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Just so I'm sure I understand. Are we saying that if I drop to a colder plug, I may be able to bump the initial timing back up without ping? I never gave any thought to plug heat range other than just purchasing plugs for a 340. That's what I get for assuming that what was listed for sale...

It definitely seems to like more initial. Idle was noticeably dirtier when I backed it off to 6* initial from 10* and off-idle tip-in wasn't as crisp. I think it would actually be happy at 12* if I wanted to try to limit the curve and the max some more. 2* initial seems to be worth about 1"...

I actually was wondering about that. I just looked at an NGK chart and a GR4 is equivalent to a 14 or 16 Champion heat range, so obviously a pretty hot plug. I got the plugs from Rock Auto when I did the cam and intake and ordered plugs for a 340 4 barrel. However, I just looked on their site...

No, I've got a non-egr Performer intake on it.

Ping update. I tore into the distributor and put the factory long spring back in place and also added a little tension with the perch. Once I got in there, I discovered that I had actually replaced the long loop spring with one of unknown origin that was lighter tension than the factory...

Finally got around to doing a compression test. Engine was warmed up with throttle blocked open and all results are dry. The first 4 or 5 cylinders reached max pressure at 5 strokes. The last few took 6 or 7 strokes as I think the starter was slowing a little even though I had a charger on...

Good point. My heat riser is actually already removed but definitely something for others with similar problems to check.

Ok, I have more info. I went ahead and re-checked the entire mechanical advance curve as follows. Initial 10* at 700 with 19" vacuum in park. Drops to 600 in gear at 15.5". 10* at 900, 11* at 1000, 12* at 1200, 15* at 1400, 17* at 1600, 21* at 1800, 23* at 2000, 25* at 2200, 30* at 2400, 32*...

Very quick update as I don't want you guys to think your efforts to help are wasted. I did get to drive the car on a hot day early in the week with vacuum advance unhooked and experienced no pinging at any time. Part-throttle acceleration definitely was not as crisp without the advance added...

I'm sure that I welded and re-machined the outside of the slots to limit the total mechanical. My approach was to find an initial setting it idled happy at and then limit the mechanical for a total of 34* I'm now seeing that there really is a lot more to it than that. I hopefully can gather...

The timing numbers I already have up to 2000 rpm are as follows - 13* at 1200, 15* at 1400, 18* at 1600, 22* at 1800, and again 25* at 2000 with the initial set at 11* at 750 rpm. I also recorded 48* at 2000 with the vacuum advance connected. Granted, that is no load revving up in the driveway...

So you don't run vacuum advance at all? I've always been told that no vacuum advance will kill your mileage but I've never tried it myself. Of course, I know not everyone is concerned about fuel mileage when it's just their "toy" car. I didn't worry much about it when gas was in the 2's.

Yes, I have ran 89 and possibly 91 in the past as a trial. It did seem to help which is why I think I've just got it set up a little too aggressive for 87, especially if I run into the occasional tank of "bad gas". Especially at the gas prices now, I'll do what I have to to run on 87 as I'm...

Yes, that is the tag that is on the distributor. I know that I already limited the total mechanical by welding and re-machining the slots in the advance plate and I know that I got rid of the heavy with long loop spring. I think I replaced it with a 2nd factory light spring which may have been...

Just noticed that I somehow messed up my last post. I added my response to Brooks James quote.

That's actually something I've been wanting to do. I've always just assumed it wouldn't have much being a 74. Although I suppose it could be carboned up. I'll put that on my list of things to do.

Thanks for the responses. I will try plugging the vacuum advance and see what the results are and also plotting the entire curve. I already have from idle to 2000, every 200. I have looked at some of Mattax's charts and that's what made me think my mechanical curve might need slowed down...

Lol, I was wondering when someone would ask that. I was using an old Sears dwell/tach when I recorded the timing numbers last fall. I have since installed a tach in the car and I have a tune-up tach that will go to 10000. I just haven't had a chance to record the upper end of the curve yet.

At risk of sounding foolish, I actually thought about trying that, but if it works I wasn't exactly sure what that is telling me. Later vacuum advance or less mechanical?

No, it will still ping even at higher revs. I don't often really put my foot in it, but when I have, I'll hear it rattle pulling 2nd gear which I know is not good for the longevity of the engine. What you recommended should help with that also.

Car and engine specs as follows. 1974 318 with Performer intake, 1406 carb, 204 214 278 288 .421 .444 112LS cam, factory 318 manifolds into duals. Short block and heads are 1974 stock original. Trans is a 904 with factory stall and rear has 2.76 gears. Idle timing is currently 11 initial at...