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Old 03-20-2021, 12:04 PM   #1
Dan-K
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Plugs for 186 heads / H.E.I.

Recently rebuilt my 350 . I put on a set of 186 heads and flat top pistons . I am running an H.E.I. . What would the recommended plugs be ? R45TS or do I need a plug that has the metal gasket ring ? My builder put in NGK BR6S plugs. I know that NGK makes good plugs but Just interested in others opinions .
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Old 03-20-2021, 01:23 PM   #2
68Gold/white
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Re: Plugs for 186 heads / H.E.I.

I don't know which type of plugs the 186 heads use. GM went to the tapered seat plugs in 72, in all brands of engines. An engine tha uses the flat washer has a sizeable flat area for the washer to seat on, it should be noticeable.
NGK and Autolite seem to be the best plugs these days. AC used to be in the mix, but most say not anymore. I know what the AC numbers are...not usre on other brands.

If your heads take washer plugs, cross the AC number R44 or R44s (extended tip version of R44) to Autolite of NGK. IF you need tapered seat plugs cross AC R44T or R44TS (extended tip version of R44T) to AUtolite or NGK

My 2 cents..
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Old 03-20-2021, 02:25 PM   #3
Louisvillekytruck
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Re: Plugs for 186 heads / H.E.I.

r45ts
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Old 03-20-2021, 02:30 PM   #4
Louisvillekytruck
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Re: Plugs for 186 heads / H.E.I.

R44t is a colder plug r45ts will make more power run motor for a few days and pull one plug out and look at it
U want it to be tan if its white its lean and needs more fuel if is black its fat has to much fuel
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Old 03-20-2021, 02:48 PM   #5
Dan-K
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Re: Plugs for 186 heads / H.E.I.

I suspected that but I wanted someone else to confirm my thoughts . Thanks , Dan.
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Old 03-20-2021, 07:02 PM   #6
Mike C
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Re: Plugs for 186 heads / H.E.I.

The 186 heads I have had used the washer seat plugs. But there may have been some crossover depending on what year they were made. Soyou need to look at the spark plug hole and see if it is machined flat for washers or taper seat plugs.
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Old 03-21-2021, 02:10 PM   #7
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Re: Plugs for 186 heads / H.E.I.

How would I tell the difference ? I am not sure exactly what to look for .
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Old 03-21-2021, 02:55 PM   #8
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Re: Plugs for 186 heads / H.E.I.

Quote:
Originally Posted by Dan-K View Post
How would I tell the difference ? I am not sure exactly what to look for .
Look at how it is machined.
Here is 2 pictures for example.

Washer
Name:  sp1.jpg
Views: 385
Size:  43.7 KB
Tapered seat
Name:  sp2.jpg
Views: 400
Size:  42.3 KB









.
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Old 03-21-2021, 04:37 PM   #9
Dan-K
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Re: Plugs for 186 heads / H.E.I.

O.K. Thanks .
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Old 03-21-2021, 07:00 PM   #10
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Re: Plugs for 186 heads / H.E.I.

Remember in the old days fuel was able to ignite easier due to the chemical nature of it.

R43 is what they use to use, then as emission standards went up they progress to the R45. R45 is a hotter plug so it will ignite the fuel mixture easier and burn off excess hydrocarbons. The HEI will act better with a hotter plug as this is what the engineers prescribed stock.

Problem with hotter plugs is they can cause detonation IMHO. Also factor in your compression ratio, I believe your 186 heads are the early higher compression heads? Correct?

Each engine will need to be tuned both at the carb and distributor curve. They all act differently with modified components.
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Old 03-21-2021, 07:01 PM   #11
dmjlambert
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Re: Plugs for 186 heads / H.E.I.

The holes in mine are not tapered and the conclusion from several members was I should use tapered plugs.
http://67-72chevytrucks.com/vboard/s...d.php?t=715320
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Old 03-23-2021, 10:18 PM   #12
Tomchev
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Re: Plugs for 186 heads / H.E.I.

The 186 heads were made in 69 and 70 they use gaskets plugs. 1971 heads used tapered seat plugs
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