Plugs for 186 heads / H.E.I. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Dan-K · 03-20-2021, 12:04 PM

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 .

68Gold/white · 03-20-2021, 01:23 PM

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..

**Louisvillekytruck** · 03-20-2021, 02:25 PM

r45ts

**Louisvillekytruck** · 03-20-2021, 02:30 PM

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

Dan-K · 03-20-2021, 02:48 PM

I suspected that but I wanted someone else to confirm my thoughts . Thanks , Dan.

Mike C · 03-20-2021, 07:02 PM

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.

Dan-K · 03-21-2021, 02:10 PM

How would I tell the difference ? I am not sure exactly what to look for .

**Getter-Done** · 03-21-2021, 02:55 PM

Quote:

Originally Posted by Dan-K

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
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Tapered seat
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.

Dan-K · 03-21-2021, 04:37 PM

O.K. Thanks .

toolboxchev · 03-21-2021, 07:00 PM

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.

**dmjlambert** · 03-21-2021, 07:01 PM

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

Tomchev · 03-23-2021, 10:18 PM

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

03-20-2021, 12:04 PM	#1
Dan-K Registered User Join Date: Aug 2009 Location: Ft.Collins, Co. Posts: 104	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 .

03-20-2021, 01:23 PM	#2
68Gold/white Registered User Join Date: Sep 2011 Location: Ark City, Kansas Posts: 3,405	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..

03-20-2021, 02:25 PM	#3
Louisvillekytruck Senior Member Join Date: Jun 2019 Location: Louisville ky Posts: 1,109	Re: Plugs for 186 heads / H.E.I. r45ts

03-20-2021, 02:30 PM	#4
Louisvillekytruck Senior Member Join Date: Jun 2019 Location: Louisville ky Posts: 1,109	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

03-20-2021, 02:48 PM	#5
Dan-K Registered User Join Date: Aug 2009 Location: Ft.Collins, Co. Posts: 104	Re: Plugs for 186 heads / H.E.I. I suspected that but I wanted someone else to confirm my thoughts . Thanks , Dan.

03-20-2021, 07:02 PM	#6
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,727	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. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

03-21-2021, 02:10 PM	#7
Dan-K Registered User Join Date: Aug 2009 Location: Ft.Collins, Co. Posts: 104	Re: Plugs for 186 heads / H.E.I. How would I tell the difference ? I am not sure exactly what to look for .

03-21-2021, 04:37 PM	#9
Dan-K Registered User Join Date: Aug 2009 Location: Ft.Collins, Co. Posts: 104	Re: Plugs for 186 heads / H.E.I. O.K. Thanks .

03-21-2021, 07:00 PM	#10
toolboxchev Registered User Join Date: Jul 2015 Location: 2nd left past the stump on a dirt road. Posts: 2,629	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.

03-21-2021, 07:01 PM	#11
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,859	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

03-23-2021, 10:18 PM	#12
Tomchev Registered User Join Date: Jan 2016 Location: Forest City NC Posts: 30	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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