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Best Spark Plugs for M20 Motor?

Discussion in 'E30 (1984-1993)' started by cramartin, Feb 28, 2009.

    cramartin guest

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    I have a 1988 325iC with about 168,000 miles on the clock. Runs pretty good with a GIAC chip I got from DynoSpot Racing in San Jose. But always looking for more low-end power.

    I was on the Bosch site and see they have several different plugs to choose from.

    4478 PLATINUM+4 Do not gap. Gap is not adjustable.
    4306 PLATINUM+2 Do not gap. Gap is not adjustable.
    4506 PLATINUM IR FUSION Do not gap. Gap is not adjustable.
    6234 PLATINUM GAP=0.028"
    4034 PLATINUM PLUS GAP=0.028"
    7509 SUPER GAP=0.028"
    7909 SUPER PLUS GAP=0.028"

    I use the standard 7909 Super Plus.

    Has anyone run the Platinum plugs? How do these other products affect performance, economy, etc?

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    • Technical Service Advisor


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    Never put single platinums in a BMW motor, but some people like the +4s and the NGK iridium plugs.
    • Member


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    Per Bentley, the correct spark plug for your M20 (M20B25) is the W8LCR plug.
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    Use the BMW suggested plug. You won't go wrong. It will probably cheaper than those "fancy" plugs and perform better. You are just paying for the marketing on those, so don't fall for it.

    94is guest

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    I've always run stock NGK's.
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    On your E36 (which is wise.) On an M20, I always make the customers buy the correct plugs or tell them that we cannot give them a warranty against misfires.
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    Well, I decided to put the +4 in my car right about 2 months after i got it, about 5 years ago. I did that based on the gains from my old Cherokee in mileage, albeit small. I discovered that the previous owner had put in +2, but I already had them bought, so i went ahead. I have no opinion really to stand on as far as benefits, but I do get ~26mpg on my 91 325iC w/ standard trans, and i drive the holy hell out of the car most of the time. I don't know the mileage on my car (typical broken odo gears). I calculate based on GPS mileage.

    All in all, as long as they light the fire reliably and at the right time, I'm not convinced there's a ton of difference. But what do I know?

    jlegleiter guest

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    BMW currently recommends two plugs for the M20.

    Bosch W8LCR - Standard Copper Core - BMW P/N 12 12 9 061 869
    Bosch W8LPR - Single Electrode Platinum - BMW P/N 12 12 1 721 895

    NGK ZGR5As should be more than acceptable as well since, if I remember correctly, M20s were equipped with this plug from the factory. At least the NGK equivelant at the time.

    I've never run a platinum plug in an M20, and it would be hard to convince me to do so. I had numereous instances of fuel fouled plugs in an M50 resulting in no-start conditions after switching to Bosch platinums. I went back to the basic copper core, and the problems did not return.

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