Spark plug

[daviddu79]

what engine spark plug do you have on your ZR-1.
I must change mine and I do not know which model to take.
thank you

[32valvesftw]

NGK BKR5E plugs gapped at .042-.045, per Corey.

[XfireZ51]

Originally Posted by 32valvesftw

NGK BKR5E plugs gapped at .042-.045, per Corey.

I’m using the BKR5E but gapped at .035”. Wonder why Corey feels .042 works better?

[A26B]

Originally Posted by XfireZ51

I’m using the BKR5E but gapped at .035”. Wonder why Corey feels .042 works better?

0.042 is in between 375 & 405 models which were spec'd originally @ 0.035 & 0.050. To the best of my knowledge, there was no change in spark components & was likely a change in thinking bigger gap, hotter spark = better propagation.

Resulting experience of owners having rough idle issues, and thinking gap @ 0.050 was too much & the cause of rough idle. Changing to 0.035 resulted in smoother idle for some.

Somewhere in the middle 0.042, is a good compromise & allows for some electrode erosion without issue.

I run 0.050 with Iridium plugs & works fine for me with 12:1 compression. I believe personal experience from trial & error will vary from person to person & engine to engine.

[XfireZ51]

Jerry,

I have tried .050” on my motor, and it certainly appeared to result in a smoother idle. However, i went back to .035 due to the apparent additional strain the larger gap puts on our ignition coils. The larger gap certainly would help in terms of flame propagation and a better burn, which is one of the reasons I continue to pursue the use of the LSx ignition system on our cars. Increased dwell times and hotter spark have a beneficial effect on a high rpm motor such as ours.
Good to know that Corey finds the NGK 5 heat range is appropriate for the LT5 because its the same conclusion I came to last year and what I have been using since.
BTW, I wrote to Corey asking for his reasoning on his recommended gap and here is a relevant portion of his response.

“Makes more power on the dyno with the bigger gap, and carries the power higher in the rpm range. I wish I could say it's just random reasons why I do the things I do, but unfortunately it's all based on years of testing and experience along with a little physics and engineering thrown in for no reason at all...”

I think Corey is being modest here. Nothing wrong with experience and using an educated guess. Knowing Pete and Marc, I can say I certainly would trust their educated guess above something strictly hypothetical. I also appreciate Corey’s very quick response to my question.

[A26B]

I concur completely. To reduce this down would require establishing all the variables, which is a sizable task in itself. Then analyze changes to each variable independently while all other variables remain constant.

Example: Given a specific engine, lets say its completely stock, changing only plug gap on the same spark plugs can yield data specific to that singular change. Introduce a change in intake cams only. May yield different power results with the same spark plug at different gaps.

For a highly modified engine, I think it would require testing of different combinations of the variables to determine the best gap. For instance a combo of specific coils, wires & plugs, (all other variables remain constant) then vary the gap to see the result. I would expect the best plug gap to be different from the basic testing which yielded 0.042 as the best gap.

My point is, There is no best gap for all engines inclusive, but rather a general "best gap" for the mean distribution. Even stock engines vary in power output and may respond differently to plug gap, depending on coil output, Plug wire resistance, etc. For the vast majority of us without the means to determine results empirically, "seat of the pants" will have to do.

[daviddu79]

I will take NGK.
thank you for your return

[jss06c6]

Concur with Dominic and Jerry that each engine has its own "personality". The only mods on my '91 are SW headers and SW high flow cats and SW exhaust along with custom tune. I am running NGK 7's gapped at .050". Could not be happier..

Sent from my XT1585 using ZR-1 Net Registry mobile app

[max76]

I have bosch fr7dc+ 0.9mm gap...like gm service manual need...the car run great...

[Hib Halverson]

The original spark plug for the LT5 was the FR1LS, at the time, GM's coldest spark plug for production engines. Right at the LT5's 1990 release, GM changed that to the FR2LS because of concerns about "pre-delivery" plug fouling in engines on dealer lots.

Other than those who own waxers and trailered show cars or others which are subjected to frequent starts without warm-ups, no Zroner needs to worry about pre-delivery plug fouling.

The AC "1" heat range crosses to the NGK 6 and the Denso 20 heat range.

With due respect to Corey Henderson, who's one of the better LT5 guys out there, the NGK 5 heat range is too hot a plug for anything other than "non-sporting" driving. If you run your car hard at all, you need at least one range colder.

At one time I used the Denso IT-20 in my LT5 but, later, in the early-'10s, I went to the IT-22, one range colder than the AC "1" heat range. For the type of driving I did with my modified '95, that was a good choice. I had hot coils so I gapped them at .045-.050-in.