Ignition guys, your thoughts

[big2bird]

Okay, this 84 454 project I am wrapping up.
The books call for R44T plugs at .045" with HEI, or #10 Rapidfires at .035" with HEI. The new gap is shown on Delco's website, Autozone, Kragen, etc. Why the narrowed gap? Misprint? Requirement?
The owner thinks #10's might be a good idea to maintain a longer tune.

 

[pcf_mark]

You can either find the gap that is right for your combination by experimenting or just go with .035 regardless of the plug. Any HEI will fire that gap under all conditions. I think the rapid fire design uses more sharp edges to promote easier arc jumping but may be more smoke and mirrors.

Depending on your compression, if you have any forced induction/nitrous and the condition of your ignition system you can play with the gaps to find a little more power. If you have any forced induction going over .040 can cause you trouble under boost and I would avoid rapid fires because they can cause knocking. Assuming no boost, good ignition wires and boots you can run .060 without a problem with 10:1 or lower. If you have an MSD box you can go even crazier with the gaps but I have never seen a gain in response or power over .060. Higher compression and you need to close the gaps. If you go too far the engine with start to miss under load at high rpm first. Feels like you hit the rev limited gently or sporadically. If you have a wide band O2 you will see it get all crazy and inconsistent because the unburnt fuel went out the pipe - this is how I spot the misses and back up .010.

If I am feeling lazy I open both ends of the plug box and flatten the box out and use it as my gap tool. The double thick layer is about .045"...

 

[mrvette]

I been using my steel machinist feeler gauge for so many decades now....

but I get lazy too, once I get the 'feel' for it, after two plugs, I do it by eye....

:beer::shocking:

Hey Bird, post a Utube of you leaning over a running engine with MSD on it, and pulling a plug wire, it should be fun to watch your knees hitting the fender......

 

[lars]

I posted info regarding plug gaps a while back:

http://www.vettemod.com/forum/showthread.php?t=3219

Lars