123 Tune Rolling Road Set-up

[astontr6]

7 minutes ago, astontr6 said:

 Hi Marco!

Is this why SAH, the tuning Guru in the 1970's,  years ago fitted a different spring to the Lucas dizzy when they tuned TR6's???

Bruce.

I have found my old SAH cat!

follow up: in my old SAH cat, it states the following about the Lucas dizzy: For 150BHp motors the CP engine use a 12 degree base plate. This engine has the best advance curve advance curve for road engines. But they do a special dizzy for competition on an exchange basis. The late models 125 BHP uses a 12 degree base plate which can be adapted and use lighter springs TT1903. These may still be available from Moss? who took over parts of SAH?

Bruce. 

 

[astontr6]

1 hour ago, astontr6 said:

 

Sorry I have done a typo? A CP engine has a 6 degree base plate and not a 12 this only applies to a CR engine!

Bruce.

[Z320]

2 hours ago, astontr6 said:

 Hi Marco!

Is this why SAH, the tuning Guru in the 1970's,  years ago fitted a different spring to the Lucas dizzy when they tuned TR6's???

Bruce.

Who is SAH.

Edited August 9, 2021 by Z320

[Motorsport Mickey]

52 minutes ago, Z320 said:

Who is SAH.

Hi Marco,

A well known old time racer of the sidescreen cars, he developed quite a few car items as he used them and then started selling the devloped items to erstwhile car enthusiates who used Triumphs. 

His name was Sid Hurrell, and he was among the very earliest of TR tuners. SAH were located in Leighton Buzzard, in England, and were a supplier of various performance parts for Triumphs. They were VERY reputable, and these days their existing parts are sought after to dress our cars.

Triumphtune (another tuning accessory firm) was his son Terry Hurrell . I think that SAH was absorbed into to TTune sometime in the mid 80's, and that many of the TTune pieces are developed SAH parts absorbed into T Tune. The decades of tuning knowledge was still relevant and utilised by T Tune.

Mick Richards

[Z320]

Hi Mick,

thank you for this information, I'm too young to know.

Cheers, Marco

Edited August 9, 2021 by Z320

[Steves_TR6]

Hi Adrian, team TR!

my approach with the 123 was to measure the advance of the original distributor every 500 revs and set this up as the starting point for the 123, and i’ve not touched it since!

car runs great but there has to be some value in a rolling road session, even if it’s just fun to do :-)

Peter is of course right about the lean spike problem of the pi system, so thats something to be avoided.

I’m pretty flexible for the Enginuity session Adrian, when’s good for you?

steve

[astontr6]

7 hours ago, Z320 said:

Who is SAH.

They were the past masters of tuning all Triumph  model cars and had the franchise from British Leyland to supply  cars from new under the Special Tuning Logo. They developed the kit to make the 125 BHP car faster and more powerful than the 150 BHP car that never existed, except in the BL Sales Literature?

Bruce.

[SpitFireSIX]

Hi,

 I do not understand why you would not want increased timing advance off WOT?

I do not have the luxury of a connection to manifold pressure for Load and have to rely on throttle position. (Alpha N. If I run with advance due to RPM only my drivability suffers. More so at low RPM.

Cheers,

Iain.

[Z320]

3 minutes ago, SpitFireSIX said:

Hi,

 I do not understand why you would not want increased timing advance off WOT?

I do not have the luxury of a connection to manifold pressure for Load and have to rely on throttle position. (Alpha N. If I run with advance due to RPM only my drivability suffers. More so at low RPM.

Cheers,

Iain.

Me? I WANT! On my carb TR4A

[Peter Cobbold]

26 minutes ago, SpitFireSIX said:

Hi,

 I do not understand why you would not want increased timing advance off WOT?

I do not have the luxury of a connection to manifold pressure for Load and have to rely on throttle position. (Alpha N. If I run with advance due to RPM only my drivability suffers. More so at low RPM.

Cheers,

Iain.

throttle position is directly related to butterfly angle, and hence to manifold pressure, so it can do the same job of advancing the spark at cruise.

[FatJon]

11 hours ago, Peter Cobbold said:

throttle position is directly related to butterfly angle, and hence to manifold pressure, so it can do the same job of advancing the spark at cruise.

There is no direct correlation between throttle angle and vacuum. There are 3 parts to the equation and you are missing the third. Without RPM you have no idea what the vacuum will be. 20% throttle at 3500 RPM cruise might be 45KPA but 20% at 1500 RPM is near atmospheric. For good clean running the manifold pressure is an essential part of the timing calculation. This is one drawback of Alpha-N using throttle position and engine speed only to calculate fuel load and ignition. I use a blended method where I use vacuum, and RPM until the vacuum nears atmospheric (circa 80KPA) and then blend over to Alpha-N when the vacuum signature becomes unreliable which is often the case with throttle bodies. The Triumph (Lucas) engineers went with what is effectively an early form of Alpha-N using only throttle angle and vacuum for fuelling but I think that was the limit of the technology then, so it was not by choice. Swapping from one calculation method to the other was an impossible dream in the mid 20th century.

Dobbing in more advance on cruise vacuum and over run makes a big difference to the manners of the engine, efficiency and emissions. You can also pull out fuelling on the over run with more modern systems but the old Lucas PI system has little understanding of adapting mixture by engine load although it was pretty impressive for the 60's.

[Peter Cobbold]

8 hours ago, FatJon said:

There is no direct correlation between throttle angle and vacuum. There are 3 parts to the equation and you are missing the third. Without RPM you have no idea what the vacuum will be. 20% throttle at 3500 RPM cruise might be 45KPA but 20% at 1500 RPM is near atmospheric. For good clean running the manifold pressure is an essential part of the timing calculation. This is one drawback of Alpha-N using throttle position and engine speed only to calculate fuel load and ignition. I use a blended method where I use vacuum, and RPM until the vacuum nears atmospheric (circa 80KPA) and then blend over to Alpha-N when the vacuum signature becomes unreliable which is often the case with throttle bodies. The Triumph (Lucas) engineers went with what is effectively an early form of Alpha-N using only throttle angle and vacuum for fuelling but I think that was the limit of the technology then, so it was not by choice. Swapping from one calculation method to the other was an impossible dream in the mid 20th century.

Dobbing in more advance on cruise vacuum and over run makes a big difference to the manners of the engine, efficiency and emissions. You can also pull out fuelling on the over run with more modern systems but the old Lucas PI system has little understanding of adapting mixture by engine load although it was pretty impressive for the 60's.

Choked flow past the butterfly delivers 0.528 atm in the manifold  https://en.wikipedia.org/wiki/Choked_flow

Choked flow around a butterfly valve occurs at <30deg opening; fig5  https://www.valin.com/resources/blog/gas-flow-control-valves

Providing the engine is powering the car then manifold depression will be near 0.5atm when butterfly is <30 deg open. This is the cruise condition. Manifold depression when accelarating will rise above 0.5 atm, but the bfly is no longer choked. On the over-run when the throttle no longer controls rpm manifold depression can be near vacuum.  Most road driving is at  cruise at modest speed where for <30 deg butterfly opening the manifold will be at 0.5 atm, irrespective of rpm.

[CK's TR6]

As a Yank, assume I don't know much. But what I do know is that the speed of combustion varies not only for the richness/leanness of the mixture but also for how well the cylinder is filled. Think of a Pub where everyone has had a few pints each, the ones where everyone is elbow to elbow or the Pubs where everyone is socially distancing IAW the diktats of late. It's hard to start a melee in the second one but the first one it goes quickly. Once the intake valve opens, the cylinder will fill depending on two things, the Manifold Absolute Pressure (MAP) the valve sees and the flow efficiency of the head and valve. A measure of how full the cylinder is how close does the pressure inside the cylinder match the MAP when the intake valve closes. That ratio is proportional to the Volumetric Efficiency  of the engine at that MAP and RPM.  The Pub population will depend on the MAP and the VE.  As the crowding gets less and less, it takes more and more time to get the fight going. For the engine to operate at it's best, it needs more and more advance to get the fight going as the crowding falls. This requirement is much much greater than the variation of timing driven by mixture. You might need up to 20 degrees more advance for this compared to 3-4 degrees for mixture. Greg Banish has published several books that are an excellent mix of theory and application.