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Xr7GT 10-12-2008 06:50 PM

Ford 390 timing
 
I have a stock 67 Cougar GT with 390. It has points. It is low miles and not rebuilt. It was a California smog package engine but the smog pump and attachments have been removed. The timing settings are listed at 6 BTDC for the smog engine and 12 for non-smog. I had set the timing at 12 and it pings really bad at WOT. I am running prem fuel. Setting it at 6 BTDC seems a little low and I have to really adjust the idle screw up to keep it running at idle. Is there some other mechanical aspect of this "smog" engine that I need to set it at 6 BTDC and will I be doing any damage by running above 6.

oldbogie 10-13-2008 10:26 AM

Quote:

Originally Posted by Xr7GT
I have a stock 67 Cougar GT with 390. It has points. It is low miles and not rebuilt. It was a California smog package engine but the smog pump and attachments have been removed. The timing settings are listed at 6 BTDC for the smog engine and 12 for non-smog. I had set the timing at 12 and it pings really bad at WOT. I am running prem fuel. Setting it at 6 BTDC seems a little low and I have to really adjust the idle screw up to keep it running at idle. Is there some other mechanical aspect of this "smog" engine that I need to set it at 6 BTDC and will I be doing any damage by running above 6.

The FE was always sensitive to octane rating of the fuel it burned. Add age, combustion chamber deposits, and the cam coming out of coordination with the crank due to timing set wear, combined with unleaded fuel and you've got a recipe for detonation.

The fact that you need to really adjust the idle up is a good indicator that the timing set has fallen retorted due to wear. Restoration of the gears and chain should wake the motor up even with 6 degrees of advance.

Bogie

red65mustang 10-13-2008 12:47 PM

agree with bogie,

simple step one is to test for timing chain slack/stretch and dist mechanical "slop" from use....

rotor pointing at a mark on the body, use a breaker bar and rotate the crank a bit in both directions to confirm the rotor moves instantly=chain is tight....
(that's why tune up spec's will often say add 2* to the original base, 6* on the damper isn't 6*'s any more due to chain stretch)

on a stock motor, with a tight chain the usual/typical spec is: "you can add up to 5* base max more for better performance, more than 5* will not help performance"
(your base was 6* so there is likely 28*+ worth of cent so 12*base + 28*cent=38* + 2* of chain stretch(?)=to much)

I'd set it at 10* and then start testing the dist cent curve with a timing light, worn/weak springs (=to much to soon) and tall rear gears may be the root problem...

the CA smog specific vac advance unit calibration may be part of the problem, test drive for ping with the vac advance disconnected and plugged....
(it can be adding to much to soon)

to know how many degrees of cent, with the base at 10* read the timing (vac unplugged) at 3500+,,,total timing at 3500 minus base=total cent....
for "no ping insurance" I would set the base for a max total of 34* at 3500

decent totally mechanically rebuilt dist (cent plate/bearings/gear/new points/condensor/etc/etc) dist is only roughly $50?
it's imperative for WOT blasts that a dist is "dead on" mechanically to work correct...
suggestion:
take your dist to a local parts house and compare it side by side at the counter to a fresh rebuilt for wear "slop"....

later, after you have used up the new points some, swap to a Pertronix solid state ign module ($70?) (always 28* dwell and more energy for a longer period during the spark event)

454C10 10-13-2008 02:46 PM

try this.
Set it at 6 degrees (without the vacuum advance), then connect the vacuum advance so it works at idle. should have around 26 at idle. That will increase the idle speed to where you need it. The vacuum advance will fall off when the manifold pressure drops.


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