What Octane will the SS be rated?

[camaro5]

^ The PCM is ALWAYS pushing the timing advance to allow a slight amount of detonation.

The value of the piezo-electric sensor is seen by the PCM as a voltage.

Higher voltage means more det.

[NUCAR]

Originally Posted by maxdmax

Back in my younger days (late 70s and early 80s) I had a friend that worked at the small airport in town. We occationally filled up my 64 Corvette and old Harley stroker with 108 octane airplane fuel. The 375 HP 327ci and 96ci harley motors loved that gas. He still works there, now they have 102 octane unleaded. I wonder if the new Camaro V8 would like this and would it damage anything?

It'll poison the cats as it contains TEL. Motor does not need it to obtain maximum performance.

[PatrickfromMD]

Originally Posted by camaro5

^ The PCM is ALWAYS pushing the timing advance to allow a slight amount of detonation.

The value of the piezo-electric sensor is seen by the PCM as a voltage.

Higher voltage means more det.

Very useful, thankyou for the contribution. I was unaware the computer would essentially squeeze every last bit out of the available octane.
I interpret from your reply that the PCM will interpret anything beyond a certain voltage threshold (as read by the piezo electric sensor) as detonation. The higher the voltage beyond this threshold, the more the detonation. This should be easy to monitor (with the right equipment) and therefore settle on a grade of gasoline appropriate for the driver wants to achieve.

[CamaroSpike23]

Originally Posted by PatrickfromMD

Very useful, thankyou for the contribution. I was unaware the computer would essentially squeeze every last bit out of the available octane.
I interpret from your reply that the PCM will interpret anything beyond a certain voltage threshold (as read by the piezo electric sensor) as detonation. The higher the voltage beyond this threshold, the more the detonation. This should be easy to monitor (with the right equipment) and therefore settle on a grade of gasoline appropriate for the driver wants to achieve.

pretty much. the thing to remember tho is that the pcm will advance it to a point that it can sustain and will retard from there. I will consistently see up to 48* advance in my LT1 and the 2 times ive ever had any knock retard, I still had 46* advance showing on the data log, but I had 7* of retard so my overall advance was only 39*

but as a general rule, the computer will advance until it gets knock and when it does it will pull timing back then gradually allow it to advance to its limit.

[NewCar]

This article was helpful for me.

http://www.imakenews.com/tomballford...bFcFg,bcRJCqRP


and I do think it is a bit rude to tell people who are asking this question they do not need a performance car. There are several reasons for asking what will happen with 87 octane. For instance, if they plan on using recommended but run into a hard time financially unexpectedly, or if They like 400 hp more than 304 but can live with 400 instead of 422 (a decrease but still much better than the V6). Or more importantly, if they let their sister or father borrow the car and they don't even ask what grade it takes and just fill it up the way they will, The owner will want to know if these people will actually damage their car. I know my father would use 87 even if I told him not to. I am glad to know he will not actually damage my car if I buy the LS3. This is some peace of mind and a good reason to ask this question.

But the price difference per year really isn't that much considering if I drive 10k miles per year (and I do even commuting) then with a car that gets 13/20 (like the LS3 G8 GXP) say I average 17mpg, then with a 30 cent difference, that only equals a total yearly DIFFERENCE in cost of 176 dollars and forty seven cents. Thats far less than the difference in cost between the 26mpg v6 and the 20mpg v8 just due to fuel economy even if they both used 87.

[NewCar]

The irony of all this is that the V6 which runs on regular 87 actually has a higher compression ratio than that of the v8 which runs on premium. If compression is the main issue, then I wonder why this is?

11.3:1 (v6)

10.7:1 (LS3)
10.4:1 (L99)

[Muscle Master]

because the V6 is DI, think about it you would need a lot of pressure

[NewCar]

so if it is so high pressure then why does it not need the higher octane to avoid knocking?

[NewCar]

CamaroSpike23
a rough guide for Compression ratio vs Octane
5:1 67
6:1 75
7:1 82
8:1 87
9:1 91
10:1 93
11:1 95
12:1 103

[DGthe3]

Originally Posted by NewCar

so if it is so high pressure then why does it not need the higher octane to avoid knocking?

Pre-ignition (knocking) requires fuel, air and a certain amount of heat. Compressing a gas heats it up, which can lead to pre-ignition if the temperatures are high enough. In some types of direct injection engines fuel is injected after the compression stroke (or at least near the very top of the stroke). This does 2 things: without fuel, it can't burn durring compression. Secondly, the spray of fuel cools the compressed air which delays ignition until the spark fires.

[UsedTaHaveA68]

Originally Posted by NewCar

The irony of all this is that the V6 which runs on regular 87 actually has a higher compression ratio than that of the v8 which runs on premium. If compression is the main issue, then I wonder why this is?

11.3:1 (v6)

10.7:1 (LS3)
10.4:1 (L99)

I believe that is due to the Direct Injection. With the LS3, the fuel is being sprayed in just above the intake valves in the intake runner. This allows the spray to condense as the droplets come in contact with each other, as well as absorb heat from the intake before it reaches the combustion chamber.

With DI, the fuel is sprayed directly into the combustion chamber at much higher pressures. This allows much better atomization of the fuel (finer mist), which cools off the intake charge much more effectively, allowing you to get away with a slightly higher compression ratio.

[spd98]

Originally Posted by UsedTaHaveA68

I believe that is due to the Direct Injection. With the LS3, the fuel is being sprayed in just above the intake valves in the intake runner. This allows the spray to condense as the droplets come in contact with each other, as well as absorb heat from the intake before it reaches the combustion chamber.

With DI, the fuel is sprayed directly into the combustion chamber at much higher pressures. This allows much better atomization of the fuel (finer mist), which cools off the intake charge much more effectively, allowing you to get away with a slightly higher compression ratio.

Thats correct also you spray closer to your firing event so there is very little of a window in which pre-detonation can occur.

[69Firebird]

I was just going to say it but spd98 beat me to it. With a DI engine the fuel is sprayed in just before ignition, better atomization and cooler charge = less detonation.

The LS3 is sweet, but if they added DI it would be out of control. More power and better fuel economy.

[UsedTaHaveA68]

Originally Posted by 69Firebird

I was just going to say it but spd98 beat me to it. With a DI engine the fuel is sprayed in just before ignition, better atomization and cooler charge = less detonation.

The LS3 is sweet, but if they added DI it would be out of control. More power and better fuel economy.

Agreed. I don't understand why engines haven't been DI'd for years now. Diesels have always been direct injected (or at least for as long as I remember). I remember when Mercury Marine came out with DI in their outboard motors back in the mid '90s, but autos still aren't getting them. Why WOULDN'T they use something to increase the efficiency of an engine?