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Toymods » General Car Talk » Higher RON Fuels: Did you know?

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trd3sg
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Location:
Sydney Australia
Registered:
June 2005
Re: Higher RON Fuels: Did you know? Sun, 19 June 2005 06:44 Go to previous messageGo to previous message
st184 sillycar wrote on Wed, 15 June 2005 19:56

As I see it, it all depands on how "smart" your car is. older carbied, distributer ignited cars will have a minimum RON needed to avoid pinging. Feeding the old girl fuel with a higher octane rating (but the same energy density) shouldn't have a noticeable benefit. Newer EFI-run cars are a different kettle of fish. A particularly clever computer can run at near-optimum on a huge range of petrols. The GenIII for exapmle constantly adjusts ignition advance, injector duration AND injector phasing according to the conditions. This "making it up as it goes" automatically adjusts for fuel RON.

Did I mention teh GenIII calculates exhaust temp & heat-soak, to prevent cat-cooking and piston damage? Pretty good eh? - although the masses of extra fuel it dumps into the ports to keep things cool REALLY kills fuel economy wen towing big, heavy trailers.


ok - this post along with mattitude's post seem to make the most amount of sense

as originally stated - higher RON fuels IN THEMSELVES AS A VARIABLE do not add any performance value to a motor - any performance gain realised from merely adding PULP will be due to other factors - like in st184's post - the reason for the increase in performance in later model cars is the "fuzzy-logic" ability of factory ECU's to 'learn' to cope with the driving habits - for instance, after gunning a motor at WOT for two minutes straight without knocking, the computer in most quality multi-point EFI cars will be able to vary ignition timing to take advantage of the 'atmosphere' provided by PULP which makes is less prone to detonation or preignition.

As a general rule, higher RON fuels burn slower than lower RON fuels - think of this scenario - you have advanced your static ignition timing two degrees - what does this practically involve - the moving forward in time of the spark before a given point of the motor's cycle at IDLE - ie, lets say 10 deg btdc - your dizzy\coil\cas\computer (ignition triggering device) will send a spark to the relevant cylinder 10 degrees on the crank before your respective piston reaches top dead centre on its COMPRESSION stroke, - ie, you are bringing it forward - now as a motor increases its rpm, then the 'window' of opportunity to induce the spark at the correct time becomes much smaller - thus why mechanical or electronic advance is used to advance the timing in increments as the revs increase - BUT THIS CAN ONLY BE DONE TO A CERTAIN POINT - the advantages of this are well documented, in that by the time the ignition actually starts in the combustion chamber the piston has completed its compression stroke and will be on its way down with a greater force due to 'perfecting' the timing - pinging exists for one of two reasons -
1. either the fuel is burning way too quickly (because of its lower RON, ie. quicker burn compared to the slower burn of the higher RON fuel) and thus the 'explosion' is happening way too far in advance and is therefore exerting a force against a mass of metal (piston) moving in the opposite direction to the force (not good).

AND\OR

2. Hot spots in the combustion chamber causing the fuel to ignite before its peak compression\timing period or before the spark is actually delivered to the cylinder (hot spots can come from ridges, faulty plugs, gunk in the combustion chamber, faulty valvetrain system etc etc) - this has the same effect as fuel burning too quickly and will be pushing down against the piston moving up to complete its compression stroke (the piston can't exactly stop in its tracks [by virtue of the mechanical rotating mass structure] and if the force of the explosion\ignition is stronger than the force of the piston somehow, then you WILL have a shattered piston guaranteed) - now if a motor's compression ratio has been increased from a standard 8.0:1 to say 10.5:1, without even altering ignition timing or fuel values at all - this may provide an atmosphere for detonation, simply from the greater compacting of the fuel, which (due its slower burn being a lower RON fuel or due to hotspots) will in itself put undue heat\force unexpected into the combustion chamber and the fuel will ignite on its own from the pressure before the spark is even delivered.

and that is what the tick tick tick or thud thud thud sound is

Now - in taking the above into consideration, if a car is fitted with a knock sensor, which tells the computer when a motor is preigniting so as to reduce ignition timing accordingly, then the performance effectively will reduce if a lower RON fuel is used than that perscribed for the motor - ie a car happily running on 95 RON fuel may ping with 91 RON due to the standard ignition and fuel values, meaning the knock sensor will tell the ecu to retard timing and this equates to reduced performance for the sake of saving the motor from preignition and possible failure

but a carb motor with points dissy and no ecu will not benefit from a change in fuel types alone - unless the motor was pinging on the fuel used previously

IT MUST BE REMEMBERED THAT PINGING IS NOT ALWAYS AUDIBLE, ACTUALLY BY THE TIME THAT IT HAS BECOME AUDIBLE THEN IT IS QUITE SERIOUS and the consequences of this audible detonation are scuff marks, piston ring land damage and other physical piston damage, as well as possible damage to all other parts in the combustion chamber (chamber, valves, plug, gasket) and in the long term, engine failure due to smashed pistons or rings.

so taking the above into account - have a logical think about fuel values and whether one variable IN ITS OWN RIGHT can alter the performance of a motor so dramatically, and gauge this thought in line with the fundamentals of a four stroke motor

Mick


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SubjectPosterDate
Read Message   Higher RON Fuels: Did you know? Matt-itudeSun, 12 June 2005 09:11
Read Message   Re: Higher RON Fuels: Did you know? justcallmefrankSun, 12 June 2005 09:15
Read Message   Re: Higher RON Fuels: Did you know? Matt-itudeSun, 12 June 2005 09:34
Read Message   Re: Higher RON Fuels: Did you know? justcallmefrankSun, 12 June 2005 09:36
Read Message   Re: Higher RON Fuels: Did you know? GBC_069Sun, 12 June 2005 10:00
Read Message   Re: Higher RON Fuels: Did you know? justcallmefrankSun, 12 June 2005 10:02
Read Message   Re: Higher RON Fuels: Did you know? riverSun, 12 June 2005 11:07
Read Message   Re: Higher RON Fuels: Did you know? ae86driftSun, 12 June 2005 11:32
Read Message   Re: Higher RON Fuels: Did you know? Matt-itudeSun, 12 June 2005 18:40
Read Message   Re: Higher RON Fuels: Did you know? riverMon, 13 June 2005 05:40
Read Message   Re: Higher RON Fuels: Did you know? thu187Sun, 12 June 2005 12:23
Read Message   Re: Higher RON Fuels: Did you know? TRD_SupraSun, 12 June 2005 13:35
Read Message   Re: Higher RON Fuels: Did you know? no_tofu_speedSun, 12 June 2005 14:09
Read Message   Re: Higher RON Fuels: Did you know? TRD_SupraSun, 12 June 2005 14:48
Read Message   Re: Higher RON Fuels: Did you know? Corona RT142Sun, 12 June 2005 23:52
Read Message   Re: Higher RON Fuels: Did you know? TRD_SupraMon, 13 June 2005 02:07
Read Message   Re: Higher RON Fuels: Did you know? ArchMon, 13 June 2005 02:38
Read Message   Re: Higher RON Fuels: Did you know? Corona RT142Mon, 13 June 2005 03:01
Read Message   Re: Higher RON Fuels: Did you know? jeffro RA28Mon, 13 June 2005 03:48
Read Message   Re: Higher RON Fuels: Did you know? ToobsMon, 13 June 2005 05:53
Read Message   Re: Higher RON Fuels: Did you know? riverMon, 13 June 2005 06:12
Read Message   Re: Higher RON Fuels: Did you know? ToobsMon, 13 June 2005 06:28
Read Message   Re: Higher RON Fuels: Did you know? CLGMon, 13 June 2005 06:42
Read Message   Re: Higher RON Fuels: Did you know? towe_001Wed, 15 June 2005 00:02
Read Message   Re: Higher RON Fuels: Did you know? trevtrevWed, 15 June 2005 03:18
Read Message   Re: Higher RON Fuels: Did you know? CLGMon, 13 June 2005 06:17
Read Message   Re: Higher RON Fuels: Did you know? riverMon, 13 June 2005 06:54
Read Message   Re: Higher RON Fuels: Did you know? bmewsMon, 13 June 2005 11:12
Read Message   Re: Higher RON Fuels: Did you know? RaineyMon, 13 June 2005 13:35
Read Message   Re: Higher RON Fuels: Did you know? bmewsTue, 14 June 2005 02:30
Read Message   Re: Higher RON Fuels: Did you know? ShrakaWed, 15 June 2005 03:12
Read Message   Re: Higher RON Fuels: Did you know? st184 sillycarWed, 15 June 2005 09:56
Read Message   Re: Higher RON Fuels: Did you know?  trd3sgSun, 19 June 2005 06:44
Read Message   Re: Higher RON Fuels: Did you know? st184 sillycarThu, 16 June 2005 10:06
Read Message   Re: Higher RON Fuels: Did you know? jeffro RA28Tue, 21 June 2005 11:52
Read Message   Re: Higher RON Fuels: Did you know? NarkWed, 22 June 2005 08:14
Read Message   Re: Higher RON Fuels: Did you know? riceburna73Thu, 16 June 2005 11:34
Read Message   Re: Higher RON Fuels: Did you know? Corona RT142Thu, 16 June 2005 22:55
Read Message   Re: Higher RON Fuels: Did you know? NorbieFri, 17 June 2005 00:52
Read Message   Re: Higher RON Fuels: Did you know? THE WITZLFri, 17 June 2005 03:50
Read Message   Re: Higher RON Fuels: Did you know? st184 sillycarSun, 19 June 2005 01:09
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