ugabulldog

I had a 93 4 cylinder toyota 4x4 pickup (pre-tacoma era) and it used to knock like crazy with 87 octane, but didn't with 91. I sold it and got a 98 4runner 4x4 and have been putting 91 in it since I bought it (since it is my baby), but with gas prices the way they are, (and only going to get worse) does anyone have any thoughts on the 91 vs. 87 octane for my baby?

hamstrungtaco

theres no need for 91 in that engine unless u have upgrades

leebee

i recall reading some posts a while back that unless you have a high performance/compression vehicle, the higher octane wont/doesnt help us much.

check the search feature, type in something along the lines of 'octane performance' and see what you get. dig a little in there, lots of info.

lee

89macrunner

www.howstuffworks.com should have an article on that im sure

jimbo74

on the old truck it was needed to avoid pinging.... putting 87 in your new truck is fine, its actually designed to use cheap gas unless there are engine modifications to it, or it has bad running problems, but im doubting it does and in this scenario, 91 might actually cuase excess carbon buildup

s_wall98

What about after doing the isr mod...in particular on the 3.0? What grade of gas will be needed? If I have to move up to 91, I dont know that it'll be worth it now. Any advice?

And I am searching in the meantime, but haven't found much.

TACOMANATOR

I'm running 87 octane with the ISR mod and open airbox with no problems on my 3.4. 91 octane should only be required if supercharged.

gwhayduke

Compression ratio is the ratio of the largest volume of the combustion chamber compared to the smallest volume. Most vehicles just need 86 octane because our compression ratios are less than 9.0:1. Read the owners manual and you'll find out what the factory suggests.

If you find their suggested octane is pinging in your engine, then you can increase the octane rating of your fuel as a stop-gap measure. But the pinging is an indicator of something else wrong in the engine, usually an out of tune engine, ignition timing, cam timing, or carbon buildup in the combustion chambers or on valves, which would need to be fixed to bring your engine back into factory specs.

kyle_22r

carbon buildup can raise your effective compression, which can most definitely cause pinging. i've never ran anything but the cheapest gas i can find(i once got midgrade since they were out of the regular stuff and it was knocked down to the same price).

and there's no "regular" and "unleaded" any more, unless you're running trick fuel.

93YODER

I run 87 octane in my 3.0,but ive also run 85 octane with no problems.

Ironmike4x4

Here's the short version. Car manufacturers design cars nowdays to run on regular gas, unless otherwise specified manual. Vehicles with superchargers or high compression engines require higher octane ratings. Older trucks need premium since gasoline is no longer leaded so the valves are not being lubricated anymore by the leads so therefore more pingings.

kyle_22r

they haven't sold anything to run on leaded gas in the US since the mid 70s.

CynicX

87 oct should be fine, if for some reason you hear knock or ping move up to 89 oct...although its rather unlikely you should hear ping and knock on 87 oct.....

Alin10123

On my 2000 when i first got it new i was very nieve and i put premium 91 octane in the truck all day long. This was all before i actually knew what premium meant. It's not necessarily a better gas, it's just got a different octane rating. So that summer i switched back to the regular 87. However, the truck seemed to be "spoiled" by the 91 octane gas. Since it would ping while going uphill and i gave it some gas. So... my conclusion is, the 4runner is designed to run on 87 regular gas. However, putting in a higher octane will change the way the engine runs by a little. (think about it, if it was pinging with 87 with mine, but it's fine in everyone else's that runs 87; the ecu must have advaced the timing a little bit). So that goes to show that the ECU is constantly monitoring the changes and making adjustments. I then put in the midgrade 89 as a comprimise and it hasn't pinged since. It's less than $2 more per fillup when i use midgrade and the engine doesn't ping at all.
I think that if i used 87 for a few tanks that the ECU would reset itself and retard the timing back. But i think that advaced timing = more power in most cases. So... long story short, i use 89.

Alin10123

Oh yea, the only mod i have in mine is the deckplate and amsoil air filter. Other than that, the engine is pretty much stock. No s/c or anything.