Lars you helped me about 10 days ago. I have the MSD distributor and I asked you whether I should run more initial with a smaller bushing and you told me to loosen the distributor and listen for the best idle and run that for initial. What I found is that I ended up at 12 initial but still am running it with the 28 degree bushing for a total of 40. Is it possible for my engine to like this much timing or are the sidepipes just making it hard for me to hear the pinging. It seems to run great at 40. I have not verified with a dial back light but it must be close. I haven't been brave enough to try any more timing. Thanks again Lars.

 

Anyone have any thoughts on this?

 

It may be that your particular engine likes 40º but without testing on a dyno or a drag strip, it may not be easy to determine what is optimum. Just because it doesn't ping or because it feels stronger at low rpms doesn't mean that the extra advance is making more power at higher rpm. Years ago I tried 42º in a 396 and I could really feel an improvement in low end torque. I was certain that I was going to get my lowest et ever and couldn't wait to get to the strip. My et's wound up being .2 secs higher! Some more experienced rodders showed me the error of my ways and, after putting it back to 38º where it had been, my et's went back to where they'd been too. The extra timing may have added 10hp to my botom end where it could be felt in the seat of the pants but it was also probably costing me 20 or more hp at higher rpm. Not many cars will spend any time under 4000 rpm or so while racing except during the launch so it's best to set it up for the rpm it will see.

 

I've always heard that its best to push initial timing as high as your starter will tolerate, get the total in before 3K and limit total to 36-38 degrees. Granted this rule will vary from car to car but its a good starting point.

I have an MSD billet distributor and experimented with the bushings. I went through all of them and ended back with the stock setup which is the 21 degree bushing (blue). I also went to the light blue springs which brings in total advance by about 3K. My final config was 15 degrees initial (& 36 total).

With the 24 & 27 degree bushings, the car was very strong but I noticed pinging at the high end of RPM curve in each gear (especially 3&4). The pinging subsided with the blue bushing & a 36 degree total advance.

Mark

 

69 -
OKay, you did the "turn-it-till-it-idles-best" trick and found that it likes 12 degrees initial at idle. That sounds right - good job!

You indicate that you have the 28-degree bushing installed in it, and therefore conclude that you have 40 degrees max total advance. If everything is right on spec, this would be right, but I'd check it with a dial-back light if I were you: my experience with the various bushings and advance slots in these aftermarket distributors is that there are some fairly wide manufacturing tolerances, so you may, or may not, be at 40 total. Hop on down to Sears and fork out $69 for their adjustable light and check it out.

If you're really running 40, I would question if this is really the best setup. It may not ping, and you're probably getting great throttle response due to the correctly advanced condition off idle and at midrange, but my experience is that you will not achieve peak WOT and top-end power with the timing advanced much past 38 - at least not down at sea level. But there are always exceptions, depending on cam and engine setup.

So check it out. If you really have 40 with a 12 degree initial, try changing it so you get 36 with the 12 initial and see how that feels - especially at high rpm WOT. Getting these cars dialed in is all a matter of trial and error and some informed tuning decisions. Sounds like you have all the "informed" stuff down - now you just need to do the trial and error part.... Good luck, and tag me back with any questions.

 

Thanks for the replies everyone. Lars you are the best. Just to give you some specs on my motor. It is the 8.75 to 1 compression iron headed hydraulic flat tappet 502 and I am in the NY metropolitan area so close to sea level. I am going to try what you said and will let you know. I always thought the more the advance the better so thanks again lars and everyone else for the info. Just like going back to school for me.

 

Check out the new Hot Rod mag. They have a octane shootout with 6 tests using 87, boosted 87, 91, 91 boosted, 100 & 114 octane using various total timing curves (31-38). 36 degress produced the highest HP in 4 out of six.

Mark