The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 454 Medium Duty V-8

**Bob B.** · 02-16-2015, 09:52 PM

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.

02-16-2015, 09:52 PM	#7
Bob B. Senior Member Join Date: Aug 2005 Location: Los Angeles Posts: 1,308	Re: 454 Medium Duty V-8 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. __________________ 1967 GMC CM-2500 Camper Cruiser, 351E V-6, NP 435 4 speed, Dana 60, and factory A/C. 2012 GMC K-3500 WT regular cab, 6.0L Vortec, 6L90.