New Caprice - Discussion forums

2011 PPV L77

A thought occurred to me...there is nothing on the dash saying "premium fuel only" etc etc and these cars have 10.4:1 compression.....

I always put super in it thinking I need to because of the compression.....but if it isn't required then is the timing really weak from the factory meaning if we bump the timing up a bunch even on a stock motor we can make a bunch more power and just have to always put super in it?

The dynamic compression is probably pretty low allowing for low octane fuel also the stock cam timing in typical GM fashion is pretty lazy. Most LS engines really wake up with a cam swap and a tune.

stock timing is all over the tables , i run nothing but 87 in mine

I had a feel it's all over the place Since it's a dog off the line then pulls real hard. I figure it's a mix of the drive by wire and the timing. But though I have HP tuners and can pull the tune to look at it, I wouldn't honestly know by looking at it if it was a lazy tune or not.

I could try to compare it to the 550hp tune in my chevelle (I didn't do the tune) but that could be like apples and oranges.

Why would the dynamic compression be low? Would it be something like cam overlap causing cyl pressure to bleed off etc?

The cars were fleet vehicles, so a requirement for the OEM was that they run on 87 octane. If you want to run premium only, then you can bump up the timing 5-15 degrees across the board.

As a side note, I have ran my HPtuners scanner in several cars that were advertised as "premium fuel only" but with 87 in the gas tank and looked for engine knock with HP tuners, and I have yet to find a stock vehicle that was "premium only" and then had knock detected with 87. So basically if you have a stock, untuned car (of any kind) you are probably wasting your money on 91-93 gas because your car isnt running timing for it even tho the manual may say so.

with gas being so expensive right now I will just run 87 until someday I do a cam and a tune.

Keep in mind that these cars are Flex Fuel also. The fuel management can tell what inlet air temp, coolant temp, throttle position, load, octane and alcohol content is available. The fuel management controls injector pulse width and the spark. The spark tables to choose from are HUGE.

Maurice

had no idea the ECU could see the octane.

That would make sense why it doesn't "require" super unleaded. if it can sense cheap gas it would pull timing I guess. I have run it with both and getting on it I can feel no difference though.

For anyone curious here are the stock timing advance maps for high and low octane. Substantial power potential difference.