Lets talk about spark plugs heat range.
 

I have been running Autolite 3924's for the last couple years. Every time I change them they still look new. As in they look like I just put them in absolutely no color change in the electrode.

I think I must be running too cold of a plug. I see they also sale Autolite 3923's and 3926's.

I think its the higher the number the hotter the plug is this correct?

What determines the heat range of spark plug that is best for an engine? I know you want a colder plug for power adder cars but on a naturally aspirated car how do you determine the correct heat range for your engine?

Thanks,

Re: Lets talk about spark plugs heat range.
 

From what I know and use, the insulator above the electrode should be light tan or ash colored if the A/F is right and the heat range is correct. If the electrode is clean, I would think that was a good sign.

Rev

Re: Lets talk about spark plugs heat range.
 

Oh, JEEZUZ, here we go. Spark plugs are about as misinterpreted as tire sizes. I'll fill you in on what I know.

First of all, how often are you checking them? When you yank a plug, and it "looks like new" how many miles are on it? Stock engine? N/A, nitrous? etc etc.

Right now, it sounds like you're a bit lean to me, and really has nothing to do with the plugs.

Give us some more info, and we'll go from there, K? :D

Re: Lets talk about spark plugs heat range.
 

I check them about every ten 1/4 mile runs (Track only car)

These plugs have been in the car for over 100 runs and still look new.

I had Box stock 192cc Canfield heads, ported cobra intake and an E303 cam on a stock short block.

My new set-up is The same 192cc canfield heads with a 5 angle valve job, blended bowls, unshrouded valves and minor port work.

Custom Flowtech Induction cam .566 lift 218 duration @.050 intake
.............................................566 lift 224 duration @.050 exhaust

Same ported Cobra intake for now all on a 30,000 mile stock shortblock.

I was worried the car was running lean before so I may really have issues now.

I am going to the track this Friday to try and get the new set-up dialed in as far as the timing and fuel pressure go. The only dyno here closed so i am going to have to tune at the track.

Re: Lets talk about spark plugs heat range.
 

Hot - Cold Issue

Here's a tip look up the MFG on the web get a catalog coming from each plug company, turn to the "Technical Info" page in each catalog and study what they say.

Plug color 1) The housing & ground electrode should show some heat after you make a run and turn the engine off, coast to a stop and check the plugs. To look at the porcline you need a doctors light with the ear attachment. look deep into the core of the plug where the porcline meets the housing and read the color there - should be light to medium gray if you run leaded gas. Look for a ring on the porcline & remember where that is (make a drawing for your records).

2) Look at the ground electrode - What you're looking for is a shiny blue ring at some point along the length of the ground wire - that ring tells you where the timeing is as a relationship to the lean-rich mixture.

3) Look at the face of the plug where the ground wire is attached - When the plug is new and you just made a run - there should be traces of heat - This looks like the cad plating is being worn off - the more heat the farther it runs down the plug into the threds.

You're running a naturally aspirated gasoline motor - You're probably not going to see more than 1` thread of heat. White on the porcline is A-OK must have a very good ignition or tht won't happen. Be sure your running cad plated plugs and not the black ones, otherwise change to Denzo, NGK or Champion. Use the cross-over chart in your cataloges. Always find the Batch Number (MFG Part Code #) not the actual plug number.

Denny@JDS Induction Products - HeadDoctor out