMS GS book has a chart with Touring, Scrambles, Clubman and Racing labels on the DB cams, more labels on the early cams but there is little mix and matching. Without access to a dyno it is hard to quantify any changes with any real accuracy so a reference would be useful in my mind.

As for Magnetoman's offer to buy the program and to run all the various profiles, I hope enough folks (8 more) chip in to make it a go as my son Rick and I are in.

Gordo


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773823
05/15/19 7:10 pm
05/15/19 7:10 pm
Joined: Nov 2011
Posts: 5,239
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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Originally Posted by Gordo in Comox
I hope enough folks (8 more) chip in to make it a go
We're up to 4.[*]

However, I understand the reluctance of people to respond. After all, who would want to squander the equivalent of two Starbuck's Venti Lattes when it only would be multiplied by 20x ($10 = $199), including being matched one-for-one ($100 commitments + $99 of my money). The only thing that the $10 would buy would be to have someone with a technical background spend his time to learn a new program (with a 323-page manual), run it for the large combination of relevant parameters (heads, cams, CRs, exhausts, and octane), and then present the results in a way that would be useful to anyone riding or building a GS or B33/34.

'Engine Analyzer Plus' clearly allows for a lot of options. However, I've written to the company to confirm that it would give the amount of ignition advance to use and onset of knock with current ethanol-containing gasolines for different compression ratios, cams, exhausts and heads. I said I have the specifics of the CR and cams, but would require generic options to enter for exhausts and heads.

Assuming six more people sign on, at some point it would be very useful to have "Gold Star Brake Test" sheets for as many models as possible. I only have this sheet for my 'Competition' with its 10:1 piston. Having the data for a Catalina, ZB, etc. would allow me to "calibrate" the simulation since, lacking flow bench data on any of them, I'll have to use generic inputs for the head and exhaust. Having the actual test data for each known configuration would let me select the right generic inputs for these two parameters. That would make subsequent simulations with different cams, etc. all the more accurate.

So, even if you aren't interested in the $10 offer, please post your engine test sheets (black out the engine number first).

[*]Update: now it's 7; 3 more to go.

Last edited by Magnetoman; 05/17/19 4:40 am. Reason: Update:
Re: Effective C:R [Re: Gordo in Comox] #773831
05/15/19 9:03 pm
05/15/19 9:03 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
BritBike Forum member
Gordo in Comox  Offline OP
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Comox BC Canada
MM: Here is a ZB34GS engine sheet. If it is too small I can email it to you. This is one of the last season of one piece type early heads and it used 2438/2436 cams and 1 5/32" TT carb. Interestingly it had a 8:1 CR putting out about 31 HP. I have several pistons to chose from so any data you come up with will be most helpful with this build.

Gordo

[Linked Image]


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773833
05/15/19 9:11 pm
05/15/19 9:11 pm
Joined: Nov 2016
Posts: 84
NY State
N
NYBSAGUY Offline

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Joined: Nov 2016
Posts: 84
NY State


MMan,

Although I can't believe I'm doing this, since I will never need the information, count me in for your Desktop Dinosaur thingy.


1949 BSA ZB34 'Bitsa'
1959 BSA DBD34 Catalina
1973 Norton Commando 850 R
1974 Norton Commando 850 R (I know, one too many)
1998 Montesa HRC Trials
2004 Ducati M1000ie
Re: Effective C:R [Re: NYBSAGUY] #773840
05/15/19 9:48 pm
05/15/19 9:48 pm
Joined: Nov 2011
Posts: 5,239
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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Originally Posted by Gordo in Comox
one piece type early heads ... 2438/2436 cams and 1 5/32" TT carb. ...8:1 CR
Gordo, that's perfect. I've already printed it and added it to my file of data sheets, doubling the number in the folder. Keep 'em coming.

Along with the 49" straight exhaust on that sheet, it has all the information needed to run an accurate simulation. The unknown in all cases is how much air any of the heads originally flowed, but a data sheet allows picking between the generic options[*] for heads to find the one that reproduces the measured curve. Since there are no other relevant parameters, fitting the curve characterizes the head. From there it is a simple (but time consuming) task of seeing how that head works with other combinations of pistons, cams, exhausts and octanes.

[*]For what it's worth, the generic option for the head in the 20-year old Desktop Dyno simulation I ran on 3/25/1998 that reproduced my Competition's curve was "Wedge/Pocket Porting, Large Valves". I don't remember what the other choices were but this must have been the one that worked best. Anyway, what matters isn't the name a simulation program uses, but that there be generic choices that don't require entering actual flow data. Presumably when I hear back from Performance Trends they'll confirm that this is the case for 'Engine Analyzer Plus'.

Originally Posted by NYBSAGUY
Although I can't believe I'm doing this, since I will never need the information,
Hey, you can't put a price on knowledge. Oh, wait, yes you can. It's $10.

Re: Effective C:R [Re: Gordo in Comox] #773851
05/15/19 11:54 pm
05/15/19 11:54 pm
Joined: Aug 2014
Posts: 423
New Jersey
Keane Lucas Offline

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Keane Lucas  Offline

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Joined: Aug 2014
Posts: 423
New Jersey
Gordo,
you may want to try this
link
Blending guide-link2
I imagine ground shipping to The Great White North,
isn't an issue.
When the AKI-R+M/2-was adopted,Sunoco 260 had
a pump number of 97.5.
It dropped to 96 before it was discontinued.
When 94 was available around here,
it still wasn't quite enough.
My 2c


1969 BSA A65T w/A70 engine
1970 Royal Enfield Interceptor S ll
Re: Effective C:R [Re: Gordo in Comox] #773854
05/16/19 12:54 am
05/16/19 12:54 am
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Gordo in Comox  Offline OP
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Posts: 2,965
Comox BC Canada
Keane: Thanks, that is an interesting product that I will keep in mind. However I am trying to make the best of available fuel. In the 1960s I ran Aviation 115/145 fuel mixed with Castrol R in a Bultaco scrambler but that was only for off road use and easy to manage with a support vehicle. I want to have a strong running engine that is happy with local fuel without having to carry something to boost it.

However I will bookmark that site.

Gordo


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773882
05/16/19 4:11 am
05/16/19 4:11 am
Joined: Oct 2001
Posts: 219
Victoria, B.C. Canada
bsahatch Offline
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MM: Count me in on the 'Engine Analyzer Plus' please.

This DBD followed me home a few months back; me on the left & Uncle Wilf on the right.

[Linked Image]


73' Trackmaster T140
69' Lightning
69' Victor
66' Royal Star - Watsonian
GS DBD
58' Super Rocket
54' Golden Flash
Rickman Zundapp
Re: Effective C:R [Re: Gordo in Comox] #773919
05/16/19 4:05 pm
05/16/19 4:05 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Comox BC Canada
MM: We are getting close to meeting your offer conditions.

I would think that any GS enthusiast would be interested in this kind of info. Given that no other Marque of Brit machine offered such an array of camshaft profiles it would be nice to really know what kind of performance each one represented. From the Bacon BSA singles book I found 17 different camshaft numbers for use in the B pre-unit engines. There could be more. I appreciate that some new numbers were just changes to a slow transition ramp in around 1952 but I do not know of any Marque that offered so many options for changing the characteristics of the engine .

It is really amazing what the BSA boys did long before computer modeling became available.

Gordo


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773926
05/16/19 5:18 pm
05/16/19 5:18 pm
Joined: Nov 2011
Posts: 5,239
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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Originally Posted by Gordo in Comox
I want to have a strong running engine that is happy with local fuel without having to carry something to boost it.
There are two kinds of Gold Star owners: those who stay within a 100-mile round-trip distance of home, and those who don't. Unless someone is better organized than I am (and I'm pretty organized), having to remember to carry octane booster on a trip along with everything else, remembering to add "a little" to the tank when they decide it's prudent to top up prior to a long stretch between towns, more from the now partially-empty booster bottle when they fill the tank, etc. is a headache. I went through this with adding 2-stroke oil to my Ariel on the Cannonball so it's certainly not impossible, just not a lot of fun. It's even more effort if you're responsible for the health of several Gold Stars on a road trip.

Personally, if I were assembling an engine from scratch, I'd rather give up a few h.p. to ensure the engine would be happy with whatever fuel I came across -- now, or several years from now. If I never wandered more than a tankful from my garage, it might be different.

Originally Posted by Gordo in Comox
We are getting close to meeting your offer conditions.
I fear you may be correct. Sigh...

Since it's getting dangerously close to me having to honor my offer, I decided to look into engine simulation software in more detail. The good news is there are a lot of choices (including Engine Analyzer, Desktop Dyno (also versions called DynoSim and DynoMation), Engine Pro, GT-Power and Virtual Engine Dyno, and probably others). The bad news, is, there are a lot of choices.

It seems there are three price points, ~$100, ~$200 and ~$500 for three levels of capabilities. Unfortunately, comparing those capabilities is problematic. The manuals available for download for two of these are 323 and 314 pages, which would be a lot of material to have to read in detail to compare just those two programs. It's quite possible one program could have more capabilities than another but be missing some useful feature that the other has. Further, since there are no downloadable manuals for the other programs, all there is for them are one or two-page descriptions on the web.

OK, given the impracticality of determining the "best" simulation program, back to 'Engine Analyzer Plus' by Performance Trends. I initially thought of them because I've used two generations of their 'Port Flow Analyzer' with my flow bench and have been happy with the software and with their responsiveness in providing me with new software keys when I migrated to new computers every few years. Also, the company has been around since 1986 and their engine software has gone through a number of upgrades since then. Given this, I've now gone through two rounds of questions with their support line and they've satisfactorily answered my questions about the capabilities of 'Engine Analyzer Plus' for present purposes:

--------------------
For any accurate simulation, accurate head flow data is critical. However, there are some generic head and intake and exhaust examples for you to pick from, inside all our Engine Analyzer programs

Predicting changes in burn rate (which determines spark advance) is not something the Plus version deals with in great detail. Still, it WILL give you an estimate of a safe spark curve for different combos of engine parts with different octane fuels.

It is used mostly to predict the different torque and HP curves for these modifications.
-----------------------

Translating the above, the first paragraph answers my question about whether the program has generic head options. It does, so this will let me use BSA's h.p. and torque vs. rpm curves to pick a generic head that reproduces the data, rather than having to input actual flow data on each head.

The second paragraph answers my question about fuels. Basically, it says that while it might estimate, say, 36-deg. for the spark advance for the stock configuration of my Competition (for which BSA says 39-deg.), it might then give a different estimate if I input a different CR. If that new figure were, say, 34-deg., that would indicate less advance would be needed with the new CR. While I couldn't necessarily rely on either value as being accurate, the relative difference would be useful information.

The third paragraph is the reason for doing this in the first place. Once the parameters fit the BSA curves for a given stock configuration, the effect of changing CR, cams, etc. on the engine performance will be determined. Instead of "I think the xx-xxxx inlet cam feels like it has more mid-range power," it will be clear whether or not it actually does.

At this point I'm willing to gamble $100 of my money (and $100 of yours...) that 'Engine Analyzer Plus' will provide the information we're looking for. Now my fingers are crossed that no one else signs up so I won't have to do this...

p.s. should my crossed fingers not work, I'll need more of those Gold Star dyno test results. So far all I would be able to do is an early ZB Scrambler and a late DBD Competition.

Re: Effective C:R [Re: Gordo in Comox] #773928
05/16/19 5:45 pm
05/16/19 5:45 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Gordo in Comox  Offline OP
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Joined: Sep 2001
Posts: 2,965
Comox BC Canada
MM: there are few test sheets in the BMS book. I have another somewhere, I got it from Ian Jackson for a pal but the machine was sold before I gave it to him. I think it is for a 350. We could ask Jon Luke the GSOC Technical Officer for a cross section of samples for you to use. He now holds the sheets.

Gordo


The roadside repairs make for the best post ride stories.
Re: Effective C:R [Re: Gordo in Comox] #773932
05/16/19 6:35 pm
05/16/19 6:35 pm
Joined: Nov 2011
Posts: 5,239
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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Posts: 5,239
U.S.
Originally Posted by Gordo in Comox
there are few test sheets in the BMS book...
Along with your sheet and mine, adding those from BMS and 'Goldie' results in a folder now holding 500cc data for:

ZB Scrambles (one-piece head)
CB Scrambles (same head as on CB Clubman)
DBD Clubman
DBD Competition

While it would reduce computational uncertainties to have sheets on all models and configurations, the three most important gaps to fill are:

1) BB Clubman (same head as the later two-piece ZB head)
2) BB Road/Trials/Scrambles (all used the same head)
3) DBD Catalina

It would be nice to have DB Clubman and Scrambles as well (different heads), but I suspect simulations of all of the above would be sufficient to deduce how DBs would behave.

Re: Effective C:R [Re: Gordo in Comox] #773945
05/16/19 8:45 pm
05/16/19 8:45 pm
Joined: Sep 2001
Posts: 2,965
Comox BC Canada
Gordo in Comox Offline OP
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Gordo in Comox  Offline OP
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Joined: Sep 2001
Posts: 2,965
Comox BC Canada
MM: I have often wondered if any BB GS machines ever left the factory as trials machines. I say that as BSA always had a BB 32/34 A (Alloy) version of the BB 31/33 to use for trials purposes. It is hard to imagine putting a trials engine on the Dyno for any real purpose. Are there dyno sheets for trials GS engines?

I agree that the BB 32/34 A (sometimes called Clipper depending on the year) had a different head than the Clubman. Are you sure that the Road and Scrambles BB engines used the trials head? I would have thought that the Road version would not have a trials head but would have a Clubman head but with softer cams.

I will ask Ian Jackson some of these questions.

Gordo

PS

I dug out some of your thread on heads and the BB 500 has Clubman's 65-1805, Road Racing 65-1501, Scrambles 65-1749, Road 65-1501 and Trials 65-1749. Were these the final numbers?

In that thread on page 15 there is a BB 34 test sheet from Seamus.


Last edited by Gordo in Comox; 05/16/19 11:23 pm. Reason: More data

The roadside repairs make for the best post ride stories.
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