Could duff spark plugs lower the compression ratio?

[Alex C]

Hi all, I'm after a few opinions!

 

As above, whilst running at the pod this weekend, the Sup developed a misfire above 1.0 bar (usually run at 1.25 / 1.3 bar UK spec TT Auto). Turned the boost down and drove 150 miles home with no problems, but the car didn't seem to pick up quite as well as normal.

 

Doing a search, plugs seems to be the first thing to try so I've got some NGK BKR8EIX Iridium's on order (Oldish IK24's in there at the moment).

 

The weird thing is my first turbo is now making a bit more compressor stall type noises at moderate throttle and the car seems very slightly more hesitant all through the revs. It sometimes did it occasionally when I was in the area around 1/2 throttle and backed off but now it is quite noticeable more often even when not intending to accelerate too hard.

 

Could this be because the poor spark is lowering compression slightly so it has to work harder to move the car at the same speed? I'm a bit paranoid as I've read the horror stories about Iridium's tips causing turbo damage etc. The car generally drives OK though, although I can notice a slight popping here and there on the overrun and very slight wobble at idle which wasn't there before.

[Homer]

Do you know how many miles the plugs have done since they were last swapped?

 

In my experience, once plugs start causing a misfire they are toast, regardless of whether you lower the boost. If you want a cheap way of checking get soem copper NGK's (£12), gap them to 0.8mm and see if your problem is solved. You'll also be able to check the tips of the iridiums when swapping, though I doubt this is your problem at such low boost.

[Alex C]

I'd guess about 20k miles Homer but maybe up to 30k, Dave the previous owner probably swapped them when he went BPU, not sure if another set went in more recently.

 

The BK EIX iridium's are already on the way (a change will not hurt regardless) but i might get the cheapo ones in there first like you say and see if it solves it. There was no problem with the car until I went for a 1.3/1.4 bar run...just into 3rd it started popping and my spotters on the bank said it sounded pretty rough. Haven't experimented too much since but there's defo something amiss:(

[Homer]

At 1.2bar my iridiums lasted 11k miles. Some have reported much more but 15k is the recommended point to swap them on a turbo car running 1bar or higher.

 

What killed mine was about 2 seconds of running at 1.6 bar (restrictor was temporarily out), the car barely ran after that. Swapped the plugs and all was okay I only use NGK coppers now and swap them every 3-4k miles.

[Alex C]

Excellent...I feel much happier now then..plug change should sort it out! Cheers for the advice.