Expert Plug Reading Wanted

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 10:02 pm

Anyway. Not intirely convinced there are signs of detonation there. You do get specks of combustion by-products on the plug normally after a few hundred miles.

But thing i will take out two degrees anyway to be safe.

I also took out 5 throu from the plugs and put them back in for now. Going to buy a set a bit colder because I think the tips of these ones are too extended (hot).

Guy · Post by **Guy** » Sun Jul 19, 09 10:06 pm

RichDeb wrote:I bet not many people knew that,Mick....I didnt..

nor me, you learn something new everyday.

challenger · Post by **challenger** » Sun Jul 19, 09 10:08 pm

with a colder plug dave you may not need to bring timing back, your call i use ngk 6,s 38 deg total regardless what folk say, it pulls a lot better than at 34 tot but not every motor runs the same

Mick70RR · Post by **Mick70RR** » Sun Jul 19, 09 10:27 pm

Guy wrote:
RichDeb wrote:I bet not many people knew that,Mick....I didnt..

nor me, you learn something new everyday.

In actual fact, they use an average of MON/RON which works out to 4-5 points lower than RON.

Anonymous · Post by **Anonymous** » Sun Jul 19, 09 11:40 pm

Plugs 1 & 7 are getting hot to the point of detonation , you can see this if you look closely @ the electrode , the heat mark on ground strap is all the way to the threads

, jet for this bank if you're tuning for the centre carb only , this tuning method is only any good with no load on the motor , if you loaded the motor with only the centre carb hooked up then plug tuning will be a waste of time bearing in mind the outboard carbs will put another spanner in the works when hooked up.

I would'nt be happy with any of those plugs , the only plugs in those pics that look 'safe' to me are #s 6 & 8 , heat is just starting to take the cadium plating off the ground straps.

Porcelane on #4 plug is glazed over , possibly due to oil in the chamber causing porcelane to overheat , can't see it being an overfuelling issue as distribution would have to be way out of whack to show two totaly different spark plug readings when fed from grouped half of manifold (1 & 4) ..............maybe the motor was misfireing on a few cylinders due to the large plug gaps , which may account for the plugs lookin like chalk & cheese.

What heat range Dave?

Dave-R · Post by **Dave-R** » Mon Jul 20, 09 8:23 am

challenger wrote:with a colder plug dave you may not need to bring timing back, your call i use ngk 6,s 38 deg total regardless what folk say, it pulls a lot better than at 34 tot but not every motor runs the same

These ones are NGK XR5. I take it the bigger the number the colder the plug??

The Champions I found in my draw from years ago look a LOT colder than these plugs.

dustymopar · Post by **dustymopar** » Mon Jul 20, 09 9:02 am

Dave wrote:These ones are NGK XR5. I take it the bigger the number the colder the plug??

Correct, Champions run the opposite way.

NGK 5's = Champion 12's
NGK 6's = Champion 9's

As an experiment run 3 heat ranges in various positions - NGK 6 & 7's appear to work best on my motor. 5's (12's) were too hot.

The only signs of detontation I saw on the original hot plugs was glasing, BUT when I removed a head, I saw specks on the piston tops too

Dave-R · Post by **Dave-R** » Mon Jul 20, 09 2:13 pm

Right. Made a decision.

Going to stick to changing one thing at a time.

So colder plugs needed as a start.

Problem is that when you go into Halfords the numbers on their plugs are different to the numbers on my Yank bought ones. So I don't know how to find XR6 plugs and the Halfords lot have no cross reference and have never heard of a Dodge Challenger of course.
Not only that the boxes are designed so you can't open them to compare without destroying the box.

Anyone know what the UK part number is?

latil · Post by **latil** » Mon Jul 20, 09 3:08 pm

NGK are BPR 5 as far as I know.

dustymopar · Post by **dustymopar** » Mon Jul 20, 09 3:58 pm

The NGK 6's I am using are BCP6ES

Anonymous · Post by **Anonymous** » Mon Jul 20, 09 4:02 pm

Those plugs are designed for High temp emissions type heads, you can't get a good clear reading on them as they stick way out in the combustion chamber and are designed to burn themselves clean.

Also I don't see why the outers are disabled ? you won't be able to read midrange and WOT accurately although they will still be contributing to the idle a tad I'd imagine.

I'd get the timing back to 34 then use a set of stock plugs to get a clear reading with the outer carbs hooked up and go from there

Dave-R · Post by **Dave-R** » Mon Jul 20, 09 6:48 pm

A 318 runs OK on a 2bbl.

I don't have idle circuits on the outers like the US versions (this is off a late Jensen) but I wasn't checking the plugs for mixture anyway.
I was using the wideband sensor to get the center carb jets right at lower rpms when the (mechanical) outers are completely closed. So i had to make sure the outers were closed so I was not confusing the issue.

I just noticed the plugs looked like they were too hot and maybe showing signs of detonation or pre-ignition.

The tips are far longer than the original plugs for these cars. Yet it is the plug NGK say is the right one for a 1970 440+6.

Dave-R · Post by **Dave-R** » Mon Jul 20, 09 6:50 pm

dustymopar wrote:The NGK 6's I am using are BCP6ES

Suitible for IRON heads??

dustymopar · Post by **dustymopar** » Mon Jul 20, 09 8:05 pm

These are for Ally Heads (14mm Thread / 5/8" Hex / 3/4" Reach)

My 452 iron's require a shorther reach plug (BP6S 14mm Thread / 13/16" Hex / 3/8" Reach)

Not sure if a longer reach plug can be used?

Anonymous · Post by **Anonymous** » Mon Jul 20, 09 8:13 pm

Dave wrote: I just noticed the plugs looked like they were too hot and maybe showing signs of detonation or pre-ignition.

BINGO.

Fit those #6 plugs , hook the outers up & tune fron there.

The plugs you're using are only good for high octane fuel like we had 30 years ago , as i keep saying , those #5 plugs are only any good if using high octane or the motors running with a 160* stat & can maintain that temp.