Sparking Plugs For Tastefully Modified VQ25DET

[Darkmeat]

Sparking Plugs For Tastefully Modified VQ25DET

During a regular service recently, the workshop fitted new plugs - NGK PLFR6A-11 Platinums - to my NM35.

And now the engine misses on boost at anything over 5,200 rpm.

The mechanic threw away the original plugs so I can't check their heat range.

But I suspect the newly fitted 6 heat range plugs are too hot.

If you had an M35 with a set of tasteful mods such as: Hypergear SS2PU turbo, fat intake, HDi intercooler, uprated actuator, Scotty dump & front pipes, Fujitsubo exhaust, HDi EBC, Walbro fuel pump and big injectors, & GReddy Ultimate ECU, etc., making 267 of Jez's kW atw, would you run a 7 heat range plug like the NGK LFR7AIX IX Iridiums, or would you jump to an 8 heat range?

Thank you.

[KiwiRS4T]

Would have thought 6 heat range ok ...maybe 7 at the most - pull out a plug and look at it. Whether or not its the correct plug for a VQ25 I don't know - have you checked that? Is it still gapped to 1.1mm?

[Scott Black]

Yeah I'd run a 7 copper plug yet I'd think it's the gap causing the miss rather than the heat range

[Scott Black]

Yet if e85 I'd prob stay 6

[Daleo]

This might help you.

[Daleo]

[Darkmeat]

Wow, thank you all!

Sorry, I should have stated: 267kw @ 5,200 rpm @ 18psi on pump 98.

I did check the older (2015) SAU Wagoneers spark plug thread.

YangLUI posted a table listing NGK Japan's recommendations for the NM35 VQ25DET:

best to normal: LFR6ARX-11P -> LFR6AIX-11P -> LFR6AIX-11 -> PLFR6A-11. (All 1.1mm gap.)

So mine are recommended for stock engines, and gapped at 1.1mm.

But further in the thread, Scotty wrote:

"Stock engine, 6 heat range is fine, so is 7. Quite often I see 5 though which is too hot.
  Modified cars LFR7, or 8 if you have the coin for HKS tax."

And further, when replying to a question about Nismo RN020-7 plugs (NGK part no LFR7AIX-P gap 0.8-0.9mm), Scotty wrote:

"Those Nismo plugs are a 7 heat range, no point getting those [Nismo's] when the LFR7's are half the price.
  Gap doesn't matter in this case, as they will still work at 4mm gap thanks to our coils."

So that's why I think maybe the 6's are too hot.

Daleo's magic table (where did you get that!?!) indicates I should be running at least NGK 2309 LFR7AIX IX Iridium Plugs (which have an 0.8mm gap).

I'll get some.

Thank you all very much. What an absolute pearl this forum is!

I'm off to donate.

[Darkmeat]

Just to finish this off, while fitting new plugs, Denso IKH24 (8 on the NGK Heat Range table,) we found the real problem is a left rear plug seal.

Oil had seeped down the plug.

The NM35DET rocker cover has the plug seals manufactured into it, dammit.

With new plugs, it's temporarily running smooth, while I try to locate a left rocker cover (anyone got one?).

For the VQ25DET, the rocker cover part numbers are:

RIGHT SIDE ROCKER COVER

maker             nissan
parts code     13264
parts no         13264-AQ801
parts name    COVER ASSEMBLY,VALVE ROCKER

Vehicle                   period                     model     fig
CEDRIC/GLORIA 1999/06-2004/10      Y34     111E
CIMA                      2001/01-2010/08    F50     111A
STAGEA                2001/10-2007/07      M35    111B

LEFT SIDE ROCKER COVER

maker            nissan
parts code    13264+A
parts no        13264-AL611
parts name    COVER ASSEMBLY,VALVE ROCKER

Vehicle                 period                         model     fig
CEDRIC/GLORIA  1999/06-2004/10     Y34     111D
CIMA                      2001/01-2010/08     F50     111A
SKYLINE                2001/06-2007/06     V35     111B
STAGEA                2001/10-2007/07      M35     111B

http://jp-carparts.com/nissan/partlist.php?maker=nissan&type=153&cartype=12&fig=111&page=8

Thanks for everyone's great help. At least I have the right plugs now!