Gas Octane

I think the only car I heard of with a V-4 was a Saab, many years ago!
Toyotas 4 (and most 4 cyl. motors) are an I-4 (inline). Subarus, and the old air cooled VWs are an H-4 (horizontal or Flat/ opposed). A V engine is between a flat and an inline.

 

Not an argument, a clarification.

Actually it's more the dynamic compression, the abilities of the valves/head/piston to conduct away heat, the quench of the charge and how evenly it propogates the deflagration wave, the temperature of the plug electrodes, and so forth.

Valve timing affects dynamic compression. This is largely why a Prius with its over 14:1 compression can run regular fuel and the K20 in the Civic Si with its 11:1 requires premium. A trick with the old d-series crowd (4th, 5th, 6th gen civic SOHC) was to run a high lift, long duration cam and retard it, and choose a piston set, often OEM for a different d-series block, to boost static compression into the high 10.x range. This combination would compromise low-end torque, but the late valve closing would mitigate the compression at low rpm, oftentimes allowing safe use of regular unleaded. This also lead to two other consequences: exceptional gas mileage due to low pumping losses (many got 45+, some 50+) on shorter EX gearsets, and rediculous high rpm power for a single cam engine. More than one exceeded 160 whp on longblocks that came from the factory with 106 hp at the crank.

If you have a scangauge/ultragauge in your Tacoma, watch the ignition advance when you start it up. Let it idle without accessories or AC. It will start at around 8° and start counting up in 0.5° increments about every 2 seconds. It increases until it finds the limit of the fuel, which with premium is about 21° BTDC. It definitely adapts.

 

Static compression is the ratio of volume at bottom dead center to volume at top dead center. Dynamic compression results from retarding the closing of the valve so that compression doesn't begin until later in the stroke so dynamic compression cannot increase compression ratio only lower it from the static compression ratio..

That suggest to me the limit, the static compression ratio, should (along with all those things as well as air temperature, altitude, combustion chamber deposits, etc.) still define the octane needs of the engine. Unless you are planning on running around with no low-end torque like that Honda crowd you described.

 

So after 31 pages, we are finally at the conclusion that as long as it doesn't knock, it doesn't need any higher octane-right? right?
Sigh

 

Or Towing

I probably wouldn't tow with regular 87.

 

Well, at least it's not damaging the engine making it 'safe' to use. Not that's its necessarily making optimum power and economy but it's not proven to be needed for that either unless stressing it hard... like towing or sustained high-speed in the mountains.

 

If it does not knock and gives you your best fuel economy then keep using it. There is no reason to over complicate that fact.

 

I know . I do tend to rattle off terms that leaves a lot of people like so thanks for clarifying it.

A VVT setup can retard the intake cam to reduce the dynamic compression in low rpm high throttle conditions. Engines don't run at constant speeds, but fuel burns at roughly the same rate if temps stay the same, so you can tolerate higher compression at higher rpm because the engine literally outruns the detonation tendency. I have a slight hunch that Toyota likes to do this to a degree with all their higher compression engines taking regular fuel without damage. The prius is the king of this principle. Its intake cam duration is so long that it's something like 30% into the compression stroke by the times the valves close.

Although I have yet to figure out why my truck misfires so badly at 4500 rpm on regular fuel. It'll do it every time and has since I bought it. One day I'll figure it out.

Guess I'm just the outlier until I figure out the root cause. On premium it behaves properly all the time so maybe I just wasn't blessed with a cheap date.

 

+1

 

Well if your getting a miss at 4500rpm it could be a lean mixture missfire. If its only at high RPM then look at your fuel rail pressure. Your fuel pressure may be bleeding off at high RPM. To check for that I'd see if a scan tool can monitor fuel pressure in a live mode. If it is a drop in fuel pressure then your in fuel pump may be to blame. Usually the fuel filter sock begins to clog at 45-60k RPM. The filter sock is a permanent mount to the pump and is not replaceable. URD has an aftermarket pump that will be roughly the same cost as the factory pump and it has a replaceable fuel filter. Doubt its a spark issue but rarities happen.

 

To make a marketable / useable car (as opposed to the Honda tuners' products you referenced earlier) a Prius is a special case and can get away with it 'cause the electric motor provides full torque even from a dead stop.

But your observation certainly helps explain why this engine, with an 11:1 ratio, gets so little benefit from premium. Makes me think it even more likely that if someone could come up with a decent ECM mapping that takes into account not only ignition timing but VVT-i timing as well then we could get more useable performance out of it. But I do have to believe Toyota chose the tuning profile they did to give best economy; they are certainly motivated to do so.

 

Octane rating does not relate to the energy content of the fuel. It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced.

On another note, RON ( Rated Octane Number) varies by region, so 91 on the eastcoast can be different from 91 on the westcoast.

With this said, is it possible to make gains with other means to improve performance? yes, however, we have very limited options in order to gain any bandwidth of real gains short of forced induction or engine modifcations i.e. high compresion and so on.
Likewise Toyota has a software routine in our ECU's that maps the knock vs output of spent gases and makes timing and spark denesity changes thus gaining "SMALL" increases.


Wiki quote:

The 1GR-FE is the 4.0 L (3956 cc) version, designed for longitudinal mounting in RWD and 4WD pickup applications. It has a 94 mm bore and a stroke of 95 mm. Output is 236 hp (176 kW) at 5200 rpm with 266 lb·ft (361 N·m) of torque at 4000 rpm on 87 octane, and 239 hp (178 kW) at 5200 rpm with 278 lb·ft (377 N·m) at 3700 rpm on 91 octane. This engine features Toyota's VVT-i, variable valve timing system on the intake cam and a compression ratio of 10.0:1.

 

OK, you've convinced me to try 91. I don't think I'll get savings though, because we have a co-op supplied chain here in MO called Break Time where you can get 89 for the price of 87 (it's all about the corn here, folks). 91 isn't cheaper than anywhere else though, so I can run 89 for about $2.99 a gallon right now or I can run 91 for about 20 to 30 cents more. I'd have to see a 2 gallon increase in mileage to make it worth it.

if the difference was only 10 cents it would probably work out in 91's favor.

 

Don't worry about the savings because you don't always get 91 anyway.

http://www.nj.com/news/index.ssf/2011/12/fourteen_nj_gas_stations_charg.html

I can't believe it's unique to New Jersey and I don't believe it's intentional. It happens because they don't mix it right when filling the truck or the truck driver filled the wrong tank or some other human error.

What ever the reason, it's prevalent and the point is people THINK it's 91 and are perfectly happy. The power of the placebo.

I can't understand that comment about RON, it should be the same regardless of region. Maybe confusing RON, MON and AKI? Both RON and MON are measured on standard laboratory engines under controlled, if different, conditions. AKI, though, is what is displayed on pumps in the US and is the average of RON and MON (R+M/2). AKI isn't used in Canada (to my knowledge) nor the EU.

Different regions have different formulations for their gasoline. Too, RON and MON can be quite different for different gasoline formulations and still average to the same AKI number. So two gasolines with the same AKI may have different RON but the gas formulation is very different. That MIGHT be what you're seeing.

Also, the octane NEEDS of a motor changes with altitude; that's why you can't find 93 in Denver but you can in LA and New York.

The WIKI quote is interesting in that HP/TQ numbers are at high RPM. It may be real (if very small) but it's not where we commonly want to operate. I'd like a torque curve to see if there's any improvement at lower RPM. Even so, it does support the argument for using mid- grade when towing or other uses when you may want better high-end performance, however small it may be.

 

What about the higher IGN values I read on my SGII when I use 93 here? I noticed the ignition values are higher when I use premium compared to regular under acceleration.

And wouldn't an advanced timing = better performance? Which is why I could see people finding a use for premium if they're towing.

 

Possibly.. but how much? 3 HP worth according to that WIKI quote. Or about that lost using 5w30 vs 5w20 oil. Is that enough to feel or measure reliably? I haven't been able to.

 

Research Octane Number (RON), Yes, i did not type the correct word, and wiki again:

• United States: in the US octane rating is displayed in AKI. In the Rocky Mountain (high elevation) states, 85 AKI (90 RON) is the minimum octane, and 91 AKI (95 RON) is the maximum octane available in fuel. The reason for this is that in higher-elevation areas, a typical naturally aspirated engine draws in less air mass per cycle because of the reduced density of the atmosphere. This directly translates to less fuel and reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill a carbureted car that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine. A disadvantage to this strategy is that most turbocharged vehicles are unable to produce full power, even when using the "premium" 91 AKI fuel. In some east coast states, up to 94 AKI (98 RON) is available.[24] In Colorado as well as parts of the Midwest (primarily Minnesota, Iowa, Illinois and Missouri) ethanol-based E-85 fuel with 105 AKI is available.[25] Often, filling stations near US racing tracks will offer higher octane levels such as 100 AKI[citation needed]. California fuel stations will offer 87, 89, and 91 AKI (91, 93 and 95 RON) octane fuels, and at some stations, 100 AKI or higher octane, sold as racing fuel.

 

That's really in interesting article in that it leaves so much unsaid...

At high altitude even NA engines won't produce full power using the 'correct' octane. That because the air/fuel charge per power stroke is a lot less than it is at sea level and can't be changed. At least with turbo'd engines you can increase boost and get full power if you could also get 93 octane premium.

Even though you can get 105 AKI fuel in Colorado, as noted it's E85 and you won't ever see as much power or economy since ethanol (85% ethanol = E85) has less energy per unit volume.

Guys looking for the racing fuel (100 octane) near race tracks: I have to imagine it's because they raise turbo boost to dangerous levels for the race and don't want the cost of it, or to chance blowing something out, as a daily driver.

Interesting...

 

I dont hear a ping in my truck using 87 oct, I dont see any difference in performance using 93...

 

Remember the octane makes more difference at low engine speeds. It may only be 3 hp peak (about 3 lb-ft too), but at speeds under 2000 rpm it may be much more significant.

It is for this reason that those that tow, or run like a hypermiler when accelerating (80% load, 1500-2000 rpm), see the benefit when running premium. The engine will pull large amounts of timing (10º or more) in these conditions if low octane fuel is used. I've actually seen it go to 4º after TDC before when it hiccuped on the 87 octane at about 1800 rpm.

Any mileage gain is due to being able to generate more cylinder pressure before the rod is at a right angle to the crankshaft. When the timing retards too much, it still gets burned all the same, but too late to do any good. Simply, at higher load and low rpm, it accelerates the truck in less time and that's your savings (instead of accelerating with 60 horsepower it might be 65 oOOh!). With a trailer load where engine load can stay in excess of 50% all the time it can help a wee bit in the cruising stretches too.

More octane doesn't help an engine as large as the 1GR when cruising as much as a smaller one because there usually isn't enough cylinder pressure. I've found on this truck the ECU will push timing on extended unloaded cruise with regular fuel just as far as with premium (until you load it up, then it'll have a fit and retard your maps for 10 minutes into your next cruising stretch).

Though my last Honda was very partial to premium thanks to its tiny motor. 10.4:1 compression, would run ok on 87 octane, but at 65 mph on 93 octane the load would drop to about 50% and on the flat it would stay between 45 and 55 mpg, rather than the 38-42 it would do on the cheaper stuff. That engine had half the intake valves on load-controlled activation under 68 mph though, so the premium fuel may have just allowed it to stay in 12 valve mode for extended periods.

As for that article... boils my blood... Just think of the lawsuits those stations may get for damaged engines that need the stuff. Dumb decision on their part.