What gas (octane) is best for TCH?
#3
10-27-2006, 04:09 PM
Re: What gas (octane) is best for TCH?
Originally Posted by flopshot
Using premium gas will do nothing extra in the TCH, but it will empty your wallet faster.
Why you ask?
Because the ECU will advance the timing to the point where the knock sensor picks up detonation and then it backs the timing down a fraction of a degree of rotation until the system is stabil.
With the high static compression (which increases with speed dynamically) - the lower octane fuel will yield less overall resistance to detonation - thereby less timing can be applied. The efficiency of the engine will increase with the longer burn of the fuel (spark advance) to the point of detonation which actually works against the rising piston(s)..
Now in a lower static compression engine, the difference between lower and higher octane is far less as the 87 Octane fuel in a 9:1 compression engine will generally run within 1 degree of timing of the 92 Octane fuel.
I would encourage people with these cars to run their own tests. Obviously you should run the tests in a "somewhat" controlled format so you are comparing apples to apples. Also over 2 or more tanks of fuel to reduce the error factor.
I plan on doing this with my car as soon as I feel the engine / driveline is broken in. Meanwhile - I feel confident that the higher octane will yield a greater efficiency in these engines.
#4
10-27-2006, 04:33 PM
Re: What gas (octane) is best for TCH?
Originally Posted by Big-Foot
I'm not so sure that this is true...
Why you ask?
Because the ECU will advance the timing to the point where the knock sensor picks up detonation and then it backs the timing down a fraction of a degree of rotation until the system is stabil.
With the high static compression (which increases with speed dynamically) - the lower octane fuel will yield less overall resistance to detonation - thereby less timing can be applied. The efficiency of the engine will increase with the longer burn of the fuel (spark advance) to the point of detonation which actually works against the rising piston(s)..
Now in a lower static compression engine, the difference between lower and higher octane is far less as the 87 Octane fuel in a 9:1 compression engine will generally run within 1 degree of timing of the 92 Octane fuel.
I would encourage people with these cars to run their own tests. Obviously you should run the tests in a "somewhat" controlled format so you are comparing apples to apples. Also over 2 or more tanks of fuel to reduce the error factor.
I plan on doing this with my car as soon as I feel the engine / driveline is broken in. Meanwhile - I feel confident that the higher octane will yield a greater efficiency in these engines.
Why you ask?
Because the ECU will advance the timing to the point where the knock sensor picks up detonation and then it backs the timing down a fraction of a degree of rotation until the system is stabil.
With the high static compression (which increases with speed dynamically) - the lower octane fuel will yield less overall resistance to detonation - thereby less timing can be applied. The efficiency of the engine will increase with the longer burn of the fuel (spark advance) to the point of detonation which actually works against the rising piston(s)..
Now in a lower static compression engine, the difference between lower and higher octane is far less as the 87 Octane fuel in a 9:1 compression engine will generally run within 1 degree of timing of the 92 Octane fuel.
I would encourage people with these cars to run their own tests. Obviously you should run the tests in a "somewhat" controlled format so you are comparing apples to apples. Also over 2 or more tanks of fuel to reduce the error factor.
I plan on doing this with my car as soon as I feel the engine / driveline is broken in. Meanwhile - I feel confident that the higher octane will yield a greater efficiency in these engines.
#5
10-27-2006, 06:05 PM
Re: What gas (octane) is best for TCH?
Toyota recommends regular gas (87 octane) for the TCH. Premium gas in a vehicle that does not require premium gas is, in my opinion, a waste of money. Also, I believe that using premium gas in a vehicle that does not require premium gas increases pollution output from the vehicle.
#6
10-27-2006, 06:59 PM
Re: What gas (octane) is best for TCH?
Originally Posted by Lilarienne
Toyota recommends regular gas (87 octane) for the TCH. Premium gas in a vehicle that does not require premium gas is, in my opinion, a waste of money. Also, I believe that using premium gas in a vehicle that does not require premium gas increases pollution output from the vehicle.
While you may believe that the higher octane would increase pollutants - it's not really the case. The higher octane fuels do burn slower and longer but not to the degree that the fuel is exhausted in a less than totally consumed state.
I've built and dyno tested a number of engines (number in the hundreds) and have not seen any appreciable difference in pollutants in the unleaded automotive grade fuels as long as the engine is running at the appropriate operating temperature and stoich.
I'm currently building an engine for one of my cars that has a static compression ratio of 9.5:1 but a dynamic compression ratio of 16:1. How can that be? It's supercharged.
I wouldn't look for this engine to be exceptionally economical though. It's designed to deliver roughly 1100hp from 7.7 liters (468 Cubic Inches) and carbureted rather than fuel injected.
#8
10-27-2006, 11:24 PM
Re: What gas (octane) is best for TCH?
Originally Posted by Big-Foot
I'm not so sure that this is true...
Why you ask?
Because the ECU will advance the timing to the point where the knock sensor picks up detonation and then it backs the timing down a fraction of a degree of rotation until the system is stable.
Why you ask?
Because the ECU will advance the timing to the point where the knock sensor picks up detonation and then it backs the timing down a fraction of a degree of rotation until the system is stable.
This is an interesting statement, but i can find nothing during my own research that backs this up. I am not claiming you are incorrect, but i am curious on what you are basing this claim in relation to the TCH.
"At partial load, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than what is available. It is only when the throttle is opened fully and the manifold pressure increases to atmospheric (or higher in the case of supercharged or turbocharged engines) that the full octane requirement is achieved." (Wikipedia)
The TCH ICE under normal conditions runs far below maximum load.
An engine and ECU tuned for higher octane fuel will "tune" itself down and decrease power output when lower octane fuel is used, and most manufactures state this. While this effect can be seen in performance like 0-60 numbers, it often does not effect total MPG for a tank of gas during normal driving conditions.
"Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark. Here is a white paper that gives an example: Link . In this example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load then the difference in octane will have even less effect." (Wikipedia)
However i can find no evidence that an engine designed around lower octane fuel will tune itself up to produce more power with higher octane fuel.
Even if an engine did tune up for more power, this alone does not appear to be a significant enough variable to effect MPG. Every attempt i have made to test MPG based on high octane fuel has produced the same results. An engine stated as designed for lower octane fuel never increases MPG statistically significant enough (if at all) to come close to the increase in fuel cost.
Going back to the original question "What gas (octane) is best for TCH" assuming "best" means best fuel economy, the answer is what Toyota specs, 87. Paying more for higher octane gas will not yield an increase in MPG.
Just my 2 cents!
Last edited by BrianAmira; 10-28-2006 at 12:53 AM.
#9
10-28-2006, 07:43 AM
Re: What gas (octane) is best for TCH?
There are hundreds if not thousands of pages on the Web which refer to this exact question.
A quick review of a few of them from Google indicate that it's almost universally considered a waste of money to put higher octane gas in an engine which does not need it.
In this case I have no doubts in my mind that the majority view is correct.
From an FTC site:
From another Consumer Guide type site:
There are many many more which say these same things.
A quick review of a few of them from Google indicate that it's almost universally considered a waste of money to put higher octane gas in an engine which does not need it.
In this case I have no doubts in my mind that the majority view is correct.
From an FTC site:
Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.
Octane Myths
• High octane gasoline improves mileage.
In general, if your car is designed to run on 87 octane gasoline, high octane gasoline will not improve mileage. If switching to high octane gasoline does improve mileage, you might find that your engine, or its control systems, need repair.
• High octane gasoline gives quicker starting.
No, it doesn’t.
• High octane gasoline increases power.
If your car is designed to run on 87 octane gasoline, you shouldn’t notice any more power on high octane gasoline. Again, if it does make a noticeable difference, your engine, or the engine’s electronic control systems, may need repair.
• High octane gasoline has been refined more – it is just a better product.
Additional refining steps are used to increase the octane; however, these additional steps do not necessarily make the gasoline a “better” product for all engines. They just yield a different blend of hydrocarbons that burn more slowly. The additional steps also increase the price
• High octane gasoline improves mileage.
In general, if your car is designed to run on 87 octane gasoline, high octane gasoline will not improve mileage. If switching to high octane gasoline does improve mileage, you might find that your engine, or its control systems, need repair.
• High octane gasoline gives quicker starting.
No, it doesn’t.
• High octane gasoline increases power.
If your car is designed to run on 87 octane gasoline, you shouldn’t notice any more power on high octane gasoline. Again, if it does make a noticeable difference, your engine, or the engine’s electronic control systems, may need repair.
• High octane gasoline has been refined more – it is just a better product.
Additional refining steps are used to increase the octane; however, these additional steps do not necessarily make the gasoline a “better” product for all engines. They just yield a different blend of hydrocarbons that burn more slowly. The additional steps also increase the price
#10
10-28-2006, 07:54 AM
Re: What gas (octane) is best for TCH?
Hi Brian,
I understand and appreciate your skepticism. I've done quite a bit of ECU programming on a few different mfgr's platforms (unfortunately none were Toyota) and can tell you that the very first instruction executed when detecting detonation is to retard ignition advance. If the advance is brought down more than a few degrees and detonation is still detected - the fuel mixture is then typically enrichened by lengthening the pulse width of the injectors.
The Wiki article is correct in that part throttle conditions will see less overall advantage of the higher octane - however - detonation in the higher static compression engines such as these Atkinson Cycle derivatives will experience a far greater level of detonation at lower RPM and loading. This is all a factor of cylinder pressure. The ECVT transmission and controls will also help reduce the dynamic loading but by doing so, it increases RPM of the engine. Maybe you can see the Paradox coming...
BTW - Engines "designed" to use lower octane fuels are either done so by physically limiting the static and dynamic compression and/or by ECU programming.
I'm certain that 12+:1 static compression is well beyond the limits of 87 Octane fuel (mechanically) so I feel comfortable in saying that the "design" is in the programming.
The ECU has no idea what Octane fuel you put into the tank. It will read that Octane via the knock sensor.
If you care to experiment on your own - please do and post your results here.
I plan on it..
Thanks!
I understand and appreciate your skepticism. I've done quite a bit of ECU programming on a few different mfgr's platforms (unfortunately none were Toyota) and can tell you that the very first instruction executed when detecting detonation is to retard ignition advance. If the advance is brought down more than a few degrees and detonation is still detected - the fuel mixture is then typically enrichened by lengthening the pulse width of the injectors.
The Wiki article is correct in that part throttle conditions will see less overall advantage of the higher octane - however - detonation in the higher static compression engines such as these Atkinson Cycle derivatives will experience a far greater level of detonation at lower RPM and loading. This is all a factor of cylinder pressure. The ECVT transmission and controls will also help reduce the dynamic loading but by doing so, it increases RPM of the engine. Maybe you can see the Paradox coming...
BTW - Engines "designed" to use lower octane fuels are either done so by physically limiting the static and dynamic compression and/or by ECU programming.
I'm certain that 12+:1 static compression is well beyond the limits of 87 Octane fuel (mechanically) so I feel comfortable in saying that the "design" is in the programming.
The ECU has no idea what Octane fuel you put into the tank. It will read that Octane via the knock sensor.
If you care to experiment on your own - please do and post your results here.
I plan on it..
Thanks!
