Pocket Aces

I have been mainly running 91 but started using 89. With the temps here in TX reaching 105 in the recent past weeks is anyone concerned if running 87 will actually be too lean? I think I am just going to stick to the safe side and stay with 89 or better but I was just wondering if anyone has noticed knocking or anything with 87.

vetsvett

Of course not, Use it in my malibu all the time.
For your vette, just use what the manual says to use. If ya wanna save a few pennies, mid grade. Otherwise high octane all the time.

Oh yeah, no knocking here either.

phileaglesfan

It won't hurt your engine, just your performance. Personally, I'll skip a couple sodas a week to pay for the premium if need be.

Pocket Aces

Actually in the corvette manual it warns you may notice knocking when using 87 octane and that your performance might be degraded.

"If your vehicle has the 6.0L V8 engine (VIN Code U), use premium unleaded gasoline with a posted octane rating of 91 or higher. You may also use regular unleaded gasoline rated at 87 octane or higher, but your vehicle’s acceleration may be slightly reduced, and you may notice a slight audible knocking noise, commonly referred to as spark knock. If the octane is less than 87, you may notice a heavy knocking noise when you drive. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you might damage your engine. If you are using gasoline rated at 87 octane or higher and you hear heavy knocking, your engine needs service.

Pocket Aces

Leave it to GM to say use 91 or higher and then say you can use 87 but then add some disclaimer. I think C6s run too rich as it is on 93 which is mostly all I see available for premium around here. 89 and 87 are available so I think I might just stick with 89.

harddrivin1le

You aren't saving anything by using lower octane gas because doing so retards the spark to prevent detonation.

That decreases the engine's efficiency.

So anything you "save" at the pump is lost in the engine via the retarded spark.

These engines DEMAND 91 octane or better fuel in order to run at optimal efficiency.

rjwoerheide

Go with Premium, bro!

harddrivin1le

I can't even believe that anyone would run 87 - 89 octane in a 10.7:1 LS3.

Premium even allows a driver with a manual to shift into the next highest gear at a lower vehicle speed. That in itself saves fuel.

Ditto for the fact that premium fuel in an LS3 allows the engine to remain near optimal spark advance under all conditions. That increases thermal efficiency, which increases fuel economy.

People who run low octane gas in an LS anything aren't saving a dime, are compromising drive-ability and are risking the long term durability of the engine.

I witnessed all of this first hand with my LS1 Camaro for 6 years and 80K miles. That car gave the best mileage AND ran the strongest on 93 octane unleaded Shell. (We don't have 91 here in the Northeast).

It ran poorer on 89 octane and poorer still on 87. The difference was especially noticeable at low rpm and under load (e.g. 5th gear @ 40 MPH), where the timing would pull way back with the lower octane crap.

87 octane CAN be used in an LS3 "in a pinch" (i.e. you're running on empty and the only gas station in sight is out of premium gas).

Pocket Aces

Actually I have an LS2 and that is what the manual says for 2007.

harddrivin1le

Read what I wrote above.

You CAN use 87 octane in a pinch.

Running it routinely when premium is available is senseless because anything you "save" at the pump will be lost in reduced fuel economy - particularly if you have a manual trans car and like to short-shift to save fuel. (I used to shift into 6th as low as 35 MPH with my LS1; the engine would only pull that gear at that speed with premium in the tank).

You're also reducing engine output under virtually all conditions when running 87 octane.

THE most economical way to run a 6 speed LS anything is to short shift it (keeping revs below 2K RPM) and use as much throttle opening as possible without invoking the richer mixture curve. (Wider throttle plate openings reduce pumping losses.) The "sweet spot" is ~ two-thirds of WOT.

I averaged 22 MPG IN MOSTLY CITY DRIVING with my '99 LS1 6 speed Z28 by doing that on 93 octane Shell. That wouldn't have been possible with 87 or 89 octane fuel because the engine wouldn't have pulled those taller gears at those low speeds.

Pocket Aces

But if you run higher octane don't you typically run rich which actually robs you of power as the fuel burns too slow? Many people say the LS2s and LS3s run rich which mean too much octane rating right?

Curtis A. Franz

It won't be too lean because that is controlled by the Oxygen sensor and the car temperature is controlled by the thermostat and the fan settings so there is no sweat in using 87 octane other than a bit of power reduction. When I travel thru New Mexico the octanes there are so low that I am using 88 or 89 and paying premium prices. Ah for the octanes of the east coast.

harddrivin1le

That statement has no basis in fact.

One more time:

Running 87 or 89 octane unleaded gas in an LS anything will result in a retarded spark, which will reduce engine efficiency. That compromises performance AND fuel economy.

The only time it "wouldn't matter" is under light throttle, steady state interstate cruising.

If that's ALL you do then run 89.

Otherwise run what the primary fuel recommended by the GM (91 or higher).

harddrivin1le

"07 Silver C6 MN6 Coupe"

That's a $50K car, give or take a few bucks, yet you're worried about "saving" 20 cents or so a gallon by running cheap gas?



Trust me on this: The ONLY way you're saving anything by doing that is if ALL your driving is light throttle/steady-state/interstate.

A smart driver with a 6 speed manual and a tank full of premium can out-MPG any C6 with a tank full of 87 or 89 in every other driving condition by short-shifting and applying wide (~ 2/3rds) throttle openings while accelerating.

Shift from 1st to 4th @ 23 MPH or so.

Shift from 4th to 6th @ 35 MPH or so.

Use wider throttle positions rather than gears to accelerate. Doing so reduces pumping losses (wider throttle plate openings) and also reduces engine RPM.

The LS engines pull like freight trains at those low rpm conditions - PROVIDED that the right fuel is used.

COAST - in neutral - when approaching lights and time the lights accordingly. My '99 Z28 coasted beautifully.

You'll beat the EPA ratings (and CAGS) everytime by doing those things and you'll STILL stay at the front of the pack!

I know this because I spent 6 years and the majority of 80K miles doing it.

Pocket Aces

Actually I am also trying to optimize performance. Not really worried to much about cost. If people are running rich at 91 what is 93 doing?

harddrivin1le

Your confused about octane ratings and "running rich."

Forget about it and run 91 or better octane in your Corvette.

Drive it like I suggested if you want to maximize fuel economy (and still have maximum performance available instantly).

TEXHAWK0

I don't see a connection between octane and running lean.
Aren't the computers going to adjust the air/fuel ratio to match the air density? Why would octane affect the A/F ratio?

richie15

I think if you're asking about it you already have misgivings about using it.Stay with what's recommended and ease your mind.

Cal Vert Man

Running Rich has nothing to do with octane rating.

Running rich/lean is referring to the fuel/air ratio.

If you think you're running rich have the dealer/mechanic check, but don't think you can correct the problem by reducing the grade of fuel you're purchasing.

dvilin