Originally posted by '99 Contour SE:
What have i started lol!



You started a ruckus. Most of this thread is lame.

You can run low octane fuel in your SVT, period.
Will it cause knock? Maybe. The chances are a hell of a lot better with low octane fuel.

Remember, the first thing that will happen when using poor grade of fuel is pre-ignition, or pinging depending on the load, outside temperature and timing.
Pinging isn't likely to damage the surfaces of the type of piston that we have in our motor.
This pinging will always precede full blown engine knock. The engine knock is what happens after preignition when the flame front (and overall cylinder pressure) gets high enough to slap the piston before the piston gets to top dead center, resulting in pushing against the piston as it comes up versus pushing it down on the downstroke.

So that tells you that preignition happens before the spark plug ignites the fuel and it happens a little too early so that a ping is made but the piston still travels over TDC in time so that the main force of the charge isn't against the piston movement.

The knock sensor is tuned to pinging and will operate as stated earlier in response to it. It will generally stop the pinging before it leads to knock.

Therefore you can run low octane fuel safely in cold weather or low load/highway cruise conditions. Mountain or hilly driving counts as HIGH load.
In summer time even low load conditions will result in pinging in a tuned performance motor and of course some motors will ping with low octane fuel at ANY time.

It is my experience with the duratec and 10:1 compression that 87 octane will suffice if ambient temps are 70F or less. 89 will work most of the time but IMHO it is a waste of money for what you get. 91 or better will always work and is a must for any temps above the 80F range.
If you drive agressively then 91 or better will always be the way to go unless the temps are really cool outside like in deep winter.


Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black