440 issue after swapping to aluminum heads, need advice

[Cheapsunglasses]

Hello everybody, I know diagnosing over the internet is challenging, I’ll try to give as much information to describe what I’m dealing with.

I have a 1968 GTX with a 1969 C body 350 horse 440. I put 440 source aluminum heads on the car recently in attempt to help with the detonation issue I was having. It has an offenhauser 360 intake with a 4966s Carter avs currently. I have a Mallory unilite distributor with vacuum advance, and Mallory coil. My timing is at 12* initial, with the factory damper idk what the total timing is, but I can see it advances with rpm. I have a walbro 190 liter per hour pump, and a pressure regulator, the pressure gauge reads a constant steady 6lbs.

I installed an AEM AFR gauge, and with the 4966s it initially was pegged 18:1 leaned, and with rpm it would get a little richer but not much. So using an edelbrock 1407 tuning kit and chart I finally got 14:1, but only to 1,000 rpm, then it would drop to 16-17:1 until 2500rpm then it would peg the gauge at 10:1 rich and it would break up at 3,000rpm. Every change I made to that carb would do the same, it always dipped a point or 2 lean for a couple hundred rpm and then shoot way too rich without much in between.

So I decided to try a couple of different carburetors I had laying around. An edelbrock 1406 was 17:1 at idle, but with rpm would richen up to 11:1, and didn’t break up, I don’t have a tuning kit for it, so this was just to test a different carb. I also had a Carter 4327s afb, and it idled at 14:1, and richened up to 13:1 until 2,500rpm, where it would peg the gauge at 10:1 rich, and start breaking up at 3,000rpm.

I didn’t have the AFR gauge installed before the head swap so I don’t have a baseline to see if the heads are the issue or if it was acting similar before. I’m trying figure out what the issue might be and how I can correct it, as nothing I’ve tried has worked. Posting this in general as I’m not sure if I have a carburetor issue, ignition issue or a bit of both.

Any advice would be appreciated. Thanks!

 

[ykf7b0]

I’m not sure by no means but at this point I’m thinking the issue is within the ignition system. How old are those Mallory components? For the record, I haven’t had a whole lot of good service from Mallory.

 

[RemCharger]

Those offy intakes were pretty poor, is that the split plane one?

 

[Cheapsunglasses]

I’m not sure by no means but at this point I’m thinking the issue is within the ignition system. How old are those Mallory components? For the record, I haven’t had a whole lot of good service from Mallory.

Any help is greatly appreciated!

Well they’re old, but I’ve had it on other cars, and I haven’t had issues. I ran it with iron heads for a year without issues too, it’s only with the change of heads this problem has come up.

 

[Cheapsunglasses]

Those offy intakes were pretty poor, is that the split plane one?

If you mean that goofy dual port thing, no it’s not that one. From what I’ve found it’s kinda like the Holley street dominator

 

[RemCharger]

If the picture is what you have, that's the goofy one I thought.
Or you're saying yours is a true single plane?

 

[hunt2elk]

If you have a vacuum leak, that will cause a lean condition.

 

[Cheapsunglasses]

If the picture is what you have, that's the goofy one I thought.
Or you're saying yours is a true single plane?

From the little information I’ve been able to find it’s a single plane, but it’s designed with a big plenum, which brings back the streetability. Extended rpm of single plane, and good streetability of dual plane. Similar to the Holley street dominator

 

[Kern Dog]

That intake is only similar to the Street Dominator in terms of being made of aluminum and fitting a Mopar engine. After that, there are no similarities. The Holley intake is a proven performer. That Offy intake isn't.

 

[pnora]

First thing is total timing. Forget everything else. Get it set at 32 to 36 all in vacuum advance plugged. Then see what it does. The breaking up most likely is nothing to do with the fuel side.

 

[69a100]

I don't understand? Is the problem with detonation or the lean/rich conditions? If detonation is still a problem, I'd look at the size of the combustion chamber of the new heads as a lot of them are smaller than stock and will raise you C.R. even higher. Good Luck

 

[WileERobby]

With what you're posting here, I'm leaning ( pun intended ) toward an ignition issue. Get a timing tape, observe what your timing/rpm is & what your total timing is at what rpm. Start from there.

 

[Kern Dog]

With what you're posting here, I'm leaning ( pun intended ) toward an ignition issue. Get a timing tape, observe what your timing/rpm is & what your total timing is at what rpm. Start from there.

I had terrible luck with timing tape...No matter how clean I get the balancer, it never stuck. A "Dial back" timing light is a huge leap over a standard one.

 

[Cheapsunglasses]

I don't understand? Is the problem with detonation or the lean/rich conditions? If detonation is still a problem, I'd look at the size of the combustion chamber of the new heads as a lot of them are smaller than stock and will raise you C.R. even higher. Good Luck

I had a detonation issue before the heads, that’s what prompted the switch to aluminum. Now I’m having lean/rich issues

 

[Cheapsunglasses]

I had terrible luck with timing tape...No matter how clean I get the balancer, it never stuck. A "Dial back" timing light is a huge leap over a standard one.

I had the same issue, so I formed a new plan, I’m going to put the tape on, and mark the balancer with a paint pen. Hopefully that helps me pin point my timing

 

[WileERobby]

I had terrible luck with timing tape...No matter how clean I get the balancer, it never stuck. A "Dial back" timing light is a huge leap over a standard one.

I heard you don't lick postage stamps good enough, either.

 

[R413]

I would dump that intake real quick. It is a POS.
4966 is one of the leanest carbs out there.

what cam do you have in there?

 

[66Satellite47]

Not sure where you installed the AFR gauge, but I can picture that manifold giving wild results. I doubt it has anything to do with the ignition in general, except when it goes way rich or lean. A basic EDE CH4B or a Torker makes more sense. I expect the Mallory stuff is pretty good. I'd add a timing tape on the damper to see what's going on with the advance.

I never had a problem getting a timing tape to stick, BrakeKleen.

 

[Kern Dog]

I only lick the ones that are not self stick....
Are you still licking windows on the public bus?

I heard you don't lick postage stamps good enough, either.

 

[Carcinogen]

$.02

With the new heads I also would have bought an Edelbrock RPM dual plane and 800 AVS2 along with new distributor. My guess is the carb is not calibrated for that type of manifold, it is kind of a strange duck that did not last long. It is also possible the old dampener has slipped and timing marks are not accurate anymore.