So who with C7’s uses premium and is it ok to run 87 octane? Do you guy recommend 91, 92 or 93 octane and who is the best. Thanks.

 

Why do you ask? Define "ok". I would think that the ECM might notice a ping, retard the timing and thus power and the mileage, bringing you back to square 1 as far as savings. Also, if there is a cumulative effect for the ping before the ECM can retard it, IDK. Best way to know is to run the car till as empty as you dare, fill up with 87 and monitor the knock counts as seen by the ECM when you hit mid to upper throttle. If there is no effect, fine. Without a scanner to see live data, I really wouldn't lower the octane. Why are you trying to do that? You may lose the mileage and thus money which might offset the gains from the lower fuel price.

 

Here's your answer from the Owner's manual:

Premium Recommended
Use premium 93 octane — (R+M)/2
— unleaded gasoline in your
vehicle. TOP TIER Detergent
Gasoline is recommended.
Unleaded gasoline with an octane
rating as low as 87 may be used,
but it will reduce performance and
fuel economy.

You will probably save more $$$ overall by using premium and driving sensibly most of the time. Save the rapid acceleration and high rpm for when you are having fun if the cost of gas is an issue for you.

If you can't afford the recommended gas then you probably can't afford the car.

Ron

 

I have the L92 Vortec (6.2L) in my 2007 Yukon Denali. It is the basic LS3 with a different cam with a taller intake and larger oil pan. The engine is serviced regularly and at 225K I pulled the plugs for inspection. With 50K miles on them I found them to be light ashen gray with no oil contamination or fuel fouling. The engine has always run well on regular gasoline and has never knocked. And it has made numerous trips west on I10 at 85mph all day long. (L92 Vortec - ratio 10.5:1, 403hp, 471 lbs/ft torque)

But getting the C7 Corvette has been a huge learning experience. Before the purchase I knew nothing of the LT1. I thought it was just a new and improved LS3. WRONG!!

The LT1 compression ratio has jumped from 10.5 to 11.5:1 over the LS3. And the hp rating has been increased by another fifty or so. The LT1 being a new design with little interchangeability among the two engines operate under different design parameters.

I recently read exactly what RonC7 posted. Premium Recommended…

More recently however, I found newer GM documentation where the following is listed on page 9-52 of the 2014 Chevrolet Corvette Owner Manual

Use premium unleaded gasoline meeting ASTM specification D4814 with a posted octane rating of 91 or higher. If the octane is less than 91, damage to the engine may occur and may void the vehicle warranty. If heavy knocking is heard when using gasoline rated at 91 octane or higher, the engine needs service.

It looks like GM dropped their recommendation for premium fuel and outright say to use premium with a minimum of 91 octane. Otherwise, beware the consequences.

I’m now using COSTCO premium.

BillT

 

The OM makes it pretty clear this is not a permanent solution, and the car should be filled up with high test asap.

It also says to be gentle on the go pedal in the meantime, or engine damage may occur.

Sure, it may retard the engine to eliminate knock, but it is a circle of bad things just waiting to happen if you use regular gas and high acceleration.

 

If 93 octane is available in your area, I would use it

 

I exclusively use premium in my car as that is what is recommended. 91 octane is what I use as there is not much else around here and the car does fine with no knocking. I would only use 87 octane gas in an emergency and replace it with premium at the first chance.

 

Use a 93 octane Top Tier gas.

Period.

 

The LS3 is 10.7:1 and the earlier LS2 is 10.9:1. Both engines can be run on low octane fuel as there are High Octane maps and Low Octane maps in the ECM. When a certain amount of knock is detwcted by the selective microphones, timing goes to the low map which is VERY conservative (even the high octane map
is conservative)

The LT1 has 11.5:1 conpression not just because time marches on but because it is Direct Injected only. The LS was port injected. With direct injection, the fuel (being sprayed directly into the chamber) at the correct time under immense pressure simply doesn't give detonation a chance to occur--or at worst gives it much LESS of a chance because thr fuel is ignited as soon as it is injected. With port injection or carburetion, the fuel has time to settle and ignite in corners of the chamber. When differing flame fronts collide with each other, that is the knock you may here.

11.5 is NOTHING for a DI motor! Ford was using 12:1 on the port injected 5.2 Voodoo GT 350 motor on 93 octane. Lamborghini is up around 12:1 on their DI motors and the old Ferrari 458 Speciale was up around 14:1 again with a DI motor.

Using less than 93 shouldn't pose an issue with the LT1, you just will be on s lower timing map and consequently, make less power.

 

For a NA LT1 preferably any top tier 93 octane ethanol free gas if you can get it.

 

The OP is fine using 87 octane in his pre-2018 LT-1 C7. At the end of the day, GM is good with it under warranty as well.

 

I really can't understand the rationale of not using the highest octane available. Let's say it's a 50 cent different from 87 to 93 octane, that's roughly 8 bucks a fill up. I can't see how 8 dollars per fill up is going to break the bank when we drive cars worth 50-90k dollars.

 

I really don't understand why someone would spend big bucks on a high performance car and even consider using 87 octane.

 

Prolonged use of 87 will cause damage in the engine. At sea level you should be using 93 octane. Out west, or anywhere the elevations are higher, premium is commonly 90-91, which is fine.

Yes the knock sensors detect detonation and pull timing, and thus, power. But it can only pull back so much, and it always tries to advance it to the other timing map.

The way to know for sure is hook up a scanner and see if a lower octane results in knock counts.

 

 

Yes, the KS will detect detonation and pull timing, thus power and mileage. However, what that means is that detonation has occurred. Yes, it is a brief millisecond and it is not significant. What I am curious about is what the cumulative effect is over the years.

 

How long is the warranty again? If it fails tomorrow and it is under warranty, no problem. Assuming they don't tear apart the engine for warranty or stick a scope into the chamber. What happens when the warranty ends?

 

As with any warranty expiration date. You're on your own B2B, minus any manufacturer recalls or warranty extensions. As often times occurs.

 

Kinda my point. This might not fail with the first tank or two. It might cause problems OUTSIDE the warranty which is why "GM is good with it under warranty" might not be as useful if it falls outside the warranty period or if they find detonation.