Spark Plug Gap Question MSD - something is different than the other threads

[XH29N0G]

After taking a look at the following threads:
     http://www.dodgecharger.com/forum/index.php/topic,63517.0.html
     http://www.dodgecharger.com/forum/index.php/topic,95601.0.html
I decided to check the gap on my plugs.  I am running NKG5671A-7 plugs that seem to come with a 0.032 gap (and that is what they were in the engine - I did not install them).  

My engine is a 3.9 stroke 383 block (450 CI) with RPM Heads and 10.3:1 compression, an MSD 6AL (looks like the ballast resistor is still being used) and an MSD distributor with firecore wires.  

The threads listed above suggested starting at 0.045 and checking up or down to find what the engine likes.  Changing the gap on my plugs from 0.032 to 0.048 caused the idle to drop and the engine to run rougher.  I have not changed timing or carburetor tuning.  As far as I can tell all boots are seated.   I am looking for help because 0.032 does not sound right from what I read and I did not anticipate the rougher running from all I read.  I will continue to explore this, but I thought I would ask the board in case there is something obvious I need to look into.  Does timing or jetting (A/F) need to change with when plug gap is changed?  Could there be an issue with the MSD install? (the engine runs on when turned off and hot - regardless of gap).  Could the gap make fouling more obvious (the plugs have carbon on them).

Thank in advance.

[XH29N0G]

An update:  I pulled the plugs this morning and cleaned them with a tooth brush and detergent which removed most of the carbon.  I also regapped them at 0.037.  The car ran better.  The idle is back up.  I am assuming I either had fouled plugs that did not work with a wider gap, or that one of the plug wires did not seat properly (though I checked this morning and they all seemed to be seated).

[firefighter3931]

That plug is too cold for a 10.3:1 pump gas combo with RPM heads, inmo. I allways use a 6 series plug in that application. Anywhere from .035 to .040 gap is fine. If the plugs won't stay clean switch to a warmer plug 


Ron

[XH29N0G]

Ron,

Thank you.  I will try switching to 6 and see what they look like.   Do you have a recommendation on what type.  I do not see a 6 (or 5) heat range for the NKG plug I have.

My 7's look like the carbon (dry) fouled pictures I see.  I just began the install of an A/F gauge (I have it wired, but need to take it to a shop to have the bung put in), so I should have that information too.  I may be back on to check into the run on issue.  Could that be related to carbon fouling?? - it happens when the engine is warmest.

[firefighter3931]

Fouled plugs will cause all kinds of headaches....loading up, poor idle, run on etc....

I would try a set of NGK  BCPR-6ES plugs and gap them at .040 with your MSD box 

Where is the timing set ? How much initial and what's the total ? What cam are you using in that stroker ?



Ron

[XH29N0G]

Ron,

The cam is .519/.511 236/246@50 (I think 280/296 is the advertised duration) with 112 LSA, 105 centerline.  It is a comp cams hydraulic flat tappet custom grind chosen by Mike at Muscle Motors.  I measured the timing last Summer when I picked up the car from the restoration shop and it was 10 degrees BTDC initial and went to 30 degrees total advance.  I don't remember exactly where it came in.  I have always assumed this is where they set it at MM, but I suppose it could have been adjusted by the shop that did the restoration and install.  

My understanding was that the timing and jetting were set when the engine was broken in and tested on the dyno at MM.  I tried (once) advancing it to 15/35 and the engine did not respond well and had a different sound and  hesitation at mid throttle so I set it back to 10/30.  Now I am not so sure it was the timing that did it because I sometimes get the same behavior and I think it is related to fouling of plugs.  

This is the same engine I asked about piston slap on a month or so ago.  I have one other question about the plugs you suggest.  On another thread you suggested using resistor plugs if there was a radio, non resistor type if there was not a radio.  I don't have a radio. Is there any engine-related reason to use the non resistor plug instead?

Thank you for the help.

[firefighter3931]

OK, now i'm remembering the piston slap questions. 

The base timing is too conservative and so is the total timing. I would install the fresh plugs and readjust the timing to 15/35. When you increase the idle timing the engine rpms will increase so afterwards you will need to readjust the idle mixture and idle speed on your carb. Using a vacuum guage ; adjust the idle mix for max vacuum on each corner. Just open it enough to the highest vacuum reading and no further. Once you've done that, readjust your idle speed to 800-850 in gear.

In your case the resistor plugs won't hurt anything....i've allways used them even with no radio. The non-resistor plug will also work as well. I've found the resistor plugs easier to find....



Ron

[XH29N0G]

Thank you.  It is a manual, so I am assuming 850-1000 RPM for final idle speed.  I am just about to run out to get plugs and it looks like resistor plugs are much easier to get.

[firefighter3931]

Yep...if it's a stick just set the idle speed at 850 in neutral after the timing & idle mixture has been dialed in. 

The non-resistor equivelant is a BCP-6ES so whichever you can get easiest will be fine. 

Keep us updated on your progress.


Ron

[XH29N0G]

Ron,

I swapped out the plugs.  I was able to find BCPR6ES-11 (which my understanding is the BCPR6ES but with a gap of 0.044 instead of 0.036).  I reduced the gap to 0.040 and installed them.  I have not been able to get the car to start - It will fire once and then just spins over.  I double checked the wires, the plugs are tightened ~2/3 turn beyond hand tight to compress the gasket and tighten them.  I did not check the exact torque on them so they may still be a little low, but I think they are seated.  I pulled one of the plugs, and it looked like it did when I put it in.  I am assuming the MSD should provide plenty of spark. 

My thinking is that the next step should be to reduce the gap further (to 0.035) and try again.  Please let me know if I should try something else.  It won't be until tonight or tomorrow though because I have to go to work.

[Tom Q]

it's not the plugs
initial timing should be at least 15 and total 30-36 depending on the car.
there may be a problem with the msd box and/or coil, grounding?
0.045-0.50 for sp gap
idle 850-900
good plug wires -  Firecore work best

[rt green]

you  said the ballast resistor was still being used?

[XH29N0G]

you  said the ballast resistor was still being used?

Yes, the ballast resistor looks like it is still wired into the system.  As near as I can tell, this should not influence the strength of the spark since this is a signal to the MSD box, and the wires to the coil and dizzy are on a separate circuit that is tied to the battery.  I assume it may affect other circuits though.  I am all ears though - I didn't do this install and don't completely understand the issues that may exist.  Otherwise, the car ran with the old set of plugs at a smaller gap (NKG5671A-7 plugs that seem to come with a 0.032 gap).  Wires are Firecore.  I'll keep looking into it, and appreciate any feedback.

[firefighter3931]

Ron,

I swapped out the plugs.  I was able to find BCPR6ES-11 (which my understanding is the BCPR6ES but with a gap of 0.044 instead of 0.036).  I reduced the gap to 0.040 and installed them.  I have not been able to get the car to start - It will fire once and then just spins over.  I double checked the wires, the plugs are tightened ~2/3 turn beyond hand tight to compress the gasket and tighten them.  I did not check the exact torque on them so they may still be a little low, but I think they are seated.  I pulled one of the plugs, and it looked like it did when I put it in.  I am assuming the MSD should provide plenty of spark. 

My thinking is that the next step should be to reduce the gap further (to 0.035) and try again.  Please let me know if I should try something else.  It won't be until tonight or tomorrow though because I have to go to work.

Sure, try reducing the gap to .035 and see how it runs. 

It sounds like the ballist resistor is just being used on the small red wire which is a trigger wire. The msd box needs 12v in both the start and run position on the key. Using the ballist which is a voltage step down resistor may be playing games with the box. Usually the ballist will reduce voltage to 9v once the engine is running and this may be the problem.

One way to insure a constant 12v signal to the box is to remove the ballist resistor and tie the wires together. If you want to keep the ballist you can simply solder in a piece of 8g wire between the top and bottom terminals (on the backside of the ballist) and that will bypass the resistor giving you a constant 12v feed to the box. 


Ron

[mopar0166]

WOW - great read !

working through a bit of a same issue.   I have a 68 440 .30 over edel heads/intake/rpm performer cam, 850 holley dp. 

I am using the edelbrock recommended plug:RJ12YC at .48 which was msd recommendation. 

Should I be running an ngk cause of all the fouling plugs im getting ? Should I be reducing the heat range?

I saw it was recommended to use bcpr-6es ?

any suggestions would be awesome!

[XH29N0G]

Mopar0166:  The letters/numbers on the plugs can be decoded using the files posted at:

http://www.gsparkplug.com/shop/spark-plug-manufacturers-code/

The Heat range numbering (12 and 6) of the two manufacturers is different.  As near as I can tell the champion is a an even hotter plug than the one I swapped in, but see what others on the list say.  (I arrived at this conclusion by looking at a plug cross listing site such as http://www.sparkplug-crossreference.com/convert/CHAMP_PN/RJ12YC (http://www.sparkplug-crossreference.com/ - for their applet) and the champion is compared to a heat range 5 NGK plug.  But see what others say.

For others:  My problem appears mostly to have been solved.  I noticed (1) that the feed wire to the MSD box from the battery was not tightly bound by the nut on the battery (I tightened that).  (2) I also jumped the ballast resistor.  The car started as soon as I bumped the starter.   I left it at 0.040 and suppose I will leave it there for now.

I reset the timing to 15 degrees BTDC and tuned on all 4 corners (each went in by amost a full turn before vacuum started to drop (vacuum went from about 10 inches to 14 inches at 850 RPM).  The idle increased slightly when I put the air cleaner back on   but the idle sounds better.  The car seems more tender starting in 1st (more likely to stall - can't just release the clutch like in a tractor and have it take off which I think it should do with 4.30 rear) and it also has some detonation in higher gears under load and at low RPM (2000 or so).  So I will keep working on it and reading and experimenting.  I am trying to figure out if the gap or timing is playing a role.  I am assuming the carburetor idle screws should only impact low RPM operation.  I also reconnected the ballast resistor and it started fine, so I think the issue before must have been the red lead from the battery to the MSD box. Oh, and I have not yet run it up through all the gears.  I think it sounds better on acceleration and does not appear to have the hesitation it had with the (fouled or partly fouled) cooler plugs.

[mopar0166]

Thanks for the reply on the plugs. 

I put a new rotor and cap on last night to my billet msd and also took out the stock bushing and put in the black bushing.  Timing was off when I got it back together but set it at around 18 and the 18 advance should of given me mid 30's.  car runs a lot better and seems a lot happier.  the numbers seem good in thought but when I put the rpm up to 2500 I was getting like 31-32 with the timing light.  might be something I have to look over again tonight along with more run time to check the color of the plugs and tighten that up as well. 

[XH29N0G]

Quick update. 

I ended up bypassing the ballast resistor, after doing some reading and understanding more about the ballast resistor (that it drops voltage when wired directly into old-style coils with points to make them live longer) and understanding that in this case it was connected to the MSD box which fed the coil separately.

I also richened up the idle circuit 1/4 turn on each of the 4 screws after reading that sometimes this helps with start up and low RPM detonation.  Both improved and now it starts in gear fine and I do not have the detonation issue I had last time.

I also had a chance to run it up through the gears and it works better than before.

Thanks everyone.  Next I will connect the A/F gauge and see whether it is good by that measure.

[firefighter3931]

Good work....and thanks for the update 


Ron