spark plug heat range questions.

[pjc360]

Got a few questions regarding heat ranges of spark plugs. Can running a spark plug with too high of a heat range cause idle problems when running a high initial timing and running vaccum advance off of manifold vaccum. and while running premium 91 octane fuel?
You see, i have my initial timing set at 14 degrees wich lands my total timing at 32 degrees, engine is a 300hp crate 360 magnum, compression ratio is 9:0.1 and i run premium 91 octane fuel in it and i live 4000 feet above sea level.
Whenever i try to run my vaccum advance off of manifold vaccum it will run fantastic, but everytime the engine is at an idle with the vaccum advance on manifold vaccum there is occasionally a thud thud thud out the exhaust while at idle, wich almost sounds like a miss. It never did occur to me untill today that maybe i need to go down a heat range or two, i'm thinking maybe with all the initial timing i'm running at an idle with the vaccum advance on manifold vaccum and along with the high elavation i live inn and the premium 91 octane fuel that maybe i could get this thudding or miss to go away while at an idle with a colder spark plug.
Is it possible that maybe the plugs i am running are too hot and that they are causing a miss at idle?
I am currently running Ngk v-power spark plugs the zfr5f-11's, i have been told this is the stock heat range for a 360 magnum. And that the next step colder plug would be the zfr6f-11. Or i could get away from the ngk's and run the autolite copper core plugs and the stock heat range for the copper core autolites is 3924 and the next step colder is the 3923's.
Is it worth trying a 1 step colder plug and seeing if this issue goes away?
Currently i have my vaccum advance running off of th ported vaccum source on the carburetor , but i have een told this is wrong and that it needs to be on manifold vaccum. according to the gentelmen that built my distributer.

 

[pjc360]

I guess i could have kept it a little more simple and asked is it possible that an engine with high initial timing settings in high elavation running 91 octane premium fuel could greatly benefit from a step or two colder spark plug? I am really considering buying the autolite plain copper core 3923 plugs wich is 1 step colder then the current plugs i am running.
I'm thinking the thudding out the exhaust that i was hearing while my engine was at an idle was caused by the spark plug heat range being too hot and causing pre ignition while at an idle. but i guess i could be wrong....

 

[toolmanmike]

It will be interesting to see the responses you get just because you have so many variables that the answers aren't textbook. You may have to just tru a couple heat ranges colder and hotter to see what results you get. I had a similar problem when I rebuilt my 273. The compression went from 10.5 down to 9.6/1 and it never ran right. I tried 3 heat ranged hotter and the idle miss cleared up and it runs , well like a new engine. I was using Autolites but went back to Champions. Good luck! tmm

 

[67Dart273]

http://ngksparkplugs.com/tech_support/spark_plugs/index.asp

http://www.globaldenso.com/en/products/aftermarket/plug/basic_knowledge/heatrange/index.html

 

[pjc360]

well today i purchased 8 brand new autolite 3923 plugs, i have heard nothing but good things about them in the 5.2 and 5.9 magnums, they are 1 step colder then stock heat range plugs. I was running the ngk v-power plugs the zfr5f11's and i was told the zfr5f11's are stock heat range, so i wanted to go to the ngk v-power zfr6f11's but the two local parts stores i have in this town didnt have the ngk zfr6f11's. So i decided screw it i will run the 3923 autolites, even tho i have no past expirence with aoutlite plugs? but since i had read good things about the autolite 3923's in the magnum engines.
So i fired it up and then i switcch my vaccum advance from ported vaccum to manifold vaccum and it still was thuddin out the exhaust, a colder spark plug did not cure that problem. So i put my vaccum advance back on ported vaccum.
Currently running 14 degrees of initial timing 32 degrees total timing and i have my vaccum advance set to add 12 degrees of timing at 18 inchees of vaccum. So i think i will leave the vaccum advance on ported vaccum and stop trying to get this engine to run right with the vaccum advance on manifold vaccum, aparently 14 degrees of initial timing i plenty for this 360 magnum of mine. It still runs good, just as good as when the vaccum advance is on manifold vaccum, the only thing i liked more about my vaccum advance being ran on manifold vaccum is that my engine was cooler while at an idle.

 

[Abodybomber]

I run a 360 Magnum,mild cam.Run 16 initial,34 total.Idles like glass.You neglected to mention the ignition system.Is the charging system functioning properly?1 volt into the primary system= 5,000 at the plug.Might run an ohmmeter on the plug wires.Good luck,man

 

[Hersbird]

Does it run as good on the carb vac? if it idles well but runs bad then see what the carb vac is giving you for timing at idle and compare that to what manifold vac is giving you for timing at idle. Adjust your initial timing so that with the manifold port you have the spot where it idles good. If it runs and idles well on the carb vac then that's where I would leave it. 91 octain is harder to burn then 87, you may want to try 87. Is your ignition stock? If you have electronic and a hotter coil I'd try a bigger gap as well.

The link 67dart273 gave says higher altitude needs a hotter plug not colder, and make sure your mixture is not to rich as the air is thinner.

Now I also read your later post better so see what you mean. Makes me thing more a hotter plug is needed as you say the motor runs cooler on the manifold vac. I'm kind of surprised the manifold and carb vac are that different at idle.

 

[slantsixdan]

Can running a spark plug with too high of a heat range cause idle problems

No.

running vaccum advance off of manifold vaccum

That can certainly cause hiccups and skips in the idle. Why not run the vacuum advance the way it's supposed to be?

maybe i could get this thudding or miss to go away while at an idle with a colder spark plug.

Nope.

Is it possible that maybe the plugs i am running are too hot and that they are causing a miss at idle?

Nope.

I am currently running Ngk v-power spark plugs the zfr5f-11's

Try ZFR5N.

the next step colder plug would be the zfr6f-11

Yes, if you want to stay with the present spark plug configuration but go one step colder, the ZFR6F-11 would be the one. But how are your spark plugs reading? That's what will give the answer to whether you need to go to a different heat range.

i could get away from the ngk's and run the autolite

That would mean going from high quality Japanese made plugs (NGK) to cheap Chinese garbage (Autolite).

Is it worth trying a 1 step colder plug and seeing if this issue goes away?

No. Waste of money.

Currently i have my vaccum advance running off of th ported vaccum source on the carburetor , but i have een told this is wrong and that it needs to be on manifold vaccum

No, it should be connected to the ported vacuum nipple on the carburetor. That's what it's there for.

 

[pjc360]

ya , i have it back on ported vaccum and am leaving it there, i'm done trying to get it to idle right on manifold vaccum. I am running 14 degrees of initial timing 32 degrees total timing with my vaccum advance set to add 12 degrees of timing at 18 inches of vaccum and the vaccum advance is on ported vaccum now. I am running the 4 pin chrysler electronic ignition, i have a wells 4 pin module and a 1 ohm 2 prong wells ballast resistor and i am running a crane cams lx91 ignition coil, its an ele coil i belive that can be ran with cd or inductive ignition. I am now running the autolite 3923 plugs gapped at .035. I will eventually go to the ngk v-power zfr6f11's when i get the money. But for now i will run the autolites, i must say the engine feels more responsive with the 1 step colder spark plugs. Must be because i have a fairly high initial timing setting and i'm running 91 octane fuel.
But i am leaving it alone, i think i have it tuned as well as it can be with what i have. I have my idle air mixture screws set to the highest vaccum reading with my vaccum gauge and i have the edelbrock performer 600cfm manual choke carburetor. I am running .092 jets on the primary side, and .092 jets in the secondary side. And i am running 7047 metering rods and the silver step up springs. I have the accelerator pump linkage in the middle hole. I have triple checked my float level and it is spot on.
future plans for ignition is ether a craner cams hi-6 cd ignition or a mallory hyfire cd ignition.

 

[Abodybomber]

A good multi spark box,does wonders for drivability nowadays.Used both boxes you listed,like the Crane better,but that is personal experience.

 

[slantsixdan]

HEI upgrade does at least as good a job with better reliability, lower cost, and much faster repair parts availability than MSD or most of the other "high performance" aftermarket ignition systems.

 

[slantsixdan]

the engine feels more responsive with the 1 step colder spark plugs. Must be because i have a fairly high initial timing setting and i'm running 91 octane fuel.

Nope, it's because of the power of suggestion. Spark plug heat range has zero influence on how "responsive" the engine is.

 

[Abodybomber]

Probably fresh plugs,over old.

 

[Abodybomber]

Sorry Dan,done both.Multi strike box,all day long.

 

[Rice Nuker]

Nevermind. Glad you got it working.

 

[67Dart273]

then 67Dart273 shocks us all with the breaking news that he doesn't like me,

.................................................................................................................................................................

 

[pjc360]

I have thought about the hei upgrade, i have a ton of stuff off the internet printed out on paper with instructions on how to do it.
the two main things that scare me away from the hei upgrade, number 1 the ability to be able to rev over 4500 to 5000 rpm is gone, number 2 its a gm ignition and i have a dodge product.
I have been a die hard chrysler guy ever since i knew what a car was, my old man was one of the biggest mopar fans around, owned countless mopar cars and dodge trucks. I have alot of friends that are die hard Gm fans, if i threw on an hei ignition on my dodge i'd never hear the end of it from them. I know that dont truely matter and i know the hei ignition is a good system. But i figure if i'm going to get a new ignition, i'll spare myself the flack i'd catch from all my die hard gm buddies and save myself the thought of wondering if i can turn to 6000 rpm or not and just get an aftermarket cd ignition.
I would most likely get the crane hi-6 cd ignition box because i already have the crane lx91 coil. I'd be looking at 249.00 for the crane hi-6 cd box and thats it, other then wiring it in wich to me appears to be very simple from all the wiring diagrams i have seen.

 

[slantsixdan]

the two main things that scare me away from the hei upgrade, number 1 the ability to be able to rev over 4500 to 5000 rpm is gone

Um…what? That's not correct. Who told you so?

number 2 its a gm ignition and i have a dodge product.

…with a Crane ignition not made by Chrysler. Does that turn your car into a Crane? No. Would putting an HEI module in your car turn it into a Chevrolet? No.

 

[pjc360]

Hasnt it been common knowledge that the gm hei ignition is not as capable of reving higher compared to other ignition set ups?

 

[pjc360]

and there is now way the engine could possibly be running better because of the 1 step colder spark plug?
I went from ngk v-power zfr5f11's to autolite 3923's.
I swear it pulls a little harder when first dabbing into the throttle from a steady cruise. since i run 91 octane fuel and run 14 degrees of initial timing isnt it safe to say a 1 step colder spark plug would be a benefit compared to running the stock heat range?
And if it doesnt help anything then why do half the people who run magnum v-8's buy the 1 step colder plugs? to help with engine ping, When your engine isnt pinging then im sure its safe to say its running more efficiently and there fore getting better fuel mileage and performin better correct?
I know they said high altitude calls for a warmer plug, i live 4000 feet above sea level, but i run 91 octane fuel and 14 degrees of initial timing, even thinking about turning it up from 14 degrees initial to 16 degrees initial. Wich would make my total timing go up from 32 to 34. Is the magnum engine going to run better at 32 degrees total or 34 degrees total?

 

[Rice Nuker]

You switched from manifold to ported v-advance didnt you?

I think your original issue was mainly due to too much vacuum advance at idle (vacuum retard under high load). Running off manifold, you may should have dialed back a little less total vac advance.

I think now your vacuum advance comes in off idle so it likes the curve behavior better.

My understanding is that ported vacuum advance still goes away under high load as well as it resides just above the throttle valve , below the venturi, to eliminate it during idle. Once the flaps are open a little they allow the port to be exposed to vacuum, the vac advance should be in full.

Unless the port is inside the venturi of the carb then vac-advance would increase as velocity thru the venturi increases. Which I dont think is the case.

I run vac-advance off the manifold on a 440 w no issues, runs quite great, but it is low comp so.

Here is a link that has good dialogue regarding burn rates, older vs modern and ported vs manifold. I am not trying to stir the pot. I just think it is applicable to your optimization.

Hopefully it doesn't upset folks that he talks about chevy. It sounds like one of the fellows is very keen on burn rate behavior.

http://www.hotrodders.com/forum/ported-vs-manifold-vacuum-advance-scenario-151264.html

Another link that I think clarifies the behavior and necessities of vacuum advance.

http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

.

 

[slantsixdan]

Hasnt it been common knowledge that the gm hei ignition is not as capable of reving higher compared to other ignition set ups?

Maybe, but "common knowledge" is often wrong. See here for info on how the mythical "4500 rpm HEI limit" probably dawned. There are dozens of different HEI modules available with different performance characteristics. If you're revving higher than a plain old ordinary junkyard stock module will take you, it's easy and cheap to buy a high-zoot module from Mallory, MSD, Accel, or half a dozen other outfits. Every ignition system will have an RPM limitation imposed by one or another component.

 

[slantsixdan]

and there is now way the engine could possibly be running better because of the 1 step colder spark plug?

Only if the hotter plugs were causing ping/running too hot (bright white insulators with tiny globs of metal on them). If they weren't, then the answer to your question is no.

I swear it pulls a little harder

Power of suggestion. Same thing happens when we wash and wax the car; it really, honestly seems to run better. Doesn't mean anything without data

since i run 91 octane fuel and run 14 degrees of initial timing isnt it safe to say a 1 step colder spark plug would be a benefit

Only if the hotter plugs were pinging. And speaking of that...why running 91 octane fuel? Does it ping on 89 or 87? Because if it doesn't, there's zero benefit to running 91, all it does is drain your wallet faster.

When your engine isnt pinging then im sure its safe to say its running more efficiently and there fore getting better fuel mileage and performin better correct?

No. If your engine isn't pinging there is no benefit to a colder spark plug. There is no way a colder spark plug makes the engine runs "more efficiently".

I know they said high altitude calls for a warmer plug

High altitude reduces octane requirement for any given engine and/or lets you run more spark advance, because at high altitude the air is less dense. High altitude by itself doesn't call for a hotter plug.

Is the magnum engine going to run better at 32 degrees total or 34 degrees total?

Too many variables to answer this question in words on a screen. See for yourself!

 

[pjc360]

the tips of my ngk v-power zfr5f11's had white on the very tips of them when i pulled them out, wich i thought was a little strange. So that means my engine was pingin if there was white on the tips of the insulators? There wasnt any metal that i could see and the white marks on the plugs werent very big, just at the tip of the plugs.
And yes, i have my vaccum advance on ported vaccum right now, i have it set to dd 12 degrees of timing at 18 inches of vaccum.

 

[pjc360]

And the reason i run 91 octane fuel in this engine is because thats what it said to run in it with the instructions that came with this engine.
My old man bought this crate 360 magnum brand new in 2001 and i still have the paper work that came with the engine. It says we recomend using no less then 91 octane fuel. Compression ratio is 9:0.1.Although it isnt extremey high compession i have ben told that you can use premium fuel in an engine with that compression ratio, and mopar reccomends running the 91 octane fuel in it.