Ideal 'classic' car contender for singlepoint conversion ideas?

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Mouse
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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#21 Post by Mouse » Tue Sep 01, 2020 1:28 am

I have a 1990 735i, so it's pretty well the same engine as your 635i, although a 635i is more desireable for many, and therefore command a higher purchase price. But all I wanted is something to waft about in, and an auto, and having worked on these cars back in the day, I reckoned now is a good a time as ever. I have a Ford XR as well, so this is in complete contrast to that. Plus, the sound of that 6 cylinder BMW is spectacular.

I have seen a few conversions to old BMW's like mine on the net, and most seem to be multipoint conversions. Having previous experience on lpg many moons ago, things have moved on a lot, so I knew that the best thing was to ask about what would be the best solution for me.

I suppose big old engined cars would suit conversion better imho. I've seen an XJ6 with a single point system fitted. Old Fords like a Granada I reckon would be a good contender. Lexus LS400 are gaining traction as a classic, but it's not what a single point system would be best suited, I reckon.

Anyway, here a pic of my car that I posted in a different thread here.

https://i.imgur.com/hZBeifo.jpg

Budgetbond
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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#22 Post by Budgetbond » Thu Sep 03, 2020 12:46 am

Yeah I was thinking of ways to try and make an older car better as well as more fuel efficient by fitting a standalone Lpg system, but 'classic' cars have changed a bit now haven't they,you've got to go back quite a way, arguably some of the classics are now better than the modern stuff.
I remember as a kid my uncle getting a new Fiat regata with a whopping 100hp from its twin cam engine that did 0-60 in less than 10seconds with single point injection d you remember that? I suppose an lpg mixer system is pretty much no less efficient as a single point petrol injection system or carburettors.
And who'd have thought initially that the Lexus ls400 would have turned into a classic.
And old Ford's have turned into gold dust haven't they your Ford XR must be worth a few quid nowadays, I used to have a Puma that was actually a cracking drivers car but unfortunately couldn't find a non rusty one for love nor money.

Pinger
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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#23 Post by Pinger » Tue Sep 15, 2020 4:05 pm

Gilbertd wrote:
Sun Aug 30, 2020 10:50 pm
Sounds a bit low to me, at 25C the engine will still be running a cold start strategy so the mixture will still be too rich. That's why coolant plumbing is important to get the reducer up to temperature as quickly as possible. The only real age related problems you get are on cars fitted with carbs when they start to wear, injection systems just work, so finding something that you can improve by fitting LPG is going to be difficult.
To my mind that is a considerable disadvantage of sequential systems.
I can see why it is that way, but can't a different reading be taken from the coolant temp sensor (such that the engine's ECU sees it as being up to operating temp) to circumvent this?

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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#24 Post by LPGC » Tue Sep 15, 2020 6:02 pm

A guy once brought me an old American classic 4x4 to convert to LPG, International Harvester or something similar. Part of his reason for converting it to LPG was because his carb(s) were worn out and it would have cost him a good fraction of the cost of the LPG install to sort the carbs out, with the LPG system fitted the condition of the carbs didn't really matter while he was driving on half price LPG...

TBH a lot of modern vehicles switch to closed loop operation soon after starting and before the coolant has even reached 20C. My own vehicles have sequential systems fitted and they switch to LPG at 20C.

It's commonly (and quite correctly) said that there are 2 main reasons why sequential systems need to start from cold running on petrol... 1. There's the fact that sequential system reducers are more prone to the cooling effect than mixer system reducers. 2 There's the choke effect as recently discussed. But there are other reasons too. 3 LPG injectors don't function the same in cold conditions as they do at normal operational temperatures, some are far worse effected by cold temperatures than others, the injectors see a further cooling effect as gas vapour under pressure flows passes through them to meet the lower pressure in the manifold. 4 LPG installers don't often set systems up to perform properly during the engine warm-up stage, their calibration settings are wrong for cold temperature gas and for the different conditions that the engine is operating under such as the engine needing more air (and gas) flow during warm-up because it is tighter before it's warmed a bit. An engine that when fully warmed up may idle with (say) 2.7ms pinj, LPG injectors pulsing for ginj of 3.8ms while receiving gas at 60C. The same engine but colder and tighter may idle with 3.1ms pinj, the LPG injectors may receive gas at 20C, for correct fuelling (and to keep pinj at 3.1ms) ginj may need to be anywhere between (say) 4.5ms and 3.6ms depending on many aspects but unless the installer has addressed/compensated for the aspects the ECU may pulse gas injectors for 4.1ms which is based on the over simplified adjustments based mostly just on the shape of the map and temperature correction when really there are other aspects at play too.

Traditionally installers also had (or still have) to edge their bets a bit regards setting changeover temperature on the basis of how the driver will use the vehicle during the engine (and coolant) warm up stage when the vehicle is running on LPG... Some drivers will drive steady on expensive petrol until the system has switched to LPG and as soon as they know they're running on half price LPG see this as the green light to immediately put their foot down! For a sequential system set to switch at quite a low temperature the driver booting it soon after switching to LPG can easily see the reducer get very cold (like -30C), the reducer will then spit out liquid gas instead of vapour, the injectors not being able to handle the pressure or cold. Set the changeover temp a bit warm and the owner might complain that the vehicle runs on expensive petrol for too long before switching to LPG.

Some modern ECU's allow a great set of compromises to be dialled in.. E.g. Set a low changeover temperature but set the system to change back to petrol (momentarily) if engine load exceeds a certain calculated percentage while the reducer and/or gas vapour are below a certain temperature. My cars switch at 20C but if the reducer temp falls below 15C at any time it will switch back to petrol until the reducer has warmed past 20c again. If gas temp falls below 0C with engine load above 20% or if reducer temp falls below 25C with engine load above 20% it will momentarily switch back to petrol until engine load has reduced or temperature(s) have increased. 20% May not seem a lot of load but it probably represents around 50bhp in real terms (the way the systems calculate engine load isn't what you'd expect) but 50bhp is more than you'd use in most vehicles in most circumstances soon after starting a cold engine (when you're likely in a built up area or have to travel a narrow road before meeting a main road where you might then put your foot down a bit). Modern ECU's feature injector pre-heating, this pulses injectors as soon as the engine is started before the gas solenoids have been opened (solenoids open when the changeover temperature has been reached). While gas solenoids are closed the injectors are pulsed slowly for short duration at first, frequency and duration increasing as gas vapour pressure decreases to manifold pressure, this electrically warms the injectors by means of heating their solenoid coils, this helps to ensure injectors will perform a bit better than they otherwise might when they first start to have to meter gas (when the system switches to LPG). These facilities allow setting up a system with relatively cool changeover temp dialled in on most (but not all) installs regardless of how the driver might drive it during the warm up stage, they also make the system 'driver proof' (the driver couldn't upset the system, cause a misfire or bring on engine warning lights if they tried during the warm up stage). But still components must be selected that will handle cool conditions, calibration, temperature compensation and aspects of the install such as reducer pressure have to be set correctly to allow this. A lot of reducers will output a bit higher pressure when they're cool than when warm, a well setup/configured system won't pulse LPG injectors for much longer duration than petrol injectors when warm (this is to allow enough window for injector pulse duration for driving flat out at high engine rpm and is a small subject in itself), with higher pressure and colder gas this (cold gas and higher pressure) could mean that for correct fuelling at high loads the gas injectors should be pulsed for less duration than petrol injectors... A lot of ECUs will pulse gas injectors for a minimum duration that is at least as long as petrol injector duration on the first occurrence of gas injectors needing to be pulsed for less duration than petrol injectors, in severe cases an overly rich mixture can cause a misfire on first occurrence that gas injector duration should really be shorter than petrol injector duration.

Some vehicles (such as some VAG stuff) also apply choke effect during high load cool engine operation (most fuel injection systems apply choke effect at decreasing rate for increasing load, so there is little cold enrichment for high load operation), a really very rich mixture on petrol can translate into a mixture that is too rich to even ignite on LPG which would then give a misfire. To counter this, some ECU's allow setting a maximum gas injector duration when the reducer is below a certain temperature.

On a lot of modern vehicles fuel (petrol) pressure isn't manifold pressure relative, it is atmospheric pressure relative, they do have a fuel return but the fuel return isn't on the engine it is simply in the tank with the fuel pump (in this I'm not talking about the well known issues regards converting Fords etc to LPG on which a separate fuel return has to be fitted by the LPG installer). A normally aspirated engine may have fuel pressure fixed at (say) 4 bar above atmospheric pressure, which means that at idle when the engine is drawing most vacuum the petrol injectors effectively see more fuel pressure than they do at full load when the engine manifold pressure is at atmospheric pressure. Yet the LPG system reducer output pressure is manifold pressure relative not atmospheric relative. If we double fuel pressure to a petrol (liquid) or LPG (vapour) injector it will flow about 1.4x as much fuel for a given pulse length if all other things are the same. For a petrol injector most other things are the same but this is only true for an LPG injector if it is pulsed for long enough duration that it's opening and closing time is only a small fraction of the total time of the pulse and if temperature remains constant (density of the gas). Opening and closing time of LPG injectors are related to pressure and temperature, this is a different effect to density, so temperature and pressure both have a double whammy effect on how much gas an LPG injector will flow for a given pulse time. On modern ECU's that allow it I dial in some compensation for manifold pressure to account for the slight difference in flow of petrol injectors for effectively variable petrol pressure. Some installers notice that on some engines they need to dial in more or less rpm correction than on others but don't realise that they are accounting at least in part for effectively varying petrol pressure on some installs and not having to account for varying petrol pressure on other installs (which have a mechanical vacuum referenced fuel pressure reg on the engine itself). RPM correction will never fully account for varying fuel pressure when other factors such as temperatures are involved, e.g. the warming engine may have faster idle than the warm engine but also have higher manifold pressure than the warm engine. It is better to account for each aspect individually, RPM correction is one aspect that should be used to account for the different response of injectors at different pulse frequencies, it shouldn't really be used to make up for shortfalls in the shape of the map. The map should be used to account for the different flow of LPG injectors (opening and closing times and difference in flow rates) compared to petrol injectors... and since petrol injectors flow is affected by effective petrol pressure, petrol pressure has to be accounted for before setting the map. For an average returnless (return at the tank) petrol system running at 4bar relative to atmosphere we're only talking a 10% range of compensation for petrol pressure but when I see some installs having a map with a relatively high multiplier at idle and very low multiplier at high loads I know the installer hasn't accounted for petrol pressure and I know it won't be able to provide good fuel trims during the warm up stage.

By selection of components / nozzles / pressure and good ECU settings / calibration / temp compensation a system can usually be made to switch to LPG at a relatively cool temp (compared to old-skool installs) and deliver good fuelling without any drive-ability problems. I started one of my cars this morning, in 20 seconds it had switched to gas and even at that point it would have driven perfectly regardless of how I'd driven it. If I were to drive on petrol for 20 seconds per day for a year this would be the equivalent of driving on petrol for a total of 2 hours per year, though of course the 20 seconds per day will increase a little during colder months and there is the chance that if I put my foot down soon after the engine has switched to LPG the system will momentarily revert to petrol for a short time until the reducer / gas vapour temp readings have increase. But I've monitored the system and it seems it never has to revert to switching to petrol during the warm up stage, this will at least in part be due to the fact I'm driving in a built up area soon after starting the engine.

Bolt on reducer heating bits are available, just a shame that they're designed to work with reducers that are not very good at handling cold temps in the first place. We could come up with other ways of pre-heating any reducer and most vehicles/ECUs could easily be made to believe the engine is starting from warm so as not apply choke effect when starting from cold. Couple those points together and most engines could be made to start OK from cold regardless of the weather/engine temp... But since my own car switches to gas in 20 seconds on a cool morning I wouldn't bother modding my own car/LPG setup to start on LPG in cold conditions.
Last edited by LPGC on Wed Sep 16, 2020 11:21 am, edited 2 times in total.
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Brian_H
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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#25 Post by Brian_H » Tue Sep 15, 2020 9:05 pm

One plus side to the starting on petrol and running for a short time, is it keeps the petrol injectors in a state where if you did need to use them, you know they work, flushing some fresh petrol through them can only really help with that too.

It doesn't really use very much petrol going by how often you refill the tank, at least I don't find it does overall. Even with the occasional bit of running on petrol due to being out of gas I rarely put more than a full tank through any of mine in a year, and thats usually to freshen up whats been sitting in the tank for a while anyway.

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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#26 Post by Budgetbond » Tue Sep 15, 2020 9:51 pm

Thanks for the great explanation and reply Simon, that's v interesting, 20secs, like you say your not getting through much petrol with that situ, well done.

It'd be interesting to know if/how other countries set there systems up in a non temperate climate like a continental one, say Poland. eg.
Driving mainly around town, itd be advantageous for me to get a prompt changeover.
I suppose hypothetically, you could probably get some sort of preheater, electrically or something.
I've sort of blanked off my radiator, tried to optimise the reducer location and coolant pipes and fuel lines.
Of course during the winter usage of the heater or air con could have an effect too.
I wonder if in any of the Scandinavian countries they differ slightly in there pipe routing/length even maybe fuel tank location!!
Having said that the last time I was in northernish Norway it was ironically way way hotter than here!!
I'm going to watch for when my car seems to drop out of open loop mode itself and play with my settings a bit.
Btw I don't even know, at what temperature Lpg turns from liquid into gas at and what say the 'flash' temperature of Lpg is and how/if that differs from petrol?
Last edited by Budgetbond on Tue Sep 15, 2020 9:54 pm, edited 1 time in total.

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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#27 Post by Budgetbond » Tue Sep 15, 2020 9:52 pm

Oh, and cheers Brian too, hope you've been doing alrite.

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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#28 Post by Brian_H » Tue Sep 15, 2020 10:20 pm

Budgetbond wrote:
Tue Sep 15, 2020 9:51 pm
Thanks for the great explanation and reply Simon, that's v interesting, 20secs, like you say your not getting through much petrol with that situ, well done.

It'd be interesting to know if/how other countries set there systems up in a non temperate climate like a continental one, say Poland. eg.
Driving mainly around town, itd be advantageous for me to get a prompt changeover.
I suppose hypothetically, you could probably get some sort of preheater, electrically or something.
I've sort of blanked off my radiator, tried to optimise the reducer location and coolant pipes and fuel lines.
Of course during the winter usage of the heater or air con could have an effect too.
I wonder if in any of the Scandinavian countries they differ slightly in there pipe routing/length even maybe fuel tank location!!
Having said that the last time I was in northernish Norway it was ironically way way hotter than here!!
I'm going to watch for when my car seems to drop out of open loop mode itself and play with my settings a bit.
Btw I don't even know, at what temperature Lpg turns from liquid into gas at and what say the 'flash' temperature of Lpg is and how/if that differs from petrol?
On the temperature side, it depends on the pressure its being stored at. Its boiling point at normal pressure is −42°C. But even a bit of pressure will increase that level. Flash points and other info like that are on wiki here > https://en.wikipedia.org/wiki/Propane

You shouldn't find masking the radiator needed for newer vehicles provided the thermostat is working properly. Older ones where the fan runs all the time and there tends to be more coolant capacity in them maybe more so.

I generally find by the time I've reached the main road by my place (distance around 1/2 a mile) that its switched over on any of my cars. I could set it slightly lower, but 2 of them are using reducers that have been known to fail at low temperatures (I've seen one of them with the seal hanging out of the side of it at Simon's place after failing like that) so better to play it safe. Its low enough usage that its not worth bothering about to me, but then i use most of a tank of gas daily with work, and once its warmed up the first time it doesn't take anywhere near as long. Of course if your replacing a carb with single point, thats a different consideration again.

And I'm fine thanks for asking!

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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#29 Post by Budgetbond » Tue Sep 15, 2020 10:53 pm

Glad to hear it Brian I've missed ya!!, think it's absolutely fascinating terrestrial rocket scientry!! wish I'd have got into this a long-time ago, and become a Wernher von Braun like Simon, and you and Gilbert too.

Anyway, yeah half a miles hardly depleting the oil fields is it, maybe best to play slightly safe, I suppose it's in winter where it may have an effect, do the rubber diaphragm s in the reducer s potentially become brittle and split when cold or something?
Are some worse than others?

I think my reducer s a fairly standard, small stefanelli, think it maybe be similar to a tommasetto or something.

It does seem like there's quite a few standard common cheap components, valtek injectors, tommasetto multivalves and reducers, simpleish but maybe not quite so durable?

How similar are components within kits pretty interchangeable?
Are Italian AEB kits all fairly similar and the Polish kits fairly generic off each other generally?
(Sorry for the digress!!)

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Re: Ideal 'classic' car contender for singlepoint conversion ideas?

#30 Post by Pinger » Wed Sep 16, 2020 8:44 pm

Post # 24. Thanks - a very detailed insight into the current state of the art. Appreciated.

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