Berto
Regular Member
The OEM spark plugs for the Z22SE are GM 91 990 38 == Bosch HLR 8 STEX
As weird as it sounds all those alphanumeric characters in the code 'HLR8STEX' have actually a meaning, but we need a Rosetta stone for decyphering the hieroglyphs:
Now courtesy of Champollion we can get more intimate with the OEM spark plugs:
I'd like to call your attention on two interesting points, ladies & gents:
· The 'H' in 'HLR8STEX means that the seat shape is CONICAL WITHOUT WASHER (as opposed to flat with washer).
^ Conical seat spark plugs interface with the cylinder head in a different way than flat seat ones, and require less tightening torque.
If we switch from conical to flat seat spark plugs (like for instance any Bosch one whose code starts with the letter 'F'), the results will be anyone's guess, from 'no problem' to 'cracked cylinder head', and anything in between.
· The 'S' in 'HLR8STEX' indicates the thread length, and the center electrode protrusion into the combustion chamber.
Again, if we switch to spark plugs with different thread length and/or different center electrode protrusion, the results will be anyone's guess, from 'no problem' to 'preignition' / 'detonation' / 'fried coil pack', and anything in between.
My humble friendly advice: Unless you're confident you know very well what you're doing, stick to the OEM Bosch HLR8STEX.
As weird as it sounds all those alphanumeric characters in the code 'HLR8STEX' have actually a meaning, but we need a Rosetta stone for decyphering the hieroglyphs:
Now courtesy of Champollion we can get more intimate with the OEM spark plugs:
I'd like to call your attention on two interesting points, ladies & gents:
· The 'H' in 'HLR8STEX means that the seat shape is CONICAL WITHOUT WASHER (as opposed to flat with washer).
^ Conical seat spark plugs interface with the cylinder head in a different way than flat seat ones, and require less tightening torque.
If we switch from conical to flat seat spark plugs (like for instance any Bosch one whose code starts with the letter 'F'), the results will be anyone's guess, from 'no problem' to 'cracked cylinder head', and anything in between.
· The 'S' in 'HLR8STEX' indicates the thread length, and the center electrode protrusion into the combustion chamber.
Again, if we switch to spark plugs with different thread length and/or different center electrode protrusion, the results will be anyone's guess, from 'no problem' to 'preignition' / 'detonation' / 'fried coil pack', and anything in between.
My humble friendly advice: Unless you're confident you know very well what you're doing, stick to the OEM Bosch HLR8STEX.
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