knock Q

[southern boost]

i been ridin car with the boost set about 18 for thelast couple of days. well to day i get in the car and my knock on my scan master jump to about 3. the Q is i havent been havin any knock at this settin what could be possible problem the only changes i know of is weather and i didnt had octane boosterwhen i put in gas this time, but 02 didnt change stay around 790-800 suggestionpls.I also would like to know what you guys consider a safe knock readin thanxs randy

 

[UNGN]

At 18 psi octane starts to become critical. O2's are not meaningful if you don't have enough octane to avoid knock.

You can have .900 O2's using 93 octane and 23 psi and you will still blow the car up.

 

[c&cgn]

IMO, no knock is okay. If you have knock then you need to solve it. Not too many guys can run 18psi on pump gas. Turn it down a pound or two and see if it is still there. You're other choice is to run higher octane gas ora pump gas xylene mix all of the time.

 

[southern boost]

i hear some guys say they have knock some times what is torreable reading i know you want 0 knock and i did turn the boost down was all but gone went .5 at 16 lb.of boost

 

[Steve Wood]

First, the octane boosters are a waste of money. You will get alot more bang for the buck buying xylene or toluene, it's a lot better in volume for the price.

Everytime the engine detonates some kinda long term damage is incurred. My opinion is that 2 degs of retard from detonation at 25# is probably more damaging than 2 degs at 15#. I am not sure if this is fact or not

For the long term good, you are much better off tuning for zero timing retard and will go faster as well. On the other hand, sometimes it just happens...maybe from a weather change or gas quality, or just because these things are perverse.

2-3 degs is not a cause for immediate panic but one should not continually run that way. A couple of degrees on the shift probably won't hurt but I would avoid trying to tune to the ragged edge.

 

[Chuck Leeper]

Octane boost what??

The fact that the engine has been run with that stuff, may be enough to crud up the plugs and cause a mis-fire under boost.
I'd pull the plugs, change them using AC CR43ts at .035 gap and try that, along w/ what Steve said; turn the boost down a couple turns. If the engine is on the ragged edge and the weather goes to low humidity and hi baro.. you will most likely go lean due to the added O2 content in the air.

The ads on stuff like 104, etc, are VERY MISLEADING, at best. The nonsense about 4 points of octane gain actually means .4 points.IE: 93 to 93.4..... NOT 93 to 97 !

 

[southern boost]

thanks guys! hey steve you talk of xylene and hear it quite often on the board , but i never have heard od it local. What would be places to ck. for it and by the way this is the first time i habe a knock detected since i have got the car, but i have very jumpy about the car seems so fragile i just dont wont to harm any parts. I really need to learn to tune this thing any help would be greatful. thanxs randy

 

[Steve Wood]

Randy, xylene is usually a major ingredient in some race fuels...it is often referred to as an aromatic.

You can usually find it in a home supply store, hardware store, or paint department...in the paint department of each. It usually costs about 7-8$ a gallon and if you can find it in five gallon cans it will be cheaper.

Xylene is 117 octane. You can normally mix it up to 30% by volume..meaning that you take 7 gallons of 93 octane and add 3 gallons of xylene and have 30% mixture which will make the total mixture to average out about 100 octane. Because it is very dry and has no lubricant package added as does gasoline, most add two or three ozs of Marvel Mystery oil per gallon of xylene.

It's a bit expensive to do all the time, in my opinion.

I would rather buy race gas for the times I need it or run alcohol injection which I do on two of my cars.

Don't worry about the random bit of retard..just don't make it a habit...