67 GTX

i bumped the timing up to 15 degrees advanced at idle, and the car runs better all around
i only use 93 octane with around 10.3 - 1 compression
can anyone give any insight to why the engine never pings

Polaradude

Well silly it's because you have zinc in yer oil. Your thinking with your dipstick Jimmy..lol
Honestly I think the 93 is high enough octane to avoid the ping.

78D200

X2

the higher octane helps to keep it from pinging. If you go with 89 or maybe even 91 octane, it could start to ping. the higher octane burns longer and helps to prevent pre-dentanation (i'm pretty sure).

67 GTX

the car was made for 101 octane though

78D200

101 octane is quiet high.

67 GTX

you could be right
when the car was new, with leaded fuel, 101 octane was standard for it

theomahamoparguy

I think the factory was kinda conservative with the timing as far as the specs. go for that very reason. Remember, these things were used for everyday transport back when they were new. So lets say that back in 67 you went for a trip somewhere out of state and the gas station was out of everything except 87. Youre not gonna wait around for the good stuff to get there, no you put in the 87 and go down the road. there was kinda a saftey margin. Example two: some old lady that ended up with a GTX for some reason. {you know it happened} she would be less likely to shell out for the high octane gas.

But, you have to be careful because there can be "pinging" that is almost impossible to hear. The old racers used to be able to tell if there car was pinging [detonation] by reading the spark plugs. It takes a teally keen eye though, really good eyes 'cause the clues are hard to see.

An idea I had was to use knock sensor [from a newer car] and listen to my engine for detonation or preignition and use a pair of head-phones to listen to the engine while I am driving.[ but I aint figured out just how to make it work yet.]

67 GTX

i think the lowest octane back then was 95, but i like your old lady idea
i thought that if an engine pinged, you'd definetly hear it

theomahamoparguy

No really, there was actually low octane in the 60's, some as low as 85 in certain states. I can remember in the early 70's my dad pulling up to the Sunoco station and using the pump with the grade selector on the side. { it had a little lever that you pulled out and then you moved a larger arm to the desired octane. It started at 85 and went all the way up to 97 or 99, not sure which but I know it was up there.} This was in new jersey and my dad was friends with the owner of the station. Usually you were not allowed to pump your own fuel. I was only 10 when I remember him explaining it to me. When he drove the 73 Porsche 911T, he always selected the 95 octane. [we also owned a 67 Chrysler town and country wagon].

No you can not always hear all of the pinging. That is why it is best to stay on the safe side. Sometimes you can feel it more than you can hear it. Feels like a mild hesitation but only at certain rpm's.
I guess the basic rule is 10 octane per 1 compression ratio. Like if you had 9.5 to 1 than you would use 95 octane to be safe but that is just a basic rule that has no connection with real world situations.

67 GTX

well, the car didnt seem to hesitate at all
it really seemed to have better throttle response, and it even started easier
but, i am surprised that with the increase in timing, that the car starts easier
usually, the opposite happens

theomahamoparguy

the easier starting is a very good sign. The other thing I was thinking about was the mark on the harmonic damper. These were known to be not that accurate [by as much as 5-6 degrees] when they left the factory. Over time they could get worse. Just something else to ponder.
This is how I like to set my initial timing. I crank up the timing til it is hard starting than I back it off til it turns over like I think it should. Usually im at 12-15 degrees initial. Most time I gotta limit the total advance {welding involved} when the initial is at 15+. Then ill put some stiffer advance springs to limit the pinging with the gas that I use. you can do the opposite with good gas.{lighter springs}. This is all cheap "street racing" stuff that I used to experiment with back in the eighties {i'm old fart}. 67 belvedere with 383 and 72 demon with 318 back then.

67 GTX

haha, old fart
i might still try to advance more, and see how it goes

Archer

Matt -

Might want to get an idea of what your total advance is as well. The BB's generally don't need or like the vacuum advance, and even with 15 initial, you may or may not be reaching 32 total, IIRC that's about where most mild BB's like to be. Just a thought.

If the car is behaving better at 15, I wouldn't sweat it too much. just make sure that there aren't any of the usual "oops".

Archer.

67440X

What is your total timing? That is what is important. I would think with 93 octane you should be able to have a total timing of about 38 degrees full advance.

ddunk80

These knocks are actually high frequency vibrations caused by detonation, or the premature burning of fuel inside the engine's cylinders.



___________________
Knock Sensor Function

TVLynn

Vacuum advance will make a big difference in gas mileage !!! It should be hooked up on street car. There are some that can be adjusted. SO you need to figure out what is in the distributor.
Get your initial 15 Plus 23 in the distributor for 38. With the vacuum advance 48 to 52 total