They have heat ranges. Who knew... OK, I do. But i don't think about it much. I mostly deal with stock parts and the stock spark plugs (stock brand too). But my brother would have thought of this right away I think, or at least after the first putt.

He's not a mechanic like me, but he plays one on T.V. -OK not really. He's just really smart.

Anyway, I made this car (Honda CRX DX/HF) with a custom transmission. When I went to buy spark plugs they gave me a choice. I chose "cold" because my custom trans runs high RPM for this 70HP 8valve engine.

fast fwd
I bought Dreya a 4spd 16valve 70hp Civic and we swapped the custom 5spd trans to it.

fine

later we changed the timing belt, swapped to a 90hp cam, ECU, and fuel system, and exchanged all the parts which go along with the timing belt except spark plugs and tune up.

Skip over-(I let Dreya do a lot of it and something minor had to be redone- it happens).

But she still has the custom 5spd trans for the 70 HP engine. Fuel economy was good. 38mpg

sputter soon after.

I changed the plugs (stock # for both the 16valve 4spd 70hp and 5spd 90hp) wires, cap and rotor button.
FIXED
no
months later sputter. I suspect the plugs are fouled.

If so I will try the the hotter HF plugs. This engine I created combined with this trans I created runs lower RPM than factory design. Sean might have thought of this if I'd told him about it.

An italian tune up could fix it right up I'd bet, but I'd prefer to attempt to modify this car to fit the driver on this occasion... bein' all customy like my brother.

He might tell you something opposite. I always tell him to stick to stock parts.

But I am. They just don't mix right sometimes.
----------------------

So she was getting 27mpg w/ the same spec engine, lighter car, and higher RPM trans.
Then ~30 in the newer stock 4spd heavier car too I think, and 38 with the 5spd in it.

I like the 38mpg for her. I just need to make it not cold sputter sometimes.

HOT PLUGS

[edited for memory]