I have a 1990 Seville 4.5L with 61,000 miles. I always run premium (93), so I advanced my timing from the base 10 degrees to 15. Great improvement in gas mileage and performance. According to all the threads, it is said to only advance the timing to 13-14 degrees - but these pertain to the 4.9L. Although they are nearly the same engine, my father has a 4.9L and has advanced the timing and has told me that they don't take as much timing as the 4.5L before they will start to ping, as he also has a 4.5L and has bumped that motor nearly to 16 degrees.
Anyhow, with my timing advance, the car will NOT ping with midgrade, even on a hot summer day climbing a hill. It will detonate with regular, but only ever so slightly. If the car does not ping with midgrade, and I run premium, do you think the engine could stand to get another 1 or 2 degrees advance? Why has everyone said only go to 13-14 if I can safely bring it to 16 degrees without any detonation? Will I gain any more improvement from an additional 2 degrees or are the benefits only seen around 14 degrees?

With premium 93, I wouldn't be surprised if my car would not ping even at 18, however, I understand you can only go so far and then you push peak cylinder pressure too close to TDC and even if you don't experience ping, you start to actually loose power. Where is best power obtained?

 

BTT - Anybody?

 

Timing can be advanced till spark knock then back 2 degrees. What is total advance at 2000 rpm?

 

Not sure. Only initial timing can be adjusted on these engines. PCM controls total advance. When put into timing mode, PCM advance is kicked out so you can set the base timing. To check timing at 2,000 the timing mark would probably be off the scale. When in set timing mode, timing does not advance with RPM.

I understand you can advance until ping, but these motors aren't high enough compression to really notice pinging with higher octane gas. I would imagine symptoms like surging or erratic idle, or hard starting might occur first. I advanced my timing 4 degrees, but I'm wondering since I have not gotten hardly any pinging even with regular gas if I could bump it another 2-4 degrees. Should I not experience any ping then, do you think I could go more? 8 degrees seems like a lot! 2 degrees back from ping timing is where you want it but I'm having trouble finding ping timing.

Lastly, even before the engine pings you can loose power and put unnecessary stress on the rods and bearings. I'd like to find at what timing the cylinder pressure is highest at an angle of the crank to optimize the power stroke. If advanced too far, even without pinging, the cylinder pressure may be closer to TDC and thus put more work (straight down) on the rod and bearing versus at an agle to the crank to apply more torque.

 

Total advance is really what is looked at as how far you can go. It is unusual to be able to advance timing that far, however fuel quality (TOP TIER) has improved greatly since the early 90's. It is also possible that balancer ( timing mark ) has shifted on hub that attaches to crankshaft.