Determining Octain levels ??

[Big Sugar]

Here's a Query;

    How do you determine what Octain level you should be Running? Is it based on Knock and ping only ?
If I'm Running an above average comp. ratio, How do I determine what is optimal for my setup ? Do I Go with what Fuel is Available and set the engine up based on that,? Or do I use a suppliment like Lucas or Rocket To get my fuels octain  into  the optimal range for my Motor ?How do I determine if the octain level is too high for the ignition curve I'm running now !
As it stands I'll run 93 octain now and add a bottle of Lucas octain boost and not notice any Difference.
I'm worried I wont hear the motor pinging if the Octain is to low, given the fact my Charger runs pretty loud under load.


Ron (stumped)

[cudaken]

 If you can not hear spark knock, you need to dump the flow masters! When you say average comp do you mean by that? From the factory real average was around 9.0. There is many many things that comes in to play.

Sorry I have no answers just questions.

                     Cuda Ken

[Big Sugar]

Well first off it's not nessesarily a me specific question ? And as far as compression ratio," Above average"
let's say 10:1 .

Ron

[cudaken]

 There are so many factors it is un real. Lets take cam over lap. My Runner has 76 degress, that lowers static compression a lot. I can run 91 with no ping.

My 70 383 Cuda when fresh and ture 10.0 to one 91 ocatne and no knock and fast advances. But after 62,000 miles she started to rattel. Cause she was getting worn and started to burn a little oil. That will lower the kindling point and cause knock. Went to 93 and it was gone.

Best thing is if you can hear it. Heck, even load can cause it. More likely to have knock in 3rd than 1st at WOT.

If you have a ture 10.0, dump in some Cam 2, I am as I try to type Ture tigh and right 9.5 engine you should be fine with 93 gas alone.

                                        Cuda Ken

[firefighter3931]

A lot of factors come into play. An engine that has tight quench will tolerate lower grade fuel better than a non-quench combination. If your engine has flattop pistons and open chamber heads....it is a non-quench combo.

Generally speaking, 9.5:1 works with open chambered non-quench iron head combos. Cylinder pressure and dynamaic compression are inter-related. Dynamic compression is a combination of the static compression and cam timing events. The resulting cylinder pressure is a good indicater of whether or not the engine will predetonate. With iron heads, anything at 160psi (or less) cranking pressure is pretty much safe. Do a compression test and see what you've got.

The sparkplugs will also show if a predetonation condition exists. Have a look at the porcelin for little black specs or little silver specs. This will be carbon or aluminum breaking off the pistons as the fuel explodes before being ignited (predetonation). Just because you can't hear it doesn't mean it's not pinging. If you can hear it that means that it's pretty bad.

There are ways to work around it ; change the ignition curve, retard the timing, decrease the compression etc...

Start off by doing a compression test and have a look at the plugs.  

Ron