[bmw] re: 92 //325i plugs

[jkerouac <jkerouac@xxxxxxxxxxxxx>]

re: 92 //325i plugs, + E36/6 cyl plugs in general:

    I've had best results with the Bosch Platinums.  Half the price of 
the OEM plug, give better economy, and, subjectively, a touch more 
power.  A bit higher idle is one effect I've noticed.
They last 10-12k miles before starting to degrade a bit.  15k is 
probably the limit if you like to keep the engine running at its best.
The OEM plugs are OEM more for being able to last longer without 
effecting emissions than any performance advantage.  Still, (in the 
E36es I've got to know) the OEM plugs show some performance degradation 
by 15k miles.  At the factory listed 30 k miles they're clearly far 
gone.  The service lights for Inspection II are just as far out of touch 
with reality as if you wait to change your oil until they tell you to. 
Imho.  Also I would make a fair guess that cumbustion chamber deposits 
are more likely to build up when the plugs are more worn also.
    Keeping old sets of plugs can be a good idea as part of document 
the engine's wear history.  Good for comparison, also when making mods.  
When I switched to a larger HFM tube, right away I saw the plugs were 
showing out leaner than any previous set.  By then upping the fuel 
pressure I got the plugs to come out now about the same as previous sets 
before the mods.
    Since we're on plugs, Bosch Platinums are not a favorable plug for 
the older 8 and 12 valve motors.  For the big blocks, try the NGK BPxET 
plugs as listed for the Mazda RX7. (x=5,6,or 7 indicating heat range.  
Lower # is colder, 6 is most common)  The T stands for triple 
electrode.  There is also a Q version in some heat ranges, Q stands for 
Quad.  Other than multiple tips, these are the same as the BPxES or 
BPRxES OEM plugs listed for some older models.  Beside the performance 
improvement, another advantage is that you won't go nuts trying to 
install all your plugs with the electrode up to make the spark face down 
equally in all cylinders.  For the E30 small 6, the OEM plug is a 
reliable first choice.
Ymmv,

'jk
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