*Theory* on big block engine casting LL - RL - RS

[SuperFlyTNT]

Note to admin: if this is not the correct subforum, please relocate this post to the appropriate forum. Thanks

Yesterday someone asked me if I knew what the cast LL stood for on his 383. Nit being exactly sure what it meant, I started looking around - including this site - and based on data available on the interwebs I came up with a theory. I also posted this on FBBO (I copied below text from a post on fb I made earlier as a response to a that question):

I am not 100% sure, BUT, the 383 and 426w/Hemi shared the same standard bore size, with the 383 being a Low deck and the 426 engines a Raised deck. On the Raised deck 426 blocks an 'RL' is often cast in at the foundry. It could be to distinguish casting molds between the Low and Raised deck engines sharing the same bore. Also, the 'LL' was already found on the first 383s from the late 50s Coincidentally a Raised version of the 383 [2120329] was also available in 1959-60 with a small bore of 4.03" and 3.75" stroke. These Raised 383s used casting RS. My guess is that the first letter designates the engine platform Low Deck or Raised Deck. The second letter could designate bore size and to be able to distinguish between molds, either Small (S) or Large (L). Small bore would be the 4.03" and I have only seen it on the RB 383. The large bore would be 4.25", which was the largest bore at the time. However, 413 blocks with casting 2468030 and bore size 4.1875" (in between 4.03" and 4.25") also had RL and it could be that these blocks have the cylinder wall thickness of a 426, but only bored to 4.1875". These blocks would have relatively thicker cylinder walls.

To add to the last item about the 413s; I know that back in the mid 60s some 413s and 426w blocks were cast with only 2468 cast in, but with RL. If 361 blocks also had LL, the cylinder wall thickness also might allow boring to 4.25", but sonic testing would give a definitive answer. *Edit* Initially I did not check the combination LS, but apparently the LS was cast on early 361 blocks (#1944959), probably using molds from the smaller bore 350 (#1944929). According to my theory this would correspond to Low deck, Small bore. Compared to the 383 available at the time (late 50s) that is exactly what the 361 was.

When the 440 was introduced, it replaced the 426w passenger car engine as the only RB wedge in the engine lineup and designation for both the Raised deck as well as bore size was no longer required (413s were still used for Industrial applications with a different casting). On the 383 it was also phased out at some point (probably after the 361 passenger car engine was discontinued), as I have seen blocks without LL.

Anyway, what I would like to find out is if the earlier 413 blocks from 1959 onwards had RL cast in or not.

What's everyone's thoughts on this?

 

[CBODY67]

Here's a few additional thoughts related to castings. In the case of the 413s, the cyl wall thickness might have been thicker on those blocks as they were used in the medium and heavy-duty truck lines, too, where additional block integrity might have been an issue. I somewhat doubt that the same wall thickness would have allowed Chry to use the same cast-bore blocks to make the larger-bore engines. Reason? The as-cast bore needs to be close to the machined-bore bore size. Less materials used in the final item and decreased boring time, too. In the replacement market (as in Direct Connection and similar), the cost to machine the larger-bore size would be the customers to use as they might desire, in the purchase of an "as-cast" thick wall block. Similar with taking a 413 casting to a larger-than-stock bore size . . . the customer pays to do that.

Any information on the 400s? How might they fit into your theory? Just curious.

Consider, too, that cyl bore increases of a significant magnitude need to be done in increments. Which means "time" to make that happen, plus re-dressing the cutting bits on the boring bars a few times, too.

Obviously, at the engine plants, when the cores were laid out prior to the actual casting process, there would be a seperate line for each bore size, with the deck height also being in the mix somewhere. Having a cast-in designation would certainly serve as a valid ID of what was going on, in the possisble addition of a more-visual paint daub or stripe. Which would also relate to how the machines were set-up on the machining line (already set-up for bore size) as to deck height. Batches of "the same" would be run, too, rather than being "mixed", I suspect.

I'll admit that I'm not a student of block casting numbers as much as others might be, just adding how some things at the engine plants might happen "on the line", from what I know.

Enjoy!
CBODY67

 

[413]

Here is a 383 RB engine.

 

[SuperFlyTNT]

@CBODY67; thanks for your input. Both 361s and 413s were used in heavy duty applications, so it may be possible for both of them to be cast using molds that would yield a bigger cylinder wall, using the 383 B and 426w RB molds as a basis with the bore molds for the 361 and 413. This would yield a block with a different geometry, hence the requirement for a different casting number that in most cases also happened to be not too far off from the 383 and 426w casting number. However, that could just be coincidence, as the casting numbers could also have just been administratively assigned without any logic in the numbering.

Anyway, looking at the casting letters used (LS, LL, RS and RL) and the engines available at the time, I am assuming that these letters were used to differentiate between engines with

A) similar bore size, but different stroke
B) different bore size for the same stroke
C) Low deck and the then new Raised deck blocks

A: Both 383B and 426w RB, the biggest displacement engines for Low deck (L) and Raised deck (R), share the 4.25" bore (L), so that could be the reason that LL is found on 383Bs and RL on 426w RBs and also 426 Hemi blocks. However, since the 413 was the first RB to be produced parallel to the 383B, I expect the RL was designated for the 413 at first and carried over to the 426w in the parts of the molds that were used on both 413 and 426 as they share a global external geometry.

B: the 361B qualitatively had a smaller bore than the 383B and was the only other Low deck engine available after production of the 350B was discontinued and could have received the LS (Low deck, small bore). There is even a picture of a 361 block on the 440Source website sporting the LS letters. The 383RB for a short time was the only other RB available next to the 413. The 383RB may have been the reason for these letters to be in existence at all since each engine has a unique casting number anyway, just to separate the 383B from the 383RB at the foundry?

As said in my earlier post; at some point the 440 was available as the only passenger car RB wedge after 1966, so apparently no designation at the foundry other than the casting number was required to identify the 440. The same I expect for the 400. I have seen 383 blocks from 1970/71 already without the LL. At the time the 383 was the only available Low deck engine available and the 400 took over from model year 1971 as the only Low deck engine.

Interesting stuff and probably nothing more than a piece of trivial information and maybe only Quality Control related, if correct. But, I like trivial information

 

[SuperFlyTNT]

Here is a 383 RB engine.

View attachment 509460

Thanks! That is the same casting number and RS as on the blue block in my original post.

Here is the picture from 440Source:

picture courtesy of 440Source.com

Casting 2205712 L S (361, Low deck Small bore according to my theory)

 

[LocuMob]

Here's a '59 350B

 

[300rag]

My '65 413. When I had it rebuilt, I was told they couldn't bore it out to a 426...

 

[commando1]

Before this gets mired down in creamy peanut butter....
What exactly are you trying do?

 

[SuperFlyTNT]

My '65 413. When I had it rebuilt, I was told they couldn't bore it out to a 426...

View attachment 509472

Thanks @300rag ; I know it is risky to make any sort of statement and/or assumption about cylinder wall thickness without actual sonic checking a particular block. I read back on the theory I posted in my original post and have to revise the piece about 413s that "...would have relatively thicker cylinder walls." Sonic checking is the only sure way to verify overbore capacity and I believe that it is highly likely that the RL has nothing to do with it. I will explain why I think that in the next post as a reaction to @commando1 's very valid question.

 

[SuperFlyTNT]

Before this gets mired down in creamy peanut butter....
What exactly are you trying do?

@commando1 ; what I want to achieve is to have a better understanding of the history surrounding the casting process of the big blocks and how those letters relate to it. And after the someteenth time I was asked the question what the LL means on 2468130 383 blocks, I started digging. I hope through this forum that I can get more insight in how the letters LS, LL, RS and RL were applied (these seem to be the only letter combinations used in the area below the casting number) by seeing pictures of other blocks that could either support or dismiss my theory.

Looking at the information I looked up and the responses I received since posting my initial theory, I can summarize it as follows:

- LS could stand for Low deck, Small bore
- LL could stand for Low deck, Large bore
- RS could stand for Raised deck, Small bore
- RL could stand for Raised deck, Large bore
- Any bore reference would be purely qualitatively, as there is no correlation to the available bore sizes when these letters were first used.
- Both Low deck and Raised deck big blocks were new at the end of the 50s and already in development since 1955.
- Since there were at least two different Low deck blocks and 2 different Raised blocks under consideration at some point, the letters may have been introduced as an administrative tool during design & engineering to be able to distinguish between all the new blocks, without people having to memorize the new casting numbers (this is an assumption). This was subsequently carried over to the foundry.
- Looking at the 1944929 350 block picture from @LocuMob , the LS letters were already used as early as 1959 (it is stated in the relevant post that the block is from 1959).
- The LL found on Low deck 383s may have already been assigned to this block during the design & engineering phase. This may have been the same for the LS on 350s, which could have been carried over to the 361 when the decision was made to discontinue production of the 350. Therefore I suspect to only see LS on the 361 blocks and not LL, as seen in the picture from 440Source. LL would be reserved for the Low deck 383, which still had to be introduced in 1959, one year after the introduction of the 350 and 361.
- There are stories that the 383RB was introduced as a 'mitigation' to keep up with demand for 383 engines, while the demand for the 413 was quite low. If my theory holds truth, then it could also be that the letters RS and RL were not used until the decision was made to start production of a 383RB, which is suggested to be unexpected. It will be difficult, if not impossible, to track down when this decision was made and if any 413s were already produced. However, if there were any 413s from 1959 out there without RL cast below the casting number, then this may point towards the assumption that 413s were already produced before the 383RB. As the only Raised deck engine up to that point, no RL designation would have been needed at the foundry
- The letters may have served a purpose in the first few years of big block production, but I suspect that at some point the letters were just a remnant from an administrative purpose they once served.
- The letters LL remained on 2468130 blocks for quite a while, even long after the 361 was no longer offered as a passenger car engine and the 2468130 383 was the only Low deck engine available for passenger cars
- The letters RL remained on the 413 blocks for some reason and was also carried over to the 426wedge and 426 Hemi as well. In any case, the fact that the same letters were used on RBs with different bore size, does not correlate to cylinder wall thickness being bigger for the 413 than for the 426. Sonic check your block if you want to be sure.
- It may or may not have anything to do with the fact that the 2468130 383 and 2468330 426H shared the same bore size throughout the production of the 426H, but perhaps there is a correlation with the moment that the decision was taken to stop production of the 426 Hemi (the only engine to have the same bore as the 383 from 1967 onwards) and the fact that LL disappeared from 383s at some point. I have seen 383s from 1969 with LL and I have seen pictures of 383s without LL and I suspect the latter ones to be from 70 and/or 71 (this would need to be confirmed)

The fact that no factual information can be found (at least not by me) regarding these letters could mean one of two things:

1. They actually do not mean anything, or anything important
2. Nobody knows what they actually mean, or the person that does has not come forward yet.

I am leaning towards number 2 The letters LS, LL, RS and RL are most likely just as trivial as the casting numbers, but the fact remains that they were cast and in such large quantities to be considered as having no purpose, in my opinion.

 

[commando1]

what I want to achieve is to have a better understanding of the history surrounding the casting process of the big blocks and how those letters relate to it. And after the someteenth time I was asked the question what the LL means on 2468130 383 blocks, I started digging. I hope through this forum that I can get more insight in how the letters LS, LL, RS and RL were applied (these seem to be the only letter combinations used in the area below the casting number) by seeing pictures of other blocks that could either support or dismiss my theory.