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Post by enigmas on Jan 16, 2013 22:42:28 GMT
Shocking stuff that E10 and all the propaganda that goes along with it.
As an aside I've seen a couple of Rover V8s fitted with twin Impco LPG carbs fitted in place of the SUs.
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Post by Warwick on Jan 17, 2013 2:20:42 GMT
A few years ago I found a couple of photos on the web of an MGB with a Rover V8 (or perhaps it was an MGC), and it had the SUs converted to take LPG. The SUs were modified - it didn't use mixer plate inserts.
I can't remember any detail and I haven't been able to find it since. It looked virtually original.
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Post by enigmas on Jan 17, 2013 22:38:04 GMT
It probably used spuds (not potatoes)Warwick. This can work well if they are placed in the correct location and is very unobtrusive.
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Post by Warwick on Jan 18, 2013 1:28:11 GMT
That's what I'd assumed too, Vince. And it also seemed logical to me that you could spud an SU where the jet enters, remove the needle and lock the piston up. But no amount of Googling found anything like that.
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Post by enigmas on Jan 18, 2013 13:36:58 GMT
Not wanting to take this post too far off the mark...but I also found some similar information Warwick. It should work for both SU & Stromberg CD carburettors. Rather than remove the piston just remove the needle and fit the 'spud' where the jet normally goes perhaps allowing it a bit more clearance due to the LPG requiring more volume. The air piston would operate normally and provide a strong vacuum signal to the spud at all RPM ranges. The system would look like a normal petrol fuelled unit. The choke if mechanical or 'water choke' (Stromberg) would still function normally, just needing to advance the throttle whilst the engine is cold. The downside would be that you wouldn't do this with 2 really good carburettors. All that is required are a functional 2nd hand set with good butterfly spindles. The other redundant 'petrol' components wouldn't matter.
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Post by Warwick on Jan 21, 2013 6:49:09 GMT
That seems logical to me too, Vince. However, most stuff I've read about SUs and LPG involve locking the piston up or using a vacuum feed to hold them fully up all the time.
When I was pondering all this a few years ago, I found an LPG car forum and asked the relevant questions. When I suggested that it seemed logical to me that the bridge in the SU where the jet enters performs the same task for the petrol that the venturi in an LPG mixer plate performs I was set upon by the various forum experts as some sort of nong and never received any informed or enlightening input from anyone else thereafter.
That sort of behaviour and attitude is not uncommon on forums, which in my opinion is one of the stand-out features of this forum.
Gianni gave me an old set of his SUs on a manifold a couple of years ago. I could try it on those ... BUT NOT BEFORE SHE'S BACK ON THE ROAD AGAIN. I MUST LEARN TO FOCUS!!
PS. Thanks for setting up the new thread John.
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Post by johnwp5bcoupe on Jan 21, 2013 8:41:46 GMT
No problem Warwick I thought it may be the best section to put the thread I am reading with interest  |
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Post by enigmas on Jan 21, 2013 12:18:03 GMT
It seems to me Warwick from the literature I've read, that quite a few Rover engine LPG carburetted V8s (Su & Stromberg CD) have issues with maintaining correct fuel delivery and tend to have lean running issues especially under acceleration.
I tend to believe that most of these issues are due to a weak vacuum signal at the mixer. Fitting after market low restriction air filters tends to exacerbate this. Leaving the slide in place would enhance the vacuum signal at all points, but the piston may need to be held-up at the rest position perhaps 10mm (I'm guessing here) due to the 'gas' requiring an area of larger volume to feed out from the 'mixing jet or spud'.
I also believe a larger 'balance hole' between the 2 carburettors (in the mounting pod) needs to be drilled.
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Post by Warwick on Jan 21, 2013 23:20:43 GMT
Some of that makes sense to me Vince. Just not sure about the action of the piston. My understanding of the SU design, and the Stromberg "copy", is that they produce a constant vacuum so it's only the needle's profile that determines fuel flow. The CD in the Zenith Stromberg model name stands for Constant Depression (vacuum).
My Rangie has the EFI engine, so it just has the one mixer plate mounted at the airflow meter well ahead of the throttle body and intake plenum. It's far from satisfactory as it necessitated moving the crankcase breather connection away from the plenum. This means oil fumes pass through the flowmeter and gas remains in the intake hose after switching off. This can lead to detonation in the intake on start-up, which blows the hose off, if you're lucky. To avoid this, I stop the engine by turning off the gas rather than the ignition.
Having said all that, the engine runs very well with this arrangement. One day I'll move the mixer ... one day.
I know you do quite a bit of random web surfing on miscellaneous Rover V8 and other engine topics, so if you stumble on anything further on this topic, I'd appreciate you posting it.
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Post by enigmas on Jan 22, 2013 3:17:02 GMT
What I was tying to explain was that the movement of the piston up and down creates a strong vacuum signal over the (petrol) jet. The same principle should also apply to a gas 'spud'. The carburettor's CD piston movement (dictated by engine demand) should also create a strong vacuum over the spud.
The vacuum signal needs to be no where near as strong for 'gas' delivery, but most setups with these carbs are very poor off idle or under hard acceleration (they go lean).
Accurate metering is not really possible unless the system runs a stepper motor and an oxygen sensor. Most open loop gas systems (such as my P5 setup) are correct at idle and at cruise. In between these ranges is a compromise as there is no jetting (unless it's fuelled by a GasResearch carb which has a unique gas jet configured to meter the fuel)
My explanation is chiefly about creating a strong vaccum signal to the gas convertor through a gas spud off idle and under hard acceleration.
As an aside, at a recent custom car and hotrod show I attended, a 1934 Ford drove in sporting a Buick 'nailhead' V8 running 6 Stromberg '97' carbs (American version not CD). This engine idled as smooth as silk. I spoke to the owner and asked how he managed to get it to run so smoothly (I presumed on petrol) He told me it was running on LPG. It looked like a petrol fuelled hotrod engine.
From a LPG convertor tucked away behind the engine a line ran to a fuel distribution block. From the block, 6 fuel lines fed out to a spud in each carburettor...just like a petrol system. The spuds entered just above the butterflies. There were no air filters fitted just 6 air horns...hot rod style. It worked amazingly well!
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Post by Warwick on Jan 22, 2013 4:01:45 GMT
Thanks Vince.
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Post by enigmas on Jan 22, 2013 6:52:09 GMT
Warwick is the setup you're interested in modifying for improved performance for the P5B?
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Post by mcgill on Jan 22, 2013 7:13:27 GMT
NOT SINGLE FUEL LPG !??!
Your ok if you live upsidedown in warmer climes,but not this side of the world.
Its not the cars running rough in icey cold,mine both start on the button from lpg no matter how cold,(bit slower to warm up) the problem is the filling stations here.
A touch of frost and lpg pumps go out of use,lpg filling stations are vanishing quick in essex,along with filling stations full stop.
Most are just building plots or eastern european car washes...
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Post by enigmas on Jan 22, 2013 11:31:42 GMT
That's truly a pity mcgill. Australia both produces and exports LPG. LPG is currently 66.9 cents in Melbourne...it should be cheaper. Dual fuel is generally a compromise unless your car runs 2 ignitions maps and E10 petrol is no solution as it's both corrosive and hygroscopic.
Even so, dual fuel may still be possible under this scenario given that this LPG discussion was meant purely for 'brainstorming' ideas.
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Post by Warwick on Jan 23, 2013 2:56:59 GMT
Warwick is the setup you're interested in modifying for improved performance for the P5B? It's to get rid of the petrol entirely Vince, and take advantage of the high compression engine. |
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Post by enigmas on Jan 24, 2013 12:10:52 GMT
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