Recommended Octane, this confuses me...

[Need4Camaro]

Typically the recommended Octane is determined by the Compression Ratio. The higher the Compression Ratio, the higher octane you'll need to prevent pre-detonation.

If you look here...

http://www.chevrolet.com/camaro/pdf/...ifications.pdf

The V6 Camaro actually has a HIGHER Compression Ratio than the V8... Yet the V8 is recommended to use Premium while the V6 is not

V6 - 11.3:1 - Recommended - REGULAR Octane
V8 - 10.7:1 - Recommended - PREMIUM Octane...

Alittle contradicting???

Anyway - at that level of compression, would you think the V6 would benefit from using Premium + a tune?

[cause4panic]

direct injection allows for a higher compression ratio at lower octane ratings

[bombebomb]

Originally Posted by cause4panic

direct injection allows for a higher compression ratio at lower octane ratings

Thats awesom iv learned something today.

[Need4Camaro]

Originally Posted by cause4panic

direct injection allows for a higher compression ratio at lower octane ratings

Cool, howcome they didnt do that for the LS3/L99 Model though? A 400 HP 87 Octane car would've been awsome...

[bombebomb]

Originally Posted by Need4Camaro

Cool, howcome they didnt do that for the LS3/L99 Model though? A 400 HP 87 Octane car would've been awsome...

My guess is cost. I think it has been discussed before.

[Grape Ape]

The V6 is from the “next generation” whereas the LS3/L99 is probably the last V8 of it’s generation. The next V8 should have DI.

The V6 is also aided by more carefully designed cooling including oil squirters that cool the pistons from below.

Detonation is cause by temperature which is the total of:

Intake air temp
+
heat left in the chamber from the last charge

These are multiplied (not literally) by compression. So if you can reduce one factor (chamber temp or intake air temp) you can safely increase another (compression).

[Need4Camaro]

Originally Posted by Grape Ape

The V6 is from the “next generation” whereas the LS3/L99 is probably the last V8 of it’s generation. The next V8 should have DI.

The V6 is also aided by more carefully designed cooling including oil squirters that cool the pistons from below.

Detonation is cause by temperature which is the total of:

Intake air temp
+
heat left in the chamber from the last charge

These are multiplied (not literally) by compression. So if you can reduce one factor (chamber temp or intake air temp) you can safely increase another (compression).

With that stated, do you think we can expect a change in the Camaro's V8 motor much like we experienced with between 97 and 98 with the 4th Gens? (LT1 to LS1)

[cause4panic]

There is no fuel in the combustion chamber to pre ignite while the compression cycle is occuring. Fuel is injected at high pressure just before ignition occurs.

[Grape Ape]

Originally Posted by Need4Camaro

With that stated, do you think we can expect a change in the Camaro's V8 motor much like we experienced with between 97 and 98 with the 4th Gens? (LT1 to LS1)

I think that when the new small block is ready GM will look around and see where the return will be highest and put them there (Cadi? trucks? Corvette?). Watch what Ford does with its new twin turbo DI V6 for hints.

If/when the Camaro gets one it will probably be pretty similar output to what it replaces with better mileage, lower displacement. Size and weight could go either way.

But I don’t work for GM and my interest in GM is all post Zeta, so I’m really just guessing so some longterm GM fans may have better guesses.

Originally Posted by cause4panic

There is no fuel in the combustion chamber to pre ignite while the compression cycle is occuring. Fuel is injected at high pressure just before ignition occurs.

Sort of. When cruising the DI injector fires close to TDC on the compression stroke to create a small stoichiometric pocket in a much greater volume of air. This means that the computer can hold the throttle open wider at a low load to reduce pumping losses and save fuel.

When under a heavier load the DI injector fires during the intake stroke and uses the incoming air‘s turbulence to distribute the fuel evenly. And of course knock is only ever an issue under heavy loads.

Here is a pretty good wiki article: http://en.wikipedia.org/wiki/Gasoline_Direct_Injection

[69-er]

There's more to cylinder pressure than just static compression ration. The effects of the cam timing can effect the overall pressures.

[SCNGENNFTHGEN]

I read it some where that the DI on the V6, has a cooling affect on the pistons, which allows the higher compression ratio with the lower octane fuel.

[Don 97 SS]

Originally Posted by 69-er

There's more to cylinder pressure than just static compression ration. The effects of the cam timing can effect the overall pressures.

Yes, I understand that overlap plays a role too.

[Chevycobb]

subscribing for any future posts with info. learned a lot in this thread that I never knew.

[Capn Pete]

Originally Posted by 69-er

There's more to cylinder pressure than just static compression ration. The effects of the cam timing can effect the overall pressures.

That and ignition timing too, right? Ignition wasn't mentioned, but it obviously plays a role in the timing of the cycles.

When I first read the spec sheet a few days ago, I was also intrigued at first about the fuel requirement differences, and the high/low comp. ratios of the V6/V8. But then I thought about the D.I. factor, and figured that must be the answer ..... clearly, that's the case .

[alexss]

great write up.. im learning alot today...