I've put a Mopar Performance dizzy in my 440 (.40 over, Eddy heads, around 9.2:1 compression, 60303 cam, 16* initial, 34* all in). I am getting a part throttle rattle at higher engine speeds (75mph with a 2.76:1 gear ... sorry, no tach). The engine builder seems to think it is detonation especially since it seems to get more sensitive as the engine warms up. It doesn't sound like any kind of ping or rattle I've hear heard. And it doesn't make the noise at or near full throttle.

I pulled the initial back from 18/36 this morning to the 16/34 I listed above. It still does it. And yes, I pulled the vacuum advance hose off and plugged it to make sure it wasn't the vacuum advance (I've also gone 2 turns CCW with the adjustment in the vacuum canister).

The engine builder gave me a bag full of springs to try out but they look to be for the older Mopar Performance Dizzy based upon what I can find here with the search function.

So, here's a picture of the springs that are in the dizzy now. What would you do?

You can see the heavier spring in the top, is slotted, so it doesn't do anything initially. two springs like the toher one would like help the problem.

You can probably get some thing that will work at a local speeed shop. just ignore the applications on the packages. I have found gm pre hei springs work well on these.

You could grind a little off the weights too if you like, but with the long slotted spring you have, it won't help. AND there isn't a lot to the weights in those anyway, so if take much off, it becomes hard to get springs that are light enough.

I did see the long slot in the heavy spring and didn't even think about it not doing too much initially. I may have a heavy spring like that without a slot to try out. Or I could go with another like the smaller one too. Looks like some experimenting is in order.

http://www.summitracing.com/parts/DCC-5153446

You might want to buy one of these kits to dial in your distributor. I bought one of these, but they are for the newer MP distributors. It shows the advance curves for each spring combo in the sheet that comes in the kit.

Looks nice, but for $40, I'll play with the hand full of springs I've got.

I've got one that looks like the big one but without the slot. I've got some blue ones. I've got some slightly heavier than the blue but smaller than the big one. And then I've got some really light ones. I think I'm going to put the one that is slightly heaver than the blue in the place of my one big one and see what happens.

The slot in the spring with the slot in it is so large that it isn't even doing anything at full advance. So I'm going to put a somewhat light spring on.

I really can't imagine preignition with aluminum heads and 9.2:1 compression. Check your cranking compression. It should be between 165 and 180 to insure no preignition. Food for thought, My engine is 11.2:1, Eddy heads. Cranking compression is 175 on all cylinders... No preignition... timing is all out by 1800 rpm (35*) with 28* of mechanical built into the distributor and no vacuum advance. Again, no preignition and I run pump gas 93 octane.

I've got some kind of noise and I don't think it is pre-ignition. Another friend thinks it is just the sound of the exhaust at that specific rpm because it goes away right away when I get into the throttle a bit more. The engine builder also suggested it could be the sound of the exhaust. I don't know though.

I swapped out for one range colder plug (the AutoLite version of the RC9YC4). That didn't make a bit of difference. I put the medium spring where the one with the slot used to be. Now my timing is all in by 3100 rpm (used to be 2400 IIRC) and it still makes the exact same sound at the exact same speed. I also tried backing the timing down again from 16/34 to 14/32 and it didn't make any difference other than the engine wanted to get a little warm in traffic.

Its gotta be something else. Right?

And I generally run 93 from Shell or something similar.

I've seen 9:1 alum motors ping when the dist is set up wrong. It's not uncommon at all

Carry on with your plan to bring in the advance slower, and see what happens.

It is an auto with a bad setup for quench (pistons are .100 in the hole), which appears to be a great combo for detonation. Maybe I'll try the slightly stiffer spring tomorrow depending on rain.

A 9 plug is too cold for that set-up. I would think a 12 is closer. Keep in mind the winter gas is crap so be consersative and re-check early summer.

Sounds to me like you have something else wrong.

unhook/plug the vac adv hose and see if it pings @ 16/32 or 18/34. If it stop pinging I'd go back to 18/34 (assuming the eng/cam likes 18 inital) and go more CCW on the vac can and probably need a can w a smaller #. Holler back. Also what rpm is the mech all in at?

It does the exact same thing at the exact same vehicle speed (like I said, no tach, I get rpm from the timing light when setup in the carport) with or without vacuum advance. I've tried several setups with the initial (18/36, 16/34, and 14/32) and get the exact same result at the exact same speed except that it likes to get warm with the low initial.

I think that it is something else at this point. I'm running Harland Sharp rockers and maybe I have too much side clearance on one pair (I tried setting them at 0.020 per set of rockers based on advice from a well respected individual here on Moparts), a bad lifter, or something like that. The sound to me is clearly from the passenger side of the engine (but I grew up on a farm around very loud equipment and have always liked loud engines and loud music and started losing some hearing a few years ago).

It could be that part of it is a mixture issue.
A quick look at the cam specs, if I was curving one for you, with that much gear, I wouldn't bring it all in till 3400.

You can do more initial, than where you are at. I think your starting at 18 was probably ok.

I think 18 initial, with 34 total(16 mechanical), all in by 3400 would be a good start.
Then do some plug reading, and see where you're at with your mixtures.

What converter are you using? that cam would seem to like around 3K or so.

tell us about the carb sounds like it me a lean knock???

The carb is a Holley 750 (80508S). I don't remember what the stock jets were but I did go up a size or two.

Thanks for all the help. I may install a heavier spring in the dizzy this evening. But I likely won't get to test it out. I don't trust Atlanta drivers as it is and then add rain on top of that and it is a bad combo.

Here's a picture of a spark plug from when I pulled them out to replace them with the Autolites.


Of course, this is after driving it normally for a few miles while trying to test the effects of the things I've been doing and not a check after running it hard.

And the converter is a TurboAction - 17805S (10").

After a normal cruise, and that much cam, it should be a lot more brown than that.

Bump it two jets up on each end, after you do the timing mods, and look again.

With that carb I can only change the primary (I think it is the primary) jets. It came with 70s and I put 72s in it. So I need to go with 74s?

Edit: I ran the picture of the plug by the engine builder and he likes the color. I've always heard it should be a little brown too but he says his "gas man" says the plug should be the same color as when it came out of the box.... my new Autolites are black, so, I don't think I want that. (some things can be taken too literally).

Changed out the spring I put in for the blue spring. Seems to come all in around 3500 now.

Now for the test drive.

That is now very close. I can still barely hear it and it is much easier to make it go away with a touch more or a touch less throttle. I ordered a set of 74 jets and they should be here Monday morning (I thought O'Reilly kept jets in stock, guess not). Maybe the jetting will clear up that last little bit.