HI... long time listener... first time caller...
I just stumbled onto this site, and I hope someone in here can help me out.
I am the owner of an original 73 LS4 t-top, bought from the estate of the 2nd owner over 20 years ago. I rebuilt the engine in 1997, and before I bought it nothing had been done under the hood.
The motor is a 3999289 correct numbers matching block, suffix code cwm,
cast K-72 (11/72). The vin shows it is an early production big block. It is an original 4 bolt main block, with HP cast on the right side, and all the correct oil line plugs above the filter boss. It is not a 2 bolt simply re-drilled to be a 4 bolt main. Alan Colvin states in 'Chevrolet by the Numbers' that "several 4 bolt LS4's have been found, but they seem to be an exception".
The people at Mortec knew of 30 or so LS4 race blocks that went out in early production orders, in 4 different GM models because the production LS4's weren't ready in time. This is all I can come up with.
I have been trying to get to the bottom of this for over 6 years now and no one seems to have any answers. I've even been in touch with the NCRS '73/74 judges, and until this, they had never heard of this, and still haven't seen one at an event. Now they're looking.
What I am hoping for is this... has anyone in this forum ever heard of this... or seen one... or owned one... anything. I'm tired of getting blown off by Vette Mag and the lame problems they do tackle in Q&A.
Anything anyone knows will be appreciated.
Thanks, I hope this isn't too windy...
Wedge

 

Hello Wedge, I too have looked in on this Forum and decided I would join, It seems to be nice. I also have a 73 LS4, 4spd that is about 98% correct, It has 30K on the speedo and I bought the car off my Father in 1989 and have had it since, he bought it in 1980.
Getting back to your question on your engine, did you look for a PERF stamp on the block? I believe it's on the drivers side near the rear of the block, this could be what your searching for. I have my car currently under cover & up on stands for some fluid change outs in the differential & Trans that I have been putting off, I researched my Vin number a few years back and found that my car was built in Sept. of 1972. my Vin is 1Z37Z3S404398, when I get time & if your interested I'll get the number off the block passenger side forward of the valve cover.

Glenn

 

Glen
Thanks for the quick reply. My vin is 407782, so mine left the factory after yours.
The only other external cast on mine, aside from the date code and casting number located at the rear of the block above the bell housing boss is the HP cast on the right side below the head. All 4 bolt main blocks can be identified by the three exterior holes above the oil filter boss. 2 bolt blocks have a 5/16" front hole that does not go into the oil galley, the center is a 3/8" npt (pipe thread) into the galley, and the third is a 1/2" coarse thread that is not drilled into the galley. The 4 bolt has a 3/8" into the galley in front, a 1/2" npt through the top of the galley in the center, and a 1/2" coarse that is not drilled into the galley in the rear. Of course the most reliable way is to pull the oil pan and count.
Mortec listed a perf block, but I seem to remember it as a replacement block that originally was intended to be used in trucks. I hope this doesn't sound too stuffy, and I am by no means an expert. Alan Colvins book has all this info listed, pp69 and 76. People always quote production numbers, but nobody seems to know about this. If you are at all interested, check the oil boss, or count the bolts in the caps and get back to me if you can.
Thanks again for the reply,
Wedge

 

Wedge, Thanks for the reply, the holes on the oil filter boss you ar referring to, can they be seen without removing the oil fiter ? or are they inside the the "o" ring sealing surface of the oil filter boss ? I will be getting around to changing the oil & filter soon so I will check this out and get back to you.

Thanks, Glenn

 

They are right above the filter on the side of the block, you'll be able to see them easily. They were there for external hook ups to coolers...etc. No need to remove the filter. Let me know what you find.
Wedge

 

Wedge, getting back to you on this Mortec question, I was able to get a photo, the best I could do laying on my back. It does have the three drilled and tapped holes, all are different sizes, and the Hi Perf raised casting is visible. I looked for some casting numbers & here are the ones I could read ; 135404398, the 5 could have been an S, also 10827CWM, these were on the block cylinder head deck on the passenger side front of block, also at the rear of the block forward the bell housing is CM9T, there are some more numbers back there but I need to clean them off to make them more legible.
Let me know if I'm one of the lucky ones to have a Mortec LS4.

Glenn


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Glen
Heres what I could find out about your car. 10827CWM is actually T0827CWM, when the block was stamped. T= Tonawanda, 08=August, 27=Day of month. 13s404398 is the vin corresponder to the actual vehicle ID, which probably is 1z37z3s404398.
At the rear of the block on the drivers side is where you found GM9T, below that (further left) you should see 3999289, the block casting number. On the other side you will find a cast code that will indicate when the block was cast. A= Jan, B= Feb etc. The next number is date, and last number (probably a 2) is year, for 1972.
The oil line holes... best way to identify is... little or big. 2 bolts have a small-medium-small configuration. 4 bolts have a large-larger-small. These are front to back of engine. The only reason for the difference was for external coolers in racing applications.
This is my 4th big block in Vettes. I've had an LS5, an LS6 and another LS4. Both the LS4 and LS5 were 2 bolt mains, and the LS6 was a 4 bolt. Any 2 bolt can be made into a 4 bolt by drilling the block and installing the caps. But the oil holes would have been hard to do, and most shops left them alone.
MorTec is an information site located at MorTec.com. Look them up... great site. I don't believe they made or make blocks, but these guys know EVERYTHING about Chevy engines.
Hope this helps.
Gregg

 

Glen... pardon my windy-ness... just found the photos. Sorry... new to attachments. I believe yours is indeed a 2 bolt block. The picture is identical to the photo on pg. 70, fig 3-5 in Alan Colvins '1970-1975 Chevrolet by the Numbers'. It is a monster book, with every number for every part on your car. A handbook for all restorers.
Still... the best way to make sure is to pull the pan. Let me know what you find.

Any other LS4 owners out there wanna help to solve this mystery?
Thanks...
Gregg