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Old 2nd June 2008, 18:24   #76
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Originally Posted by ravikn View Post
does this mean LPG is more efficient fuel and should be used as it is 101 octane
LPG is cleaner burning yes. But it has a lower energy content & slower burning fuel than Petrol. So a very high compression engine would be necessary to extract the maximum out of LPG.
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Old 2nd June 2008, 21:13   #77
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Originally Posted by Sankar View Post
As far as my understanding the ECU cannot detect the octane rating of the fuel. But it can detect the engine knocking, so if the engine knocks with a lower octane fuel the ECU would retard the ignition timing curve. And if the engine does not knock it will use the optimum ignition timing which is hardcoded into it's brain. So if you use a higher octane fuel ECU is not going to re adjust the ignition timing from the set factory optimum to utilise the higher octane fuel fed to the engine.
This may vary from engine to engine. I had a look at the following website:

http://www.caranddriver.com/reviews/...ature/(page)/1

In particular, look at the quotes below:

Quote:
Conversely, in some engines designed for regular fuel, you can advance the timing if you burn premium, but whether this will yield additional power varies from engine to engine.

Knock sensors are used in virtually all new GM, Ford, European, and Japanese cars, and most DaimlerChrysler vehicles built today. According to Gottfried Schiller, director of powertrain engineering at Bosch, these block-mounted sensors-one or two of them on most engines and about the size of a quarter-work like tiny seismometers that measure vibration patterns throughout the block to identify knock in any cylinder. Relying on these sensors, the engine controller can keep each cylinder's spark timing advanced right to the hairy edge of knock, providing peak efficiency on any fuel and preventing the damage that knock can do to an engine. But, noted Schiller, only a few vehicles calibrated for regular fuel can advance timing beyond their nominal ideal setting when burning premium.
[...]
We should note that even cars designed to run on regular fuel might require higher octane as they age. Carbon buildup inside the cylinder can create hot spots that can initiate knock. So can malfunctioning exhaust-gas-recirculation systems that raise cylinder temperatures. Hot temperatures and exceptionally low humidity can increase an engine's octane requirements as well. High altitude reduces the demand for octane.
I tend to push my Santro hard most of the time. E.g. on the highway I often shift from third to fourth at 60-70 kmph and from 4th to 5th at 80-100 kmph. For this style of driving, I believe the ECU may well kick in and detect that the factory-set timing is not optimal. Not sure about this, but there is a noticeable, if slight, improvement in performance with Speed 97. Maybe because my Santro is old and has already done 73000 kms now.
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Old 2nd June 2008, 21:39   #78
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Originally Posted by pranil View Post
My Santro on the oother hand improves in the bootm end torque on the higher octane( This is 1999 Santro - One of the few old origanal Epsilon engines) No idea of compression ratio though
I heartily second this observation. With Speed 97, my 2000 model Santro seems to work up to 120 kmph noticeably quicker than before. But you need to drive the car around for a couple of tankfuls of Speed 97 in order to get rid of all the old fuel and also to give some time for the ECU to adjust (assuming it does that).
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Old 8th June 2008, 23:05   #79
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Quote:
Originally Posted by Sankar View Post
As far as my understanding the ECU cannot detect the octane rating of the fuel. But it can detect the engine knocking, so if the engine knocks with a lower octane fuel the ECU would retard the ignition timing curve. And if the engine does not knock it will use the optimum ignition timing which is hardcoded into it's brain. So if you use a higher octane fuel ECU is not going to re adjust the ignition timing from the set factory optimum to utilise the higher octane fuel fed to the engine.

So imo if the engine runs without an knocks on 91 octane the ECU would use the optimum factory set timing curve. And if you use the 97octane and the engine does not detect any knocks and it will still use the optimum factory set timing curve which would be the same timing curve as the ecu used with 91 octane.
I think what you are saying is true of the older ECU's, say prior to the late 90's. Here is a very important website that gives information on this issue:

Welcome to Land Cruiser Owners On Line

Quote:
In recent years, Toyota had been quite proactive in adopting advances in engine management and implementing them on the Toyota 4WD range. One of these advances was an ignition advance system that slowly advanced ignition timing to the point where minor detonation would occur and was registered by the engine knock sensors. The engine management system would then retard the ignition timing slightly and after a period of time without further detonation, slowly advance timing again. This ensures that the engine runs as efficiently as possible given the fuel quality available. The tuning industry’s term for this adaptive system is one that “runs on the knock sensors”.
This is not to be confused with less advanced systems that run a predetermined ignition advance map and use the knock sensors as a safety precaution to retard only when serious detonation occurred.
Prado petrol engines are equipped with adaptive ignition timing however the rate at which the timing advances is very slow indeed. In addition, if even minor detonation is registered at one part of the RPM range, the entire ignition map is retarded across the entire RPM range.
When high octane fuel is used, the likelihood of detonation is diminished and the engine management system can advance the ignition timing further than that with standard fuel. Resulting in higher efficiency, greater power and torque as well as reduced fuel consumption.
However, in the range of Prado petrol engines, the rate of ignition advance is very slow indeed. This means that one needs to run high octane fuel for many km before any change in performance or economy is fully realised. In the case of the 3.4L V6 in the 90 Series, 5,000 – 7,000 km and for the 4.0L V6 in the 120 Series, 3,000 km – 5,000 km.
Generally after one or two tanks full, the owner will give up and return back to standard fuel because he notices no difference – and does not realise that it takes so long. However if you persist, the benefits are real and quantifiable – more so in terms of fuel economy.
A direct example that I can quote is my wife’s 120 Series 4.0L V6 petrol Grande. She is a most consistent driver in that she travels the same roads and highway day in day out. In addition, her driving habits do not change over time.
Fuel economy with standard unleaded was consistently 15.5 l/100km. However, with 98 RON Shell Optimax, fuel economy is consistently 13.1 l/100km – a reduction of 2.4 l/100km or in percentage terms, a reduction of 15.5% in fuel consumption. This incidentally is greater than the price difference between standard unleaded and Optimax, so in her case, running the better quality fuel results in an overall saving in fuel bills, extended range – and of course the additional engine performance is free!
The secret is though to persist with the better quality fuel for a long period of time.
Note that the "In recent years..." in the above quote refers to the post-1996 period. Because the 90 series Prados were introduced in 1996 and later replaced by the 120 series in 2003. E.g. see the following website:

Toyota Land Cruiser Prado - Wikipedia, the free encyclopedia

The most important information in the above quote pertains to the fact that the ignition timing is automatically advanced by the ECU when a higher octane fuel is used, but over a very lengthy period. You actually need to run the car for upto 5000-7000 kms to see the full benefits of a higher octane fuel.

Note also that the 90 series Prados had a compression ratio of about 9.4, not much higher than my Santro's 8.9. So if 98 RON petrol is optimal for 90 series Prados, it would not be unreasonable to conclude that Speed 97 is close to optimal for my Santro. Your table also confirms this expectation, as does my experience.

Now that I think about it, my car was having pronounced jerks at low speeds in second gear for a few thousand kms after I started using Speed 97. These jerks persisted even after the recent sevrice at 70500 kms. But at 73500 kms (maybe ~10000 kms after I started using Speed 97) the jerks simply disappeared on their own. Quite possible that the ECU was in a transient phase and now sorted itself out. Right now the car is really going strong in terms of performance, after 10000+ kms with Speed 97 (and only Speed 97). Fuel economy is quite good, at about 12.5 km/lit. Maybe an increase of about 0.5 to 1 km/lit with Speed 97, but not very sure about this.

Last edited by rks : 8th June 2008 at 23:20.
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Old 9th June 2008, 19:06   #80
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Quote:
Originally Posted by ravikn View Post
does this mean LPG is more efficient fuel and should be used as it is 101 octane
Yes but it needs higher compression ratio then normal petrol engine & higher ignition timing. In general we cant have access to such special engines developed to use with lpg.We fit an aftermarket kit in petrol engines which are designed to run with petrol.

Energy content of lpg is less compared to petrol.So to extract same power output as that of petrol we need slightly rich mixtures supported with high CR & increased ignition timing.

This is the reason we get less FE when we shift to lpg.
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Old 9th June 2008, 19:13   #81
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@sankar, finetuning,

Thanks a lot for the response.

Quote:
Energy content of lpg is less compared to petrol.So to extract same power output as that of petrol we need slightly rich mixtures supported with high CR & increased ignition timing.
Could you please explain more regarding this. am using a BRC sequential kit on my Palio 1.6. I feel that there is a slight power drop when I need to do overtaking. Would it be possible to use any mixtures that can deliver more power and mileage with LPG. Is it safe to use?

Last edited by Rehaan : 19th June 2008 at 01:16. Reason: Quote fixed.
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Old 9th June 2008, 21:30   #82
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ravikn,

You can increase your lpg mixture by simply turning lpg knob at your vapourizer end.I dont know about your BRC kit but its that simple.Getting best FE & power in lpg is not always possible or very difficult to achieve unless you have certain modification for power improvement.

Diesel has roughly 1,39,000 BTU per gallon where as petrol has approx. 1,24,000 BTU per gallon and lpg has around 90,000 BTU. Hence diesel produces more torque compared to other fuels.

Now if we increase lpg supply making mixture rich to improve performance at par with petrol we get yet lower FE. Again its a finetuned job of a good mechanic to strike a balance between power & FE.
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Old 10th June 2008, 14:01   #83
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Thanks finetuning

This really helps. will get this fixed with my mechanic this weekend
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Old 10th June 2008, 14:35   #84
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ok im having a problem with my 02 santa fe
i was using 95 octance fuel herein the gulf since forever its a alltime 4 wheel drive and it used to return me avg 6-7kmpl but now its summer and im using the ac all the time and ive also started filling up 91 oct fuel cause i dont see the need the guide says use min 91 oct but then im getting fuel av of 4.5-5 kmpl

whats wrong is it the lower octane or cause of the AC
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Old 18th June 2008, 15:04   #85
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Hi guys

I have a CRV 2.0 which has a compression ratio of 10.5:1

The manual does not mention the recommended fuel octane and I have not heard back from Honda on the same.

What octane fuel should I use in the car?
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Old 18th June 2008, 17:49   #86
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Hi Guys,

I have an OHC Vtec 2001 Model - 63000 Kms. I was using the normal unleaded petrol for some time but have now changed over to Speed. I don’t find noticeable difference in the FE but, initially i did find some difference in pickup (which is not noticeable since i have got used to it) but power and pickup has never been a problem for the OHC Vtec.

Request your suggestions on what fuel I should be using to attain:-

Better FE
Better performance, life
Therefore better cost effectiveness in terms of FE and Maintenance.

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Old 18th June 2008, 19:26   #87
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Welcome to the forum KSM, for regular Vtec normal unleaded fuel is fine, ie 91 octane, since the car has been already detuned for the same.

Regular service as recommended + Oil changes + Checks on plugs, air filter and fuel filter are good enough to keep your car in good shape and reliable.

If you drive a Vtec in a smooth fashion it will return very good FE also.
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Old 19th June 2008, 10:11   #88
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Jaggu - I thought regular unleaded fuel was 87 octane and speed is 91. Speed is no better than regular in terms of FE. I would rather use the regular unleaded fuel and save 5 bucks per litter. What say?

Besides, all the regular oil & cleanup I do very meticulously.

What does detuned mean? And my Vtec gives an FE 0f 10 without AC in city. Is that good?

Last edited by Jaggu : 19th June 2008 at 11:18.
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Old 19th June 2008, 11:21   #89
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In metro's only 91 Octane is allowed as far as i know. So spending additional moolah for speed (additive, cleaning agents) is not worth it if you ask me. Use System G instead on alternate tank fulls.

Detuned as in compression and ecu retuned to take care of our pterol. FE of 10 sound ok if you are driving in traffic with AC.
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Old 19th June 2008, 11:32   #90
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Quote:
Originally Posted by Jaggu View Post
In metro's only 91 Octane is allowed as far as i know. So spending additional moolah for speed (additive, cleaning agents) is not worth it if you ask me. Use System G instead on alternate tank fulls.

Detuned as in compression and ecu retuned to take care of our pterol. FE of 10 sound ok if you are driving in traffic with AC.

I am getting 10 without ac.

Also plz pardon my ignorance, i am not going to feel shy to ask questions which may appear foolish to you guys. But, what is System G, how much does it cost, how does one use it?
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