Another plug gap question Sorry!!

[robzombie]

After reading many threads on this subject,I'm wondering why my combo likes .38/.40 gap running 18/19lbs. of boost??
Plugs in my car are cr42ts and I've tried gaps as low as .32 with my results getting worse, not better the lower I go with the gap.

My mileage goes down and the tighter the gap the rougher the idle. I have no KR or spark blow out issues like others seem to have when running .35 gaps let alone .38/.40 that I'm running.

The reason I'm asking is that I plan on pushing the boost up to 26/27 lbs. and was wondering if that could be a problem at my current gap or just try it and see what happens.

I know that boost/rpm/fuel/cylinder pressure and other things dictate what gap is ideal, but it seems that the only clear agreement is that as boost goes up the gap goes down.

 

[blackgn1]

I bet you start having the spark blow out when you get up around 26psi.

 

[robzombie]

I thank you for the very informative and technical answer.

I learned alot from it.

 

[blackgn1]

To make more sense with the answer. You will see guys running tight gaps. .35 down to .28 The reason is because with high boost the spark gets blown out. If you are having trouble tighten the gap I would be looking for the reason. It's simple. You can't run a big gap with high boost. Why are you running a projective tip plug anyway?

 

[kidglok]

I run .35 with bobs TR-6, no issues

 

[robzombie]

Those were the plugs in it when I bought it. BTW they are r42ts not cr42ts, my mistake.

I was wondering more why it runs rougher at smaller gaps and was hoping that someone experianced the same thing and changed the plugs and the problem was solved.

These plugs only have five thou on them and looked good when I regapped them but it ran rougher, so I put them back to .38 and the car ran great again.

I shouldn't have a rougher idle with a .35 gap like I did. Just thought I missed something or some quirk about this motor that I haven't learned yet.

I guess I'll just buy new plugs and see if that takes care of the rough idle.

 

[blackgn1]

You could have a bad plug wire. I've never heard of a tighter gap causing your kind of problem but I guess it's possible.

 

[robzombie]

Wires are good and it runs better with the bigger gaps,[smooth idle], .32 shouldn't give me a rough idle, it does use more gas also with small gaps.

Maybe I'll give it a computer relearn when I get new plugs and do it again after I gap them lower , I don't know why it's like this and that's why I asked the question in the first place, I've never had this happen before.

Lower mileage with smaller gap is normal but not rough idle unless loading up on fuel which it's not doing.