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87 octaine vs 91 octaine
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grimsin
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PostPosted: Fri Aug 19, 2011 7:43 am    Post subject:  87 octaine vs 91 octaine Reply with quote

This might be all in my head thats why i wanted to ask people on here.
before i seafoamed the car my brother put 91 octane in..I know our impala stock gm tune is for 87 octaine but will the impala run better on 91 octaine? seems like im getting way better mileage(might be in my head lol) but i dont want to be hurting the engine. so my question is it ok OR better to put in 91 octaine In, will i get better MPG? lower KR? more power?
Thx in advance.
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PostPosted: Fri Aug 19, 2011 8:06 am    Post subject:   Reply with quote

Stick with 87. I'm sure someone will chime in with the details but the car isn't programmed for 89 or higher.
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PostPosted: Fri Aug 19, 2011 10:51 am    Post subject:   Reply with quote

Don't waste your money on 91 octane (unless you have a tune that requires it). It provides you precisely zero benefits in an engine that doesn't require it.

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PostPosted: Fri Aug 19, 2011 12:45 pm    Post subject:   Reply with quote

IffyG wrote:
Don't waste your money on 91 octane (unless you have a tune that requires it). It provides you precisely zero benefits in an engine that doesn't require it.


[/thread] Perfect Mr. New Mod

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PostPosted: Fri Aug 19, 2011 2:33 pm    Post subject:   Reply with quote

This topic gets beat to death on just about every vehicle forum imaginable.
It really all depends on brand/distributor, location, if the fuel has been contaminated, etc.

I will say that SOME cars, as they age, tend to do better with higher octane. You may be getting better mileage with the higher octane simply because the fuel is of better quality. Some of the gas stations around here, even though they say it's 87 gas, the true octane rating is probably around 83 or 84. This often causes poor mileage, pre-ignition (very audible spark knock/pinging) and all around poor performance. Pre ignition results in loss of power as the fuel is burning simply by being compressed rather than being ignited, and can eventually damage your engine. The more octane in fuel, the higher compression it can withstand before it ignites.

Like I said, as a car ages, sometimes it will do better with higher octane fuel, even without a PCM tune which goes into the nitty gritty of changing ignition timing, MAF readings, etc. It all just depends on the compression ratio of your individual car. If you open the throttle and you don't hear any pinging/spark knock, you are doing just fine and don't need to run the higher octane. If you do get a lot of spark knock, try cleaning or replacing your MAF first and see what you get. If it still knocks, you might need to try the next grade for a few tanks.

Higher octane gas is also generally better quality gas, hence you will probably perform better on it. If you actually get good quality 87/89 octane gas that is actually 87 or 89 octane, your car should will do just fine if it hasn't been re-programmed to use high octane. I recently took a trip across I-10 from TX to FL. I have gotten 87 gas that I barely got 300 miles on a tank whereas another time I got 500. Not all fuel is created equal, and not all 87 is the same Smile Even within the same "brand" of service station....

I ran 87 in my Impala up until I dumped it with no issue. My Tahoe, however, requires at least 89 to not ping and knock and complain when I open the throttle up.

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billy101
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PostPosted: Fri Aug 19, 2011 3:27 pm    Post subject:   Reply with quote

Arvetus wrote:
This topic gets beat to death on just about every vehicle forum imaginable.
It really all depends on brand/distributor, location, if the fuel has been contaminated, etc.

I will say that SOME cars, as they age, tend to do better with higher octane. You may be getting better mileage with the higher octane simply because the fuel is of better quality. Some of the gas stations around here, even though they say it's 87 gas, the true octane rating is probably around 83 or 84. This often causes poor mileage, pre-ignition (very audible spark knock/pinging) and all around poor performance. Pre ignition results in loss of power as the fuel is burning simply by being compressed rather than being ignited, and can eventually damage your engine. The more octane in fuel, the higher compression it can withstand before it ignites.

Like I said, as a car ages, sometimes it will do better with higher octane fuel, even without a PCM tune which goes into the nitty gritty of changing ignition timing, MAF readings, etc. It all just depends on the compression ratio of your individual car. If you open the throttle and you don't hear any pinging/spark knock, you are doing just fine and don't need to run the higher octane. If you do get a lot of spark knock, try cleaning or replacing your MAF first and see what you get. If it still knocks, you might need to try the next grade for a few tanks.

Higher octane gas is also generally better quality gas, hence you will probably perform better on it. If you actually get good quality 87/89 octane gas that is actually 87 or 89 octane, your car should will do just fine if it hasn't been re-programmed to use high octane. I recently took a trip across I-10 from TX to FL. I have gotten 87 gas that I barely got 300 miles on a tank whereas another time I got 500. Not all fuel is created equal, and not all 87 is the same Smile Even within the same "brand" of service station....

I ran 87 in my Impala up until I dumped it with no issue. My Tahoe, however, requires at least 89 to not ping and knock and complain when I open the throttle up.


My dad tested using a tester from his work, the octane that I got from our local Sheetz where I put in "87" octane gas and he said it was only about 84 85 octane rating. I now only put 89 in my tank and I seem to get around 300ish miles to a tank city.
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PostPosted: Fri Aug 19, 2011 6:05 pm    Post subject:   Reply with quote

billy101 wrote:

My dad tested using a tester from his work, the octane that I got from our local Sheetz where I put in "87" octane gas and he said it was only about 84 85 octane rating. I now only put 89 in my tank and I seem to get around 300ish miles to a tank city.


Yeah, it all depends....that's about what it is around here in this part of TX too...SUCKS!

However, last month, I filled my Tahoe up with 87 at a BP in Scottsmoore, Florida (just north of Titusville on 95), and drove from there to Mobile, AL and still had 1/4 tank left. That's darn close to about 550 miles.

Which is why the OP is probably seeing a noticeably difference when using higher octane. Not that 91 is any better than 87 with the OEM PCM tune in the Impalas, but that he is likely only seeing 83 or 84 when he uses the 87 spicket....

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PostPosted: Fri Aug 19, 2011 11:13 pm    Post subject:   Reply with quote

Arvetus wrote:
billy101 wrote:

My dad tested using a tester from his work, the octane that I got from our local Sheetz where I put in "87" octane gas and he said it was only about 84 85 octane rating. I now only put 89 in my tank and I seem to get around 300ish miles to a tank city.


Yeah, it all depends....that's about what it is around here in this part of TX too...SUCKS!

However, last month, I filled my Tahoe up with 87 at a BP in Scottsmoore, Florida (just north of Titusville on 95), and drove from there to Mobile, AL and still had 1/4 tank left. That's darn close to about 550 miles.

Which is why the OP is probably seeing a noticeably difference when using higher octane. Not that 91 is any better than 87 with the OEM PCM tune in the Impalas, but that he is likely only seeing 83 or 84 when he uses the 87 spicket....


Yeah, totally. We tested our Sheetz's 89 octane, and it was dead on. So, I now fill up 89 in my Impala. With my tuned PCM in my city MPG's keep on going up. With the new tune I've been doing a bunch of WOT pulls and my DIC still reads 19.3MPG which aint too shabby around town and doing a LOT of WOT pulls. My next tank will be 89 as well, and I will drive it like normal again and hopefully I can pull 22+ around town. I'll keep ya posted!
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PostPosted: Fri Aug 19, 2011 11:26 pm    Post subject:   Reply with quote

I did a rough test on my ATV with gasoline. It's has a magneto ignition and 1 barrel carburetor. No fancy knock sensors. I found that 91 RON from BP knocked pulling a hill and 87 from Phillips 66 didn't. So I've been using Phillips in my car with no knocking ever. Even with and approaching 120,000 miles. The Citgo BP replaced was just as bad IMO.

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PostPosted: Sat Aug 20, 2011 8:19 am    Post subject:   Reply with quote

Yeah, like I was saying, my Impala rarely complained about the gas put in it...but my Tahoe on the other hand, did not like the same gas. It would knock and ping like crazy at WOT when going up hills or passing or whatever.

I had the PCM tuned to remove some of the torque management and firm up the shifts a bit and found the MAF was way out in its readings, hence giving me the knock. A little cleaning and some adjusting some of the PCM tables and it runs very well on 87/89 now...

My 91 Buick (before the Impala) used to run real good on 89/91 and there was absolutely NOTHING done to that car. Of course, it was old and had a ton of miles on it. That was my car as I was just getting started on my own and had NO money to do anything. Smile

So, good rule of thumb...if it doesn't knock, there is no need to put higher grade gas in it. It's a waste of money. If you can't get rid of the knock by cleaning the MAF, then try the next higher grade. Always run the lowest grade you can run without it spark knocking.

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PostPosted: Sat Aug 20, 2011 10:59 am    Post subject:   Reply with quote

I guess my opinion is if you have audible knock, you have bigger issues than what gas you are putting in the car.

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PostPosted: Sat Aug 20, 2011 11:14 am    Post subject:   Reply with quote

Once the 91 was all used up i put my usual 87 octaine and got the same mileage. so was just all in my head lols. i would still like to get a 91 octane tune for some better mpg one day.
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PostPosted: Sat Aug 20, 2011 1:40 pm    Post subject:   Reply with quote

IffyG wrote:
I guess my opinion is if you have audible knock, you have bigger issues than what gas you are putting in the car.


yes, that is very likely... usually it's a MAF

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PostPosted: Sat Aug 20, 2011 2:24 pm    Post subject:   Reply with quote

Arvetus wrote:
IffyG wrote:
I guess my opinion is if you have audible knock, you have bigger issues than what gas you are putting in the car.


yes, that is very likely... usually it's a MAF


I get absolutely no knock with 87 on my 3.4 Impala. I cleaned the MAF so hopefully it'll stay that way. Think was pretty dirty too. Shocked

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PostPosted: Sat Aug 20, 2011 6:18 pm    Post subject:   Reply with quote

I suppose it would be possible to have a ton of carbon in the cylinders increasing the compression, with 87 octane it would retard the timing...but seafoam should take care of something like that.

Question for ZSPOT - GM upper cylinder cleaner/lube how does that compare to seafoam?
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