Need some advice: Application is a 1970 LT1 ----- The owners manual specifies ACR43 or 44 --- the plugs currently in the car is ACR43 ---- the Auto Zone data base shows ACR43S

Please HELP !!!!!!!!!! Thank you!

Note: the engine runs great with the current plugs ACR43.

 

If the engine is running great, I wouldn't make a change. As they say, if it ain't broke, don't fix it!

 

Caution on using the "S" extended tip on a '70 LT-1. If the engine is still configured with the stock 11:1 pistons, you would be at risk of the piston contacting the tip of the plug.

Many parts suppliers list the "S" style for the '70 LT-1, this is incorrect and can cause damage to your engine.

As a note, a 43 heat range is really too cold for street driving. In AC, I believe the 44's are no longer made, not sure about the 45"s.

The last set of AC plugs I purchased a few years ago were dreadful. The quality of manufacture was the worst I had ever seen on a plug.
I used them for a short while, they never worked very well.

A few years ago I purchased a set of NGK BR6S, Stock number 1294.
These plugs are the direct replacements for AC R44/45

The NGK plugs look and work great and I'm very pleased with them.
GM has been using NGK plugs in new cars for many years now.

Barry

 

The correct style of plug should be with a gasket or sometimes called washer for the plugs. The 45T plug is a tapered seat plug and will not seat correctly in the cylinder head for a 1970 LT1 engine.

Others have already addressed the correct heat range.

 

Two thumbs up for the NGK I will never buy any other.
They are worth the extra money.

 

Sorry to hijack your thread , but im having the same problem ! Im tring to find sum desent plugs also but i have gmpp bowtie heads and they call for a plug with a 3/8 reach or .3750 . I also like the ngk plugs but when i do a search on my model year the ngk # 2869 plug has a .460 reach which is longer .Is it ok to run a longer plug in my aplication ?

 

Hello,
I copied the following information from the AC Delco Spark Plug web site. http://www.acdelco.com/parts/sparkpl...tification.jsp

The S designation is for an extended tip. The T designation is for a tapered seat. You can find the numbering system and the meaning of the letters and numbers from the informaiton below.
kdf




Prefix and suffix letters are used to identify a specific type plus the numbers relate to thread size and heat range. For example, the R45TS spark plug shown is:

R = Resistor
4 = 14 mm Thread
5 = Heat Range
T = Taper Seat
S = Extended Tip

Numbering
1st number denotes THREAD SIZE
2nd number denotes HEAT RANGE

Plug Identification Table Suffix Identification Code Description
A = Cap Gap
C = Copper Core Center Electrode
C = Colder Version of M44 Plub
E = Special Design Electrode Extended Tip
F = 1/2" (12.7 mm) reach
FF = 1/2" (12.7 mm) reach, fully threaded
G = Pin Gap (cold-running)
I = Iridium Center Electrode
J = Boot Release Agent, Anti-Seize Compound
K = Special Design
L = Long Reach
7/16" = (11.1 mm) reach, (14 mm) thread
3/4" = (19 mm) reach, (18 mm) thread
3/4" = (19 mm) reach, (14 mm) thread (fineline)
LT = Long reach, .715" (18.16 mm), Tapered Seat
M = Special Design Electrode
N 3/4" (19 mm) reach, 3/8" (9.5 mm) thread length
R = Resistor (Sport Vehicle Plugs)
S = Extended Tip
S = 7/8" (22.3 mm) Moderate Long Reach
23/32" (18.25 mm)
T = Tapered Seat Shell Design
TS = Tapered Seat with extended tip
XL = Extra Long Reach, 3/4" (19 mm) fully threaded
Y = 3-Prong Cloverleaf Electrode
Z = Special Gap (usually denotes wide gap)
5 = .050" (1.3 mm) gap
6 = .060" (1.5 mm) gap
8 = .080" (2 mm) gap
100 = Iridium
600 = Resistor Type
800 = Platinum Type
900 = Double Platinum Type



Suffixes are combined to form such AC suffix designations as FG, XLS, TS, FFM, TSX, SZ, etc.

 

The AC43R you are runung is the correct plug.
DO NOT USE A EXTENDED TIP IN YOUR LT1!!!!!!!!!!!!!