Should I be using Premium Gas?

[Rick '79 FJ40]

I recently put a tank of premium in my '40 and it seemed to run a LOT better! It quieted the valves down (which I know need adjusting) and seemed to have a bit more power.

Does everyone else run premium in their rig and I'm just the last to think of it, or should it run OK on regular?

BTW, mine has headers, a weber 38 and is de-smogged with a 2F.

Thanks!

 

[Poser]

Don’t quite follow the correlation between Premium fuel and less-noisy valves...

 

[bull]

I know in higher compression engines you can have pinging with lower grade fuel.

I run mid grade fuel and never have any issues.

 

[rusty_tlc]

Interesting reading on the Wiki page.

 

['74 UA FJ]

It should run fine on regular. If it's pinging with regular, which it shouldn't, retard your timing a hair.

 

[cruiser_guy]

You're not driving a Ferrari or other high performance engine. It's a tractor engine, it'll probably run on dirty water!!

 

[idus25]

I know in higher compression engines you can have pinging with lower grade fuel.

I run mid grade fuel and never have any issues.

I have a 72 which I am dropping a Chevy crate which calls for "high octaine. What is considered high octane and is this because of knocking valves???

 

[JJS]

I have a 72 which I am dropping a Chevy crate which calls for "high octaine. What is considered high octane and is this because of knocking valves???

High octane is 93 or Premium at the pump. The "pinging" with lower grade is referred to as spark knock, and is caused by the lower octane fuel detonating too quickly in the combustion chamber. Hopefully, I explained that right.

 

[camcruiser13]

hell no

save your money

 

[JJS]

hell no

save your money

x2. If you're compression ratio is 9:1 or lower, then I see no reason why you should run something over 87.

 

['74 UA FJ]

High octane is 93 or Premium at the pump. The "pinging" with lower grade is referred to as spark knock, and is caused by the lower octane fuel detonating too quickly in the combustion chamber. Hopefully, I explained that right.

That's correct. Detonation can be caused by timing that is too far advanced and high compression.

 

[pb4ugo]

I have a 72 which I am dropping a Chevy crate which calls for "high octaine. What is considered high octane and is this because of knocking valves???

It's not the valves knocking, It's the rod bearings knocking against the crank and if not corrected you will eventually spin a bearing. Which is major trouble.

 

[rusty_tlc]

I have a 72 which I am dropping a Chevy crate which calls for "high octaine. What is considered high octane and is this because of knocking valves???

Post #4 has a link that explains it pretty well.

 

['74 UA FJ]

It's not the valves knocking, It's the rod bearings knocking against the crank and if not corrected you will eventually spin a bearing. Which is major trouble.

 

[FJBEAR]

as noted, unless your motor is a high compression motor, or forced inducted, you do not need to regularly run premium fuel.

But once in a while it is a good idea to run a tank of the good stuff through it, to keep the internals clean and carbon build up knocked down.

I put my supercharger on my taco before the gas prices started going crazy. I am forced to use the "good stuff" which is the only draw back I have with the blower!

 

[bsevans]

I've been running premium/high test fuel in my '78 for 22 years. The only time I've used regular has been in the White Mountains of NE Arizona at an elevation of 9K when only regular was available. The engine would ping often with regular grade fuel. Before I refueled and had premium in the tank there was no pinging at that elevation.

 

[Living in the Past]

I just bought a 76 with the owner manual still in it. I think it call for 90 or 91 octane. I don't know if they changed how they rated octane since then but it seemed high for a 2F. This is a Federal emissioned engine. The cruiser is just store right now and I've never driven it (deal was just to good to pass up) so I can tell you how it runs at different grades. The manual is now being stored out of the vehicle up north so won't be able to check for a couple of weeks. Some else should have a 79 manual available.

John

 

[Degnol]

I've been running premium/high test fuel in my '78 for 22 years. The only time I've used regular has been in the White Mountains of NE Arizona at an elevation of 9K when only regular was available. The engine would ping often with regular grade fuel. Before I refueled and had premium in the tank there was no pinging at that elevation.

That could also be a result of you running an HEI/DUI that is not curved for your motor and is providing too much mechanical advance.

Where exactly did this thread turn off the main road? Pinging, knock, pre-detonation is a function of compression and/or timing and carbon buildup. There is nothing mysterious about a Toyota F or 2F that allows it to escape the normal causes of knock.
If your head has been shaved, or your block decked, you may have higher than normal compression, and as a result may need higher octane fuel. If not, your timing is too advanced, either static or due to some oddity in the vacuum or mechanical advance.

Ed

 

[rusty_tlc]

That could also be a result of you running an HEI/DUI that is not curved for your motor and is providing too much mechanical advance.

Where exactly did this thread turn off the main road? Pinging, knock, pre-detonation is a function of compression and/or timing and carbon buildup. There is nothing mysterious about a Toyota F or 2F that allows it to escape the normal causes of knock.
If your head has been shaved, or your block decked, you may have higher than normal compression, and as a result may need higher octane fuel. If not, your timing is too advanced, either static or due to some oddity in the vacuum or mechanical advance.

Ed

Degnol: Wouldn't higher octane fuel mask the symptoms you refer to? So it's possible that some folks experience pinging/knocking due to timing problems and "solve" the problem by running higher octane fuel?


Back On Topic: I'm guessing the guys that use FJ40's in the third world don't check the octane rating before they fill up. Remember these truck were designed to run in remote areas with little or no maintenance, and on whatever fuel is available.

As far as cleaning the engine out with high octane, how would that work? Don't all grades of fuels have detergent additives? Since Octane is a rating of how well fuel resist pre-ignition why would a higher rating mean it would clean out the engine?

 

[F-junker]

Cheap gas at stations with old tanks are what I avoid, I use only Shell ,Exxon, Texaco, Bp etc. I try not to buy gas at stations that have been around a long time and may have contaminated fuel.
I have noticed big differences in fuel quality over the years. For the toyota though I notice little to no difference in low octane vs. 93. I always add lucas FI cleaner at every few tanks. It does keep things clean.