454 Medium Duty V-8

[ClassicTVMan1981X]

How many of you here own a 1979-80 Chevrolet C70 or GMC C7000 with the rare, tall-deck 454 V-8 engine?

This engine was not used in the mediums from 1981 to 1998, but it would return for 1999 as the "Vortec 7400 MD" to replace the ubiquitous 366 and 427 big block V-8s in the then-current C and T series. In 2002, it was replaced by the Vortec 8100 MD engine, which lasted through the early part of the 2010 model year.

~Ben

[KQQL IT]

Never seen one. Always the 427 or 366, didn't think a 454 TD was factory

[KQQL IT]

10134366 is the casting #.
Learn something new everyday

[special-K]

I went and looked at a guys stuff one day and he had a thing for those 454TDs, I guess. I didn't think anything of it, but he had a few trucks of this era they all had 454s. I was more interested in earlier stuff and didn't know a truck 454 was anything uncommon or I would have paid more attention

[DirtyLarry]

I don’t remember ever hearing of a tall deck 454 either. 366 and 427 always come to mind when thinking of tall decks. Learn something new every day!

The later Vortec 7.4L in the medium duty was an L21 while the L29 Vortec 454 was used in everything else. I don't recall the L29 being used in the medium duty and I don’t recall the L21 being a tall deck either, but I could very well be wrong as I've only seen one loose L21 ever. It was an odd engine as it had coil on plug and an electronic throttle body. It was found in RV stripped chassis and medium duty trucks. Many people confuse these engines for 8.1L’s because of the coil packs.

[ClassicTVMan1981X]

Something tells me that when the 454 tall-deck engine showed up for the mediums in 1979, the timing of its introduction couldn't have been worse, because of that year's fuel crisis, which I believe is why the 454 MD did not return for '81.

~Ben

[Bob B.]

I don't think the L21's were tall deck, though all the 8.1's were. Of course, the '79-'80 would have been a Mark IV, the '99 a Mark VI.

Never sure why the 454 was released as a medium duty engine for '79-'80. H.P./torque was only slightly better than the 427, fuel economy was about the same. I am thinking it was either because of emissions or GM was moving to eliminate the 427. The 427 was not available in California certain years in the early 80's.

[DirtyLarry]

Originally Posted by Bob B.

I don't think the L21's were tall deck, though all the 8.1's were. Of course, the '79-'80 would have been a Mark IV, the '99 a Mark VI. .

I’m privy to a lot of things 8.1L related and never known it to be a tall deck. I’m going to have to disagree on that one.

[Bob B.]

Originally Posted by DirtyLarry

I’m privy to a lot of things 8.1L related and never known it to be a tall deck. I’m going to have to disagree on that one.

That's what I was told some years ago, but I never measured one. The story was GM went with a tall block casting to be able to increase the stroke over a 7.4L and not have rod angularity problems. The 8.1L does not have a 4 ring piston like a tall deck Mark IV but does have a .25" longer rod.

Now I am confused!

[ClassicTVMan1981X]

Originally Posted by KQQL IT

10134366 is the casting #.
Learn something new everyday

Sorry to re-open this thread, but besides this part number you mention, there was also one that said 14044807, which may or may not have applied to the 1999-2001 7400MD "Vortec" version. Both variations also have a forged steel crankshaft to distinguish them from the lighter-duty 454s in the pickup trucks.

~Ben

[LT7A]

No need to apologize. New info is good info.

[Old_Green]

I had done a bunch of investigating on 427 Tall deck blocks when I purchased a 427TD out of a 1972 C50 (casting# 374776). I had known about the 427 and 366 engines for some time, and when I started looking into the engine I had, I talked to the local Chevrolet dealer parts guy. He said there wasn't a stock production 454 tall deck, but that Chevrolet performance has 454 tall deck aftermarket crate engines available. These are "Bowtie" engines and are sold for racing only. They were not used in stock production vehicles. They have a bowtie cast into the side of the block as additional identification.

Because of that, I started looking into the history, and checked as many sources of casting information as I could find, and so far, all of them show the same information. There were only three 454 tall deck casting numbers. All three are "Bowtie" performance engines.

Casting # Desc.
10134366 Bowtie, Gen.V, Tall deck
14044807 Bowtie, MkIV, CNC prep, Tall deck
24502506 Bowtie, Gen.V, Race prep, 10.2 "tall" deck height

several links to casting information:
https://www.mortec.com/bbc.htm
https://www.chevyhardcore.com/news/r...sting-numbers/
https://macc.chevelles.net/bbcast.htm
https://chevygeek.com/chevy-block-ca...l-list-lookup/

I also came across an article from motortrend talking about the "Bowtie" motors.
https://www.motortrend.com/how-to/16...ugh-the-years/