Background:

440 with stealth heads and forget pistons. 11:1 CR and 170 psi cranking compression with XE274 cam. Topped with edelbrock dual quad intake. Car is a 70 charger, auto, 3.23 and 30" tires. Initial timing is 10 deg, total 30, no vacuum advance. Car run on european 95 octane=91 us ?
Plugs look good, exhaust smells terrible rich.

Problem:
With above configuration car drives fine but exhaust burns eyes and advancing timing more than 10/30 (init/total) we get pinging while the rpms rise and combustion gets definitely better. We tried drilling butterflies but this barely helped. Controlled vacuum leak helps alot - rpms rise.

I advised him to play with different timing curves (we bought set of distributor springs) but it seems to have no effect. Leaning the idle circut (screws) has no effect - engine still runs (I guess butterflies are open and expose main circuit).

Any ideas how to tackle this problem?

VERY INTERESTING!!! I'm on an ALLMOST EXACT situation with a MORE LESS similar engine specs ( but stroked 400 3.75 ). Pings at around 4K RPMs or in the front to rear butterflies opening transition ( I think, or at least I think to feel it at gas pedal ), when giving gas because I'm requiring power going up a hill.

I'll be allert to this thread

give it more initial timing and shorten the slots in the dist.

what is your fuel pressure? too much and it will push gas resulting in your smelly problem. As mentioned 10* initial isn't enough and 30* total isn't enough. It could be pining if you are sucking oil from the intake and it doesn't take much and you might not see any eveidence of it. How do you have the carbs set up? Is it rich at idle or in the cruise circut? I'd try initial at 15* total at 34* in full early...like 2200rpm. Then I'd adjust the carbs for best vacuum. Are you sure it's not going above 30*?

On the carbs, loosen the little doors above the primary metering rods and slide them over enough so you can see the metering rod piston top and tighten the door down to hold them in place(they will come out of the primary jets and may not be suck back into the jets when you start the motor if you don't do this) start the motor up and watch all four pistons, metering rods, if they stay down in nuetral idling then have someone put the trans. in gear, if they stay down idling in gear your good. If they DON"T stay down idling in gear you need to trim the springs under the pistons a little at a time until they do stay down idling in gear Please let us know what you find out I don't think that cam is big enough to cause this type of problem, but it may, depending on what lobe seperation angle the cam is installed at If the pistosn and springs are okay the next thing to do after changing the timing is to try the next size leaner rod on the economy step

I was writing on behalf of my friend. I'll forward him your advice and we'll see. He says anything more than 30* total and it pings badly from the beginning, not only at higher rpms.

I recommended him more initial (I run 22-24* in my 383) as this clears idle very well but it doesn't work with his 440 - I guess he must play more with springs'n'slots to get shorter but gentle curve.

As a last ressort he can play with gasket thickness and lowering CR but I read it may aggreviate pinging (less quench). BTW dont know how far in the hole the pistons are but he bought some forged with 4cc valve pockets.

I'd set the initial with the "vacuum gauge method" & yes you need more than 10 then shorten the slots to get 36 total then play with spring/combo staying just under the pinging point at WOT up thru the gears & you may need heavier springs. I'm thinking that ain't too wild of a cam & if not I'd solder the butterflies closed & concentrate my efforts on the dual carb system (not sure if you're on both idle circuits or not) & I'm not knowledgeable on dual carb setups. You would want the butterflies closed their normal amount or close to it I'd think. Make sure the floats ain't waterlogged & their level is correct & check fuel psi. Holler how it goes

IMO the dual quad setup is biasing here. It would be easier to tune the engine with a single holley than 2 edelbrocks. But he has the engine assembled and detailed and is reluctant to swap the manifold and carbs.

The engine definitely likes more advance at idle - but 30* total is a little conservative... how much HP could he gain having 34* without pinging? Car has iron manifolds but 3" exhaust.

I have a dual quad '58 era iron single plane intake with a pair of 4131 OE 3 step AFB's converted to eddy 2 step rods/jets going onto a 451 so I will be learning how to tune them also (the idle circuits are my concern). I'd set the initial with the vacuum gauge method then shorten the slots to get 36 total then check/correct a few things on the carb setup: floats not waterlogged/correct float level settings/fuel psi within limits. Then concentrate on the idle mixture screws/throttle position to get it to idle acceptably (which I think'll be the hard part) then play with the springs staying just under the pinging point at WOT up thru the gears. then hookup/tune the vacuum advance if you want to use it (& I would). EDIT Not sure if you need to change anything with the holes in the throttle blades or not

We tested the car yesterday and when really hot it started slightly ping even with 8/28* setting. Pinging occured at every rpm/load. We wait for the package with different distributor springs.
One more fact - the engine diesels for 1-2s after shut off. We tried 3 different plug heat ranges and no difference. Also minimizing advance even to 0/20* does not eliminate it. Idle is 900 rpm.

Does all your pump gas have Ethanol in it now? It sounds like you guys have some really bad pump gas over there What color are the spark plugs, can you post a picture of one or two of them as removed from the motor with no idling time and after a normal drive for you guys I hope so

very good post.i noticed that it was mentioned to check the slots in the dist to limit how much mech/ total advance. can this be done with a timing light hooked up and watching the timing marks as you rev up the motor? thanks

What size Edelbrocks? (post the number(s) if possible)
My gut impression is it's lean, not rich. Both will cause a fuel smell, and both will cause pinging that won't go away once it starts.
Other things to check: what radiator is in it? What's the operating temp? Does it ahve an overflow? What pressure is the cap?

all the advise has been good so far. how hot is that engine running? and are you sure of the comp ratio?

If it has not been said, check fuel pressure while driving and under acceleration. You'll want 4.5 to 5 psi min. under full load.

News:
Marcin tried shortenning the slots and eliminated the play on the thick spring in the distributor. He got 15*/28* then and the idle rpm rose so he could close the throttles a little bit. The idle got better, the throttle response is much better now and... no pinging during 4 miles of ride.

Also the dieseling is gone!

The induction is 2x600 cfm edelbrocks and idle vacuum 16", the metering rods are suck down at both N and D.

Edit:
whether it is lean on the main circuit - plugs look great (Marcin is a long time moto mechanic) but idle burns eyes. When I follow him in my challenger every time he nails it I see a puff of black smoke and I can even smell the gas! So I doubt the secondaries are lean.

The CR is high as he used special order forged pistons with 4cc pockets, flush with the deck and stealths are milled over 0.040". Cranking Cr is 170-180psi with XE274H cam.