AC Delco spark plug codes

englemac · May 18, 2001

My engine calls for an AC delco R43LTS. I went to a few parts stores and could only find the R43TS. What does the "L" mean and could not having it cause the engine to run rough and occasionally miss during idle at park?

Huck · May 18, 2001

The L stands for "long". The threaded portion is about 5/8", rather than about 3/8", if I recall correctly. Needed these for my Vortec heads to get the nose out of the plug thread area and into the chamber. You don't want the short ones, if your heads need the long ones - the exposed threads in the heads will cause hot spots that lead to detonation. The thread length on the plug should match the thread length in the hole. The LTS's are out there - but they're a little harder to locate (and most parts stores have either no info, or no interest in helping you sort out the nomenclature). If you need LTS's, you really don't want to use TS's.

ilbl8 · May 18, 2001

go to this web page. AC Delco has posted there plug marking's for you to decode.
but here is a decode for you.

R - Resistor

4- 14mm thread

3- heat range

LT - Long reach, .715" (18.16 mm), Tapered Seat

T - Tapered Seat Shell Design

TS - Tapered seat with extended tip

LTS is a long reach tapered seat plug with a extended tip.

TS it a tapered seat plug with a extended tip.

you need the LTS as the TS plug will be too short. here is the link to the plug marking's. and the link to the AC Deloc home page. you can cross your plug over useing there on line catalog too.
http://www.acdelco.com/parts/sp_ident_set.htm

http://www.acdelco.com/

hope this help's ya out buddy!

edit,

huck you dog, ya beat me! i guess i should have just not decoded the plug's for him!!! oh huck a 1/2", there is no 5/8th's, thread is marked like this-R23LS or R53LS.

2- 1/2" tapered seat

5- 1/2" gasket type

[This message has been edited by ilbl8 (edited 05-18-2001).]

Huck · May 18, 2001

They oughta be able to order them for you, at the very least, if you give them the number you've got.

englemac · May 19, 2001

Well, that was a major part of my problems. I did manage to track down some R44LTS vs. the 43s at a dealership. I guess the longer plug does make a difference! They told me for these Vortec heads, the shorter plugs arc over to the inside of the threads of the plug hole, and not over the gap of the plug - that was causing a lot of the roughness in the running. Thanks again!

Bow_Tied · Jan 11, 2011

ilbl8 said:
go to this web page. AC Delco has posted there plug marking's for you to decode.
but here is a decode for you.

R - Resistor

4- 14mm thread

3- heat range

LT - Long reach, .715" (18.16 mm), Tapered Seat

T - Tapered Seat Shell Design

TS - Tapered seat with extended tip

LTS is a long reach tapered seat plug with a extended tip.

TS it a tapered seat plug with a extended tip.

you need the LTS as the TS plug will be too short. here is the link to the plug marking's. and the link to the AC Deloc home page. you can cross your plug over useing there on line catalog too.
http://www.acdelco.com/parts/sp_ident_set.htm

http://www.acdelco.com/

hope this help's ya out buddy!

edit,

huck you dog, ya beat me! i guess i should have just not decoded the plug's for him!!! oh huck a 1/2", there is no 5/8th's, thread is marked like this-R23LS or R53LS.

2- 1/2" tapered seat

5- 1/2" gasket type

[This message has been edited by ilbl8 (edited 05-18-2001).]

Updating an old thread for the new AC Delco plug link:
http://www.acdelco.com/parts/spark-plugs/identification.jsp

AC Delco spark plug codes

englemac

Huck

ilbl8

Huck

englemac

Bow_Tied

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