porsche 944 turbo

[Uros Piperski]

Ma ima njih koliko hoces, nije to problem






I alfa 147 ima trubice (4kom, koliko tebi treba?)
Mozes jeftino da nadjes karburatore od 40mm (dcoe, dhla). Oni imaju po dva leptira od 40mm i kostaju oko 25e/kom. Iseces deo koji ti ne treba, zadrzis leptire i vozis. Jedino je problem sto je 40mm mozda malo, a oni od 45mm su mnogo skuplji.
Ako nista ne uradis, ja pravim leptire za drugi motor pa se javi ako treba i tebi.

[ale944]

@uros
4 leptira mi trebaju, snaga svakog cilindra je trenutno oko 40-ak kw, pa onako , "od oka" bi 40 mm bilo sasvim dovoljno. Posto je motronic u pitanju, sistem meri kolicinu vazduha preko VAF-a (volume air flow meter, sa klapnom), trubice bi morale vuci vazduh iz neke vrste komore na koju bi opet morao biti vezan protokomer. ovo je bitno prvenstveno da bi ecu na osnovu "load-a" odredio paljenje, posto me fuel ne zanima preterano. voleo bi da vidim tvoj sistem koji radis, pa mozes na pp da mi ostavis neki kontakt tel. pa da se cujemo oko toga... hvala

[Uros Piperski]

Sa 40mm bi bio na granici za tih 40kw, sto znaci da bi ti toliki leptir smetao za svako dalje povecanje snage. Ja bih isao na najmanje 42, bolje 45mm.
Trubice bi svakako bile zatvorene u air-box na koji bi isao filter, pa izmedju box-a i filtera mozes da smestis protokomer. Jesi li razmisljao da predjes na AMM ili MAP? Klapna u protokomeru pravi veliku smetnju za strujanje vazduha.
Idemo na PP, ubice nas Dora

[*Egon*]

Nece da vas ubije Dora, nego predjite lepo u drugu temu.

[ale944]

.....evo proslo je dve godine od poslednje poruke, pa da malo osvezim temu
posto su se od vremena kad sam poceo temu promenile dosta cene uredjaja za ubrizgavanje gasa, to se nametnulo kao logican izbor.
ugradio sam stag ecu, tomaseto arctic reduktor i valtek dizne.
od boce do reduktora naravno 8ica, multiventil totalno razbusen zbog sto manje restrikcije protoku gasa, i isparivac takodje razbusen na kriticnim mestima. tokom niskih temperatura je bilo karakteristicnih problema za ovakve konfiguracije (turbo), pa ako sipam "losiji" gas, i bude ispod nule jednostavno cim proradi turbina ostane bez goriva, i za to nema leka.
primetio se da se to redovno desava kad sipam na MB gas pumpi, dok je na Kryo gas pumpi uglavnom bila dosta bolja situacija, pa nije bilo problema osim pri bas niskim temperaturama i praznijim rezervoarom.

kad je to sve leglo kako treba, razlika u snazi je bila minimalna u odnosu na benzin, ali sam resio i uspeo da prevazidjem i taj problem.

pre par dana uz veliku pomoc Gumetine sam ubacio cip optimizovan za lpg. ideja nam je bila naravno da pomerimo paljenje u napred, ali za koliko i u kom rezimu smo samo pretpostavljali. napravljeno je nekoliko razlicitih mapa paljenja, i probana jedna po jedna, i od njih smo izdvojili jednu koja se najbolje pokazala. inace razlika u udnosu na originalnu mapu se oseti, nije nista spektakularno ali taman onoliko koliko se oseti pad snage na gasu sa neoptimizovanom mapom. inace zanimljivo je da je motor trazio mnogo veci advance u odnosu na benzin na nizim obrtajima i opterecenjima (5-10 stepeni) dok je na visim mapa skoro ista, tj, 2-3 stepena ponegde pomerena. naravno sledi razrada mape koju smo izdvojili kao najbojlu za eventualna dalja poboljsanja.

ovo pisem najvise zbog toga sto vidim da na forumu ima dosta ljudi koji i dalje gledaju na gas kao nesto sto skrnavi performanse motora, i uporno odbijaju da shvate da dobro podesen gasni sistem ima mnoge prednosti u odnosu na benzin, ne samo zbog cene gasa vec i zbog njegovih kvaliteta u pogeldu sagorevanja.

ako bilo ko sumnja u ovo sto pisem moze se uveriti u jednoj test voznji kako to izgleda, uvek sam raspolozen za tako nesto.

znaci ukratko dobro podesen sistem + optimizovano paljenje i nema razloga da vlasnici jacih masina koji zele da im masine i ostanu jake ili postanu jos jace beze od gasa, naprotiv.

takodje posto imam knock monitoring gas je daleko superiorniji od benzina dozvoljava veci boost i ukoliko iz bilo kojeg razloga dodje do siromasne smese, i dalje nema knocka, dok na benzinu samo vristi....

[sw.brick]

super za jasan napredak

da li bi mogao da izdvojis pri kom natpritisku turbine se desava knock na benzinu a nema ga jos na gasu ?
i kada pocinje knock na gasu ?

ako jos mozes i da se prisetis kako je to sa starom mapom paljenja a kada sa novom, sve sto sam hteo da znam a nisam smeo (znao) koga da pitam bice ispunjena znatizelja.

[dranix]

Ja bi ovde dodao jos nesto.
Kod luksuznih ili sportskih oldtimera ili auta starijih godista iz doba kad su carovale k-glave danasnjom ugradnjom savremenog sekvencijalnog sistema se podize ubrizgavanja (goriva) gasa na daleko visi nivo po pitanju preciznosti sto je ogromna tehnicko-tehnoloska prednost.
Naravno da je potrebna i modifikacija upravljanja sto nazalost trazi eksperte za to i malo a ponekad i malo vise eksperimentisanja, strpljenja i proba.
Raduje me da takvih jos uvek ima. Samo napred.

[ale944]

da li bi mogao da izdvojis pri kom natpritisku turbine se desava knock na benzinu a nema ga jos na gasu ?
i kada pocinje knock na gasu ?

ne bi mogao da dam neki precizan odgovor, jer je u toku eksprerimentisanja dosta stvari menjano, pa je suvise promenljivih ulazilo u igru da bi znao sta je tacno koja i kad prouzrokovala. sa pritiskom punjenja sam isao do 1.2 - 1.3 bara, ali je to previse za fabricku kkk k26#6, izlazi iz polja neke prihvatljive efikasnosti .. ali i na tim pritiscima nije bilo knocka na gasu sa benzinskom mapom paljenja. na benzinu nisam probao (jesam ranije ali nisam imao knock indikaciju pa ne znam sta se desavalo)
overload je trenutno podesen na 0.9-1 bar i sve dalje navedeno se desavalo na ovim pritiscima.
na benzinu se knock javljao sa malo siromasnijom smesom na ovim pritiscima sa benzinskom mapom paljenja, dok sa istom mapom sa skroz siromasnom smesom gasa nema knocka. ovo je probano cisto eksperimenta radi da vidim kako radi knock sensing.
na gasu se knock javljao samo pri eksremnim uglovima preptaljenja (23-24 stepena) na full loadu pa je spusteno na 17-18 gde nema problema.
to je i dalje zvuci kao veliki advance, ali s obzirom da je geometrija glave
takva (sporogoreca, 2ventila) to je sasvim ok.
na benzinu je original mapa bila na 15-16 stepeni na full loadu.

[sw.brick]

sasvim jasno, hvala.

[lule]

Mali doprinos temi da ne padne u beznadje...

General Information
905 - Ignition timing for engines converted to run on LPG


It is important to remember that the burning rate of LPG differs from that of petrol. At low RPM the burning rate is slower and more advance is needed. At high speeds the burning rate is faster, consequently less advance is needed.
When an engine is converted to run on LPG as a single fuel engine the ignition timing should be revised to give more ignition advance than the petrol engine at low speeds, and less than the petrol engine at higher speeds. This means that conventional distributors must have adjustments made to the mechanical advance mechanism to reduce the rate that advance increases with speed. Merely altering the static timing is not correct.
In the case of a dual fuel conversion the matter is complicated because the ignition timing needed for optimum performance on petrol will give too much advance at high speeds when LPG is used. The difference could be as much as 10 degrees, see graph below. This graph shows typical timing for a petrol engine tuned for petrol only, a correctly calibrated LPG setting and compares these with incorrect timing for LPG achieved when the distributor has been advanced with no adjustment for rate, "Petrol+adv".


These ignition advance curves are notional only and not specific to any engine type. They include static advance and mechanical advance (which is speed dependent) but do not include any part throttle advance as this is manifold vacuum dependent.
These graphs show the following;
• An engine tuned for optimum performance on petrol and running on LPG will have too little advance at low RPM and too much at high RPM. It could therefore encounter detonation at higher RPM.
• An engine tuned for optimum performance on petrol and running on LPG with the distributor advanced but not recalibrated with a different rate will have excessive advance at high RPM, and a higher probability of encountering detonation.
• An engine tuned for optimum performance on LPG and running on petrol will have excessive advance at low RPM and therefore a possible detonation problem.
• Incorrect ignition timing on any engine will lead to problems. Detonation is not always audible. The nature of the problems encountered will vary with the engine type, the octane rating of the fuel (petrol or LPG), engine speed, and in the case of LPG the installation and type of conversion and the source of the LPG.

Here is a list of some typical and some less common effects observed on dual fuel engines operating in Australia:
• Piston land or crown erosion
• Ring land breakage
• Groove wear
• Skirt scuffing (usually on the thrust side only) or breakage
• Top ring scuffing or breakage or molybdenum flaking out
• Spalling of the chromium on oil ring rails

Unfortunately it is not possible to optimise the ignition advance rates for petrol and LPG with the one setting on a distributor so a compromise setting will usually be obtained. From a performance point of view this may represent little problem since the engine is most likely to run on petrol only occasionally, i.e. when the gas tank is empty. Later engines with engine management systems and the more sophisticated LPG conversions can have the advance rate and initial spark timing settings optimised for both fuels.
Ignition Switching Devices
The best way to be sure that the ignition is optimised for both fuels is to install an ignition switching device, known also as "Dual Curves". These units are wired into the ignition system and switch automatically to the LPG or petrol setting when the fuel switch is activated. They will give more initial advance than the petrol setting when the engine is running on LPG, and as speed increases they will give less advance than the petrol setting. Although these are usually pre-calibrated for a range of applications (i.e. not necessarily calibrated for a particular engine) they will give a much better approximation to the ignition requirements for engines being converted than the incorrect practice of merely altering the static timing.
Small Engines In Commercial Applications
It can be seen from the graph "LPG" that there is less advance needed at higher operating speeds for any engine running on LPG. For larger more powerful vehicles operating in city areas the engine is seldom operating at maximum power so is possibly going to be less liable to damage as a result of incorrect ignition calibration.
However smaller engines fitted to delivery vans operating in city areas will usually be operating at higher loads and frequently at maximum throttle. These applications are typically Mazda FE and MA engines in light commercial applications and they work much harder due to the weight of the vehicle and even the way in which these vehicles are driven. If they are merely given some additional static advance (as often seems to be the case) the error is exaggerated at higher speeds because there was already too much advance at high speed when the ignition was set as standard. Referring to the graph again, note the error that would occur if the LPG engine is operated on the petrol calibration at high speed. That is bad enough, but now if the static timing is advanced as per curve "Petrol+Adv" (i.e. by merely advancing the distributor) then the error is doubled!
For this reason it is even more critical that any dual fuel LPG conversion in such an application includes a dual curve ignition switching device. (There is one made by AEB and available from major LPG conversion companies).
Nevertheless it is the responsibility of the customer to ensure that the engine is not damaged by continued operation with ignition settings not optimised for the fuel being used.
LPG Fuels
LPG fuels vary far more from state to state, area to area, and from time to time than petrol. The variation is often due to the proportion of propylene in the fuel which is based mainly on propane and butane. Propylene depresses the octane number. The octane value of LPG is usually regarded to be 100 to 105 RON. However it is understood that octane levels in some cities are often as low as 96 which is the same as super grade leaded petrol. Consequently there can be abnormal combustion problems (i.e. detonation) in LPG fuelled engines where the compression ratio has been raised to take advantage of the supposedly higher octane number of LPG. Also there could be problems in these engines where the compression ratio is standard, (or slightly increased as a result of reconditioning) where the ignition has been incorrectly advanced at static only. Remember that for every degree of mechanical advance you add the initial static advance to it. In other words if the distributor mechanical advance is providing 4 degrees at 600 RPM and the static timing is 6 degrees BTDC the total advance that the engine sees at 1,200 RPM is 14 degrees. Also if the compression ratio of an engine is raised for any reason the amount of ignition advance that is needed to achieve best performance usually decreases and failure to take account of this can lead to detonation occurring.
Summary and Recommendations
• Ignition requirements for LPG are not the same as for petrol operation
• The octane rating of LPG (i.e. its knock resistance) cannot be assumed to be the same in all areas of Australia and at all times.
• Advancing the static ignition setting without also modifying the advance curve to reduce the rate of advance is incorrect and will promote abnormal combustion.
• Detonation problems are likely to be encountered if the ignition is not optimised for the fuel being used at the time.
• Switching devices which automatically alter the ignition advance and static settings are available and their use is strongly recommended.
• Compression ratio should not be increased for LPG unless the octane number of the fuel to be used is known to be 100 or greater, and maintained at that level.
• Small engines doing a big job (i.e. in light commercial applications) are more prone to detonation induced problems due to their duty cycle being mostly at high loads and speeds.
• It is not the responsibility of a product supplier, nor the engine reconditioner, to ensure that an engine is properly tuned since neither can be fully aware of the operating circumstances and the degree of modification which has taken place since the engine was originally designed (to run on petrol) and manufactured.
• Ultimately it is the responsibility of the owner of the vehicle to ensure that the appropriate measures have been taken to avoid abnormal combustion in any vehicle converted to LPG.




Author: Kathy Dimovski 11/11/98 14:16:00

[dranix]

Veoma zanimljiv clanak kao primer sta sve citamo na netu.

Ovako pisu NOVINARI. Nije navela ni jednu cifru sto je pametno jer mozda i ne zna.
Motor ne radi po principu necije logike nego po fizickim zakonima.
Nema svaki motor (zbog svoje konstrukcije) mogucnost da istom brzinom sagoreva gorivo. Zato se mape i stimaju za svaki posebno a na stranu sto se moze dobiti drugaciji karakter motora u zavisnosti od rezima tj. opsega u kome se najvise KONKRETNO koristi.
Daleko od toga da je ikome cilj da ide tako "daleko" da dodje do zveckanja motora. Kao sto doticna kaze to se ne cuje bas uvek.
Zato postoji knock senzor koji "cuje" UVEK a njegovi podaci se procesuiraju i ulaze u konacnu odluku o tome koliko advace je potrebno u TOM trenutku da bude max a sigurno za motor.
Ne kazem da je svaki motor sa upravljanjem kao Saab koji "zna" ( u oktanima) koje gorivo trenutno trosi ali ni ostali nisu bili bas tako naivni u ONO vreme osim sto se tada nije mislilo na ekologiju a sad to MORA sto zbog dzepa, sto zbog rigoroznih normi.
Tekst lici na Frankenstajna koji je malo izgubio pojam o vremenu i prostoru.

Sta li je ovde htela da kaze?

It is important to remember that the burning rate of LPG differs from that of petrol. At low RPM the burning rate is slower and more advance is needed. At high speeds the burning rate is faster, consequently less advance is needed.

[sw.brick]

i meni to zapada u oci, kako se menjaju hemijske osobine goriva sa promenom broja obrtaja motora ?

prvi put cujem ovakvo obrazlozenje.

ne znam ni kada je ovaj tekst pisan, ako je to bilo negde 60tih ili 70tih godina proslog veka mogu da razumem, tada se jos lutalo sa LPG, sistemi paljenja su bili analogni (da ne kazem primitivni, tj nisu bili samouceci), kompjuteri nisu bili uposljeni za paljenje i ubrizgavanje (osim rektih izuzetaka) itd.

na vise mesta u tesktu se pominje problematicno stanje sa snabdevanjem LPG po osobinama, i mogucnosti da se natoci LPG van normi, tj subpstandarnih osobina /kvaliteta.

AEB je poznata italijanska firma i ima podosta takvih elektronskih spravica koje se pominju u tekstu, ali se prevashodno koriste za CNG tj metanski gas a moze i za LPG.

moze li se dobiti linka ka originalu, ili priloziti ovde grafikoni koji se pominju u tekstu da vidimo o kojim se brojkama radi.

Boschovi sistemi paljenja jos od kraja 80tih godina nemaju taj problem koji je opisan u tekstu, i samoprepoznaju oktanski broj goriva i shodno tome sami nauce koju krivu paljenja treba da naprave- tokom voznje auta.

tekst se sa razlogom osvrce na probleme prilagodjavanja motora upotrebi razlicitih goriva, mada mislim da se pomalo preteruje sa brigom.
bar kada je u pitanju evropski prostor gde nema loseg goriva, tj nema LPG ispod 100 oktana nigde u ponudi.

[lule]

Evo linka: http://www.acl.com.au/web/acl00056.nsf/ ... enDocument

[sw.brick]

ok, hvala 1998. godina.

to oko promene brzine sagorevanja goriva sa menjanjem obrtaja mi i dalje nije jasno..

[ale944]

ovo sa promenom brzine sagorevanja nije bas netacno... sad da li se radi bas o brzini sagorevanja ili samoj dinamici procesa - period inicijalnog paljenja smese,period sirenja plamena i period potpunog sagorevanja na kraju... izgleda da niko ne pouzdano ne zna, ili ja nisam uspeo da nadjem pravi odgovor.
svojevremeno sam isti podatak nasao na vise razlicitih strana i skroz se zbunio... bilo je iskustava ljudi sa cistim propanom, sa raznim mesavinama lpg-a itd... kontaktirao sam neke ljude koji su jaki u ovoj materiji i najprecizniji odgovor koji sam dobio je otprilike bio "moz' bidne al i ne mora"
tacnije, zavisi dosta i od vrste motora i od sastava lpg-a. koliko se secam ova pojava je izrazenija kod propana nego kod butana gde cak ni ne mora da je bude. u nekim slucajevima na koje sam natrcao cak trebalo i smanjiti pretpaljenje u o odnosu na benzin, a informacije su bile dosta relevantne jer se radilo ili o istrazivanjima raznih naucnih institucija ili ljudi koji se profesionalno bave motorima/lpg/cng-om.
u mom slucaju se pokazalo kao tacno, dosta veci advance u odnosu na benzin je na nizim obrtajima, dok na visim 5-6k rpm advance je tek malo veci nego na benz , oko 2st., i tad mi se ponekad javi knock, pa cu verovatno ostaviti u tom rezimu skoro istu mapu kao i za benzin.
dakle ova pojava definitivno postoji, ali nije pravilo.

It is important to remember that the burning rate of LPG differs from that of petrol. At low RPM the burning rate is slower and more advance is needed. At high speeds the burning rate is faster, consequently less advance is needed.