[Z06] will 93 octane over 91 prevent KR?
Le Mans Master
Joined: Sep 2014
Posts: 5,278
Likes: 539
From: Kelowna BC
Yes; stock, tuned, modded all matters. I had mine tuned for 93 octane (use 94). The OP's car is stock and knocking on 91 octane... maybe needs to look into a tune?
Last edited by grantv; May 16, 2017 at 09:54 PM.
Thread Starter
Racer
Joined: Mar 2016
Posts: 399
Likes: 31
No--i cant hear any knock--i just want the car to stay in the high octane table--so will be mixing 91 with unlead sunoco 100 to about 93-94 octane--also have a vararam so inlet temps should be good-live in vegas HOT summers
Last edited by royal flush; May 16, 2017 at 10:03 PM.
Melting Slicks
Joined: Feb 2006
Posts: 3,191
Likes: 43
From: Scottsdale Az
I understand, I'm in AZ. We don't bother with mixing and if you're stock you don't need to worry about it. Yes you may have KR if you're racing in the middle of summer because your IAT sensor will be conservative but I doubt you'll get KR due to actual knock.
Pro
Joined: Jun 2015
Posts: 551
Likes: 102
From: Madison WI
Sounds like you are not exactly stock.
Basic performance 101: increase airflow to increase power
Since you have increased how much air the engine can inhale the PCM must add some fuel to get back to the commanded AFR. Even though the computer can compensate, it is far from perfect and thus tuning is the best way to get the best performance with any change in airflow.
Even a mail order tune will get those LTFTs back down closer to 0. Far cheaper in the long run than always running 93+.
What I believe is happening is the added airflow has required additional fuel which the computer isn't able to get just right and you are sometimes a bit lean and even with stock timing it is causing a KR to occur. Lean KR can be troublesome because it can heat up the chamber and cause additional KR... turning into a constant power robbing situation.
Plenty of times you can have KR without hearing it - data logging will be needed to know for sure if the computer detects it.
Basic performance 101: increase airflow to increase power
Since you have increased how much air the engine can inhale the PCM must add some fuel to get back to the commanded AFR. Even though the computer can compensate, it is far from perfect and thus tuning is the best way to get the best performance with any change in airflow.
Even a mail order tune will get those LTFTs back down closer to 0. Far cheaper in the long run than always running 93+.
What I believe is happening is the added airflow has required additional fuel which the computer isn't able to get just right and you are sometimes a bit lean and even with stock timing it is causing a KR to occur. Lean KR can be troublesome because it can heat up the chamber and cause additional KR... turning into a constant power robbing situation.
Plenty of times you can have KR without hearing it - data logging will be needed to know for sure if the computer detects it.
Drifting
Joined: Sep 2007
Posts: 1,649
Likes: 50
From: Goldsboro NC
You should be fine in a stock car. Unless its been tampered with, your car doesn't reach commanded factory PE until 5500rpm anyway. With 95deg heat your IATs overtime will pull timing. In a stock car 93 or 91 is wont run much different, if it all.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Banned Scam/Spammer
Joined: May 2007
Posts: 15,685
Likes: 1,330
From: Machineguns, because I don’t compromise
Mine got knock on 93. Changed the front knock sensor. Still got pinging and knock.
Took the heads off. Plenty of carbon. True knock. Removed the carbon, no more knock.
Higher octane gas wouldn't have been the solution. If you're getting knock (hence the computer pulling timing and throwing a knock code) you have issues other than 91 octane.
If you're in hot climate, consider spending for a 160* thermostat. Will help when rolling down the road, will still get hot (fans won't turn on sooner without tuning) below 35mph. Better than factory 195*
Took the heads off. Plenty of carbon. True knock. Removed the carbon, no more knock.
Higher octane gas wouldn't have been the solution. If you're getting knock (hence the computer pulling timing and throwing a knock code) you have issues other than 91 octane.
If you're in hot climate, consider spending for a 160* thermostat. Will help when rolling down the road, will still get hot (fans won't turn on sooner without tuning) below 35mph. Better than factory 195*