Kingtal0n

The engine in my car part throttle knocked about 3 times in special spots of the timing map, when first installed and it was still on its partial factory timing map, which I quickly fixed, and it never knocked again, even on 87 octane fuel which I use frequently to ensure the knock is truly gone. You can tell by reading the plugs if things are good at WOT easily enough also.
Its been over a year and 17,000 miles and it hasn't 'knocked' since. I log every drive and have hundreds of logs with no knock in them. Ive also increased the sensitivity of the knock sensors to be sure.

Also, at 20psi+ of boost pressure on 93 if you 'knock' once its over. sorry pal 1 shot kaboom

Tuned 150+ cars never have knock in them, 7 different ECU and who knows how many different platforms. The part throttle knock only occurs if you get bad gas which is why I run silent exhaust and warn my tuned cars owners to use methanol injection. it isn't a tuning issues its a fuel issue.

JerryU

We all learn from the Forum! Glad you posted and also glad you have researched more and understand the possible consequences of low octane!

RE blending what you have with 100 octane?? I would not bother. Just start using the highest octane available in your area. Lots of places only have 91 octane, which is fine. Avoid lugging the engine at low rpm and no WOT until you go though say two tanks and you'll be fine.

SIDE BAR
My markting communications manager got a great deal on a new sedan but he didn't understand that 6 cylinder engine he thought would be great for gas mileage had a turbocharger. He refused to use the recommended hi test gas the owner's manual said was required. He never used hi test and wasn't about to start!

Made the same suggestion to him, just don't put your foot to the floor and don't lug the engine. With an automatic trans that usually takes care of the lugging issue, i.e. if you use a lot of throttle starting at low rpm it will down shift automatically. It's only us with standard shifts must be careful.

He had that car for a number of years and the way he drove he never used close to WOT anyway. Car was fine and he was happy buying regular gas!

johno504

What octane do I need at -2 ft elevation? will 103 work ?

Kingtal0n

its over 9000

owc6

Ok, I'll play, and to lighten up this: Snorkel octane.

Stardusterone

For what it's worth, in a normally aspirated airplane (non-turbocharged), a properly leaned engine produces approximately 75% power at full throttle at 7,000 ft msl.

This would apply to a non-turbocharged ground-bound vehicle at the corresponding altitude.

Stardusterone

JerryU

That last post remined of my favorite Jerry Clower Joke!

This famous PhD petroleum engineering professor was giving talks all around the country. He was making so much money he hired a chauffer to drive him. After 1 year as they were going to a University to give that talk, the chauffer said, “Professor I have listened to your talk over 50 times. Here you are making all this money and I’m just getting by! In fact I bet I can give that talk better than you!” The Professor said, “Well let’s see. I have never been to the University and we’re about the same size. Let’s switch cloths and you give the talk.” The Chauffer did an outstanding job giving the professor’s speech with more expression and enthusiasm. He got a standing ovation.

Then the moderator said we have time for one question! A student asked, “Professor if 2 million years ago a dinosaur died and is now covered with 6350 feet of sediment and a drill bit hits that area, what will the ph of the soil be? The chauffer said, “Sir I am surprised that let someone like you in this prestigious University and you ask such a simple question. To show you how simple, my chauffer is in the back of the room, I’ll just let him answer!”

ON SUBJECT:

I view this octane and altitude question rather simplistically. At lower engine speeds if with excess timing or a lean mixture you get some pining when you put you foot to the floor, just give it less throttle and it goes away. You have less cylinder pressure as the manifold pressure was lower due to throttle butterfly position. As altitude increases it’s the same as not having the throttle open fully, i.e. less octane is needed to avoid preignition with altitude!

CJ Willys

You have money for a C-7, and dare put anything but the highest octane?!?! SMH

ztheusa

False economy!!!

Use 87 and the computer just says "the idiot is using 87" and retards the spark.

Then the gas mileage goes down, and cost goes up.

Premium is cheaper to run!!!

<<<<<------------my first Corvette. Bought new in 1967

okaythen

I am in Vegas and I mostly run 91 since that's what's available here, elevation here is 2000 and I often drive it hard during the summer. Did I damage the engine some? Maybe some knocks since it's only 91 and hot here?

Really need 93 min huh?

rb185afm

rogergcam

Why would you even risk this? The possibility of ANY damage, to the engine, far outweigh ANY savings. What's that old saying? Penny wise and engine foolish? Just not worth it IMHO!!!!!!!!!!!!!!!!!!!

LarryFL

Funny how some think there is a sensor to determine the gas you use, like some sort of fuel analyzer or something. The truth is there is a sensor that determines engine pre-ignition (knock) and reacts to your dumb decision to put 87 in. It then adjust the timing to minimize the negative effects.

okaythen

Ok so no problem with 91 then, some post said with 91 you want to take it easy on the car and outside temperature can't be too hot like 95F I was like??????

Drag racing does Z06 need 100 octane? 100 is for road racing tracks right?

James Dean

You can run 87 octane if you are in the middle of Alabama and need to get home but all they sell is 87.

91-93 is recommended for usual use even if you aren't racing. On a Z06 or ZR1 it's HIGHLY suggested that you run the best fuel possible or else.

In my 2006 Honda S2000 I run premium and get better fuel economy and about 20whp more on a dyno. The engine's computer will automatically adjust timing, hopefully before any major damage, and reduce performance. That car doesn't have direct injection, is half the cylinders, and nearly half the horsepower. My wife ran 87 in it and prior to a mountain weekend and we got some light pinging on The Back of The Dragon. Kept it easy, used some octane booster and things were good. No major damage done. Probably 200ish thousand miles on that engine (AP1 2.0 in AP2 body) and I'd treat the Corvette better but if it works for you then keep on until it doesn't.

rb185afm

Mad*Max

I am interested in using 91 versus 93 because we get an ethanol free version here but not in the 93.

Kingtal0n

Ethanol is racing fuel. For example E85 is incredible. I'll take the 10% added to gasoline as a bonus.

Patman

A lot of people in Canada prefer ethanol free fuel though, better MPG and you don't need to worry about your fuel system when the car sits in storage all winter long. And up here it actually costs less to use ethanol free premium from Costco compared to the other brands with 10% ethanol. (and for those that don't use Costco, our Shell premium is ethanol free too)

JerryU

Yep, I use E85 when I fill up a rent-a-car when bring it back! It's cheap BUT you get about 20% less mpg! It has less energy!

Works in race cars as the octane is much higher and you can run very high compression that more than compensates. That extra fuel it uses does help cool down the mixture.

The 4 cylinder Offy engine dominated Indy and other series from the 1930's to 1970's because it could run 15:1 compression on Ethanol. With it's one piece cylinder head and block- no head gasket issues! That 252 cid engine could produce 420 NA hp!