lpg performance
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From: Noddy on 30 Aug 2007 04:02 "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. -- Regards, Noddy.
From: John McKenzie on 30 Aug 2007 04:09 Ron wrote: > > John McKenzie <jmac_melbourne(a)bigpond.com> wrote in > news:46D6466D.441B(a)bigpond.com: > > >> With the XJ6, the timing has to be changed from 6 BTDC to 12, > otherwise > >> it gets very hot :-) > > > > Which makes perfect sense Ron, but the problem is that at higher rpms, > > once the mechnical advance comes in, it will be 6 degrees more advanced > > at the higher rpms (for any given rpm point, in effect it'll be 6 > > degrees more advanced). > > > > Now that _is_ generally what you would want and need up to about > > 2500-2600rpm (possibly 3000rpm, but I'd want to look at the factory > > curve, and for that matter the dizzy period, as the advance springs > > would have almost definitely have sagged altering the scenario too). > > > > What you might actually find is that the springs _have_ sagged, and > when > > you adjust it to 12 initial, the mech advance has already come in > > somewhat due to sagged springs and it might therefore actually not have > > more advance up higher than if you had setup a brand new stock curved > > dizzy in there. > > > > So in that instance, you might actually have lucked into a situation > > where running 12 degrees initial _was_ alright all round for lpg. I > > wouldn't bet on it, but it's certainly not inconceivable given the > > circumstances as I've inferred/interpreted them to be. > > > > John, > > That is indeed possible, the distributor is 33 years old :-) > 3000rpm is as high as I ever take it, and it runs out of power at 4000. > > Recently I had it on initial of 8BTDC and the car ran out of puff at > 3000rpm. If you kicked it back to 2nd at 100kph, nothing happened, it > could not gain speed :-) It never used to be like that, so I guess I > should take it to a LPG joint and get it tuned. > > Perhaps I should overhaul the dizzy first:-) Remind me Ron - I do recall you posting an engine bay pic - it was a twin carb setup I believe with twin spuds to convert to lpg? I know this is a bit off track but bear with me. What I'd suggest (get Atec off his bum and get him tracking down the bits and helping with the fitment) is giving thought to the following. If you do upgrade the ignition - look to getting something which is hei. The petronix conversion you have is _probably_ (atec can check) still running a points spec coil (and hence similar output) but electronic triggering. This _is_ a step up over points for two reasons - one is that it doesn't wear out or close up the gap, or (depending on specific model) have points bounce issues. The other is it _always_ has near optimal signal and voltage/current to the coil - so it basically works like a hypothetically perfect and optimal points setup _all the time_ HEI, is the next step up - with much hotter spark. It's absolute gold for lpg, well worth the price of admission. I'm not sure if anything later will retrofit into the jag engines (it's been a good 17 years since I worked on them) but it's certainly worth investigating. If not there's probably a conversion of some sort from another engine that jag enthusiasts might know about. On the dizzy itself - imo - if you get it recurved definitely get it recurved for lpg. There's just no good reason to ever run it on petrol again. Even if you did _have_ to you could just go a touch easier on the throttle at mid range rpms (which for this specific engine and driver and needs etc would be from 1000-3000rpms). There's been a fair bit of info in this thread, which is fairly accurate, but a little confusing too. Short version - you'll want more initial (you might even want as much as 14-16 - it'd take a little testing) and have the mech advance curve altered so that with 14-16 initial you have only 30 total by 2800rpm. that might seem low. It _would_ possibly end up wanting more than that - it'd depend on how low the compression ratio is. Being that it's fully rebuild not that many years back, it would (as a result of even the minimal shave of the head and block to clean it up during the reco, but also if it was bored to the next oversize, more capacity squeezed into the same space, or in fact a smaller space as well (due to the machining) will mean a higher than factory comp ratio)) have a higher than std comp ratio, so you'd have to factor that in. further along - the omvl is ok for towing and not really interested in peformance stuff. I'd suggest perhaps an alternative. They aren't the 'worlds greatest' or anything, but a pair of impco 200 gas mixers - with either factory or adapted from a small 4cyl twin efi throttle bodies would really help give it enough flow to give it some zip.. You're probably reaching the limit of the omvl. I've heard a few figures thrown around - 200bhp is about the most I have heard of. On lpg as they run out of flow, they just drop power, but don't show what might be a blatantly obvious clue as to what's happening - often just written off as 'typical power drop from lpg' which it technically isn't . -- John McKenzie tosspam(a)aol.com abuse(a)yahoo.com abuse(a)hotmail.com abuse(a)earthlink.com abuse(a)aol.com vice.president(a)whitehouse.gov president(a)whitehouse.gov sweep.day(a)accc.gov.au uce(a)ftc.gov admin(a)loopback abuse(a)iprimus.com.au If you didn't know it was wrong,why did you cover it up? abuse(a)msn.com $USER@$HOST $LOGNAME(a)localhost -h1024(a)localhost root(a)mailloop.com abuse(a)federalpolice.gov.au fraudinfo(a)psinet.com abuse(a)cia.gov $USER(a)localhost abuse(a)sprint.com abuse(a)fbi.gov abuse(a)asio.gov.au $LOGIN(a)localhost
From: John McKenzie on 30 Aug 2007 04:10 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) -- John McKenzie tosspam(a)aol.com abuse(a)yahoo.com abuse(a)hotmail.com abuse(a)earthlink.com abuse(a)aol.com vice.president(a)whitehouse.gov president(a)whitehouse.gov sweep.day(a)accc.gov.au uce(a)ftc.gov admin(a)loopback abuse(a)iprimus.com.au If you didn't know it was wrong,why did you cover it up? abuse(a)msn.com $USER@$HOST $LOGNAME(a)localhost -h1024(a)localhost root(a)mailloop.com abuse(a)federalpolice.gov.au fraudinfo(a)psinet.com abuse(a)cia.gov $USER(a)localhost abuse(a)sprint.com abuse(a)fbi.gov abuse(a)asio.gov.au $LOGIN(a)localhost
From: Daryl Walford on 30 Aug 2007 04:12 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
From: Ron on 30 Aug 2007 04:41
"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.. |