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From: Ron on 30 Aug 2007 04:42
Daryl Walford <dwalford(a)internode.on.net> wrote in
news:13dcv07kt6imvbb(a)corp.supernews.com:

> Ron wrote:
>> Daryl Walford <dwalford(a)internode.on.net> wrote in
>> news:13dckuhs1igtjf0 @corp.supernews.com:
>>
>>> Ron wrote:
>>>> "Jason James" <at(a)peace.com> wrote in
>>>> news:46d56fee$0$15512$c30e37c6(a)pit-reader.telstra.net:
>>>>
>>>>> "Paul Saccani" <saccani(a)omen.net.au> wrote in message
>>>>> news:lvpad39vevt1g2gcf6tgcgfn8k56vu9f6l(a)4ax.com...
>>>>>> On 29 Aug 2007 09:34:24 GMT, Ron <dodo(a)hotmail> wrote:
>>>>>>
>>>>>>> motoxxx43(a)hotmail.com wrote in news:1188375500.446790.194600
>>>>>>> @q3g2000prf.googlegroups.com:
>>>>>>>
>>>>>>>> hi i have recently have had my toyota 4runner converted to lpg
>>>>>>>> and have loss significant amount of power and was wondering if
>>>>>>>> this is just normal for gas and if so what sort of engine mods
>>>>>>>> work good with lpg? any info on this wold be greatly
>>>>>>>> appreciated thnks
>>>>>>>>
>>>>>>>>
>>>>>>> Tuning, you may have to retard the ignition
>>>>>> It's the other way around - you advance the spark curve at low
>>>>>> RPM, and retard the high end *compared* with a petrol curve at
>>>>>> high RPM
>> by
>>>>>> as much advance as you added at low RPM.
>>>>>>
>>>>>> This used to be done by distributor modifications, but it hard to
>> get
>>>>>> these done nowadays, so you could use something like an AEB
>>>>>> "Electronic Spark Advance Variator", which comes in a range of
>> models
>>>>>> to suit different kinds of ignition systems. Besides being
>>>>>> easier to set up, it runs dual curves, one for Petrol and one for
>>>>>> LPG.
>>>>>>
>>>>>>> and increase the gas flow.
>>>>>>> It will use more gas, but it is cheaper :-)
>>>>> The theory is, as far as I can dtermine, that LPG/air burns slower
>>>>> than petrol-mist/air, and hence this imparts a higher octane
>>>>> rating. The Cleveland 5.8L I have on gas will not ping with quite
>>>>> high advances up to 50 degrees BTDC. Hasten to add I didnt leave
>>>>> it like that, the "HEI" dizzy I bought new was set-up that way
>>>>> initially.
>> This
>>>>> engine also has a significant power drop on gas, and after much
>>>>> investigation including a wide range of inneffective mixture and
>>>>> ignition timing settings, Athol who is an engineer here, passed
>>>>> the opinion that its likely the "mixer" is too small and is
>>>>> limiting intake. The carter carby has quite high CFM figures, but
>>>>> opening the secondaries doesnt alter engine output, or more
>>>>> significantly, doesnt cause a mixture change, hence the open secs
>>>>> are only acting as a larger intake manifold 'mouth' size without
>>>>> any chnage in flow thru the mixer on top, as its already
>>>>> maxed-out. Not saying this is the OP problem, but thought it worth
>>>>> mentioning.
>>>>>
>>>>> Jason
>>>> With the XJ6, the timing has to be changed from 6 BTDC to 12,
>> otherwise
>>>> it gets very hot :-)
>>> In other words you have advanced it 6 deg which is what is normally
>> done.
>>>
>>> Daryl
>>>
>>
>> Is going from 6BTDC to 12 BTDC advancing?
>
> Yes, 12 deg BTDC occurs earlier than 6 deg so its advanced.
>
>> I would have thought that is retarding the spark?
>
> Nope.
>
>
> Daryl
>

So I've discovered. You are never too old to learn :-)

Cheers,
Ron
From: Noddy on 30 Aug 2007 05:21

"John McKenzie" <jmac_melbourne(a)bigpond.com> wrote in message
news:46D67B90.3852(a)bigpond.com...
> OOPs sent it too soon.
>
> Those impco 200s would be mated to a single impco model E convertor
> (*for cost, availability and flow reasons, in about that order)

Which would make a good all round system.

--
Regards,
Noddy.


From: Clogmeester on 30 Aug 2007 20:32

"Toby Ponsenby" <me(a)privacy.net> wrote in message
news:fb7dpb$slk$1(a)registered.motzarella.org...
> On Thu, 30 Aug 2007 08:41:20 +0000, Ron blathered on:
>
>> "Noddy" <dg4163@(nospam)dodo.com.au> wrote in
>> news:46d67988$0$90162$c30e37c6(a)lon-reader.news.telstra.net:
>>
>>>
>>> "Ron" <dodo(a)hotmail> wrote in message
>>> news:Xns999CA56C2934DGPS(a)64.209.0.82...
>>>
>>>> Is going from 6BTDC to 12 BTDC advancing?
>>>> I would have thought that is retarding the spark?
>>>
>>> No, it's advancing.
>>>
>>> BTDC is advanced, which means the plug is firing "X" amount of
>>> crankshaft degrees in advance of the piston reaching top dead centre.
>>> The higher the figure "X" is, the more advanced the timing. Retarded
>>> is the opposite, where the plug is firing "X" amount of degrees after
>>> top dead centre.
>>
>> Well I'll be fucked!
>> Thankyou for the explanation :-)
>> I never did really understand ignition timing..
>
> OMG...
> I hope to hell you remember that for long enough to not drive me nutso
> with any more impossible scenarios from your engines:-)
>

The mind boggles doesn't it...



From: Jason James on 31 Aug 2007 07:48

"Ron" <dodo(a)hotmail> wrote in message
news:Xns999CA56C2934DGPS(a)64.209.0.82...
> Daryl Walford <dwalford(a)internode.on.net> wrote in news:13dckuhs1igtjf0
> @corp.supernews.com:
>
> > Ron wrote:
> >> "Jason James" <at(a)peace.com> wrote in
> >> news:46d56fee$0$15512$c30e37c6(a)pit-reader.telstra.net:
> >>
> >>> "Paul Saccani" <saccani(a)omen.net.au> wrote in message
> >>> news:lvpad39vevt1g2gcf6tgcgfn8k56vu9f6l(a)4ax.com...
> >>>> On 29 Aug 2007 09:34:24 GMT, Ron <dodo(a)hotmail> wrote:
> >>>>
> >>>>> motoxxx43(a)hotmail.com wrote in news:1188375500.446790.194600
> >>>>> @q3g2000prf.googlegroups.com:
> >>>>>
> >>>>>> hi i have recently have had my toyota 4runner converted to lpg and
> >>>>>> have loss significant amount of power and was wondering if this is
> >>>>>> just normal for gas and if so what sort of engine mods work good
> >>>>>> with lpg? any info on this wold be greatly appreciated thnks
> >>>>>>
> >>>>>>
> >>>>> Tuning, you may have to retard the ignition
> >>>> It's the other way around - you advance the spark curve at low RPM,
> >>>> and retard the high end *compared* with a petrol curve at high RPM
> by
> >>>> as much advance as you added at low RPM.
> >>>>
> >>>> This used to be done by distributor modifications, but it hard to
> get
> >>>> these done nowadays, so you could use something like an AEB
> >>>> "Electronic Spark Advance Variator", which comes in a range of
> models
> >>>> to suit different kinds of ignition systems. Besides being easier
> >>>> to set up, it runs dual curves, one for Petrol and one for LPG.
> >>>>
> >>>>> and increase the gas flow.
> >>>>> It will use more gas, but it is cheaper :-)
> >>> The theory is, as far as I can dtermine, that LPG/air burns slower
> >>> than petrol-mist/air, and hence this imparts a higher octane rating.
> >>> The Cleveland 5.8L I have on gas will not ping with quite high
> >>> advances up to 50 degrees BTDC. Hasten to add I didnt leave it like
> >>> that, the "HEI" dizzy I bought new was set-up that way initially.
> This
> >>> engine also has a significant power drop on gas, and after much
> >>> investigation including a wide range of inneffective mixture and
> >>> ignition timing settings, Athol who is an engineer here, passed the
> >>> opinion that its likely the "mixer" is too small and is limiting
> >>> intake. The carter carby has quite high CFM figures, but opening the
> >>> secondaries doesnt alter engine output, or more significantly, doesnt
> >>> cause a mixture change, hence the open secs are only acting as a
> >>> larger intake manifold 'mouth' size without any chnage in flow thru
> >>> the mixer on top, as its already maxed-out. Not saying this is the OP
> >>> problem, but thought it worth mentioning.
> >>>
> >>> Jason
> >>
> >> With the XJ6, the timing has to be changed from 6 BTDC to 12,
> otherwise
> >> it gets very hot :-)
> >
> > In other words you have advanced it 6 deg which is what is normally
> done.
> >
> >
> > Daryl
> >
>
> Is going from 6BTDC to 12 BTDC advancing?
> I would have thought that is retarding the spark?

As the engine turns clockwise (viewed from the front) each cylinder
approaches the top of its stroke on the compression stroke. Typically on
petrol, the plugs are fired just before the piston reaches it uppermost
position. This is because it takes time for the fuel to start burning and
finish burning..so they start the burn early by typically 5-8 degrees before
TDC (BTDC). Now because LPG is slower than petrol,..they *advance* or make
the sparkplugs fire even earlier before TDC, say an additional 4 degrees,
bring the ignition timing to around 12 degrees of advance. This is called
advancing things, as you are making it happpen earlier in time. I f you
leave the spark until later than optimum,..you are slowing the firing time
or retarding it. If an engine is firing at or after TDC (atdc) this means
the cylinder walls will be exposed to more end-burn, hence more heat
dissapation. This end of the burn doesnt contain any significant power as
all the useful gas-expansion has occured from roughly TDC onwards.

Jason


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