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Altitude compensation for Lucas MU really works?


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Hi All,

Took my supercharged TR6 (Holley carb) over the Gross Glockner pass (8000 ft) on last years 10CR, Only issue was a reduction in tickover and a need to change to third gear on some of the steep bits (would have been 4th normally). 

I had PI for sometime before fitting the supercharger and I think the reason some people get away with altitude is the setup of their PI. out of the box they are rich, partly to make up for the lack of an accelerator pump but also to be on the safe side. To lean at full throttle can be bad! Using an AFR meter I was able to back off on the mixture a fair way and the car remained entirely driveable. You can tell when you have overdone it as the car hesitates at snap throttle openings. The whole process added a fair few MPG to boot... 

I followed the German modification of the MU to adapt to altitude. Nice piece of work but could help but think that for all the effort you could have EFI.

 

Tim

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4 hours ago, stuart said:

Found the one of it fitted to a saloon.

Stuart.

post-10590-0-60986100-1322348391.jpg

Thanks Stuart. It looks like someone's fitted an automagically compensated MU to that saloon.

I take it no one has any knowledge of how the World Cup cable-operated altitude MUs work?

Cheers, Richard

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Nice piece of work but could help but think that for all the effort you could have EFI

Of course EFI can solve that. No doubts. But I want to drive my TR "analogue".

 

Edited by Casar66
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15 hours ago, Spit_2.5PI said:

Thanks Stuart. It looks like someone's fitted an automagically compensated MU to that saloon.

I take it no one has any knowledge of how the World Cup cable-operated altitude MUs work?

Cheers, Richard

Im sure there was a topic on it before somewhere on here .

Stuart.

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I can concur with Tom that carbs are fine at altitude. I've done numerous European trips involving various mountain passes in my 2500 saloon and TR6, both running on humble twin SU HS6s. Whereas they are still pulling quite happily all the way to the top, friend's with PI-equipped cars are beginning to struggle, literally gasping for air!

 

Matt

Edited by matt george
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Bit late at coming into this discussion but I thought it worth mentioning that Triumph themselves stopped specifying the high altitude unit for the TR6 and 2.5PI following tests that they carried out which showed that the export metering unit RKC 0094 met the requirement for high altitude countries. Their newsletter 333 for week ending 19th January 1973 refers, an abstract of which I have attached here.

cheers

Derek

IMG_0374.JPG

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There is a list of part numbers in the Lucas Triumph Cars document LSS/047/014 dated March 1974.  There are no diagrams and why they are listed in the 1974 rather than 1973 is beyond me.

cheers

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Ok, now I got it, 0095 was replaced by 0094 für all PIs. But that means also that all the MU from 1973 should have no problems at high altitude. But only for the Triumph engineers.

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The Lucas books say from October 1973 for the home market TR6 however more likely from when the RKC0220 units ran out in production sometime after CR5001. They were differentiated by a green top on the metering unit.

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I would have thought it would be possible to make a mechanical link to the maximum fuel stop on the bottom of the metering unit. This is the little screw with the lock nut and the flats on the thread.

Although it is now over 20 years since I last had Lucas injection, I regularly checked and if necessary reset the clearances in the metering unit, particularly on my PI saloon which was doing 12,000 miles per year. It was simple on the saloon as the metering unit could be accessed while still fitted.

IIRC the max fuel setting was about 56 thou. If the thread on the stop was about 32TPI (guessing), then that is about 30 thou per turn.

If it was possible to press a short lever onto this screw and attach it to a choke cable you should be able to move the screw about a quarter of a turn which would give about 7-8 thou adjustment or about 14 % of max fuel.

It wouldn't affect the idle fuel and the reduction would be proportional to how far along the track the rollers on the metering unit were sitting, ie half the effect half way along.

Neil

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3 hours ago, Stagpowered said:

I would have thought it would be possible to make a mechanical link to the maximum fuel stop on the bottom of the metering unit. This is the little screw with the lock nut and the flats on the thread.

Interesting that this comes from a Stag Fan.

I know from The Stag Pope Dieter in the NRW Area that he did such a thing on his PI

setting the fuel stop to lean and added an electric main beam adjuster that pulls a rod in and out to the

enrichment lever. He could now adjust the lever with a two way switch how much the lever is pulled.

If done properly and movement is not too coarse this will do a nice job.

 

Anyway a engine set lean will not be killed in the mountains, it runs a bit ugly but thats it.

In addition as to be seen in Tom's picture on top of the hill it is often cold what has the opposite

effect of altitude on the mixture.

 

It is all a question how much oxygen parts are in a litre of air. Warm air expands and air with lower pressure

expands, too. Also the air gets thinner and can better flush through the inlet

but that does not fully compensate the loss of oxygen parts.

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I know from The Stag Pope Dieter in the NRW Area that he did such a thing on his PI

setting the fuel stop to lean and added an electric main beam adjuster that pulls a rod in and out to the

enrichment lever. He could now adjust the lever with a two way switch how much the lever is pulled.

If done properly and movement is not too coarse this will do a nice job.

one photo or two would be nice 

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25 minutes ago, Casar66 said:

one photo or two would be nice 

Youve already posted the pictures at the beginning of this thread as I believe thats the one referred to.

Stuart.

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The one I have posted weren't the pictures of the "Stage pope Dieter".  My pictures belongs to a formerly TR5 driver and and enthusiastic precision mechanic. He builded that without ever using it in the high mountains. 

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Further to Stuarts photo of one fitted to a saloon what follows is a photo of a slightly different one fitted to one of the World Cup Rally 2.5PI, KNW 798, which was on display at the 2010 International TR Weekend. The second photo shows the manual adjuster in the passenger compartment. There were also two Lucas fuel pumps in the boot, presumably one was a standby.

Incidentally the first post by Casar66 shows one of my photos that I took at TR Bitz many years ago way back in 2003. I do have other photos taken on the same day of the same unit, and I will upload an image of the reverse side as a following post as the site won't let me upload the third image!!

cheers

Derek

 

P1020045.JPG

P1020044.JPG

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3 hours ago, saffrontr said:

photo of a slightly different one fitted to one of the World Cup Rally 2.5PI, KNW 798

Thank you for posting those pictures Derek. The cable operated altitude adjust mechanism looks to be a standard MU body with a lab-built box attached to the bottom. From the position of the lever my guess is that it has to do with the maximum fuel adjustment. Perhaps a cam in place of the screw? Anyway, that's satisfied my curiosity!

Cheers, Richard

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