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PostPosted: Thu Oct 20, 2011 9:48 am 
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Location: Rotherham, South Yorkshire (civilisation)
I've been 'fiddling' with the gas tuning on The Old Girl for a while now. Sometimes with the aid of an exhaust gas analyzer and sometimes by ear and then going for a run to test the results in 'the real world'. No matter what I do she won't start on gas from cold and often the tuning seems to drift one way or t'other in a fairly short time. Although she runs adequately on gas the consumption is higher than previously so I think it's got to the stage where it will be more economic to get someone with more experience than myself to wave his magic wand over her (izzy wizzy, let's get busy?).
The current system was installed by Warrington Autogas before they changed name and location.
Living in Rotherham I'm aware of the guy at American & British Sports Cars as he's done some work on her in the past, but all he will say about the current LPG setup is "That's not how I would have done it" and "I can rebuild it my way for £x00".
Does the forum Brains Trust know of a reliable, honest and competent gas tuner in the South Yorkshire area centred on Rotherham?
Thanks.

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PostPosted: Thu Oct 20, 2011 11:42 am 
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Morning Sir! It might be well worth you considering a closed loop control for the ol girl if you do not all ready have one? This should make it a lot easier to set up and keep the mixture correct whilst driving.
Besides that the best chap I can offer you in the sort of Warrington area would be David Stanley at autogas northwest, Sutton Weaver. Very helpful chap in my experiance. ( 01928 710011)
Hope this is of some help :)

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PostPosted: Thu Oct 20, 2011 12:07 pm 
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Unfortunately a closed loop system would require a lot of additional and/or replacement parts. The engine in The Old Girl (a 6.8 litre V8) currently runs on an open loop system through twin spud pipes simply dumping the gas into each inlet tract some distance in front of the twin HIF8 SU carbs. Due to the way the inlet manifolds are set up each carb supplies the fuel/air mix for 2 cylinders on its own side and 2 on the other, so using a Lambda sensor on each side wouldn't provide the correct feedback for a closed loop system and I doubt that a single one after the exhaust join would be much, if at all, better.

By the way: Although I had the conversion done over in Lancs, I live in Rotherham, South Yorks and so I'm looking for a tuner (even a mobile one) based in the Rotherham/Sheffield/Barnsley/Doncaster area(s).
Thanks anyway DT.

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PostPosted: Thu Oct 20, 2011 10:25 pm 
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But if you could nail it it would definately solve any tuning issues. So if you got 2 lambdas, and two Econ ec (VIP 100's) that would be absolutely perfect. The stepper motors one on each carb, they would run independently of each other it would probarbly pay for itself in no time if you did a few miles, probarbly just to the shops and back !


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PostPosted: Thu Oct 20, 2011 11:31 pm 
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Since the lambdas would each be reading the mixture of 2 cylinders from each bank (half the throughput of each carb) they would give poor results at best. The only practical way of going down that route would be to combine the outputs from the 'vap into one big mixer in the middle feeding both carbs simultaneously and having just the one lambda where the 2 downpipes join at the front of the engine.

It could work, but I'd have to check out what other parts/components/assemblies would be needed to build it into the carburation.

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PostPosted: Fri Oct 21, 2011 9:36 am 
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You know the set up better than me, after-all im just guessing at it.
So what you are saying is one carb feeds 4 cylinders on opposite banks ? That would require a bit of thinking about. Do the exhaust branches join together from opposite sides ? If there is anywhere the exhaust joins together then yes you could possibly tee the feed pipes together and put a single stepper pre tee so to speak. It depends how far down they join together i suppose. If you use a 4 wire probe you should be ok.


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PostPosted: Fri Oct 21, 2011 11:19 am 
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The left hand carb feeds the 2 end cylinders on its own side and the 2 centre cylinders on the right hand side with the right hand carb feeding the opposing cylinders, whereas each exhaust manifold ducts the exhaust gasses from all 4 cylinders on one side only. Each of these then joins to fairly short, but unequal length, downpipes which come together at the front left hand side of the engine before travelling the length of the car as a single system with several boxes of various types and functions.

Although I've got a couple of 4-wire lambda probes (which I bought before I realised the way the carbs were feeding the cylinders) I've had to since replace the full exhaust system so I never got around to testing or fitting them. If someone could point me towards some more info on the extra components I would need to go down this route I could have a go at making the changes to the gas system to a more closed loop one than is currently the case. At the moment the gas useage seems to be down around the 9mpg mark compared to the 11 I was getting when the system was first installed nearly 3 years ago. Since The Old Girl only does 14mpg on unleaded around town this is still a reasonable saving on fuel costs, although it could be better.

Fortunately I have a diesel MPV which runs happily on filtered WVO for longer trips or to tow my 20' caravan and I'll be getting a Honda engined Rover 216 Cabriolet next month for use in the warmer weather. No wonder I've got no money!

Ta very glad Old Chums.

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PostPosted: Fri Oct 21, 2011 6:01 pm 
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Sir Henry wrote:
and I doubt that a single one after the exhaust join would be much, if at all, better.


Why would a sensor in the 8into1 collector not work?

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PostPosted: Fri Oct 21, 2011 7:54 pm 
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With the current setup feeding the gas through separate pipes to each carb a single lambda would be reading the average of the two. If one was running rich and the other weak there wouldn't be a comprehensive feedback signal that would make sense. That's why I later suggested merging the outputs of the OMVL 'vap into a single mixer at the central point of the air trunking where it should automatically balance the air/fuel mixture to each carb. Until or unless I do this any lambda output wouldn't be of any use either as a diagnostic tool or for controlling a simple closed loop system. I may yet plump for this option, but I would have to know more about the pros and cons of going down this route before I do.

Since there's no existing EMU to latch on to I assume that I would have to source and fit something along those lines, along with all the ancillaries it requires. This may yet turn out to be economically viable, although I don't yet have enough data to make an informed decision.

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PostPosted: Fri Oct 21, 2011 8:05 pm 
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I am just learning myself.
If you made 2 gas pipes from the VAP (equal length to the spuds), and you had 1 stepper motor placed in both gas pipes(2 stepper motors), and a Lambda in the 8into1 collector. That would be a simple setup .I may be wrong , but if i was throwing something custom together for my V8 and i wanted to use as much of the existing setup as possible , thats what i would try.
The equal length gas pipes and unified steppers would create good average , wouldn't it?

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PostPosted: Fri Oct 21, 2011 8:43 pm 
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Put the lambda sensor in the exhaust after the collectors so it is seeing an average from all cylinders. Connect one white wire on the lambda sensor to an ignition switched 12v supply, the other white and the black connect to earth and take the lambda output from the grey wire to your closed loop controller (use something like the VIP 100 rather than a Leonardo as you've no TPS to connect to). You don't need an EMU or anything else. My P38 Range Rover uses 5-0 v lambda sensors for the petrol system and the AEB controller doesn't like them much so there is a separate 0-1 v 4 wire sensor in one of the downpipes purely for the LPG controller.

Now on most systems you've only got a single mixer but it would still work on your dual fed system. Put the stepper in the hose from the vap and then feed the gas into a Y piece. If your spuds are identical and the hose lengths between the Y piece and the spuds are the same, it will work. There may be a very slight imbalance between the two intakes but as long as the spuds are as near to identical as you can get them, it won't be enough to worry about. If you find that the plugs are a completely different colour depending on which intake a pot is being fed by, then you may need to do a bit of fiddling to get the gas flow to each intake the same.

and stop referring to Rotherham as Civilisation, my ex came from Rotherham.......

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PostPosted: Fri Oct 21, 2011 9:09 pm 
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Gilbertd wrote:

and stop referring to Rotherham as Civilisation, my ex came from Rotherham.......


And the late SWMBO came from Tyneside. You have a point?

Still ... I'll take on board all that's been suggested and look into it in the next few days - other calls on my time permitting.

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