WR7DC+ plugs in a tuned G40

[Dirrt]

Hi all,

I'm Dirrt's fiancée, I've been working on her G recently and have a question.

A couple of years ago Dirrt's G40 blew a hole in it's piston, and half-melted another couple while it was at it. It was having issues with a lambda sensor, and spark plugs (they were a three-pin style), the car was running badly basically. So the lambda was replaced with a new one, and the plugs were replaced too by her friend.

The next day, all was running fine for a change, and driving down the motorway the car started misfiring (only at around 80mph, normal throttle etc) so she pulled over and long-story-short, the G had melted piston 2!

Anyway, the engine has now been replaced and whilst scavenging parts from the old engine, I noticed the old plugs were actually WR7DC+ items. I'd been googling this week to find what plugs to get, and stumbled across a thread on here between Saf and Yoof talking about NGK BP7EVX's being equivalent to the standard G40 Bosch WR5DP0's. So I realised when seeing these plugs, that they were totally WRONG for the G40 engine.

So I ordered the NGK's anyway, that's not a problem (I hope), but looking back I'd like to know if these WR7 plugs could've caused detonation and ultimately a melted piston? I previously thought the lambda may have caused most of the damage, and despite changing it and the plugs, it was too little too late, but having found these "new" replacement plugs were actually wrong, I am questioning if these could've been the sole problem.

So boost guru's, could you please enlighten me with your input and experience?

Oh, and here's some pictures of the two damaged plugs from the old melted engine, note the piston melted over the ceramic on the one plug! The other plug was just melted but the piston was still intact. Enjoy the high resolution of my work camera haha.










Cheers!

[grungeisdead]

ive never had a melted piston before, so cant talk from experience, but i would always want to ensure the injectors are in tip top shape, you can get them ultrasonicly cleaned, PPP offer the service, as many other companies would do if you went hunting on yell.com , think Karl knows a place local as he always went on to me about getting his GT ones done.

that way you can always be sure they arent going to be a limiting factor, especially on boost when you need enough fuel to keep it from leaning out.

quick bit of googling suggested that the WR7DC+ plugs are for 1.6 and 1.8 8vs mk1-3 golfs, so probably not the best. would be worth getting the car on a rolling road so they can see whats going on with the engine across the rev range.

good luck anyway, ill leave you now in the capable hands of all the resident boffins, who know more than my pikey self =D

[Yoof]

I'd say the plug took the piston, usually the other way round!

NGKBP7EVX are good plugs, standard replacement for G40 equivalent to W5DPO, I run NGKBP8EVX (A Ferrari derived plug) which is the equivalent of a W4DPO.

W7 is way too hot, and the resistor isn't needed (G40 has a supression resistor in the rotor arm) I'd say this was deffinately the main (if not root cause) of piston failure. 

Are there any deposits on the valves at all?

Cheers
Pete

[ereeiz]

Are W5DPO's not available anymore then? Or is it the old £10-15 a plug issue?

[hayesey]

still available but £40+ a set still

[Dirrt]

Hi all. Mike again.

Thanks for the info! And yoof, thanks for the confirmation of my fears. Hopefully this means we won't have the re-run of what happened to the last engine.

To those remarks about the Bosch or the price, I wasn't being tight, I just googled for the plugs and know that yoof is a man who's g40 opinion is to be trusted, so I went with what he said in a previous thread. I think Dirrts current spec should hopefully be ok with the BP7's.

Yoof, the valves did seem to have bits of melted piston all over them. I'll get some geeky high-resolution pictures of that too if you're interested? Haha.

[PeteG40]

head i saw after a melted piston is all over the valve stem and in the inlet port!

i've used bosch and ngk and never had issues with either tbh

[hayesey]

No was t calling you tight, I have ngks in mine

[Dirrt]

  He knows you weren't.
We're proud to be tight anyway got 3 cars to tax, MOT and insure this month aswell as buy parts for them 

Dirrt.

[Yoof]

Mike- better off with the NGK for sure I couldn't run nitrous and 22psi on Bosch W4, but have been fine on NGK BP8, have the added advantage of being cheaper too  

Hopefully the deposits from the pistons won't have buggered the valves, you going to try re-facing them? (Big Valve Head isn't it?)

Cheers,

Pete

[Justin14100]

What is the advantage of a slightly cooler spark plug?

[Yoof]

It doesn't melt... 

[Justin14100]

It doesn't melt... 

oh so if your are having heat issues a colder plug can help? never known G's to ever really suffer from heat