Vacuum Pipes on series 3

Talk about the E-Type Series 3
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jagwit
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#21 Re: Vacuum Pipes on series 3

Post by jagwit » Mon Jul 30, 2018 7:05 am

MarekH wrote:
Mon Apr 09, 2018 9:05 am
firstly, it provides no vacuum signal at all at idle as the vacuum capsule sees atmospheric air pressure on one side and only airbox air pressure on the other, which with a closed throttle means the airbox and the outside world have not enough pressure difference to affect the capsule;
What are the objective(s) with having no vacuum advance during idle?
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)

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#22 Re: Vacuum Pipes on series 3

Post by MarekH » Mon Jul 30, 2018 9:06 am

Everything you need to know about the vaccum connections is in the manuals. Look in the Parts Manual which has the different setups listed by car number and look in the tan coloured Owners Manual booklet whicxh explains their functions. Failing that, it has been covered many times already in this forum and the jag-lovers.com forum.

Philip, the reason why you may wish to eliminate vacuum usage at idle and set advance using static only (centrifugal provides no advance at idle), as you will have with the ported vacuum, will be that there will be no variations over time and reliabilty and maintainability will be better than having to worry about the condition of the vacuum capsule. Idle speed is now simply a function of the default throttle opening. This means the advance has a big tip-in on initial throttle opening with the ported mechanism.

Also, feel free to post up the results/graphs of the work I did on ported vacuum and how it works. (For those who don't know, I fitted multiple manifold pressure sensors inside the manifold, outside and at the throttle tappings, went for a drive and datalogged how they all interacted.)

kind regards
Marek

kind regards
Marek

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#23 Re: Vacuum Pipes on series 3

Post by jagwit » Mon Jul 30, 2018 9:38 am

MarekH wrote:
Mon Jul 30, 2018 9:06 am
there will be no variations over time and reliabilty and maintainability will be better than having to worry about the condition of the vacuum capsule. Idle speed is now simply a function of the default throttle opening.
So, if I understand correctly, the reason for having no vacuum advance (or centrifugal advance for that matter) is to have a perfectly reliable and stable idle over time, such that neither centrifugal issues nor vacuum related issues can impact on idle.

So, none of the following aspects relate?
- Rapid warm-up of the engine?
- Engine efficiency (fuel consumption during idle)?
- Emissions?
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)

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#24 Re: Vacuum Pipes on series 3

Post by MarekH » Mon Jul 30, 2018 10:49 am

I think it is swings and roundabouts because what you take away or alter from vacuum advance/retard, you'll partially put back in with static and centrifugal advance, just in a slightly different mix.

The reasons you post are all secondary concerns which will have been addressed later and are really just fine tuning a basically simple but working system.

For example, the desire for rapid warmup of the v12 (i.e. an emissions issue) was addressed on the xjs by having a 45 second timer which retarded the ignition for the first 45 seconds if the appropriate temperature sensor was not already above a certain temperature - the so called "thermotime" switch. When the fuel crises hit, Jaguar wanted more fuel efficiency and focused on partial throttle lean cruise and used the high torque capability to sneak in a 2.88 differential.
These days, the first thing you hear when the lights turn green is the startup of starter motors as fuel efficiency at idle is "100%". No doubt it is done for emissions reasons.

The tan coloured Owners Manual shows the great lengths they went to to alter a normal car engine to meet the needs of the day. Similarly, the Roger Bywater website has a great explanation of how the cocktail of solenoids and vacuum switches achieved the same once fuel injection was adopted. It also points out that all of these alterations were shelved either because they only made a small net difference or because the advent of programmed ignition overtook them all. The Parts Manual shows that complicated vacuum plumbing all abandoned for the final cars - there really wasn't much sense in running an air pump from a pulley on the engine to inject air into the exhaust when you could drop the emissions by 10% by making the basic engine do 10% less work instead, so to speak.

kind regards
Marek

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#25 Re: Vacuum Pipes on series 3

Post by jagwit » Mon Jul 30, 2018 11:23 am

MarekH wrote:
Mon Jul 30, 2018 10:49 am
The reasons you post are all secondary concerns
With respect Marek, this comes as a (big) surprise. It has never occurred to me that emissions was a "secondary concern" from the manufacturer's perspective. Emissions (it seems to me) is very much the manufacturer's PRIMARY concern with everything else being a rather distant secondary? Everything I read e.g., on the vacuum retard system on the V12, points to Jaguar's need to meet the emissions requirements of the day, the biggest of which was rapid warm-up.

The point I'm trying to get to is that emissions regulations (not emissions per se) directly influence manufacturers to implement specific solutions aimed to meet the regulations of the day. The vacuum retard on the V12 is a good example, the recent VW debacle is another (and I aim to prove that ported vacuum advance is yet another (less extreme) example - unless I'm forcibly silenced in this matter)
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)

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#26 Re: Vacuum Pipes on series 3

Post by MarekH » Mon Jul 30, 2018 12:27 pm

I agree with you, but it is a question of timing.....

The VW emissions scandal proves quite comprehensively that people go to great lengths to play by the rules, whatever those rules are at the time of manufacture, even if that means being "unconventional" in how they implemented those rules. There is today, (in this country) no need to even meet those same rules as a classic car will typically be free from emissions testing and even free from MOT now if you declare it substantially meets type approval of the day.

Deciding what to keep and what to strip off in terms of all of these extra bits is now a matter of choice and has little or no impact on net emissions or anything much else for that matter.

What is important is to understand what all these bells and whistles do and how they do it, hence my coming back to the manuals. The owner can then decide which bits to replace, remove or repair to meet the objective they have.

So from my perspective, I wouldn't put any of these devices on to the car if starting with a clean sheet of paper but I may repair a few of them if they are not currently functional rather than remove them. In that respect, they do now perform a secondary function today and sometimes don't perform it very well.

From the perspective of time of manufacture, it was always cheaper to adapt or slap on a small variation than it was to redesign something to meet new needs. The classic example of that is the etype wiring harness which has its roots in the xk120 design and which is seriously lacking by 1974.

kind regards
Marek

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jagwit
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#27 Re: Vacuum Pipes on series 3

Post by jagwit » Mon Jul 30, 2018 1:31 pm

MarekH wrote:
Mon Jul 30, 2018 12:27 pm
Deciding what to keep and what to strip off in terms of all of these extra bits is now a matter of choice
I have a passion for EFFICIENCY when it comes to these old cars. I want my cars to be the most efficient they can under ALL circumstances - if possible.

This is where I find myself compelled to advise my fellow enthusiasts as best I can, presenting to them THE BEST solution - even if at odds with "the rest of the world", not the "this is how it always been done" version or the "this is how Jaguar did it" version. Of course the owner STILL has the choice but at least he can now make an INFORMED choice!
MarekH wrote:
Mon Jul 30, 2018 12:27 pm
and has little or no impact on net emissions or anything much else for that matter.
I find it hard to agree on this statement Marek. When one solution results in a higher fuel consumption , hence more heat being generated, more emissions resulting, more demand on the cooling system, more demand on alternator, more demand on the owner's pocket (ito fuel consumption and labour for mods to the car), risk being incurred ito shoddy workmanship, and whatever else I did not think of when typing this, over another, I feel its very important that the community at least KNOW of it, regardless of whether they DECIDE to use it.

To this end I am starting a thread on a very contentious and hotly debated subject in the "Technical" section of this forum, as it relates to all models of classic Jaguars and most older cars in general.
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)

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#28 Re: Vacuum Pipes on series 3

Post by MarekH » Mon Jul 30, 2018 1:54 pm

Granted, it may be quite a step forward by comparison to a similar car with type appoval, but.....

In the round, my view is that it has little impact because the car being "improved" sits in the garage 350 days of the year and still has one third of the economy of a small turbo diesel instead of a quarter. Put another way, the best v12 etype does ~17mpg instead of 11mpg but is still way off a basic v12 fuel injected car and way off modern technology which sees cars doing 60mpg.

Within the limitations of still having the classic v12 experience that we have, achieving the cash equivalent of up to 40mpg AND having ~20% more torque AND ~20% more power is achievable but even that doesn't make a dent in comparison to what modern cars can achieve.

I think you are completely right to put these small improvements in front of everyone and let them decide.

kind regards
Marek

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#29 Re: Vacuum Pipes on series 3

Post by jagwit » Mon Jul 30, 2018 3:14 pm

MarekH wrote:
Mon Jul 30, 2018 1:54 pm
In the round, my view is that it has little impact because the car being "improved" sits in the garage 350 days of the year
An extremely valid point. I drive my car an avg 6000km/y, and did not consider that perspective. I prefer to compare the car to its peers and derive great pleasure in knowing and experiencing that the car is the best it can be and is so much better than the day it left the showroom floor.
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)

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#30 Re: Vacuum Pipes on series 3

Post by Holeshot » Mon Jul 30, 2018 3:47 pm

Hi vee12eman

You mention that "air is taken from trappings on the manifolds, difficult to access and that goes into the temp sensors". Can you describe which part of the manifold it the trappings would be(presume exhaust manifold?) - I've got the manifold all exposed at the moment and can't see where this might be so any help would be good :smile:

Also, do you know where you can get the temperature sensors?

Many thanks,
Hilton.
Hilton - V12 2+2

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#31 Re: Vacuum Pipes on series 3

Post by vee12eman » Tue Jul 31, 2018 4:35 am

Hi Hilton,

In the interest of keeping the information in one place I have edited my original post with the requested information, amending a couple of typos along the way. Tappings (as opposed to Trappings) are on the opposing faces of the INLET manifolds and temp sensors were obtained from SNGB.

Have a look at the original post which I hope is clear now.

Regards,

Simon.
Simon S-Y
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#32 Re: Vacuum Pipes on series 3

Post by Holeshot » Tue Jul 31, 2018 9:11 am

Hi Simon,

Thanks very much for the enhanced explanation - really appreciate your edit.
It's de-mystified what those parts are actually for.

I've had a look at at the various parts on mine as I've got them all dissembled at the moment.
The flap mechanism seems to work under vacuum(it opens/shuts by sucking it!).
I can see the temp sensors but don't know if they work - guess I'll just have to connect them up and see - I presume that's the only way of testing them?.
I checked with SNGB and unfortunately they don't stock them anymore.
I'll have a proper look this evening for the tappings as I could only glance at them this morning.

Thanks again for so much good information :bigrin:

Cheers, Hilton.
Hilton - V12 2+2

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#33 Re: Vacuum Pipes on series 3

Post by vee12eman » Wed Aug 01, 2018 1:05 am

Hi Hilton,

Glad to have helped. I did a quick search and whilst SNG do now list the sensors (and their replacements) as no longer available, if you do a search for the later design by part number (C38357), there are a couple of companies that claim to have some in stock – you could try them if you are really interested. I just searched by C38357 Jaguar, on Google.

As for testing them, they are bimetallic strips operating an air valve. Put some tube on each port, blow (or suck) through them, then drop them in hot water and see if the results change. From memory, the bimetallic strips of my old units still functioned (why wouldn’t they?), but sadly the valves they operated would not seal – you may be able to dismantle and repair, though this would probably be tricky.

If you decide to remove them, they are probably best left in situ to prevent unfiltered air passing into the air box (and thus carbs/engine), just remove the connecting tubes and ensure the take of points of the inlet manifold are properly blanked.

Regards,

Simon
Simon S-Y
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#34 Re: Vacuum Pipes on series 3

Post by Holeshot » Thu Aug 02, 2018 7:25 am

Thanks Simon.
All this really helps.

I found the small tappings which are hidden under the larger balance feeds that have the rubber ‘T’ vacuum pipe between the two manifolds. Veery hard to spot if no pipe connected to them. On mine they are only on one manifold per side of the engine. One side had a small length of tube still on but blanked off. The other side had nothing so must have been sucking in air - which must have been causing the slightly uneven running I’ve been trying to track down. Hopefully this thread and advice has cured a really annoying problem for me!!! I’ll only know when I reassemble it all in a few days time. Am quite looking forward to finding out!
SNGB don’t do the tubing any more either so will find a supplier and rig the whole lot up and test it out, though if I can, I’ll try the hot water test on the sensors in the meantime.
Thanks again for the great thread and the great advice :smile:

Cheers, Hilton
Hilton - V12 2+2

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#35 Re: Vacuum Pipes on series 3

Post by lowact » Thu Aug 02, 2018 7:50 am

Hi Hilton, interesting that you only have 2 such tappings. I have 4, one on each manifold. As per my 7Apr reply on this subject: two are for the air inlet temperature control, these is what you seemingly have now figured out. The other two, one supplies vacuum to activate the gulp valve, the other supplies vacuum to each of the 4 carburetor bypass valves. I'm curious, do you not have carb bypass valves (do u have stromberg carbs), do u have a gulp valve? If yes, where are they getting vacuum from?
Regards,
ColinL
'72 OTS manual V12

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#36 Re: Vacuum Pipes on series 3

Post by Holeshot » Thu Aug 02, 2018 8:30 am

Hi Simon.
There are other tappings for other uses but whilst everything’s apart, I’ll take some photos as my explanations aren’t always so good!
Will be back later this morning.
Cheers, Hilton
Hilton - V12 2+2

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#37 Re: Vacuum Pipes on series 3

Post by Holeshot » Thu Aug 02, 2018 3:05 pm

Hi Simon.

Here you go. (And sorry for the rubbish annotations - I’m on my mobile!)
LH & RH rear inlet manifolds showing the vacuum tappings we’ve been talking about.
The other two feeds are for the distributor vacuum and the servo feed.
See what you think.
Oh, my carbs are Strombergs.
Cheers, Hilton
Image

Image

Image
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#38 Re: Vacuum Pipes on series 3

Post by lowact » Fri Aug 03, 2018 1:18 am

Tis not Simon this time.
The plot thickens.
I interpret that the vacuum for yr distributor is taken from the LH rear manifold from the tapping point above the hose to the brake servo. This gives vacuum all of the time.

Your distributor vacuum module, the spigot that the vacuum hose connects to, does this spigot point forward towards the radiator or backwards towards the firewall? If forward you have a vacuum retard distributor. If backwards you have a vacuum advance distributor.

If you have a vacuum advance distributor (spigot pointing backwards) vacuum connection to the tapping above the brake servo hose would be ok. NOT ok if you have a retard distributor, you'd lose out in a drag-race with an Austin.

With vacuum retard distributor, you only want vacuum when idling (if at all), NOT when driving. For retard distributor vacuum is taken from underneath the LH rear carburetor, you can't see this, only feel it, here is pic:
Image

From this tapping u only get vacuum when the throttle plates are closed (idling).
If u have an advance distributor, or don't want to use retard, this tapping needs to be capped (as mine is) otherwise u have major vacuum leak when idling, can't balance carbs.

Also shown in the above photo is where the carburetor bypass valves should be (on my car i have removed them and fitted blanking plates). Here is pic of one of the removed bypass valves, showing what they look like:
Image

Do you have these, do they have spigots on top as in the photo? If so these would have originally been connected to manifold vacuum...
Regards,
ColinL
'72 OTS manual V12

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#39 Re: Vacuum Pipes on series 3

Post by vee12eman » Fri Aug 03, 2018 3:04 am

Hi Colin, Hilton,

A couple of points. Firstly,I am not going to get into the debate about vacuum advance vs retard. This is being considered elsewhere and without studying it, this is beyond my full understanding and ability to explain correctly. I aim to look into it soon and consider modifying my own car. However, Colin is correct that the original design was for retard at idle, with a tapping taken from underneath the left carb as he showed. This original version should connect to the vacuum retard unit on the distributor which has the pipe connected on the same side as the distributor. If the tube enters from the opposite side, then the unit is a vacuum ADVANCE unit.

Regarding the bypass valves, although Colin showed a photo of a carburettor with external tapping, which connects to the manifolds, early carbs did not have the external connection and instead relied on internal drillings.

Manifolds for different markets and years of cars, also those from XJ12 vs E-type V12, all have different vacuum take off points, so you need to ensure the connections are correct for the emission control set up, transmission (Auto vs manual), distributor vacuum unit (original retard vs modified advance type) and any other differences. Any unused tappings, whether on manifolds, carbs or other vacuum driven accessories or controls, should be blanked off securely. This is especially important for tappings on manifolds or carbs. Leaks make the carbs impossible to balance and can lead to rough/uneven idle and hesitant constant throttle operation.

Regards,

Simon
Simon S-Y
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#40 Re: Vacuum Pipes on series 3

Post by Holeshot » Fri Aug 03, 2018 1:51 pm

Hi Colin & Simon.
I’m afraid I’m hopelessly undereducated as far as retard/advance pros and cons go, so can’t comment.
All I can say is that my ignition is the original set up with the vacuum retard and understand the compromises of this. The vacuum feed for the distributor comes from the rear of the rear left hand inlet manifold (pointing to bulkhead). The car has always performed well like this, other than when the ignition system went south recently.
There are no vacuum feeds from the carb.
Don’t know if this agrees with any of the above.
I’m just trying to figure out the quick warm up facility on the air filter trumpet/housing and get it back to how it was born. I’m pleased I’ve found this thread as it may have inadvertently discovered the source of uneven tickover through an uncapped tapping.
Thanks anyway guys.
Cheers, Hilton
Hilton - V12 2+2

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