new 501 pinging

lessloop · #1 (**permalink**) 03-28-09, 03:08 AM

Hi all! What a great forum. I just put in a fresh 501 long block in my '73 Eldo. New (rebuilt) distributor, new EGR, new diverter valve on recently rebuilt smog pump, fresh PVC, etc. Timing was set at 8 degrees BTDC. Started and ran great. After 100 miles I took it on the freeway and noticed some pretty nasty pinging at mid to full throttle. (Premium gas) I took the timing down to 6 degrees and it got better. At 2 degrees, it won't ping. It definately wasn't pinging before. How come I can't run the stock 8 degrees w/o heavy pinging all of a sudden?

cadillac_al · #2 (**permalink**) 03-28-09, 09:29 AM

What distributer are you using HEI or points? Maybe the vacuum advance isn't the correct one or the advance springs could be weak. Decreasing initial timing would compensate for that.

534BC · #3 (**permalink**) 03-28-09, 01:49 PM

If the compression is not real high (most are 8:1 dogs) then it is lean mix . Second guess is too much advance or hight temp/hot spots.

lessloop · #4 (**permalink**) 03-28-09, 02:58 PM

Hey guys. Thanks for the super fast feedback. I started the project with a new Accel HEI distributor. But as suspected from reading this forum, it didn't clear the double fan belts. Unfortunately, I got the best price for the Accel distributor from Pep Boys, so I went with their rebuilt stock distributor when I returned the too large for the belts Accel HEI. (I put the Pertronics electronic ignition conversion into the stock Pep Boys distributor with a Flame Thrower coil & wires before I installed it.) My first thought was possible weak advance springs in the possibly crappy Pep Boys distributor too. The wierd thing is that I'm almost positive the pinging wasn't happening in the first 100 miles. Definately not heat related. I did the reduced pinging 6 degrees and the no pinging 2 degrees last night running at 180 degrees F.

534BC · #5 (**permalink**) 03-29-09, 12:43 PM

If it does it at mid-full throttle and is too much advance , then check it and see if it does it at high rpm too (mid to wot)

lessloop · #6 (**permalink**) 03-29-09, 05:56 PM

That's the tricky thing. It seems to be more heavy load related than RPM related. I guess that means that if it's the distributor then it must be the carb driven vacuum advance on the dist. and not the springs?

534BC · #7 (**permalink**) 03-30-09, 09:53 PM

If it is heavy load (full throttle) then there's little to no vacuum advance in the picture. It still can be too much timing , but can also be lean mix or a bit of both. If retarding the timing fixes it then run that timing at that load and rpm.

lessloop · #8 (**permalink**) 03-31-09, 02:57 AM

Hey 534BC. Thanks for sticking with me. I guess I didn't understand that vacuum diminishes at WOT. I thought it was the other way around. But I am definately way out of my lane on this stuff. I wonder how I could be so lean as to cause this massive pinging after the 1st 100 miles with a new (rebuilt) carb & fuel pump. Maybe I should get a fuel pressure test gage to see if the new fuel pump is coming up short on high demand? I looked at an advance timing light today that has the dial to read timing advance at higher than idle rpm. But you need to know what the advance is supposed to be at set rpms. Certainly isn't in the service manual. I was thinking of starting a new thread to see if anyone knows the advance values for higher rpms for the 501. As I said before, I have to dial the base timing all the way down to 2 degrees BTDC to make the pinging go away, and I don't think I should run the car with only 2 degrees base advance. Thanks again! Marching bravely forward.

lessloop · #9 (**permalink**) 03-31-09, 05:02 PM

I just read some info here on old post #188 about setting for total advance. Sure would like to know what the total advance should be for my '73 501. That could be an eye opener for chasing this pinging?

cadillac_al · #10 (**permalink**) 03-31-09, 09:33 PM

Is the vacuum advance hooked up to ported vacuum or full time vacuum? Full time might cause your problem. This distributer is a new replacement right? The springs and vacuum advance should be correct. It sounds like it may need some tuning; stiffer springs or limit the vacuum advance.

lessloop · #11 (**permalink**) 04-01-09, 02:08 AM

Hey cadillac_al, thanks for your thoughts. Yes the distributor is new, but as I mentioned earlier I got stuck with getting it at Pep Boys which probably wouldn't have been my first choice. The vacuum advance is hooked up directly to the ported vacuum port that is designated for the advance on the stock rebuilt rochester. That's all I hooked up. The high temp. manifold thermal vacuum advance switch is in the trash. So short answer- ported advance. Again, the bizarre thing is that it was fine with no pinging for the first 100 miles. Maybe I'll just return this distributor and get one from Napa. I would still love to find out what total advance should be and at what RPM. Then I could get one of those fancy total advance timing lights and check it. I've been all over the internet today and couldn't find those values for a '73 500. Thanks again.

cadillac_al · #12 (**permalink**) 04-01-09, 10:39 AM

I wonder if the engine is running hotter than it should. Total timing numbers are pretty general for most engines. I think it is usually in the 32 -38 range. An advance timing light is handy to diagnose and measure the centrifigal advance and the vacuum advance seperately and tune from there. Is there any adjustment to the Pertronix unit? I'm not familiar with them but if there is any adjustment there, that will affect the timing too. If there is just too much vacuum advance, I don't see a big problem with compensating for it with less initial advance. Maybe the idle would be less than ideal. In that case I would do some more tuning, ie limiting vacuum advance. I have to wonder if they custom tune all rebuilt distribters or just put generic springs and advance cans on all of them.

534BC · #13 (**permalink**) 04-01-09, 01:21 PM

I would think that low compression can be around 36-38 deg , unplug vac hose to check it.

lessloop · #14 (**permalink**) 04-03-09, 12:46 AM

Hi guys. Thanks for the input. The engine was running a steady ice cold 180 degrees F at night when I did my reduced base advance test. (Brand new Auto Meter temp gauge and sender.) I had to take it all the way down to 2 degrees BTDC to make the pinging go away. Something else has to be wrong. There is no timing related adjustment to the Pertronics. ( They like you to adjust to a minimum air gap between the magnet and the pickup, but it is in a fixed spot in rotation and so does not effect timing.) If I can get a good fix on total advance, then I would know if the springs or advance can in the Pep Boys distributor are wrong. I'm wondering about quality control in rebuilt distributors as well. 32-38 is a pretty big spread? I've never measured total advance before. 36-38 seems like a workable range. It would be great if I could get a lock on the correct total advance number.
Thanks a million!

534BC · #15 (**permalink**) 04-03-09, 01:27 PM

It will depend on many things. Probably the two most influential are fuel octane,vacuum,compression. Cam, misture, combustion design,valve timing, ect all come into play. We set thjem on the dyno always for max power and whatever it is it is.

My best guess is 38 degrees if all is normal. If you engine detonates at 30 degree then something is wrong somewhere else.