Gas Octane

It actually doesn't ignite as quickly... lower octane gas does ignite at a lower temperature... and older cars had pinging (pre-ignition) and dieseling on hot days because the low octane gas would ignite BEFORE the spark plug lit, and while the piston was still moving up!

 

I gotta test this out!!

 

I have the 4.0 engine. All ways ran 87 in it.
So far, it's had all the power it's need to do what I ask it to.

 

I commute almost 100 miles each day so mpg is pretty important to me, used to drive a 3 series BMW and would always use 93 octane as I would get better gas mileage, been using 87 in my Tacoma since I got it two weeks ago, might try 91 to see if there are any differences.

Been getting about 19.5 mpg with 87 with a very light foot, I burned through my first tank of gas the dealer put in, but was pushing the truck a lot.

 

I posted this is another octane thread, but recently on an all-highway trip where I burned an entire tank, I filled completely up with premium before and got 22.6 MPG (with cruise set at 70MPH for 350+ miles). On the same trip on the way back I got 21.0 by using 87.

What I calculated at that time was that in this case, it was about a 7% increase in MPG using premium with about a 6.5% increase in the price per gallon. There was no statistically significant monetary benefit.

 

The trip there is different from the way back, wind, altitude, temperature, traffic, many things could explain the difference in mpg besides octane.

 

I agree, although there was no difference in elevation, my overall point was that there's no reason to suspect that mileage is much greater, to the point where it makes it worth the money.

 

91/93 gets me a tad better performance, but ultimately 1 mpg better on premium, so it pays for itself.

 

In a standard compression engine, the regular grade octane that is appropriate for your climate (here it is 87) will burn more completely and is more effective than higher octane grades that are intended for higher compression engines since higher octane rating increases the compressibility of the fuel before it spontaneously ignites. (So basically, higher octane fuels actually are more difficult to ignite and can actually increase your emissions (slightly) and decrease your MPG (slightly). Most cars' computers can compensate for both too high or too low; except carburetted engines.

SOME higher octane fuels, usually the highest grade, contain more cleaning agents with the mid grade being a mix of the two.

Don't worry about it. Regular isn't mediocre.

 

One doesn't need no dyno results, but when I tow I always use '91 gas
for better performance.

 

Its funny to read how much people are misinformed about high octane gas. Remember it is just a truck not a Ferrari.
It would be interesting to see two identical stock trucks with auto trans (to eliminate bad shifts) do a 1/4 mile. One with 85 and the other with 93.

 

I would like to run 87, and most of the time it runs fine on that, but when the humidity is right I'll get misfires at high throttle on the regular stuff. It has happened from different gas stations on different sides of the state in different months so it's likely not a bad batch issue. On days when it does this I put in premium and the problem disappears after about 15 miles.

Maybe my truck is finicky, maybe something else is out of spec, but either way it runs better on premium.

I have noticed that when running premium the ignition advance at 55 mph will stay between 29° and 31° BTDC even on fairly substantial hills around here (meaning maybe a 3% grade, they're not that big), and on regular fuel it likes to dip down to the 18°-20° range with even a slight increase in load. The average difference across the tank isn't much but the instantaneous mpg values at that speed are much better.

 

I run the highest grade and my tailpipe looks like it still came new from the dealership....it's sooo clean

 

I prefer to run the highest octane I can get. Around Ohio, that is usually 93 octane. Through 40 years of driving, I have found better performance and better mileage per gallon. I get enough mileage increase that it always offsets the higher cost and then some.

As for brand name gas verses discount, you get what you pay for. I try to run only brand name, here it is Marathon and Shell, There is a mileage and to a lesser noticable extent performance differance between national and discount gas.

 

Everyone claiming better mpg is.
You must be getting more power per gallon if your mileage goes up.

 

I think a lot of you are confused. It has nothing to do with 91>87, or horsepower, etc..The fact of the matter is the 4.0 V6 has the VVT-i engine. It requires 91! Your engine is not performing adequately if not supplied with 91. VVT-i is similar to Honda's V-TEC(also requires premium).

Engine knock,ping,etc..are bound to happen.

If you have the V6 id say 91+ octane and for the V4 87 octane

 

You've got to be kidding me....so all these little civics with their vtec require premium? looool

On our trucks the ECU controls the timing. You put in regular 87, the ECU retards the timing (if it's knocking)...Put in Premium, the ECU advances the timing.

I think toyota revised the manual eventually, but in my 08 it says 87 is the minimum, and Premium is recommended, not required.

 

Not all Honda's with v-tec use premium. Only certain models. The civic si has a 2.0
Liter engine that has 11:1 compression and revs to 8500rpms. Plus it can advance and.retard timing similarly to toyotas vvt-I but Honda takes it one step further. It actually switches.between two cam.profiles. One cam profile is for gas mileage and when the engine hits a certain rpm range, that is determained by the computer depending on several different factors it switches to a more agressive cam profile for more torque and hp. So those Honda engines really do need premium in order to not detonate.

 

You seem confused too... octane reguirement of the engine has nothing (directly) to do with VVTi, V-TEC or any other variable valve timing technology. It's compression ratio and FI that drive octane requirements and tuning can mitigate it.

 

V4

Some one is confused.