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I need some quick help, I’m in the middle of changing the spark plugs on my 1974 454 and I have a question about the correct spark plug. In the service manual it recommended the R44T, but when I pulled the plugs they were R45TS. They appear to be the original plugs or close to it (made in USA). So I picked up a new set of AC Delco R45TS plugs from the store and they are way longer (see picture from top to bottom - R45TS plug I pulled, new R45TS, R44T)
. What plugs am I supposed to be using? What is the deal with the difference between the two plugs with the same part number? Any help you could provide would be greatly appreciated. Thanks!
You should have taper seat plugs. The 44 and 45 are heat range. The T and TS are for extended reach tip. Unless you have dome pistons it won’t matter except one reaches deeper into combustion chamber. The extra length is in the upper end which won’t matter unless you have headers. What was the color/burn pattern of the ones you took out?
Last edited by Vette5311; Apr 3, 2021 at 05:54 PM.
You've got them aligned by the porcelain to hex joint; instead align the taper just to the right of the threads and compare the length of the threaded portion and tip/strap. That's what's important in this comparison. The length of the porcelain won't affect anything other than how close to the engine the spark plug boot sits.
'72 454s are spec'd to use R44T
Last edited by barkingrats; Apr 3, 2021 at 06:29 PM.
Thanks! So one of the previous owners must’ve purposely selected the R45TS plugs. Here is a picture of the taper comparison:
The R44T is on the top, and it looks like the taper is comparable but the length to the tip is different. So I should be fine to use the R44Ts right? I’m concerned that ACDelco today doesn’t equal ACDelco from yesteryear (from a specs perspective). The R45TS plugs I bought are completely different from the ones I took out of the car.
44T is fine. 45TS is one step hotter and an extended tip (electrode). Either is ok if your engine does not have milled deck/heads or big dome pistons. Previous owner may have gone hotter and extended tip for any number of reasons.
The AC sparkplug catalog dated 1-74 indicates the correct plug to be R44T. The fact that your photo shows the plug you removed has a thick green ring at the top, means that this is a later replacement plug. Original plugs of this year would have 4 thin green rings. A photo in the catalog of the tapered seat plug shows the 4 thin ring configuration. As was said before, an extended tip ( "S" suffix) or a "5" heat range would be just fine. It must have a "T: suffix as this stands for tapered seat. You can't make a mistake since the standard plug just won't go in. Hope this helps.
Jeff
Run the TS or the NGK equivalent.....the extended tip is beneficial in the super large area at TDC that this engine has and the longer plug is better to keep the boots out of the way.......
Yes they were purposely installed and someone did their homework.....
1973 454 Spark Plug Help Needed
