opus ignition system

Talk about the E-Type Series 3

42south
Posts: 141
Joined: Sat Aug 18, 2012 9:07 pm
Location: Ohope beach, New Zealand
New Zealand

#21 Re: opus ignition system

Post by 42south » Sat Jan 06, 2018 9:37 pm

Hi Colin,
As usual our resident expert Marek has posted the good gen.

Here are a couple of websites I used to research when I was doing the mod on my car.
The british vacuum site is useful to ensure you have the appropriate vacuum module.
Following his advice I wound up using the 54405202 unit which is marked as 5-15-12, but actually is rated at
5-15-8. I run 95 octane gas over here with no problems.

https://www.britishvacuumunit.com/distr ... nit--.html

Paul clarksons site has some good pictures and story of how he drilled his carb for ported vacuum.

http://www.pclarkson.plus.com/Ignition1.html
Cheers
Mark
Mark Brown
1971 S3 Etype
Son: when I grow up, I want to be a pilot
Dad: You’ll have to choose.

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

jagwit
Posts: 338
Joined: Thu Oct 18, 2012 6:52 am
Location: Pretoria
South Africa

#22 Re: opus ignition system

Post by jagwit » Mon Jan 08, 2018 7:32 am

42south wrote:
Sat Jan 06, 2018 8:42 pm
Isn’t the issue that, in your case, with vacuum still being provided to the advance capsule at idle, then extra advance will be provided at idle,
Absolutely correct.
42south wrote:
Sat Jan 06, 2018 8:42 pm
which I believe is undesirable.
I want to understand WHY it would be undesirable. See test below.
42south wrote:
Sat Jan 06, 2018 8:42 pm
Well jaguar thought so which is why they set up the system to avoid this.
The fact that "Jaguar set it up like this" means nothing to me for the very simple reason that manufacturers do things to meet emissions targets (OF THE DAY) first and foremost. Engine efficiency comes after that. Emissions targets is why the series 3 V12 E-type is fitted with a vacuum RETARD ignition system when most other engines have vacuum ADVANCE systems. It is also an excellent example how rules and regulations did not necessarily result in most efficient engines. (This sounds familiar.... VW etc)

Here is a very simple test on a car fitted with ported vacuum advance while idling:
1) Remove the pipe that provides vacuum source to advance diaphragm and plug it towards engine;
2) now apply vacuum on the pipe. (sucking hard on it is sufficient)


I expect that you will find engine rpm will INCREASE. WHY?
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

Link:
BBcode:
HTML:
Hide post links
Show post links


MarekH
Posts: 749
Joined: Wed Jul 21, 2010 8:30 pm
Location: Surrey
Great Britain

#23 Re: opus ignition system

Post by MarekH » Tue Jan 09, 2018 10:24 am

Philip,

Consider what you want the advance mechanism to do overall:- you want a stable, steady and unexciting idle and then once you get going, you want it to increase the advance and provide some oomph. With the retard unit plumbed as it is and the centrifugal advance cutting in rapidly above idle, you get this because the retard stops retarding immediately the throttle is opened.

It sounds to me that you may be simply asking to achieve much the same by having less static advance, no retard and then adding vacuum advance at roughly the same point where your car would previously have dropped off its retard signal.

What would be a useful exercise would be to somehow plot the various retard and advance capsules' advance curves against load and rpm and compare that to the mapped ignition you were running with Megasquirts installed on your previous cars. I think these things are difficult to compare without specifying all of the parameters that vary:- some cars have HE engines, some have four small throttle butterflies attached to carburettors in place of the later six-way plenums which will make the same throttle opening give a different vacuum signal to the same engine.

Perhaps what is needed is for someone to go to the dyno, plot out the ideal mapped ignition and then look at how well the various option for static, centifugal and vacuum advances add up to mimic the desired result.

kind regards
Marek

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

lowact
Posts: 97
Joined: Mon Oct 09, 2017 10:05 am
Location: Canberra, Australia
Contact:
Australia

#24 Re: opus ignition system

Post by lowact » Sun Jan 28, 2018 1:22 pm

As I understand, the theory for no advance when idling or for retarding the ignition when idling is as follows, there are two benefits:
1) To deliberately make the combustion less efficient, to produce more heat that: i) warms the car up faster: ii) the hotter exhaust promotes after-reactions in the exhaust to hopefully convert some of the poison’s. Because the retard is only at idle, there is no reduced performance. The car is not driving, therefore there is no “work” being done, every drop of petrol ends up as heat. If the ignition is retarded the combustion is inefficient, there is less torque & more exhaust heat produced, heat in the exhaust has some benefit reducing emissions. Alternatively, if the ignition is advanced the combustion is more efficient, there is more torque & less exhaust heat produced. However, the additional torque spins the engine faster, producing more friction, so instead of the heat going out the exhaust it is picked up by the cooling water and is dissipated by the radiator. Of course, you don’t need the engine to idle that fast so u wind it back. Net effect is, the engine that is relatively retarded when idling will have the same performance but somewhat increased fuel consumption, depending on how much time u spend idling, it’s the cost of being cleaner…

2) 2nd benefit of vacuum retarded ignition when idling is a natural tendency to stabilise the idling speed; i.e. if idling speed tries to increase the stronger vacuum causes further retard thereby preventing the increase, etc. By comparison a vacuum advance system has natural tendency to destabilise idle speed; i.e. if idling speed tries to increase the stronger vacuum amplifies the increase, etc. I believe this is the main reason that vacuum advance is mostly never applied at idle?

Regarding the vacuum source for a vacuum advance ignition system; for me, modifying a dump valve so I can use the existing tappings will be a whole lot easier than precisely drilling a new tapping point. Also as reported by Paul Clarkson (thx Mark), with a TT/U (top/upstream throttle edge tapping) the vacuum onset is very abrupt, as the throttle plate opens there is change from zero to extra-high vacuum advance almost immediately. Extra-high because throttle edge vacuum is initially a lot stronger than (deep) manifold vacuum due to the relatively high air velocity thru the small throttle openings causing extra low local pressure at the tapping. Seems it was for this reason (civilised transition from idle to driving) that Jaguar’s ultimate solution was to not use a throttle edge tapping as the vacuum source, instead to use a regulated deep manifold vacuum for ignition advance ie:
https://1drv.ms/b/s!AiSPBKa26IcchJgz_vFYjJKROLFR9g
The vacuum regulators are now NLA. Hopefully my modified dump valve will serve in place of a vacuum regulator, as well as not requiring me to drill new vacuum tappings …
Regards,
ColinL
'72 OTS manual V12

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

jagwit
Posts: 338
Joined: Thu Oct 18, 2012 6:52 am
Location: Pretoria
South Africa

#25 Re: opus ignition system

Post by jagwit » Tue Jan 30, 2018 5:45 am

lowact wrote:
Sun Jan 28, 2018 1:22 pm
As I understand, the theory for no advance when idling or for retarding the ignition when idling is as follows, there are two benefits:
1) To deliberately make the combustion less efficient, to produce more heat that: i) warms the car up faster: ii) the hotter exhaust promotes after-reactions in the exhaust to hopefully convert some of the poison’s.

2) 2nd benefit of vacuum retarded ignition when idling is a natural tendency to stabilise the idling speed;
Thanks Colin

#1 has been my conclusion as well.
#2 is new to me but the idle on my car is as stable as it gets.

My mom used to have a 3rd gen '87 Honda Civic 1500 carbed . This car has permanent vacuum applied to its vacuum advance, std from factory. BTW, this car is still running as good as ever, now with 250 000 Km on its clock. Cloth seats look as good as new despite not having had seat covers, ever. Dash vinyl has been affected by our harsh sun but is still "presentable".
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

Link:
BBcode:
HTML:
Hide post links
Show post links


Woolfi
Posts: 278
Joined: Thu Jan 28, 2010 5:57 pm
Location: Germany
Germany

#26 Re: opus ignition system

Post by Woolfi » Tue Jan 30, 2018 7:04 pm

1. A motor is working well , with a advance of roundabout 10 - 12 degree at iddle.
2. The motor is working well, if advance is at roundabout 35 +/-3 degree at throttle wide open.
To generate the iddle advance you need a fixed advance at roundabout 10 degree befor tdc.
To generate the correct timing of ignition at wide open throttle at roundabout 4000 - 6000 rpm, the ignition timing is managed by the advance system with the wights and the springs.
3. At part throttle with no vaccuum advance, the time of ignition is too late. A part throttle mixture is exploding less qick than the micture at full throttle. The highest pressure inside the burning chamber of a cumbustion engine shall ocure at roundabout 8 - 12 degree after top dead center. Engeneers have testet this.
If the mixture at part throttle , which is burning slower mostly at the first 10% time of the explsosion, shall explode, that the peak of pressure is roundabout 10 degrees after tdc, it must be ignited earlier. Earlier ignition, slower burning, same time of peak pressure. Correct ?
To reach the goal of a earlier ignition at part throttle, the car engineers have developed a system with the adcance capsule and a well designed point of vaccuum take-off. This piont is roundabout 2 - 4 mm before the butterfly.
1. No advance at iddle.
2. Low vaccuum ad full open bitterfly.
3. High advance at low opening of the butterfly.
I have a book from Bosch "Management of the Otto-motor" in which is all explained very well plus diagramms and pictures.
I have mounted this "system" in my car 12 years ago. It works very well. I have a good iddle, low part throttle consumption and good power. I have drilled my stromberg 2 times. The first time the whole has been to much in frnt of the butterfly.
I have put a vaccum gauge to the hose to the advance unit and checked the avaccum at driving. The amount of vaccuum is like it shall be.
I put a hand driven vaccuum pump to the advance unit and drove with roundabout 70 mph on a empty autobahn. When I drove at part throttle at with a lot of hand driven vaccuum und opened a valve at the hand pump, that the vaccuum fall down immediately. I could feel, that the car breaked slightly and drove roundabout 2 - 3 mph less quick than with more vaccuum.
With the vaccuum advance the power of the motor is a little bit higher than without the vaccuum. Therefore the efficiency of the motor is higher and the gas consumption is lower at the same speed. This is the reason, why this type of advance management was developed in the car industry. Today this is all done by a ignition-computer. The curves have been developed in hundrets of hours an a dyno.
CollinL, why don't you drill one Stromberg ? Your carb is no virgin. After drilling a virgin is not anymore a virgin, but a carb is a carb. Buy a damaged used carb from ebay and make a test drill. I found a site in the internet with pictures of this drilling.
If somebody is interessted in the 2 pictures of the Bosch Book "Ottomotor-Management" , he can send me his mail-adress and I will send the pictures. Also I can send pictures of my drilled Stromberg.
Resumee: I have done it on my 5,3L V12 and later on my 6,0L and all is working well.
Regards Wolfgang Gatza

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

lowact
Posts: 97
Joined: Mon Oct 09, 2017 10:05 am
Location: Canberra, Australia
Contact:
Australia

#27 Re: opus ignition system

Post by lowact » Wed Jan 31, 2018 1:31 am

Woolfi wrote:
Tue Jan 30, 2018 7:04 pm
CollinL, why don't you drill one Stromberg ?
Hi Wolfgang. I have 2 options. I could drill a throttle edge tapping as you (and others) have done, let’s call this the “Woolfi solution”. Or I could use an existing tapping on the manifold as Phil has done, let’s call this the “Jagwit solution”.
The differences are:
The Woolfi solution gives NO vacuum at idle and GOOD vacuum when driving.
The Jagwit solution gives FULL vacuum at idle and GOOD vacuum when driving.
I.e. both solutions would have the same performance when the car is driving, the only difference is when the car is idling. Phil has managed to set his car up such that there are no issues when idling. So why wouldn’t I do this?
What I am planning to use is the Jagwit solution with one small addition, I will use a modified dump valve to automatically switch off the vacuum when the car is idling. Then I will have a modified Jagwit solution that operates like a Woolfi solution.
I could easily drill the carb, currently these are all off the car and the drill press is only 2 m away... But more fun I think, to try something different? It helps that I already have a dump valve, from my spare parts engine. Here is my spare parts engine on the test stand I am building in preparation for developing the ultimate (closed loop, full sequential, distributorless engine management system.
https://1drv.ms/i/s!AiSPBKa26IcchJY1MTy46l7ysgXxdQ
This project is currently on hold while I wait for Trump to trash the US economy sufficiently for what I want, incl. 5speed, to become available at a better price. I hope it doesn’t take too much longer. Meantime I’m just experimenting, seeing what can be done with carbs… :bigrin:
Regards,
ColinL
'72 OTS manual V12

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

lowact
Posts: 97
Joined: Mon Oct 09, 2017 10:05 am
Location: Canberra, Australia
Contact:
Australia

#28 Re: opus ignition system

Post by lowact » Thu Feb 08, 2018 12:24 pm

Hey Wolfgang check this out – my carb is no longer a virgin :bigrin:
https://1drv.ms/i/s!AiSPBKa26IcchJoTYUr_r89uAX_6Mw
Removed the carb, didn’t dismantle it, didn’t even drain it
Measured and calculated
Marked and punched a drill start-point that (fore-aft) was in the middle of the 15 mm wide boss provided and (upstream-downstream) 6.5 – 7.0 mm back from the manifold mounting face.
Bolted the carb (manifold face) to a bit of marine-grade plywood, clamped the plywood square in a vice from a drill-press
Angled the bed of the drill-press at 10 degrees.
Placed the vice (with carb) on the angled bed of the drill press slightly behind the drill head and check measured – that the horizontal distances from the vertical drill axis to the start point and to the desired exit point were the same – yep.
https://1drv.ms/i/s!AiSPBKa26IcchJoJmikSxUIq8-TK-A
Moved and clamped the vice in position on the angled bed, drilled 17.5 mm deep for a press-fit 3/16 dia. brass tube, then drilled through with a 1 mm dia. bit (with soft foam holding the throttle open and to catch the swarf).
https://1drv.ms/i/s!AiSPBKa26IcchJoKGMKJzWenlnKeKQ
The 10 degrees, 6.5 mm and “middle of the boss” are interdependent. This gives me a vacuum advance tapping point that starts to open immediately the existing vacuum retard tapping point has been completely closed off.
Next is to fit the vacuum advance module (5440520 unit, thx Mark) and test it …
Regards,
ColinL
'72 OTS manual V12

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

jagwit
Posts: 338
Joined: Thu Oct 18, 2012 6:52 am
Location: Pretoria
South Africa

#29 Re: opus ignition system

Post by jagwit » Sat Aug 11, 2018 4:26 pm

Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

Link:
BBcode:
HTML:
Hide post links
Show post links

Post Reply Previous topicNext topic