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87 or higher octane fuel??

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Posted by: blkZ28Conv

Our vehicles call for 87 min octane fuel. I only use 93-94 octane on my similiar engine in my Z28 (higher compression vs Escalade). Owners manual calls for only 87 min.
What octane do you guys use? I have read it is a waste to use higher octane fuel when vehicle does not need it and that actually may create problems from incomplete combustion.
What are your thoughts. TIA

Posted by: Jibit

Quote:

Originally Posted by blkZ28Conv

I have read it is a waste to use higher octane fuel when vehicle does not need it and that actually may create problems from incomplete combustion.
What are your thoughts. TIA

I've never heard of hight octane (except racing fuel) causing problems for an engine. Actually, I think its the opposite. Guys correct me if I'm wrong but when you use lower octane gas you get that pinging sound for the incomplete combustion. As far as a waste, I know in my lincoln I get better gas mileage using the premium grade gas compared to just regular.

Posted by: Katshot

"Theoretically", it IS a waste to use higher octane than the engine & engine management system are designed to use. But in REAL life, I would always suggest to use one grade higher as a safety margin to guard against dishonest gas stations/distributors that DO at times sell fuel that is below the stated octane. Even "if" your engine is equipped with a knock-sensor, detonation can occur and it WILL damage your engine over the long-haul. A few extra bucks a year is worth the peace of mind to me.

Posted by: BigT

Over ten years ago my wife had a Tarus that I told her to put the middle grade gas in instead of the cheap regular. After a couple of tanks the car starting running rough, hesitating and hard to start. I took to the local Ford dealer that a friend of mine was the service manager and I told him the problems we were having. The first thing he asked me was what gas was I using and I told him we were using the mid grade. He said the cars computer was programmed for regular and would not run right on higher grades of gas and cause the problems we were having. I switched to regular gas and after one tank all the problems went away and didn't come back.

Posted by: Katshot

I've never seen that happen before. One grade higher should not make enough difference to cause a problem but in your case it apparently did. Hey, I guess that would answer the question for THAT car's owner. If it won't run on anything else, I guess you're stuck with the cheaper fuel. What a shame huh?

Posted by: blkZ28Conv

Quote:

Originally Posted by BigT

Over ten years ago my wife had a Tarus that I told her to put the middle grade gas in instead of the cheap regular. After a couple of tanks the car starting running rough, hesitating and hard to start. I took to the local Ford dealer that a friend of mine was the service manager and I told him the problems we were having. The first thing he asked me was what gas was I using and I told him we were using the mid grade. He said the cars computer was programmed for regular and would not run right on higher grades of gas and cause the problems we were having. I switched to regular gas and after one tank all the problems went away and didn't come back.

This is the scenerio that I hear from my mechanics. Because of electronics in todays vehicles the recommended octane is the one to use. I also see the point of mixing a higher octane fuel periodically just to get peace-of-mind that the min is covered.
I guess I should follow the manufacturer's recommendation with the same conviction that I do with my higher octane requiring vehicles.
Z28 and LS400 require premium by Manufacturer
Escalade needs min 87 by Cadillac recommendation.
Thanks everyone for your insights.

Addendum: The octane rating has nothing to do directly with the power produces by an engine. Octane is a pre-ignition (knock) inhibitor not a power additive. If all ignition perimeters remain at their maximum (not activating anti-knock timing retardation) both fuels will produce the same power.

Posted by: Katshot

Quote:

Originally Posted by blkZ28Conv

That's not entirely true. True, most motor fuels (gasolines) produce roughly the same amount of energy (BTUs) but not "exactly". And the designed-in ignition timing is optimized for the specific burn rate of the fuel suggested. I know this may seem like nit-picking but there actually is enough deviation among brands of fuels, let alone differing octanes that it is easily possible to track power output changes on any specific engine (even with static timing)when run on different fuels.

Posted by: blkZ28Conv

Touche'

That is correct. That is why people desire certain brands of gasoline (i.e. Mobil vs Citco) and actually feel a seat-of-the-pants differences. This is related to the refining process but very little to do with octane rating or anti-knock activity.

Small poll:
What octane rating to you run in your vehicle? What is the recommended requirement?
(Let's take cost difference out of the equation but focus on engine care and performance).

2000 Escalade: I use 87 (fulled with 93 last time). So far no discernible difference. I will check mileage.

Posted by: Katshot

Quote:

Originally Posted by blkZ28Conv

Touche'

That is correct. That is why people desire certain brands of gasoline (i.e. Mobil vs Citco) and actually feel a seat-of-the-pants differences. This is related to the refining process but very little to do with octane rating or anti-knock activity.

Small poll:
What octane rating to you run in your vehicle? What is the recommended requirement?
(Let's take cost difference out of the equation but focus on engine care and performance).

2000 Escalade: I use 87 (fulled with 93 last time). So far no discernible difference. I will check mileage.

Years ago when I was doing field testing with Cadillac on the Northstar, we found that dropping even one grade could reduce both MPG and engine power output by roughly 10%. We also found that carbon deposit formations were much more rapidly formed in the combustion chamber, which ultimately lead to carbo-knocking in a large percentage of the test group. Of course this was only pertaining to a Northstar but similar tests were done on other engines with similar results. Ultimately, this testing lead to a revision of a field memo from Cadillac that stated that the Northstar COULD be run on Regular fuel. It should also be noted that this whole thing was done prior to 2000 when the production Northstar engine was redesigned to run on Regular fuel.

Posted by: blkZ28Conv

Hi Kevin,
I am again a little confused. From your tests even a small change lead to a significant reduction in HP (10%) and a change for the worst for MPG. Why would GM recommend the usage of lower octane fuel with these perimeter changes and the potential of carbon deposits and its subsequent problems?
I want to run the best fuel for my vehicle, the 3-4 dollar difference on a full tank is not a deal buster.
TIA

Posted by: Katshot

Quote:

Originally Posted by blkZ28Conv

Hi Kevin,
I am again a little confused. From your tests even a small change lead to a significant reduction in HP (10%) and a change for the worst for MPG. Why would GM recommend the usage of lower octane fuel with these perimeter changes and the potential of carbon deposits and its subsequent problems?
I want to run the best fuel for my vehicle, the 3-4 dollar difference on a full tank is not a deal buster.
TIA

The problem at the time was that Cadillac was getting a lot of pressure from vehicle owners about the high operating cost of the Northstar-equipped cars due to the high octane requirements. In our fleet, every penny I saved in fuel cost translated into approx. $8000/year. So if you do the math, if I could use say, mid-grade vs. premium, I would directly save say $40-$50,000/year. So it makes sense for me to look into the feasability of using lower octane fuel. After myself and MANY OTHER fleet owners/managers made the inquiry, Cadillac offered a memo saying that you "could" use lower octane but it would cause a drop in MPG and power output. We changed our fuel to mid-grade and within a couple weeks or so, we reported back to Cadillac that the Northstar WOULD NOT tolerate the lower octane feul as they said without some major side-effects. They quickly revised their position on the subject and decided to redesign the engine instead. They released the new design in 2000 but we still had "some" isolated problems with the Northstar STILL forming carbon and having carbon-knocks. Cadillac never made any "official" comment about it but we ended up going back to premium fuel and our problem was cured.

Posted by: SC_Steve

i've heard, as far as power is concerned... that the lowest octane you can go, before detonation, will yield the most power. Not sure how accurate that is... or how dramatic the difference in power is... but intresting. Anyone know anything about that?

BTW... I usually use 89 in my mark VIII... but every once in a while I'll throw in some 91 octane. I would use it all the time, but I hate paying 2.40 a gallon

Posted by: blkZ28Conv

Thanks Kevin,
Appreciate your presentation of your experiences.

Posted by: StRyKr

probably true but with the prices of gas and if engine performance is not really a factor. in the end its always... it all depends on that certain engine

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