Would 100 LL AV gas be OK for the C8 it is low lead and higher octane that car fuel ?

 

No.

 

No real need to put in something that exceeds the octane rating recommended by GM IMO.

 

Not if you like your cats and O2 sensors.

 

Higher octane won't help power output. In fact, it can actually lower the energy content in the fuel due to the anti-knock additives. Best to just follow what the car manufacture recommends.

 

Stock up on cats and 02 sensors. Hopefully you’ll be able to get volume pricing. You’ll be needing a lot of them, and some deep pockets. On the plus side the exhaust will smell incredible, so there’s that.

 

Thanks forgot about the C Converts

 

AV gas 100LL is loaded with lead. It would kill your cats in a minute.

 

The light blue (100LL) has lower lead than the purple gas (115/145) but it still has lead, enough to destroy the cats and O2 sensors.

There are a number of other avgas grades with higher octane ratings than mogas 93 that contain 0 tetraethyl lead, but there is no benefit to higher octane ratings unless tuned for it.

 

I personally like the chop chop sound I get and the amazing exhaust smell when I put diesel in my C8. You can't beat it

 

You will destroy those parts & wouldn't gain any performance either

 

As others have said, using gasoline with ANY amount of tetraethyl lead is going to potentially do a lot of harm to your engine. Bad idea!

The higher octane (above 93) really isn't going to help your car run any better or faster, either.

 

For street use, the manual requires:
"Premium unleaded gasoline meeting ASTM
specification D4814 with a posted octane rating
(R+M)/2 of 91 or greater is required."

But for track use, the manual requires this:
"Unleaded gasoline, rated at 93 octane or higher, is required."

 

Yep need ONLY octane high enough to prevent detonation. Any more is waste and actually has slightly less energy!

Recall back in the day (early 1960's) in a Lab having to test required octane in a single cylinder variable compression (test) engine. Not a Pic of what we used (although looks like from the era, can tell by the meters!)

Those 3 cylinders on the right look like an Orsat exhaust gas analyzer. Before electronics it used three containers of chemicals that absorbed CO2, O2 and CO and determined exhaust gas composition.

 

We buy the best grade available at the stations we frequent. High volume busy locations. Always 91. And we sleep just fine at night.

 

Well, its true that you don't want any detonation, and its also true that beyond a certain timing advance, the engine will not be able to use a higher octane fuel. But the C8 allows for a range of octanes (91 or higher for street use, and 93 or higher for track use). The earlier owners manuals even stated that while 91 octane is ok, you will have reduced performance.

It has knock sensors and reduces the maximum timing advance to accommodate a lower octane (namely 91) without knocking (so no detonation) but it allows the maximum advance to increase with a higher octane fuel and specifies the use of 93 octane or higher for track use. So it can fully use 93 octane fuel. It does not say whether there is even more headroom to advance the timing for a higher octane in the description, but the owners manual says "93 octane or higher" for track use.

Its described this way in the Service Manual: "If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module
will always try to work back to a zero compensation level, or no spark retard." The older systems, as you know, just used a combination of vacuum and centrifugal advance, and the maximum advance was determined by properly aligning the distributor. I use an Advance Timing Light and measure the actual advance as a function of RPM with my C1 Corvette to set that. And, you could, to some extent, accommodate a lower octane fuel by rotating the distributor back a bit. That adjustment we used to make manually can now be done automatically using the signals from the knock sensors.

Its my speculation that "zero compensation level" is for 93 octane (or maybe higher) fuel. It will back off the max timing advance if you use 91, which is ok by the Owner's Manual. If you use below 91 that apparently exceeds the dynamic range of the timing compensation and it will experience knock (so the Owner' Manual seems to imply).

 

^^^^
The first 2020 C8 Owner's Manual (see below) said with 91 Octane the power was reduced. Then that changed to eliminate those words. My Guess is folks in CA (and other places) were only 91 octane is available, those words made them mad so were not used later!

Fact is at 11.5:1 compression ratio even with aluminum heads back in the day needed Sunoco 260 ~100 octane! But combustion chamber design, swirl generation, DI have all helped reduce detonation. Expect the air/fuel/timing Map may allow more power with higher octane.

BTW they have said there are multiple knock sensors so you won't hear detonation as the timing quickly reduces. They may also use a slightly higher, less economic fuel air mixture that helps. It does say if detonation is heard get to the dealer!

From 2020 Owner's Manual page 204:
Use premium unleaded gasoline meeting ASTM specification D4814 with a posted octane rating of 93 — (R+M)/2. If unavailable, unleaded gasoline with a posted octane rating of 91 may be used, but with reduced performance and fuel economy. If the octane is less than 91, the engine could be damaged and the repairs would not be covered by the vehicle warranty. If heavy knocking is heard when using gasoline rated at 93 octane, the engine needs service. Do not use any fuel labeled E85 or FlexFuel. Do not use gasoline with ethanol levels greater than 15% by volume.

 

Properly running engines usually don't pull timing until they are hot and working hard. I don't know if you could get into the conditions on the street that would pull timing on a C8 running 91 octane. It would be interesting to see someone log the information during hard street driving. On the track, sure. It will even pull timing with 93 octane.

 

Regarding knock sensors, I believe very few owners think of the following. If the knock sensor does it's job of adjusting the timing in response to knocking, that is past tense. Knocking has already occurred, And, at high rpm, that could have been many separate knock events in any given cylinder. I had rather try to have the best fuel available to try and prevent knock in lieu of sensing it.

And regarding fuel octane rating/cost, as others have stated, I am not going to own a vehicle like my C8, and try to save a few dollars a year on fuel.

 

We ran aviation 100LL in aircraft designed for 80 octane av gas. The 100LL had four times the lead from what I was told. In small continental engines we constantly had issues with lead fouling plugs and valve issues.

That stuff would wreak havoc on a C8 engine I would imagine.