Spark Plug Gap

[ZR-FUN]

OE gap is 0.05. I'm wondering what the best gap for a stock ZR-1 ('90) w/ NGK iridiums is... I hear a lot of different opinions from the GM for plugs...

Edit: Maybe this should be in the tech section.

[tomtom72]

I don't know that this will help as I use the stock GM replacement plugs, the 402's, in my '90, but I use 35 as my gap as per the FSM.

[jonszr1]

first off be very carefull when cking the gap on these plugs . i use a ring gap tool and go until it just bearly touches . i found with these plugs that 45 thou is max for me .i settled on 40 thou for the ngk. hope this helps

[ZR-FUN]

OE specwas 0.05. then they said use 0.035 as your doing. for the rapid fires they said 0.045. so its confusing.


But, NGK's come at different factory gap. And a different gap for each type of plug they make for the LT-5. so i was wondering what was best for the NGK iridiums.

So, 0.04 for the NGK iridium?

[jonszr1]

yes ,being an old drag racer i have gotten used to reading plugs and at .40thou. they seem to burn the cleanest . jmho

[karterdon]

keep in mind that you do not have a high performance ignition system - So your coils can only produce so much voltage to jump the GAP - the bigger the gap the more umpf you need - So I would stay between the .035 - .040 gap. The plug is not the issue - Its the ignition system we have.

Don Yoakem
91 - #267
Dark Red Met.

[jonszr1]

i agree . its the coils that limit the gap

[Pete]

1990 has .035 from the factory.
I wouldn't go more then that with stock ignition..

Pete

[jonszr1]

pete , just wondering why is the 90 different than the other years ?

[Pete]

pete , just wondering why is the 90 different than the other years ?

It's 1990-1992 have .035 factory specs.
1993-1995 are .050 factory specs.

I think for idle quality and they went with those 100,000 mile spark plugs,not 100% sure.
Pete

[jonszr1]

so would you suggest 35 for every year ?. guess i am going to try 35thou at the strip on fri . i have maybe mistakenly so used 40 -48 thou as gap .it will be fun to find out if it helps at all . thanx for the info pete :thumbsup:

[karterdon]

THe reason for the change in gap is that the ignition system received a boost. That's why the gap increased. It was not because of the plugs. If you change your coils to MSD - you could go to a slightly larger gap. The MSD coils have a bit more voltage out put then the factory coils. So if your current gap is .035 I would leave it there or go a go slightly tighter to .032. Coils can work easier.

Best of luck

Don Yoakem
91 #267 Dark Red Met.

[Pete]

THe reason for the change in gap is that the ignition system received a boost. That's why the gap increased. It was not because of the plugs. If you change your coils to MSD - you could go to a slightly larger gap. The MSD coils have a bit more voltage out put then the factory coils. So if your current gap is .035 I would leave it there or go a go slightly tighter to .032. Coils can work easier.

Best of luck

Don Yoakem
91 #267 Dark Red Met.

Brad,yes i would go .035 on any year Z.

Don, you are the man .032 is perfect, like you:)
I agree with Don on this.

Pete

[karterdon]

I am just a humble supporter of making things go faster with less work. :wink: