Just wondering who is running 87 vs 91 octane to see if there is any major concerns?

 

I run regular unleaded. I ran premium and plus - 92 and 89 octane - and just didnt see a huge difference.

 

Running low octane with a turbo is not a good idea. Although the admonition by GM that premium is "recommended" as opposed to mandatory may allow some latitude, with F/I the line between an innocuous ping and destructive detonation is narrower than in a N/A motor. Contrary to some beliefs, there is no sensor in the fuel system that determines octane (as opposed to the fuel sensors in flexfuel vehicles). With most modern ECMs, there is an octane scaler, which increments and decrements between the high and low octane spark tables. When knock is detected by the knock sensors, the spark is adjusted accordingly. The difficulty with this type of systems is that it's reactive, not predictive. That is, knock must occur before the timing is scaled back.

Moreover, with the advent of the new LNF turbo upgrade kit, the tune is more aggressive than a standard SS, which is why the warning sticker is supplied to indicate "premium fuel only" Clearly the margin between non destructive knock or ping and events serious enough to damage pistons, rod bearings, etc. is even slimmer than in the stock version.

 

I have run both regular and premium. I don't normally drive it hard and I have not experienced much of a difference. I can say that when I run regular, my ScanGauge occasionally reports knock detection during normal driving. When I am running Premium I never see knock detected.
Also, the knock detection makes its adjustments long before you can hear any knock.

 

As I understand it, you have to run the different octane for a couple weeks before the ECM learns and fully adjusts to the new octane. So, first tank going from 87 to 91 should produce a large increase in ft-lbs & hp, until the ECM learns to adjust for the higher octane back to 260/260. First tank of going from 91 to 87 should produce a decrease in ft-lbs & hp, which normalizes gradually as the ECM learns to adjust for the lower octane and back to as near nominal output as possible. Of course, lower octane will produce slightly less output. 87/91 * 260 = 249, but it's anyone's guess whether that translates to real world output. Something tells me those dyno freaks out there might have trouble running 87 octane for 3 weeks before being able to give a conclusive answer...

 

Running regular in an SS is NOT a good idea. I have seen first hand the knock and LOW whp/wtq numbers that have come up on the dyno from using regular fuel. There are reasons that GM "recommends" premium.

 

That runs contrary to my experience with octane scalers in GM ECM's. They react instantly and often severely, depending on which load cells are knocking. It only takes a few seconds of severe detonation to completely destroy a piston, ring land, or rod bearing. In a couple of weeks, I could easily lunch half a dozen engines and still have time for bowling.

 

Unless your a power fanatic run whatever you want.Ive towed with reg and got excellant milage.Sure you see a power increase with premie because of the timing allowance,but if your not one to keep your foot in it,go for it.All the non SS cars out there I doubt premie gas will do anything for you unless youve made some performance mods that can take advantage of it.As far as milage..Ive not seen any increase using one over the other.It does scoot better with the better gas but other then that no real difference.The knock you do not hear but the computer picks up isn't any different then a carburated motor that had no controls,and those motors worked out just fine.If GM wanted you to use premie only,,they would have said so. GM wouldn't alllow you to use a gas that would effect reliability when they know they would have to fix it for free. Though in states where you run into extreme hot weather I would use it all the time because of the hotter air.Colder climates can run reg all the time.

 

In the SS version it DOES state on the fuel door that GM recommends Premium fuel. If you run regular fuel in an SS ESPECIALLY a turbo/supercharged vehicle you run a HIGH chance of getting knock which in turn means you COULD blow the motor from detonation. I know first hand that those motors WILL knock with regular fuel.

Let me tell you what...Run regular in an SS, and when you blow the motor, go ahead and tell GM that you ran regular fuel when they recommended premium and watch them NOT warranty the motor.

Sorry to be getting to excited about this subject, but I don't understand why anyone would splurge to buy a performance vehicle and put cheap fuel in it? I can give you another for instance with the fuel differences...Not only did this HHR SS knock with regular, but it put down 190whp in an auto on a Mustang Dyno. Once they got all the regular out and put Premium in, she put down 220whp on that same dyno. Keep in mind that Mustang Dyno's rate lower then DynoJet.

 

Any idea how long it had been running the low-octane prior to that 190 whp rating?