Octane Question

[tone357]

I have an 02 2500hd with the 8.1 Allison and was wondering, with this setup being designed to run on 87 octane, would there be any benefit to running 93? Or would it be a complete waste of money.

[Big black truck]

Depends on what you are looking for. If you don't want to race everyone or are not towing a lot then 87 is great. I have a tune and run 91/93, but then I also pull heavy.Mileage is about the same.

[jro909]

dosen't matter, octane is mainly for the compression ratio of your motor...if the motors built for 87 then run it, my truck will pull like a champ on 87 any day of the week

[ATMINF]

There is no benefit to run anything higher than 87 if you have a stock tune. The engine is setup for this fuel. If you get a aftermarket tune that calls for a higher octane then you will see the gain form a higher octane, as the computer will run a higher advance etc.. giving you more power.

[Kodiak450]

I would never use 87 in an 8.1, you should be uses 89 or higher. Just because GM uses a good knock sensor doesn't mean you should use low octane rating fuel. I don't even use 87 in my small engines. You don't need a tune to notice the benefits in higher octane, run a few tanks of higher octane and you will fell better peformance and slightly better mileage, also will be treating your engine better. Also with higher octane fuel, some gas brands have beneficial additives. When I fill up with Sunoco's 89 or higher I noticed the power feels more responsive, especially when towing and plowing.

 

You will find many debates and opinions about higher octane whether it's better or not, but most of these opinions and debates you find online are with cars, not trucks. I feel a better performance in low end and overall performance when running 89 in my 6.0. I've driven 8.1's with 87 and they perform poorly imo. Fill up with 89 or higher and you will notice a little difference all around. You'll see better mileage when towing heavy loads using a higher octane and your engine will thank you over the long term. Some fuel brands where I really notice a difference in their 89 grade are Sunoco, BP FKA (Amoco), Shell, and Exxon. Valero is not bad, nor Hess, but I'd prefer the first two at of them all as my first choice.

[Big black truck]

The difference between the 2 is that the 93 octane has a more complete burn. They both have the same burn speed. So after compression and ignition, there will be slightly more unburnt fuel with the 87 vs 93. This is why the high octane will give a slight better performance. That's why I use it for performance and towing.

[Gregorio]

It all depends. Some manufacturers have a minimum octane and a recommended octane requirement. The recommended octane number is the level the engine was designed to run on without detonation. The minimum number will cause detonation but is the least amount of octane the engine can tolerate as it adjusts power down to compensate. Often times, power and mileage will suffer on the lower octane rating fue because of thisl. This is a clear sign that the engine was designed for a higher octane rating and engine management is sensing detonation and adjusting for it.

 

If you have the time and patience, you can test a couple of successive tanks of higher octane fuel and compare the mileage over similar conditions. If your mileage is higher, you have found that your engine runs better with the better grade of fuel. Also, you just might find that the increased fuel mileage pays for the higher cost of the fuel. Skip the butt dyno testing. Even the most highly tuned one is still not very accurate.

 

If your mileage tests out the same, then you pretty much know the engine is running just fine on the lower grade fuel. There is no benefit to running a higher octane than what is recommended for your engine. However, there can be some minor variability in the actual octane of a fuel vs. the pump rating. In other words, you are paying for 89 but due to a variety of factors, it might test out to 88.5 or in extreme cases, 88. This is not a problem in nearly all of the street driving we do but combined with some extreme towing/hauling on a hot day in the mountains and it could lessen your available power. If they know they will be driving in these conditions, there are many people that will spring for a tank of Premium fuel (91-93 octane) to ensure there will be no detonation and the engine management computer can apply the highest available power mapping.

 

When it comes to additives, there is no rule to what or how much a fuel supplier will add to the various grades. It is not always a safe assumption to think that the higher grades have better additive packages. In most cases, they are identical within a brand. Across brands, however, there are big differences. In general, the major suppliers like Shell, Chevron, 76, etc all have pretty decent additives to keep engines running clean. Also, the direct effect these additives have on power is none. That they do is keep deposits from forming on valves and pistons which helps prevent hot spots where detonation likely occurs. Dirty engines will detonate more readily than a clean one given the same octane rated fuel.

 

Hope this helps.