Sense of Timing
|by Bill Boyle|
|Oh yeah, ignition timing matters! I have this project car (sound familiar) and it just wasnt accelerating very well from a dead start. (In fact, the engine seemed off on power.) Now I am not talking a WOT start, just your basic acceleration from a traffic light or stop sign. Anyway, I wasnt happy with it at all. While doing some repairs on the engine and transmission, I discovered a bad torque converter. The converter had a high stall and it didnt complement the engine power (or the car for that matter). A previous misinformed owner (and there were many) installed the unit so I opted to replace it with a near stock converter.
Just from that little fix the car was more responsive off the light. Better, I thought. However, the more I drove the car, the more dissatisfied I became with the engines overall performance. The next thing was to have the Quadrajet rebuilt. Fellow Pontiac enthusiast, Cliff Ruggles, helped me out with his rebuilding expertise that eliminated the stumble, however, there remained a flat spot that I didnt like. Again, as the car was driven, I sensed it was not the carburetor or fuel delivery, so I focused on ignition timing.
I checked out the timing and it appeared to be correct for stock OEM specs. Okay I thought, but I wasnt sure this engine was stock. Who knew what the previous owners had done. Rummaging through some papers that came with the car, I discovered a cam card. Based on my review, the engine had a mild grind in it similar to the specs of a 068 camshaft. As an experiment, I boosted initial timing by 4 degrees. Idle increased above the normal 800 rpm but I left it alone for the time being. I test drove the car and noticed that off idle performance was a little better. Then I took the car down a deserted back road where I could let it rip for a good 10 seconds. The engine seemed more responsive above 3000 rpm than before. I thought I was now on to something. Back in the garage, I bumped timing a few more degrees. The engine fired right up so off for another test-drive. Everything seemed about the same. The engine was now up to temperature and still no hard start problems. Great I thought.
Next step was to see what total advance this little bugger had. With my trusty timing light in hand I was surprised to see that the mechanical advance was nearly non-existent. The curve, what there was of it, came in quickly but the actual advance was next to nothing. No wonder this car runs so badly, I thought. My next step was to pull the HEI distributor and go through it carefully.
|The following day, I pulled the distributor to check out the movement of the weights. First off, the distributor was really gunky. The weights seemed to move freely but there was a slight hitch to it. As is, I commenced to run a base line test of the unit on my Sun Distributor machine. What I discovered supported my initial observation seen with the timing lightsomething was amiss. The distributor machine reads in cam degrees, which is one-half of the advance at the crank. The distributor test run showed me little advance form the weights as rpms were increased. This meant that increasing initial on the engine bumping it up like I did amounted to just about the entire advance the engine was seeing. No wonder the car was a slug!|
|Next step was to disassemble the HEI and to check out all the mechanical components. The weights were rusted, as were the springs. The HEI appeared to have stock components so I cleaned up everything and reassembled the unit. A little grease and the movement seemed smoother. The HEI went back on to the distributor machine for a second test. As I ran from idle to 4000 rpm (equivalent crank degrees) the HEI was now responding, but not as well as it should for the engine. Total number of degrees was 12. This would mean that if I set the timing at 10 degrees the maximum mechanical would be a mere 22 degrees. Yikes, not where it should be. I wanted to see 36 degrees total for this engine and I wanted the curve to be responsive from 1200 rpms up. Not only was the HEI giving only 12 degrees advance, the movement was erratic. The old rusted springs were not working well.
Again, as an experiment, I removed the old springs and replaced them with new ones appearing to have about the same tension. The next test on the distributor machine showed a marked improvement. The curve was improved in that it was smoother in operation. The numbers at different rpms proved that out. However, the total amount of advance was still not great enough. I ran the distributor machine rpms up to 4000 which was 8000 rpms at the crankfar higher than wed ever see on our Pontiacs. At 6200 engine rpms I saw an erratic movement. The timing bounced a little, meaning it varied about 2 degrees at that rpm. Total mechanical advance was not increased significantly by the change in springs. The HEI was now producing a total of 14 degrees mechanical advance. I wanted more.
The HEI was partially disassembled again and the center plate removed. Noting where the weight head made contact on the center plate, I decided to remove some of the metal from the center plateboth ends. Very little metal was removed. The unit was reassembled and retested. I saw a little more gain early in the rpm band, but there was hardly any advance at the other end. More grinding was needed.
Same routine. More was filed off the center plate and the unit was again reassembled and retested on the distributor machine. This time 3 more degrees showed up on the distributorequivalent to 6 more mechanical degrees at the crank. The HEI was now producing 20 degrees mechanical advance. Much better I thought.
I doubled check the advance curve once more and found that 15 degrees of total advance came in by 2200 rpms. The remaining degrees were mostly in by 3000, and one more degree came in at 3200. The distributor was retested 3 more times and the exact numbers were verified. Okay, I thought, put it back into the engine and do another test drive.
One-half hour later I pulled out of the driveway for a quick (I hoped) test run. Shazaam! What a big difference. Combined with the rebuilt carburetor and a decent torque converter, the car jumped off the light and chirped the tires in the 1st to 2nd shift under full throttle acceleration. The distributor was set at 12 degrees initial advance giving 32 degrees total mechanical advance by 3200. More power and function, I thought. Things were getting better. Was there more power to be tapped? More to come