Question: 12* BTC Timing

[Tim81]

Can someone please explain to me the benefits of adjusting your base timing at 12* BTC versus 6* BTC as the factory manual suggest?

Thanks Tim

 

[RC81]

More advance in the curve and more power. I dont know how much more it makes, sure would like to know. I have heard of some running at 14*

 

[bill81vette]

Be careful you don't damage your engine doing that!

 

[spikebot 81]

Give the engine what it needs. The P.O. installed a engine from a 1970 1/2 ton truck in my 81 and I'm running 16 deg inital. I once had a 351 winsor ford motor with lots of engine mods that wouldnt run with the timing advance off the scale. I was working in a independent car garage at the time. The boss put a tach on the distributor and ran the engine up to 2100 rpm and advanced the timing until it started to miss then backed it off alittle. The motor ran great for years.

The early smog year cars where not tuned for performance but for pollution control. Thats why only 6 deg by the factory spec. I think you'll be very safe at 12 deg advanced. If you hear a engine ping under hard accelleration retard the timing 2 deg.

 

[Peer81]

I would also say the modern heads have better combustionchambers so they don't need that much advance.
You can also play with the advance to see what the motor likes best, less advance will give higher exhaust temp, more advance higher oil / water temp.

Greetings Peter

 

[Hib Halverson]

I need to correct some misunderstandings here about spark timing.

Less advance---retarded timing---makes the engine run hotter, both coolant and oil temperatures increase

More advance, to a certain point, makes the engine run cooler.

I don't recall the specifics of the 81 engine controls but if an 81's spark advance is controlled by the ECM, as are 82 and later systems, and the system has a knock sensor, simply cranking up the initial advance by moving the distributor may not actually advance the spark.

That said, there might be some advantage in increase spark timing. It depends on what the factory spark curve was.

 

[Peer81]

You're absolutely right Hib! I mixed up the words
Btw. the spark advance is controlled by the ECM but without a knock sensor.

Greetings Peter

 

[Hib Halverson]

Ok, so MY81's ECM controls spark but lacks EST. Following up, since I don't have an 81 FSM, are those cars like later models where, to set base timing, you have to pull the "timing connector" apart, set the initial spark advance, then reconnect the timing connector and clear codes?

 

[Tim81]

Hib, you are correct. To adjust the base timing the 4-pin connect from the dist. to the ecm must be disconnected. I was setting the timing today with a vac. gage and timing light, just to see what happens when the timing is advanced, The motor pull the best vacuum at 14* BTC the Vacuum was steady at just under 20 Hg's. At 6* BC which is the factory setting the Vac. was 15hg. I don't like the idea of running the timing at 14*, so I settled for 10* BTC at 18 hg of vacuum.

Tim

 

[Sensei]

The ECM advances spark blindly from the base timing, so yes, changing base timing will make a difference.

6 BTDC is not for optimal performance. Around 12-14 will give you performance gains all around. After setting more advance, always listen for detonation on hard acceleration. If there is detonation, you must retard until it is gone (usually 2 degrees).

God bless, Sensei