Spark plug reach, 1969 472

[WTL]

I went to see if I could go 1 step colder on my spark plugs, just to see if I could make pre-ignition on big hills less likely...

It looks like I have autolight 64s in there.  There is a 63 available, so that would be the ticket for 1 step colder...but in reading it seems there are plugs that are longer and plugs that are shorter...

According to jegs, autoliye 64s are .750 long.  Is that correct for a 1969 Fleetwood, or should I find a shorter plug?

Thanks in advance

[Big Fins]

Why not use the correct AC Delco plugs in your car? Autolite is a Ford based product.

[WTL]

Pretty sure the original Delco plug is not made anymore, and even if it were I'm running an HEI.

Im fine with delco, but wasn't trying to change too many variables as it runs alright, and I have used autolite with good results in a lot of non ford cars.

My question still stands...specifically because I saw a single person on another board suggest that the heads of a 69 required short reach plugs.  I figured confirmation could come from this board, or, that it could be set straight. 

["Cadillac Kid" Greg Surfas 15364]

Yes,
An Autolight #63 is "colder" and is the proper length, HOWEVER I run Autolight 66's with a VERY HEI ignition gapped at 0.050" in a 10:1 small chamber head (same as yours) with no preignition under very full throttle.  I would suspect something other than spark plug heat range if the only time you experience "pre ignition" is on long hills.
Greg Surfas

[WTL]

Thankyou Greg, that answers the question of reach. 

Its had just a little pinging for as long as Ive run it.  It makes me drive like a little old lady whenever I hit a decent hill, which might even be worse because its more of a lower RPM-high load event.   I know that there can be a lot of different causes, and its got to be something off so I am trying to see what I can find. I've rebuilt the carburetor, done timing chain, but as far as I know the intake has never been off...it could be a vacuum leak although Ive looked everywhere visible, or something making it lean, or the radiator not keeping up with the southern heat or probably a lot more.   

[TJ Hopland]

How about trying a hill climb with the vacuum advance disconnected?  That should tell you if its a hot spot or timing issue.   

Since you mention HEI I assume at least parts of the distributor are newer?  Do you know what the mechanical curve of it is?  In the late 70's they were doing some odd things with the timing and had a several models of distributor and gear ratios.  IF someone has put a typical aftermarket 'recurve kit' in it that isn't going to help you since those are intended for much higher revving 350 ish motors.   How about how much the vacuum pulls?   All the newer vacuum cans I have encountered have way more range in them than the originals did.     

If it was me I would get a tach, vacuum pump gauge, and timing light and take readings of what the distributor is doing.  You could then compare that data to what the shop manual says the original was.  That may give you some clues or things to try. 

I would also set up the tach and gauge in the car so I could see them while driving and take some notes.   With those notes you should be able to get a reasonable guess on what the timing is doing especially in your hill climb.   My guess is that you are still going to see decent vacuum on the climb which means you are going to have fairly advanced timing which could be a big part of your detonation.   It may be as simple as limiting the range of the vacuum a few degrees.  They make adjustable ones.   There is basically a cam you adjust that acts as a stop on the rod.   

[WTL]

TJ,

Good idea on disconnecting the vac cannister and seeing outright if I can still make it ping.  If it still pings when it is really retarded I guess that will say something. 

Unfortunately, I tried adjusting the mechanical curve last year to copy that of the points distributor from that year, both in the amount of the advance and the way it came in.  I even remember grinding on the center plate of the hei and testing it, and fitting the springs. I got it where the car runs fine, just the periodic pinging keeps driving cautiously...I also installed a stop on the vaccum to limit it a bit, cant remember if I took it off.

I will go out this evening with a timing light and see if I can recheck the curve to see where I am at at 1000, 1500, 2000 ect.  I want to say the pinging is mostly in between 1500 and 2100.  If I get up to 2800, its because the black helicopters are chasing me again (a rarity these days)

["Cadillac Kid" Greg Surfas 15364]

Mechanical advance plus initial advance should be a total of just about 32 degrees at 3500 rpm. If you have a vacuum advance from a late 70’s distributor it most likely has WAY too much advance for your motor.
Greg Surfas

[TJ Hopland]

Just trying to add some more theory to this....   At idle more advance usually lowers temps?  But was bad for emissions so most of the time we were using ported vac for the distributor so at idle there wasn't extra advance?    Is the same true under load?    So would disconnecting the vacuum and doing this hill tell us if it was a early spark detonation or a hot spot?  Disconnecting the vacuum will for sure retard the spark but what will it do for temps?   Would it make them go up so if it fixes the problem we will know its spark not a hot spot causing the issue?   And by hot spot I mean possible the plug itself but more likely some carbon build up in or near the combustion chamber. 

["Cadillac Kid" Greg Surfas 15364]

"Trying" various changes can only lead to a very subjective diagnosis.  Check the mechanical advance by either a dial back timing light or marking the damper 2.3 inches back from the "TDC" line. That should give you 32 degrees at no less than 3500 RPM.  Do this of course with the vacuum advance disconnected. Then check the vacuum advance with a hand vacuum pump and see what you have.
Without going through all the numbers, the late 70's HEI's are across the map on their specific specs, and unless you had someone like DUI make and set up this for you you have no idea what the curve might be.
Greg Surfas