The pinging has to stop on the wife's Metropolitan, #2 & 3 plugs are getting small alloy measels on them. The poop sheet that came with the huffer, sez 35 degrees max total advance, 15 deg initial. I was able to tweak on the stock vac dis and hit 35deg but it would spark knock at speed limit, it pulled good and did not ping with peddle floored, but as soon as the engine is cruzing at 65mph (3100rpm) it would knock. The curve was set to hit 35deg @ 3000rpm, 15 deg initial and 20deg with the weights = 35deg. It ran better without the vac adv hooked up, but still pinged. So to throw in a wrench, I buy a mech adv Mallory & spring kit & read everything I can find on the net & books about timing and adv curve. The question is do I have to think different about initial timing with a mech adv compaired to a vac adv dizzy? Do I set the same 15deg at idle and set the mech adv stops to the remaining degrees to total 35? Is it this way only for vac adv dist? Or do I set the dizzy to a 30 deg adv stop gap and initial of 5 deg? I have read both ways in my info. I made a choice on springs, set the adv gap to 20 deg, initial @15. Tested with light the adv stops at 3000rpm and starts at 1000rpm, test drive had no ping at crusing speed, now it will only ping before the trans downshifts. Should I change spring? A engine can ping from too much total or from too soon advance. Does anyone have any ideas or input?
A little knock is usually ok, but if you're seeing aluminum pox on your plugs, eeeooooo. You're wise to flag that. How much boost are you running? Have you tried using premium fuel? I couldn't determine from your story if you're still using the vacuum advance or are only using the mechanical advance. Here's a quick answer on keeping or tossing the vacuum advance. If you're always racing (at WOT), the vacuum isn't doing anything for you, so leave it off. But if you're primarily on the street, where part throttle fuel economy is important, then keep it. I can certainly go into way too much detail on that -- it's my training from the good old U of M. Here's a proposed experimental plan... PHASE 1, WHAT THE ENGINE WANTS: Dump in some aviation gasoline -- oh, wait, is that illegal? Maybe look for some unleaded racing gasoline, just one tankful for the sake of experiment. See if that takes care of the knock. Then try a few different initial timings and see how you like the power and response. If you discover that you like the driveability of 12 deg better than 10 deg, but just as much as 15 deg, then 12 is probably a good number for you. That's the answer assuming an unlimited fuel budget. PHASE 2, THE BEST COMPROMISE GIVEN YOUR CHOICE OF FUEL: Then go back to whatever pump gas you want and see if it still knocks. Then retard until it doesn't knock on whatever fuel you can afford.
Thanks for the input, I run 93 oct, and 7lbs boost, I do have a pulley for 1 lb less boost, I will try that if I can not get it to run better. I am now using a mech adv dist and do not care too much about MPG. I will do more testing today.
I'm certainly not an expert but Joe Abbin knows a little about blowers. For the flatheads (doesn't mention 4-bangers) Joe feels total advance should not exceed 16 degrees. That's where I run my Merc and have no pinging or knocking. The 16 degrees in in @ 2500 rpm and I run around 6 #'s of boost on 93 octane.
Vac advance is good; without it you lose power and efficiency in 90% of your driving, and the retarded part throttle operation also fouls plugs...but it sounds like you have too much advance adding in at cruise. Your mechanical advance is entirely RPM based, and will always be the same at any given engine speed. Vac advance depends on LOAD, think throttle position, which controls vac at the speed in question. 2500 RPM at steady level cruise+high vacuum, 2500 RPM when accelerating up a hill at full throttle+zero vac. Tune car with vac disconnected until you have happy full throttle performance. Assuming your advance is all in at a reasonable engine speed, as it normally should be, map it--a few minutes with a timing light will allow you to figure out your advance at different revs. Next, get a vac gauge and find out your vac at different cruising conditions, especially those where pinging occurs, with distributor still disconnected. Next, with car idling and same gauge hooked into a rubber hose connected to distributor but not engine, apply vac to distrib using one of those mightyvac devices and find out how many degrees happen with what vacuum. Once you know the basics of what's happening, figure out how to mechanically block vac advane mechanism to a useful # of degrees and experiment wit manifold vac and ported vac ( manifold here obviously meaning above the blower!) You should be able to experiment with help while driving at the critical speeds and adding vac to distrib with hand pump. There are cans available from early turbo cars that can retard as well.
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