Gash

Gash

Well Known Member
I am using automotive spark plugs in my IO-375 with dual P-Mags. Just wondering what gap I should be using for the NGK BR8ES plugs. They come out of the box with .025 gaps, so I installed them as is with no change. They seem to run fine after a couple of test flights. But I'm wondering if anybody has actual data showing how/why it would be better to use a different gap. Thanks!
 
Always check the gap of plugs before installing them. I have seen them come out of the box and be all over the place.

To answer your question, I have mine set at .032.
 
Okay guys, thanks. I did measure the plugs individually, and they were very consistent at .025 right out of the box. The plane seems to run fine (no CHT anomalies, etc.) at that gap.

But...

You say that "the manual" says the range is .030 to .035. Which manual is that please? I've been digging around in my manuals and haven't been able to find that yet. If you could tell me which one to look in, that would help greatly.

Finally, what might be the consequences of running these automotive plugs at .025?
 
Look at page 8 of the E-mag manual. As for your 2nd question. No consequences that Iknow can thimk of.
 
E-mag/P-mag Manual

Oops, sorry Karl, thought you could read my mind:D Bill has it right. You can go to the Emag website for a quick download of the manual.

Cheers,
 
I don't know if Emag is different from lightspeed however they recommend you gap the plugs based on timing which normally is a function of compression.

Engines normally timed at 25 degrees BTDC:
These are normally engines with compression ratios less than 8.7:1. Gap spark plugs fired by the CDI to .032"-.040".
Engines normally timed at 20 degrees BTDC:
These are usually engines with compression ratios of 8.7:1 or higher. Gap spark
plugs fired by the CDI to .026"-.035".

George
 
Gap to the low side so it can wear to the high side. An oversize gap will stress the coils.
 
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