Colder Spark Plugs

[ukkid35]

After years trying to reduce pinking at low revs, I have tried fitting colder plugs

This has definitely helped, especially when the engine temp rises in traffic

However pickup is now jerky below 3k at partial throttle openings

The engine note is 'fluffy' and not as crisp as before, perhaps not all cylinders are firing at low revs

Compression is high and equal across all cylinders, and I've fitted new HT leads

Is this and inevitable consequence of using colder plugs, or is there anything I can do to improve low rev running?

[stevieturbo]

if you have "pinking" at low revs...tune ignition timing correctly.

At low rpm it is extremely unlikely plugs are in any way whatsoever the issue.

And "colder" means nothing without a reference.

Have you went from 5's to 9's ? 5's to 6's ? What ?

[ukkid35]

stevieturbo said:

And "colder" means nothing without a reference.

Have you went from 5's to 9's ? 5's to 6's ? What ?

From BKR5EKU

To BCPR7ES

[stevieturbo]

That's a huge step on a n/a car. ( 2 heat ranges is pretty big step on a boosted car too )

Is it now fouling the plugs ?

[anonymous-user]

Plug temp is simply not going to be an issue at just 3krpm on an N/A engine..........

Get you MBT ignition timing set right !

[DVandrews]

Max_Torque said:

Plug temp is simply not going to be an issue at just 3krpm on an N/A engine..........

Get you MBT ignition timing set right !

This.. 100%

Dave

[ukkid35]

The plugs were new old stock, and must have been very old (red packaged Unipart branded)

When I removed them I found that most of the caps were loose or just finger tight

But the main problem was that the electrode of one plug had been hit such that the gap had closed to almost nothing

I simply hadn't thought to check them carefully before fitting, mea culpa

After regapping them the engine is now running smoothly with no sign of fouling and much less pinking when heat soaked in traffic

[Yazza54]

stevieturbo said:

That's a huge step on a n/a car. ( 2 heat ranges is pretty big step on a boosted car too )

Is it now fouling the plugs ?

The rule of thumb is one step colder for 70-100hp added, or if you're running a lot more timing, or racing... Or a combination of those three.

Sounds like your plugs are probably fouling at low RPM.

The other complication is that they aren't the same type of plug, so it might not be like comparing apples with apples. Do NGK not do a 6?

[Yazza54]

Here's the same plug as you first had but one step colder ..

https://www.opieoils.co.uk/p-63575-ngk-bkr6eku-699...

[ukkid35]

Yazza54 said:

Sounds like your plugs are probably fouling at low RPM.

No problem at low revs at the moment

If that changes I'll try the BKR6EKU as you suggest

[Yazza54]

So it's specifically just at 3k ?

[stevieturbo]

Yazza54 said:

The rule of thumb is one step colder for 70-100hp added, or if you're running a lot more timing, or racing... Or a combination of those three.

Sounds like your plugs are probably fouling at low RPM.

The other complication is that they aren't the same type of plug, so it might not be like comparing apples with apples. Do NGK not do a 6?

There is no rule of thumb. I've run plugs only 2 heat ranges higher than OEM with 5x the power.

But yes, there are many factors.

[ukkid35]

Yazza54 said:

So it's specifically just at 3k ?

The pinking, if that is what it is, only happens under 2200 with sudden throttle openings, and much more so when heat soaked

It is much reduced now especially when hot, although obviously I drive to try to avoid it happening as it is so painful to hear

It has never resulted in plug damage, but it has in the past knocked a valve guide loose

[Yazza54]

stevieturbo said:

Yazza54 said:

The rule of thumb is one step colder for 70-100hp added, or if you're running a lot more timing, or racing... Or a combination of those three.

Sounds like your plugs are probably fouling at low RPM.

The other complication is that they aren't the same type of plug, so it might not be like comparing apples with apples. Do NGK not do a 6?

There is no rule of thumb. I've run plugs only 2 heat ranges higher than OEM with 5x the power.

But yes, there are many factors.

That's the rule of thumb NGK give, so yes, there is... Granted it is a very basic starter for 10 and not remotely gospel.

Stated simply to suggest that he's possibly gone too far with two steps colder.

It does sound like there's potentially something not quite right in the fuel/ignition mapping.

Edited by Yazza54 on Sunday 23 May 22:23

[stevieturbo]

Yazza54 said:

That's the rule of thumb NGK give, so yes, there is... Granted it is a very basic starter for 10 and not remotely gospel.

Stated simply to suggest that he's possibly gone too far with two steps colder.

Then their alleged rule of thumb suggests I should be 8 heat ranges higher with an additional 800hp.....which makes zero sense and is a far cry from any reality, when 2 colder work perfectly.

[Yazza54]

stevieturbo said:

Yazza54 said:

That's the rule of thumb NGK give, so yes, there is... Granted it is a very basic starter for 10 and not remotely gospel.

Stated simply to suggest that he's possibly gone too far with two steps colder.

Then their alleged rule of thumb suggests I should be 8 heat ranges higher with an additional 800hp.....which makes zero sense and is a far cry from any reality, when 2 colder work perfectly.

Obviously some common sense has to come in to play. They won't even make a plug at that theoretical heat range. So out of interest, what plugs are you running?



It also comes down to the type of use, not just the state of tune. A standard engine that gets its arse kicked non stop for 20-30 mins in a sprint race is a good candidate for one step colder even if in a relatively standard state of tune. An engine that gets 15 seconds of use on a drag strip, maybe not.. forced induction also makes it less clear cut because you do other things to mitigate the possibility of detonation like building with much lower compression etc. Ultimately at that point it all becomes very specific to the state of tune.

What it does suggest though is that two steps colder
for the OPs application is one step too far, and your experience also backs this up..

If the OPs car is mildly NA tuned and used on the road I'd wager any more than one step is too much, but it also sounds like the problem lies elsewhere in the mapping.

Edited by Yazza54 on Sunday 23 May 22:57