New Caprice - Discussion forums

Ive seen from multiple sources that these cars (L77) are rated for 87 or above octane. My car has just over 20k miles on it now and since day one Ive used 87, havent had any issues and my fuel mileage averages about 22mpg 90% highway @70-75mph.

I read in the owners manual the other day and it stated, vehicles with the V8 engine are supposed to use 91 or above octane. So the last tank I kissed my wallet and decided to throw in a tank of 93....

OMG what a difference, very noticeable change and it took about 1/2 tank for the ECM to adjust itself. Fuel mileage went up about 30-45 miles on a tank, and that is with very spirited driving.

On a normal fill up, the onboard display would read between 385-400 miles to empty, now, with 93, it would read 420-430 miles to empty. Next thing I need to do is drive like I used to and see what fuel mileage I attain.

One - I can't fathom 30-45 mpg in any sort of driving. I don't want to call BS but... BS.
Two - Are you sure these performance gains are as dramatic as you are making them sound?

I want to believe - don't get me wrong - but I doubt youre the first one to use 93 octane in our cars. And I know from my experience with other cars that 93 doesn't seem to make a difference unless the tune was different for the change.

30-45 miles more on a tank, Not 35-45 MPG.

Huh, 11 owners manual does not mention anything about it but 14 does, interesting:

Ahhhh I apologize!

I thought you were going nuts, but it turned out it was me being the nut!

the L76(G8 non-flex fuel) and L77(ppv flex fuel) are both 10.4-1 motors

in most theory's we should use 91 , but alot depends how you drive , i drive mostly in traffic and rarely put my foot in it , so ive used nothing but 87

Hahaha 45mpg, in this car, I wish.
Thats why my "daily" is a TDI Jetta, thats my 50mpg car.

But yea, I never had an issue running 87, like I said, 20k miles worth of it. But it was a noticeable difference switching fuels. Now, cost effectiveness...thats a different story. It would normally cost me 39-42$ to fill up 87. With 93, 48-50$ a tank full.

that along with bumper to bumper i just use 87 , ill be glad when the weather cools enough to use my 96 sunfire more , i get 3 weeks to a tank in it and less than half that in the ppv , but the ppv is alot more comfy compared to a lowered 170k beater , lol

with my commute, its 3 days @ 30$ for the tdi or two days @$40 in the chevy. But the chevy has AC, the Jetta currently doesnt.


BUT, what I will do, just to make sure I am not going crazy, is measure 0-60 times with 87 and 93 and compare. Give me a week and Ill produce some numbers.

The stock tune Lo Octane spark table have as much as 12 degrees of timing retard compared to the Hi Octane table in the mid throttle areas. On LS engines this area usually corresponds to the peak torque, so what you feel is not imaginary.

Thats good to know!