VVC Spark Plugs

[Andy Checkley]

This is a long one, (surprising for a techy forum "bobble hat" wearer eh Anna!), so I apologise in advance for all the detail.

 

I have been having a lot of problems with spark plugs on my VVC. Normal road driving doesn't cause a problem, but when the engine is worked hard on a track day, by lunchtime I start getting a misfire with the engine under load at between 5500rpm-6200rpm. If I then change the plugs over lunch, the afternoon session is fine. These new plugs will last until the next track day, when generally the same thing happens.

 

I know that it seems odd that this problem is so repeatable, but this pattern has been the same since I have had the car, last summer and I have now done 5 track days in it.

 

The VVC uses different plugs to the NGK's used in the Supersport K series engines. It uses the Champion Platinum plugs, which are cripplingly expensive, about £60 per set of 4. These plugs are of the resistive type and I think it is the resistive compound that normally suppresses electrical interference, which is breaking down, as when I check the impedance of a problem set of plugs one plug generally gives a different reading. i.e. three plugs at 25K ohm, and one at 12k ohm. Incidentally, this is not cylinder related, I have had the 12K ohm plug come out of 1,3,& 4. Visually the plugs look as if they are running fine but perhaps a little on the hot side. I.e. very few deposits and slightly glazed.

 

I have spoken to Caterham and they have suggested using the K series Supersport NGK plugs which are £10 per set. I presume that they are colder running plugs although I haven’t confirmed this yet. I have tried them briefly on a short road run and the engine appears to run smoother. Is there anyone out there that can confirm or give me any pointers as to whether these plugs are suitable in a VVC? After all I not bothered about the radio interference suppression side of things.

 

Thanks in anticipation.

 

[Moderate Clam]

Background research: I've just checked up on the price for the NGK equivelents (PFR6N-11) and they are the same price as the Champion plugs. The reason for the very high price is that they do not fit anything else - Bloody stupid if you ask me.

 

Right then, as you've said they are designed to work at much higher temperatures (platinum core), which the VVC engine apparently requires. However, as you've said they are failing on a regular basis, so I don't feel you have anything to loose by using the normal K-Series plugs. They are both the same plug (K & VVC), apart from the platinum core and that the price is a whole lot cheaper for the std plugs.

Are you sure that the std plugs don't have resistors? If this is true, you can buy a set which are the same, but with resistors - if you wish. But I thought that the K-Series engines used the resistor plugs (at least the K-Series engines in Rover cars).

In short, I would try a set of the std plugs and see what happens. The only danger is that the K-Series plugs will over heat.

 

 

Edited by - moderate clam on 10 May 2000 12:49:21

[Mike Bees]

The K-series does use resistor plugs. Non-supersport engines use NGK BCP6ES, Supersport uses BCP7ES. The latter should be fine in a VVC.

 

I suspect that the VVC uses platinum jobs because it's a wasted-spark setup - each plug gets to spark twice as often and therefore will wear out twice as fast. If you use the non-platinum ones you may have to change them fairly frequently, but they're cheap so who cares?

 

Mike

[Tim Seipel]

The VVC engine uses Platinum tipped plugs for service life (66,000 miles) because it's a complete pain to continually remove the inspection hatch on MGF just to change plugs. Each time you do this on a car, you stand a chance of damaging the seal around the hatch and severely affecting noise quality. Also cost of ownership i a major aspect due to reduced service requirements.

 

However, DO NOT fit the standard K series plug in a VVC. It is the wrong temperature grade especially if driven hard. A champion RC7YCC will do and costs very little.

[Andy Checkley]

Thanks for your feedback. Regards, Andy Checkley

[Mike Bees]

For what it's worth I believe that Champion RC7YCC and NGK BCP7ES are the same heat-wise.

 

Mike

[Moderate Clam]

I agree. Although it's been a while since I worked in a car spares shop, I seem to remember them being the same plug (just different labels and boxes).