Detonation

[Aussi440]

Everyone, I haven't posted in a while but I am stumped by this, I have a bone stock 68 charger, 440 motor, stock 375 horse cam, stock carb, 4 speed, 3.23 gear, I lowered the compression just a bit around 9.4 static, around 160-165 cranking.  Problem is, I can only get 25 -27 degrees total timing in it without detonation.  It will detonate throughout the rpm range whenever under load or hard acceleration.  Curve comes in by 2500 so nothing crazy, I am running sunoco 94 gas, the carb isn't running lean, thermostat is a 180 and never runs hot.  Has anyone had this problem?  I can't really run 110 octane all the time.  Is it realistic I could get 36 degrees ever out of it or do you always have to run the timing back unless you run 110 octane?

Thanks Ryan

[Aussi440]

Everyone, only other thing I forgot, I have a stock distributor with a pertronix ignitor in it, I am using the vacuum advance and it does work and comes back like it should under accceleration. 

[justcruisin]

You shouldn't have a problem running mid thirties for timing. First thing I would do is disconnect the vacuum unit and try it. Then I would verify your TDC mark with a piston stop, maybe the outer ring on your damper has moved.

[Aussi440]

Where do I get a piston stop, and how does it work, can I do this without taking the heads off?

[Dino]

Where do I get a piston stop, and how does it work, can I do this without taking the heads off?

Remove spark plug #1 and slowly turn the pulley until the piston is at its highest.  I use a small wooden dowel to feel where the piston is.  Disconnect and cap vacuum advance before setting timing. 

[cudaken]

Here is a video on finding TDC.

http://www.youtube.com/watch?v=bhIP5YKCgRE

Seems pretty simple after you have a piston stop. I all so wounder where to get one. 

Cuda Ken

[fy469rtse]

It goes in spark plug hole , disconnect coil, turn motor over by hand socket on crankshaft turn engine over by hand until piston stops at stop, put a texter mark on damper and turn engine back the other way until it touches stop, put a texter mark again on damper,exactly in between is your tdc mark, top dead centre. Should match damper or harmonic balancer mark,
Does it make sense that you don't have to have stop or piston completely at top, just turn it over both ways until it hits stop and in between is top dead centre
Do not i repeat try to turn engine over by starter unless you want stop mounted in the top of your piston, if its hard to turn over take spark plugs out

[fy469rtse]

 I was shown how to make one out of an old spark plug, break the ceramic part off, drill the centre, run a tap through it , long bolt with a nut to lock it, file or grind bolt end that will touch piston round, it just has to stop piston. No sharp edges that can mark piston head

[68CoronetRT]

I just went through all this and ended up being 1 whole cylinder off(really bad detonating too). Tried the piston stop deal with an old spark plug but couldn't get the porcelain out. Ended up just having someone hold a screw driver in the #1 and felt it come to the top, and just made a mark there. Is it accurate? Probably not, is it really really close? I'd say "yes".

After I figured that out the timing came into spec and she timed great!

[Back N Black]

Make sure you are on compression stroke and not exhaust stroke. If on exhaust stroke you will be 180 degrees out.

[71 SE3834V]

I was shown how to make one out of an old spark plug, break the ceramic part off, drill the centre, run a tap through it , long bolt with a nut to lock it, file or grind bolt end that will touch piston round, it just has to stop piston. No sharp edges that can mark piston head

An old timer made this for me back in the mid '80's when I was working in a shop R & R'ing engines. The bolt is a 1/4" machine screw so the plug didn't need to be tapped for those w/o a tap & die set.