Spark plug Q


Aug 7, 2001
I did a complete tuneup on my '84 Cutlass over the weekend (N/A 3.8L 2bbl) and noticed that the plugs that were in the motor are not what was called for.

It had AC Delvo R44TS8, I replaced them with the recommended R45TSX. I'm not real sure what the number mean, anyone care to enlighten me? I know my Camaro uses R43TS. The electrodes on the plugs that came out were white.

The car runs a ton better, but I don't think the sparkplugs had as much do with that as the fact that everything was worn out.
I beleive that the numbers/letters go against the heat range of the plugs.
The white on the plugs mean that you were running lean and/or to hot of a plug.
It was a good thing you replaced them.
Tightening the gap on hot plugs also help.

My car calls for the R45TSX wi th a .60 gap.
I'm testing CR43TS with a .35 gap, so far so good.
The engine will occasionally throw rich exhaust codes (and has never thrown a lean code), so of the two choices you gave (lean or too hot), I'll vote for too hot. The porcelain of the plug was slightly burned as well, which made me think the plug might have been too hot.

I figured the numbers were the heat range, but I have no clue which direction means what. Is 43 a cooler or hotter plug than 45? I don't have any idea what the X or the 8 are for either.

The new plugs were installed at the recommended 0.60 gap. Any idea why the gap is so big?
43 is colder than 45. The X and 8 refer to the gap they are set at when you buy them. Once you reset the gap, it doesn't matter anymore.

I think you'll want to stay with a wider gap for a NA engine.

If your getting codes, I would consider changing the O2 sensor. If it's reading rich, I will be telling the carb to run lean. Use a AC Delco sensor.
The 'S' stands for an extended tip. The '8' stands for the .080 wide gap. The '44' means a cooler running plug. OEM on mine call for the R45TS8.

'T' would mean taper seat and 'S' is extended tip. The 'X' is for the wide gap.
The codes only pop up occasionally. I replaced the O2 sensor at the last oil change (about 2000 miles ago) with no help.

I really don't think it was a false rich code. When it threw the code, you could smell it in the exhaust. At any rate, not one code since the tuneup, so I guess it's possible it was misfires causing it. The motor runs a lot smoother now :).

Thanks for the explanation on the spark plug codes. I thought the gap on the plugs looked huge, so perhaps they left the gap at 0.080. I've always gapped my small block plugs at 0.040 to 0.045, but I'm new to the 3.8s so I followed the factory recommended 0.060.
Originally posted by Ttype83

My car calls for the R45TSX wi th a .60 gap.
I'm testing CR43TS with a .35 gap, so far so good.

You experiment w/colder plugs & smaller gaps so I'll go the other way w/hotter plugs & a wider gap & lets see what happens?.
I know w/the boost & all ppl say to shorten the gap to keep the plugs fire from blowing out. But w/our cars it's not like we're making 25 psi. plus if your actually blowing enough air thru the cyl. to "blow out" the flame, I would think you would need a hotter ignition, not a tighter plug gap. I can see going to a cooler plug since DT's make soo much heat but I'm running an alc. kit anyway & that should (could) help w/that. Some even use H2O/alc. kits on N/A motors so that the can run a butt load of timing advance w/out detonation. With our cars knock sensors I wouldn't think a timing advance couldn't hurt none either. At least until it starts fouling the plugs or setting off the knock sensor.