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ACDelco R46SZ vs. R47SX spark plugs (Eldo 1979)

Started by T.Skytte, February 02, 2017, 08:25:24 AM

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T.Skytte

February 02, 2017, 08:25:24 AM
Hi,

5.7L EFI

I managed to order some ACDelco R46SZ plugs and now I just noticed in the service manual it says to use R47SX.

So I found this to help decode the numbers:
http://www.78ta.com/HTAF/index.php?topic=6782.0

It seems the difference is: 6 is slightly 'colder' than 7, and also X=Wide Gap vs. Z=Special Gap.

Would the difference matter much? And what is the exact difference between X/Z (if any)?
Apparently to use a colder plug makes sense if vehicle is under higher load/going faster more often.
I think I drive 50/50 highway/city.

Best,
TS
----------------------------
1979 Eldorado Biarritz

TJ Hopland

#1
February 02, 2017, 08:53:43 AM
A colder plug is safer to try than a hotter one.  The risk with a colder plug is it won't burn off deposits so it could end up with a short life.   A hotter plug will burn off crud but could end up being a hot spot in the cylinder which could then cause detonation / knock / ping.   Detonation can cause physical damage to the engine and by the time you can hear it its pretty bad. 
73 Eldo convert w/FiTech EFI, over 30 years of ownership and counting
Somewhat recently deceased daily drivers, 80 Eldo Diesel & 90 CDV
And other assorted stuff I keep buying for some reason

T.Skytte

#2
February 02, 2017, 09:07:51 AM
Quote from: TJ Hopland on February 02, 2017, 08:53:43 AM
A colder plug is safer to try than a hotter one.  The risk with a colder plug is it won't burn off deposits so it could end up with a short life.   A hotter plug will burn off crud but could end up being a hot spot in the cylinder which could then cause detonation / knock / ping.   Detonation can cause physical damage to the engine and by the time you can hear it its pretty bad.

Ok thanks, so I'll have an excuse to floor it once in a while  >:D >:D

"But honey, I have to accelerate fast to burn off deposits!"   ;D ;D

Best,
TS
----------------------------
1979 Eldorado Biarritz

TJ Hopland

#3
February 02, 2017, 09:39:45 AM
I don't know that I would try that excuse.   Both 'honey' and 'officer' don't tend to like excuses.       
73 Eldo convert w/FiTech EFI, over 30 years of ownership and counting
Somewhat recently deceased daily drivers, 80 Eldo Diesel & 90 CDV
And other assorted stuff I keep buying for some reason

bcroe

#4
February 02, 2017, 10:32:17 AM
I'd say if the car does some long expressway drives use the
cooler plug; otherwise use the hotter plug.  Gap, easily changed
if not correct.  My 79 Toro with 5.7L carbed engine managed 0-60
in 10 seconds.  The Eldo with a lower compression version of that
engine and a 2.2:1 final drive (instead of a 2.4) will be a bit slower. 
It can be pepped up quite a bit with a better exhaust system and
a 2.73:1 final drive.  Bruce Roe
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