383 Magnum Spark Plug Question/Thoughts

[Craigmorgan3]

  Hey all, long time reader 1st time poster!

My name is Craig and I'm the proud owner of a 1973 challenger with a 383 Magnum engine.

I'm running the MSD Atomic EFI with edelbrock performer rpm intake, stock heads and valve train.
Idle and cruise AFR are 13.5 and WOT is 12.3
Rear gears are 3.55.

I have been trying to resolve a lean condition under heavy acceleration and decided to swap out plugs (NGK V power XR5) for new ones (champion P/N RJ12YC) to start fresh.

The old plugs had a strange color gradient going from light to dark as you look from front to rear on each side of the engine.  What do you think this means?  Any ideas?  First pic is of drivers side and second is of passengers side plugs.

My last oil change I added a bit too much oil, could this cause excess oil to run down the rear valve guides?

Any thoughts or suggestions are appreciated.

Thanks!!

Craig

[ireland383]

looks like oil on the plugs. How is your intake seal? Why such a hot plug? What is your compression ratio?

[Craigmorgan3]

I don't know the exact compression but I would assume its stock for a 383 Magnum.

The plugs removed were put in by a shop about a year ago (NGK) but I thought the campions (rj12yc) were the stock replacement type.  Should I be using something else?

I didn't remove the intake to check the seal but that should be an easy check once it stops raining.  Could that cause the plug condition?

Thanks,

Craig

[ireland383]

It sure could. As far as the plugs you stated a 14.  I wasn't sure if you were talking about Champs or not. 12's are about right for a stock 383.  Ngk's are good plugs if you have the right heat range. They are opposite of champs as far as heat range.  Higher # is a hotter for champs and lower # is hotter for Ngk's. Hope this helps.

[Road_Runner]

383 Magnums came stock with a Champion J11Y or equivalent which are way colder than your 14's.  Unfortunately, Champion hasn't made this heat range for quite a while and Champion listed the J12Y as suggested replacement.  If you're running more compression / HP most would suggest dropping to J10Y or equivalent plugs.  I don't know that this would in any way address your sooty plugs but I personally wouldn't run plugs as hot as you're running.

Later, Jim

[Craigmorgan3]

Sorry for the confusion but I'm running RJ12YC plugs now.

I pulled the intake manifold and found the gasket was "welded" on the first few intake passages where the lighter colored plugs came from and easily removed from the passages for cylinders 7 and 8.  I don't know if this means anything but I'm going to get a new gasket set anyway.

I found that the exhaust crossover was blocked by the gasket pan, should I leave it like this or should it be open?  Can this cause any issues being blocked?

[Road_Runner]

=I found that the exhaust crossover was blocked by the gasket pan, should I leave it like this or should it be open?  Can this cause any issues being blocked?

A lot of folks block the heat cross-over on purpose to keep heat away from the carb & intake cooling the intake charge.  If you live in cold climates and want the standard choke to work as designed then get a pan gasket with the necessary openings, otherwise I'd leave it the way it is for better running in warm weather, etc.

Later, Jim

[cudabob496]

how do you know its lean under heavy acceleration?

[Craigmorgan3]

Cudabob496,

I can tell it goes lean through the Atomic EFI handheld O2 sensor output and my Inovate widband O2 sensor output.  I have a sensor in each header collector.

Light acceleration will yield a gradual increase in richness on the gauge and good acceleration. If I hit the throttle fast I get a lean spike, the car noses over, but picks up and accelerates a second or two later.

I was afraid that after seeing my plugs that the Atomic EFI computer was getting a bad O2 reading due to oil fouling and possible air leaking into the intake.

I figured it would be best to rule out an intake leak before chasing down anything else.

Craig

[cudabob496]

Cudabob496,

I can tell it goes lean through the Atomic EFI handheld O2 sensor output and my Inovate widband O2 sensor output.  I have a sensor in each header collector.

Light acceleration will yield a gradual increase in richness on the gauge and good acceleration. If I hit the throttle fast I get a lean spike, the car noses over, but picks up and accelerates a second or two later.

I was afraid that after seeing my plugs that the Atomic EFI computer was getting a bad O2 reading due to oil fouling and possible air leaking into the intake.

I figured it would be best to rule out an intake leak before chasing down anything else.

Craig

well, I have a wide band O2 sensor, but not EFI. In general, I would not look at the plugs for many answers, as there are so many variables as to why
a particular plug might be a certain color, though the light colored plugs may be confirming your lean situation. I would guess there may be a programming
or some other type of malfunction with the EFI (like faulty O2 sensor), and would focus there first. But I have limited experience with EFI.

From my experience, the O2 sensor readings are more reliable when the throttle is steady, rather than when accelerating or decelerating.

And reading plugs is generally done after a wide open throttle run on new plugs.

If it was a big Holley regular carb, I would just be increasing jet size to eliminate the lean situation.

[Chryco Psycho]

Welcome , what intake are you using , the Eddy performer is notorious for doing this , also you may be over jetted on the primary & lean on the seconday in the carb the O2 will only give an average , what carb also ?

[Craigmorgan3]

Chryco Psycho,

The intake is the edelbrock performer rpm intake P/N 7186 I believe.

Any tips for new gasket install?  I see a bit of variation with some people using only the metal pan, others use the metal pan with gasket between the head and pan , and some use metal pan with gaskets on both sides.  Any thoughts? I would assume a liquid sealant is a must too to prevent any future oil leaks between the gasket material.

The throttle body is not a carb on my application.  I'm using the MSD Atomic EFI. 

Craig

[high perf mopar]

the top right plug looked like all of mine!!!solid medium gray..im going up a few jet sizes to richen it up.i have a freeway speed ping only that im trying to get rid of..im running ngk plugs also r-5671..had the a9 in there now going to the coldest ava at a11..eddy heads r a tuning nightmare....

[Chryco Psycho]

Running EFi the first thing I would do is use the 1214 FelPro intake gasket & block the heat crossover , I use a side gasket beween the valley & the pan to seal the crankcase so no oil comes up there  & no gasket above the pan .
The plugs definatly look lean at the rear of the engine  & too dark at the front , is this a T body injection sysytem instead of multiport

[Craigmorgan3]

Running EFi the first thing I would do is use the 1214 FelPro intake gasket & block the heat crossover , I use a side gasket beween the valley & the pan to seal the crankcase so no oil comes up there  & no gasket above the pan .
The plugs definatly look lean at the rear of the engine  & too dark at the front , is this a T body injection sysytem instead of multiport

Does the metal valley pan to intake manifold joint get any sealant or is it just metal to metal dry seal?

The front plugs were actually the light colored plugs and the back were the rich/oil fouled ones.
This corresponded to what I found when I pulled the intake manifold and inspected the gasket.   Rear gasket area was oil soaked and not a tight seal.

The Atomic EFI is a throttle body EFI system.

Craig