90 VS 95 Octan
#2
04-04-2010, 05:46 AM
Re: 90 VS 95 Octan
You should use the octane as specified in the owner's manual.
Anything more will just be a waste of money. (in my un-educated opinion).
Higher octane (than needed) doesn't make a car run better.
It just costs more
Anything more will just be a waste of money. (in my un-educated opinion).
Higher octane (than needed) doesn't make a car run better.
It just costs more
#3
04-04-2010, 07:10 AM
Re: 90 VS 95 Octan
Under some VERY specific conditions (high ambient temps, low elevations, high loads) the higher octane may do some good by letting the ECU keep max advance. The Camry has a knock sensor that backs the timing off when it detects engine knock; the conditions above are the ones most likely to produce pre-ignition.
For most normal light-load running, the higher octane may actually decrease FE, cause stumbling and other driveabiltiy issues. Unless you have specific reason to do so, 87(R+M/2) 90(R) octane is the preferred fuel for the US-spec Camry, as per your owners' manual.
#4
04-04-2010, 09:16 AM
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Re: 90 VS 95 Octan
"....has a knock sensor.."
Yes, a knock sensor that in conjunction with the crankshaft position sensor is used to determine if the knock/ping occurred prior to spark ignition (detonation, dieseling) or as a result of....
When knock/ping is the result of the timing being too advanced for conditions it will be retarded. On the other hand if it is already fully or optimally retarded, or the knock/ping is prior to ignition, then EFI will be used to enrich the mixture. On some occassions, knock/ping due to engine "lugging", a (virtual) downshift will be the result.
HSD systems provide lots of new "toys" for the programming team to "play" with.
Yes, a knock sensor that in conjunction with the crankshaft position sensor is used to determine if the knock/ping occurred prior to spark ignition (detonation, dieseling) or as a result of....
When knock/ping is the result of the timing being too advanced for conditions it will be retarded. On the other hand if it is already fully or optimally retarded, or the knock/ping is prior to ignition, then EFI will be used to enrich the mixture. On some occassions, knock/ping due to engine "lugging", a (virtual) downshift will be the result.
HSD systems provide lots of new "toys" for the programming team to "play" with.
#5
04-04-2010, 10:57 AM
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Re: 90 VS 95 Octan
What higher octane gas does is resist pre-ignition better. This is solely needed for higher compression engines. If your car needs it, it will be spec'd. in the Owners Manual.
That said, one instance where higher octane might be needed but not spec'd. in the Owners Manual: an older vehicle where the engine has accumulated enough carbon build-up in the cylinder head to actually reduce the air volume when the piston's at the top, in turn increasing the compression ratio.
That, coupled with all the possible ignition sources (the carbon will tend to have glowing points), might increase the odds of pre-ignition.
If higher octane gas is spec'd for your car, and you put regular octane in, the car's computer will likely detect pre-ignition starting to happen, and retard ignition timing a little, ie: make the sparkplugs fire a little later. This in turn will prevent pre-ignition, your engine will run a little cooler, but you will take a performance hit.
If I'm car shopping and see some particular car will need premium fuel, that crosses it off my list. Cars needing premium fuel tend to be high performance models, tuned more max acceleration, trying to get more horsepower out of a smaller displacement engine. They're more costly to fuel and tend to sacrifice fuel economy. Also, I suspect they will be more prone to engine problems down the road.
That said, one instance where higher octane might be needed but not spec'd. in the Owners Manual: an older vehicle where the engine has accumulated enough carbon build-up in the cylinder head to actually reduce the air volume when the piston's at the top, in turn increasing the compression ratio.
That, coupled with all the possible ignition sources (the carbon will tend to have glowing points), might increase the odds of pre-ignition.
If higher octane gas is spec'd for your car, and you put regular octane in, the car's computer will likely detect pre-ignition starting to happen, and retard ignition timing a little, ie: make the sparkplugs fire a little later. This in turn will prevent pre-ignition, your engine will run a little cooler, but you will take a performance hit.
If I'm car shopping and see some particular car will need premium fuel, that crosses it off my list. Cars needing premium fuel tend to be high performance models, tuned more max acceleration, trying to get more horsepower out of a smaller displacement engine. They're more costly to fuel and tend to sacrifice fuel economy. Also, I suspect they will be more prone to engine problems down the road.
Last edited by Mendel Leisk; 04-04-2010 at 11:04 AM.
#6
04-05-2010, 11:03 AM
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Re: 90 VS 95 Octan
What higher octane gas does is resist pre-ignition better. This is solely needed for higher compression engines. If your car needs it, it will be spec'd. in the Owners Manual.
My '01 Porsche 911/996 C4 has a 300HP very seriously HIGH COMPRESSION engine. When I picked it up at the factory in the spring of 2000 for our travels thoughout europe the only caution I was given was to be very careful to not fuel it with leaded fuel. They would test it on my return and if I had used leaded fuel both catalytic converters would be replaced on my nickel.
When I asked about octane levels I was told the fueling with regular would not be problematic. I was told that the A/F mixture ratio would be adjusted automatically to accommodate the fuel octane.
That said, one instance where higher octane might be needed but not spec'd. in the Owners Manual: an older vehicle where the engine has accumulated enough carbon build-up in the cylinder head to actually reduce the air volume when the piston's at the top, in turn increasing the compression ratio.
That, coupled with all the possible ignition sources (the carbon will tend to have glowing points), might increase the odds of pre-ignition.
If higher octane gas is spec'd for your car, and you put regular octane in, the car's computer will likely detect pre-ignition starting to happen, and retard ignition timing a little, ie: make the sparkplugs fire a little later.
No, as I understand today's engine control computer firmware specifications the timing will only be retarded if the knock/ping is the direct result of the (too early) ignition timing itself. Otherwise the mixture will be enriched to alleviate the knock/ping or it is even possible that the automatic transmission will be "commanded" that a downshift is required.
This in turn will prevent pre-ignition, your engine will run a little cooler, but you will take a performance hit.
If I'm car shopping and see some particular car will need premium fuel, that crosses it off my list. Cars needing premium fuel tend to be high performance models, tuned more max acceleration, trying to get more horsepower out of a smaller displacement engine.
Are you aware that most gasoline engines in these "fuel-sipping" modern day HSD hybrid systems have an unusually HIGH compression ratio, 13:1....? And that will like go up to 15-16:1 once the problems of DFI are resolved.
The newest, 2010, HSD models even leave the EFFECTIVE compression ratio at or near 13:1 (DFI/15:1 coming soon) as long as the cylinders are to be only partially filled with mixture.
They're more costly to fuel and tend to sacrifice fuel economy. Also, I suspect they will be more prone to engine problems down the road.
My '01 Porsche 911/996 C4 has a 300HP very seriously HIGH COMPRESSION engine. When I picked it up at the factory in the spring of 2000 for our travels thoughout europe the only caution I was given was to be very careful to not fuel it with leaded fuel. They would test it on my return and if I had used leaded fuel both catalytic converters would be replaced on my nickel.
When I asked about octane levels I was told the fueling with regular would not be problematic. I was told that the A/F mixture ratio would be adjusted automatically to accommodate the fuel octane.
That said, one instance where higher octane might be needed but not spec'd. in the Owners Manual: an older vehicle where the engine has accumulated enough carbon build-up in the cylinder head to actually reduce the air volume when the piston's at the top, in turn increasing the compression ratio.
That, coupled with all the possible ignition sources (the carbon will tend to have glowing points), might increase the odds of pre-ignition.
If higher octane gas is spec'd for your car, and you put regular octane in, the car's computer will likely detect pre-ignition starting to happen, and retard ignition timing a little, ie: make the sparkplugs fire a little later.
No, as I understand today's engine control computer firmware specifications the timing will only be retarded if the knock/ping is the direct result of the (too early) ignition timing itself. Otherwise the mixture will be enriched to alleviate the knock/ping or it is even possible that the automatic transmission will be "commanded" that a downshift is required.
This in turn will prevent pre-ignition, your engine will run a little cooler, but you will take a performance hit.
If I'm car shopping and see some particular car will need premium fuel, that crosses it off my list. Cars needing premium fuel tend to be high performance models, tuned more max acceleration, trying to get more horsepower out of a smaller displacement engine.
Are you aware that most gasoline engines in these "fuel-sipping" modern day HSD hybrid systems have an unusually HIGH compression ratio, 13:1....? And that will like go up to 15-16:1 once the problems of DFI are resolved.
The newest, 2010, HSD models even leave the EFFECTIVE compression ratio at or near 13:1 (DFI/15:1 coming soon) as long as the cylinders are to be only partially filled with mixture.
They're more costly to fuel and tend to sacrifice fuel economy. Also, I suspect they will be more prone to engine problems down the road.
Last edited by wwest; 04-05-2010 at 11:06 AM.
#7
04-06-2010, 01:05 AM
Re: 90 VS 95 Octan
My 2003 GMC with the 6.0L (364 CID for us old folks) LS1-type engine has 2 knock sensors, and pulls timing when knock is detected. I can put up log graphs showing this, as well as the timing tables, trigger points, etc. if anybody is interested.
The reason the TCH engine has such a high static compression ratio is because it is an Atkinson engine, which has a very late intake valve closure point, which reduces the dynamic compression ratio to a normal level.
The reason the TCH engine has such a high static compression ratio is because it is an Atkinson engine, which has a very late intake valve closure point, which reduces the dynamic compression ratio to a normal level.
#8
04-06-2010, 08:03 AM
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Re: 90 VS 95 Octan
My 2003 GMC with the 6.0L (364 CID for us old folks) LS1-type engine has 2 knock sensors, and pulls timing when knock is detected. I can put up log graphs showing this, as well as the timing tables, trigger points, etc. if anybody is interested.
What if the knock/ping is the result of detonation, spontaneous mixture combustion prior to spark ignition?? In that case of what good does it do to retard the spark...??
And what about knock/ping due to lugging the engine?? Knock/ping as a result of the piston being "restrained" from moving downward as fast as the flame front advances....??
The reason the TCH engine has such a high static compression ratio is because it is an Atkinson engine, which has a very late intake valve closure point, which reduces the dynamic compression ratio to a normal level.
What if the knock/ping is the result of detonation, spontaneous mixture combustion prior to spark ignition?? In that case of what good does it do to retard the spark...??
And what about knock/ping due to lugging the engine?? Knock/ping as a result of the piston being "restrained" from moving downward as fast as the flame front advances....??
The reason the TCH engine has such a high static compression ratio is because it is an Atkinson engine, which has a very late intake valve closure point, which reduces the dynamic compression ratio to a normal level.
In the newer HSD models the engine is "multimode". These new engines use e/VVT-i, extended VVT-i to switch engine modes. As long as the cylinder "charge" does not approach maximum the engine remains in standard "Otto" mode, static/base 13:1 compression ratio. "Mash" the gas pedal, go WOT, and e/VVT-i is used to switch the engine into Atkinson mode, reducing the effective CR to something more in the "standard" range, ~10:1.
Whole new world out there, RAPIDLY changing world, get used to it.
There might even come a day soon when you will have 2 fuel tanks on board. One with low octane for running in gasoline DFI DIESEL mode, and a second, smaller one, for high octane WOT operations.
What about an onboard oxygen generator(separator) to raise the effective engine displacement...??
Use the "separated" nitrogen along with EGR to reduce "cruise" mode pumping losses plus compress the oxygen into a small tank for use in WOT "mode"
Or what about a LOX tank to boost the effective engine displacement by a factor of 3-4 for REAL acceleration...??
Last edited by wwest; 04-06-2010 at 08:12 AM.
