Most (99%) of the gas stations here in Oklahoma City have 91octane for premium. After reading a post by Micah, I found out there is one Shell station that has 93octane. I went there today to fill up and the guy was telling me they also have 101octane, but were out. He said the truck would be there this evening to fill up the 101octane tank.

I have a tune and can't decide if it would be better to get the 93 or 101
What do you guys think?
jeff

 

93 would be fine.....

 

The 101 will be a pure waste of money. Your Dynamic compression ratio of your stock engine is set up for max horsepower on 91 octane. If you want piece of mind, the 93 octane is all you need unless you mechanically alter your compression ratio.

Hammer

 

Count your blessings. I would run the 93, because of the fact that the 101 may not be readily available when you need it. Unless you can tune for it and not have a knock when using 93. I' sure someone will chime in with better info...my $.02

 

93 is great!

 

Well, you know how we get sometimes...if 93 is good, then 101 must be better! lol

So, just for fun, will the 101 hurt anything besides my wallet?
jeff

 

You may get some added deposits; higher octane burns slower.

Go with what the engine was designed to run on. For example, my bike was designed to run on 86 or higher, it runs best on 86. It's actually a little sluggish on 91. Lower octane has a lower flashpoint, it burns faster. So unless you are running high boost, high compression, leaning out with 93, or have it tuned to use the 101 for every tank, its not worth it. However, dont go under the octane the engine was designed for as you will get a lean condition, spark knock and eventually a blown engine. I believe the corvette's computer will retard the timing with sub 91 so this wont happen though... but that change in timing kills your performance.

I'm no chemist, but it's just my opinion after digging around numerous times on the same subject for all of the vehicles I've used.

 

I could be wrong but I believe that the owner's manual recommends 93 octane.

 

I'm pretty confident it calls for minimum 91.

Hammer

 

Thanks for the replies. I'll go fill up with 93 and see if it makes any difference over the 91 I've always used. I cant see 2 octane doing much if anything.
jeff

 

if you were in europe...in most places you wouldnt find anything less than 91...but the prices are a lot higher obviously

 

Jeff, when I was using nothing but 93 and was forced to use 91 on my trip from Seattle to Charleston, SC I had a lot of pinging and such, I try to stick with 93 octane.

BTW, good to hear you found the secret spot. Funny, I am in town for a day and ahalf and I am helping you out.

Micah

 

All grades of gasoline burn at the same rate and same temperature.

The octane rating only refers to the resistance to knock.

Use only what you need, any more is simply a waste of money. There is no difference in performance with a higher octane (for better or worse)

 

They don’t measure the octane rating the same way, thus the higher numbers.

 

Depending how much the 101 sells for, you can pump 87 into your tank and top it off with 101 and in some cases it will be cheaper than if you just pumped 93.

 

Jeff

Where did you find the station? I would like to try the 93 in mine but all I have ever put in is 91. I do get a slight ping for about 1/2 sec when hard acceleration with the 91, maybe 93 it would be undetectable.

Thanks

 

On your ping note...it took a couple of hundred miles and a tank of 93 to start working it out. The station is on the "upscale" side of town. That is what I was told, it was an area known for it's money. Hope that helps. I can say that the station is more old school and not as fancy as the newer stations are.

Sorry for being so vague.

 

From page 6-3 of my '99 owners manual:
"Use premium unleaded gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle may not accelerate as well".
It says later:
If the octane is less than 87, you may get a heavy knocking noise when you drive."

I have run regular in my '99 without the slightest hint of a knock.
If there was any decrease in accleration, it was undectable to me.
I had a 300 HP Northstar powered Cadillac and it said exactly the same thing. I eventually ran only regular, since I could tell no difference.
The dealership mechanics concurred.
My engine is stock, maybe a tune would make a difference, but I will guarantee that 87 octane will not hurt a stock engine.

 

I wouldn't doubt it, these cars come rich from the factory so the computer retarding any timing is probably not detected by the good ol butt dyno. Had it been tuned for 91, you would likely get knock or noticeable decrease in performance (or both) when going to 87.

But still, the difference between 91 and 87 after you put 15 gallons in is what... 3 bucks? I only fill up about 3 times a month. If you arent going to be flooring it and just commuting, 87 probably wouldnt be a problem.

 

The computer in the car is designed to be somewhat adaptive, by that I mean that to the guy that said he's only running 87 octane. Your car may be running fine but I'll bet that if you pull your ECM fuse, put it back in and let the ECM basically re-boot then go out and get on it with only the 87 octane in your tank...it'll ping!
The reason that it's not making any noise and running "okay" is more than likely because it's learned that you're only running that octane and therefore any time you start to accelerate hard enought the computer just retard's your timing or does whatever it has to to make up for the loss of octane(or ability to resist detonation).
Just my 2 cents and I'm only a 20 yr old kid but just like all the other fluids in the car...if the manual recommends 91 octane for best performance and probably 95% of C5 owners are running it with no detonation problems(stock motor/tune). That's reason enough for me...
I mean the 87 octane may not necessarily "hurt" the engine but I would bet that it's definitely not running at it's peak performance, therefore it actually is hurting the engine by not just running the 91 octane...
Donnie