Dave Vincec

Hi all,


Woe and confusion here..


I read somewhere that post 1970 big blocks take tapered plugs... so i bought a set of Autolite 145's for my 454, which is wearing a set of '72 LS6 open chamber rectanguar port heads.


I pulled a plug last night... to find a) the plug isnt tapered... and b) it's a .690 inch plug; vs the .460 plug that i bought.


Question is... have i bought the wrong plug... or does it have the wrong plug in it?


Many thanks for thoughts.


David

MelWff

1. It appears based on your description by year the wrong plug is currently in the engine.
2. Can you see the spark plug seat in the head and confirm it is tapered versus flat.
3. How did you end up with Autolite 145 as the correct plug. The Autolite site and vendor sites do not list that number for a 72 454.
http://www.jegs.com/webapp/wcs/store...ear=4294829731

gbvette62

I think the original plugs were either AC Delco R43's or R44's, with R45, R43S, R44S and R45S also recommended, depending on usage (city, highway, etc). None of these are tapered plugs, that I know of.

The current replacement conventional plugs, recommended by Delco are CR43TS & R43XL, and the platinum equivalent is the 41-803. Delco has various other 44 and 45 heat range plugs available too.

A quick look at Autolite's website, shows that their 24 & 25 plugs, are the replacements for R43TS, and AP24 & AP25 as the platinum replacements.

Dave Vincec

Bought over the counter from someone who told me they'd be fine in a 454...


I've just looked - and yes - they will be fine in a 454 - even a '72 one... as long as it's a truck or a bus; either of which presumably have a peanut port head...


so.. in conclusion - probably both sets are wrong... will try to confirm by inspecting the seat when i get home.

jeffstuarts

1972 engines. both small and big block, used an R44T plug which is a tapered seat plug (no gasket). The 1971 LS6 engine used used an R44XL which is not tapered seat, is 3/4" reach and fully threaded. This is the listing from the 1974 AC Spark Plug catalog. The 1970 listing for LS6 is R43XL.
Jeff

MelWff

The Autolite 145 is a retracted tip plug, the ceramic is further in the metal shell of the plug. The 26 is an extended tip plug and would be the equivalent of an AC Delco R44TS or R45TS which would be the correct plugs.

Dave Vincec

The plug in it is fully threaded and about 3/4 inch, at a guess.. markings illegible though as the plugs are god knows how old..

Dave Vincec

Casting and date below; if it makes a diff..

MelWff

I thought you were going to look at the spark plug seat to see if it is tapered or flat? The head casting calls for the Autolite 26 plug or the AC Delco R45TS

Dave Vincec

I was.. but didn't get a chance yesterday; and realised the casting pix on my phone already...

Thanks for that... is there an online reference by casting number that you can share so as to save me getting into a pickle on this stuff in future?

Btw... I'm running hei.... thoughts as to whether the oem plug is still the best option?
(Actually - I've just looked up the plug and it's original fitment - it went into loads of hei equipped cars so that isn't a question now....)

But. What is a question is compression.. this plug was used in low compression applications, and I saw a debate suggesting that it would promote detonation in higher compression motors.. my motor 'just about' runs on premium pump fuel.. but diesels badly on regular... was told when I bought it that it was about 10.25 compression but don't know that for a fact a small I havnt had it apart... do any other plugs have comparable fitment but are more suited to higher compression?

MelWff

the only thing that would change with higher compression is the heat range of the plug. Even with that it may vary with the kind of driving you do as to whether a colder plug can be tolerated without fouling. In AC Delco with a high compression engine and driving that does not involve a lot of stop and go I would go with the R44TS which would be in Autolite a 25.