87hillbillyoter

So i used to run 91 octane in my truck, but then a couple of my buddies said that was bad for the engine because they were specifically designed for 87 octane. so ive been running 87 for a while, but i wanted to know if this was true. thanks yall

myyota

Its not true, and it won`t hurt anything. But it is a waste of money to to run 91 octane in your truck because its not a high performance engine. 87 or 89 octane gas will work just as well and save you a little money as well.

greatskiiiier

a 22re prob wont benifit from anything about 87, maybe .5mpg better from 89?
i just put 89 in my 22rte to see if it helps gas mileage at all, ganna fill back up later today and let you know

4bangercraig

It certainly won't do any harm, but it won't help the cause much either. I use 91 in mine, but mostly because the P.O. put 91 in it for twenty years before selling the truck to me. It's mostly superstition, but I've had a couple nonsensical breakdowns right after changing something that should be totally arbitrary. So I'm sticking to my guns.

Google fuel octane. Wikipedia and Uncle Sam agree- higher octane in a truck engine don't do diddly but to your wallet. Unless you got knocking. In which case you might want to check your timing...

blake.nemitz

i use 91 because i run my timing at 17* BTDC. this prevents pre detonation, octane in gasoline slows the burn for high compression or forced induction motors. if you put 91 in an old carbed 22r you would probably get less power than with 85 being a lower compression motor and natrually aspirated because the burn is longer than it needs to be and thermal efficency is wasted

blake.nemitz

and it runs 100 times better with 91 and advanced timing, my milage is dead at 20 with 35's and the truck pulls hard. we have awesome gas in CO though, cant say that for you east coasters out there. my milage is at 20mpg with advanced timing and 91, with 85 i got around 12-15 with my timing at 8* btdc

4bangercraig

17 BTDC matched with 91 octane. Hm. But if your timing is advanced and creating an early detonation, but your fuel doesn't explode until later because it requires greater compression...I don't get it. Explain? I'm fascinated.

HighRunner

Basics of fuel:

Lower octane fuel = More energy and fast burn
Higher octane fuel = Less energy but a slower burn

Like it has been said before that is the basis of octane fuel ratings, it is a rating of the rate at which fuel combusts.

On a low compression engine such as in older Toyotas, you will most likely actually make more power running 87, it has more inherent energy than say 91 or 93 and since the compression is low enough and there isn't a whole lot of timing pre-detonation will not occur.

It's only when you start running an engine with increased cylinder pressures from either a high compression ratio or from forced induction such as a turbocharger or supercharger that you need higher octane levels. Increased cylinder pressures (and timing) cause fuel to combust faster which will unfortunately cause pre-detonation (which is the pinging sound). If pre-detonation is allowed to occur and is severe enough it can cause massive damage to the engine. This is one of the biggest causes of failure in performance engines, people pushing too much boost/timing with not enough octane, you can literally melt pistons.

I also own a 2003 Twin Turbo Cobra and that's why I know a thing or two about tuning. You've really gotta be careful when you start pushing more boost and timing.

saitotiktmdog

Wikipedia is your friend.
http://en.wikipedia.org/wiki/Octane_rating

tried4x2signN

And I just bet that's speedometer corrected, right?

tried4x2signN

Poor man's high compression, if I'm understanding it correctly...

The timing is advanced so the piston can get as high as possible to TDC, and the fuel prevents pre-detonation or "pinging"...

Pre-detonation (fuel will Diesel) is ping or pinging.

You can do it to a 3Fe Cruiser too, but IMO that's a whole nother ball of wax.

dropzone

iTrader: (6)

x2, how are you measuring your mileage? I use a GPS

saitotiktmdog

It has nothing to do with how high the piston gets. He is advancing the timing. He added 2 degrees of advance, I think. I cant remember if stock timing is 12 or 15 degrees btdc at idle. The extra octane helps with this. Advancing timing gives more power. retarding timing and you will lose power. On a NA engine. I retard timing under boost to prevent detonation but the extra air and fuel makes up for it. If you could run 30 pounds of boost at a 30 degree advance you could make some serious power, but it woul have to be built like a tank and weight a ton. Or be a diesel.

tried4x2signN

dangit! I meant advanced...

I believe it also lets the fuel mix longer .

tried4x2signN

And pre-detonation is a killer for you...

The piston will still be coming up in its stroke and if the fuel detonates, will bend a rod right around a fu-bar your engine... Or any other Turbo engine for that matter...

blake.nemitz

i also have 4.88 gears, and my odometer is dead on with the mile markers on the road, but most of my drive is flat highway

saitotiktmdog

The extra air and fuel makes up for the loss of power due to retarding the timing. You can add extra fuel to guard against detonation. Thats why under high boost you want air fuel ratios of 12:1 to 10:1. This is typical of high boosted applications. Detonation usually breakes chunks out of your pistons and burns holes in pistons before in would bend a con rod.

sb5walker

Gasoline is an amazingly variable blend of any number of fractional distillates of petroleum and other compounds. You'd be amazed what can be in there. Different brands can have vastly different constituents, but there is a standard measure called "Octane Rating" which attempts to qualify how the substance will burn in your engine.

Octane Rating relates to how likely the fuel is to spontaneously combust in your engine when subjected to heat and pressure, instead of the normal burning initiated by the spark plug. When fuel vapor spontaneously ignites, it's called detonation or "pinging".

The benchmark for the octane rating is a reference blend of iso-octane, a specific fractional distillate of petroleum, which is not too likely to cause detonation and is assigned an octane rating value of 100, and heptane, which is very likely to spontaneously combust, and which is assigned a value of 0. If your witches brew of gasoline has the same likelihood of detonating as a blend of 87% iso-octane and 13% heptane, then your gasoline is assigned an octane rating of 87, regardless of what's in it.

There are substances that are more likely than heptane to spontaneously combust, such as hexadecane, which has an octane rating of less than minus 30. Diesel fuel has an octane rating of 15 to 25. Toluene, which comprises about one third of typical gasoline, has a rating of 114, meaning it is highly resistant to spontaneous combustion. Alcohols such as methanol (113) and ethanol (116) likewise are resistant to detonation, which is why they're used in ultra-high compression engines like the ones on dragsters. Propane, interestingly, has an octane rating of 103 - lots of stuff is more explosive than it is.

Higher octane fuels allow you to advance the timing, increase the compression ratio, or use a blower (which again, increases the compression), all of which gives higher horsepower and lower fuel economy. Just using a higher octane fuel in a given engine doesn't buy you much, unless you need it to stop the pinging, in which case it's very useful. Premium fuels may have other useful compounds such as lubricants or solvents that prevent or remove deposits from injectors, however it seems a matter of blind faith: the gas companies don't tell you what's in there and nobody is publishing test results of the different brands of gas, at least that I'm aware of. One company's 87 octane may have better additives than another company's 90.

Be aware of the link between octane and timing. High octane fuels tend to burn more slowly than low octane. As a result, peak cylinder pressure comes later. If you use a higher octane fuel than what the motor was designed for, you run the risk of causing peak cylinder pressure to occur later than where it ideally should (about 15-17 degrees after TDC). Unless you used high octane to stop pinging, you probably should advance the timing if using high octane so that peak pressure happens at the right place for power and efficiency.

Other factors can cause pinging: clogged injectors, or bad O2 sensor or air flow meter, or a vacuum leak can cause lean mixture and increased pinging. A non-functioning EGR can likewise cause high combustion temps and increased pinging. Carbon deposits on valves or piston heads can cause pre-ignition. On my 3VZE, years of pinging ended when I replaced the distributor (to solve a different problem: bad bearings). So if your engine is pinging, try to fix the cause rather than just trying to cover up the symptoms by using higher octane. Both the 22RE and 3VZE should run fine on 87 octane if injectors, piston heads and valves are clean, there is good compression and no vacuum leaks, the timing is set to spec, the engine control systems are working right, and tune-up items like filters, plugs, cap, rotor & plug wires are in good shape.

(BTW, on the 22RE I would consider replacing your thermostat with one for a 85-88 22RTEC - the turbo engine. Part number 90916-03083. That is a 180 degree stat vs the 190 deg stock one and will help keep the motor from overheating and will help prevent pinging. The stock 3VZE thermostat already is a 180 degree one. Use the thermostats from the dealer - they are way better than the aftermarket ones.)

There is a difference in energy content per gallon between the average high-test and low-test fuels, so it's theoretically possible to get better mileage with premium fuels, but most engine control systems fail to capitalize on the difference. Low octane fuel contains about 35 megajoules of energy per liter, while the average high octane contains about 40. That's a 14% increase in energy content for premium gas, but you'll never see that much increase in power or economy (unless you advance the timing with the premium fuel, in which case you'll see an increase in power and likely a decrease in economy).

Many of the high octane fuels, however, have significantly lower energy content than typical gasoline. Propane, for example, has about 26 mj/l, ethanol about 24 mj/l, and methanol only about 16 mj/l, or 60% less energy per liter than premium gasoline. So, if you think your truck has less power when running on gasahol, you may be right.

MudHippy

Combustion chamber and/or piston face design can also influence an engines tendency to exhibit spark knock/pinging.

The 3VZ-E is particularly resistent to pinging based solely on that factor alone. As well as, due to that and other factors, being initially designed to accept higher octane fuels. In that case one should, as you've stated, advance the ignition timing to adjust for earlier peak combustion pressures. Which, as you also stated, can increase power and possibly decrease fuel economy. That really depends on what you mean by economy however. Economy as in mpg? Or economy as in $pm, or dollars per mile(the cost of the gallon in relation to how far that gallon got you)?

I've found that running 91 octane in my 3VZ-E, when properly tuned for it(advanced ignition timing, larger spark gap, and leaner AFM adjustment)yields more low-mid range power and better mpg, without effecting high-end power too drastically(if at all...I still can't feel any difference there, good or bad, to be honest). It does NOT result in better economy as in the cost of the fuel vs. how far that fuel gets me though. Meaning the mpg increase is not proportianal to the increase in price of the 91 vs. 87 octane gas. I roughly estimated that I'd need to get 25ish mpg for the money spent on the 91 octane to be worth it in that respect. I get 22-23ish mpg at best with 91 vs. 20-21ish with 87, neither of which could be achieved with stock tuning though. The tuning is the critical factor there, as Toyota likes to tune their engines to run rich from the factory, which directly causes lower mpg(and arguably lower HP as well). I still run the 91 octane because I'd rather pay a little more for just the power increase on it's own. Though it's also a sacrifice in the engine longetivity department too. Advancing ignition timing alone causes undue stresses, and coupled with running lean(er), is undoubtably slowly taking it's toll. I've taken such things into consideration and still feel it's worth it. I can always rebuild it if need be...well...not always...but you get my point.

See how this page states that they used 91 octane in the lower compression 3VZ-E to establish the power output compared to the higher compression 5VZ-FE. Also notice those numbers are strangely the ones that are stated for a stock 3VZ-E(150 HP & 180 ft.lbs. of torque). Which is supposed to run on 87 octane pump gas...right? Or is it?

tried4x2signN

RON = Research Octane Number...

PON = Is what you get at the pump...

And don't forget. Modern engines with their ignitions are cheating basically rewriting all this.

The V8 in the Lexus 400 will run off of low octane, and will get more power and fuel economy on higher...

Previous engines like a Cadillac's for instance would not adjust for the wrong octane being used...