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Old 11-09-2020, 06:45 PM   #1
Squally the Trolley's Avatar
Join Date: Apr 2019
Location: Everywhere
Posts: 17
Year: 1994
Chassis: GMC
Engine: 454 Big Larry
454 engine swap

After 2 years of building, Iíve slowly started to realize the 454 gas motor in my bus is on itís way out. I should have known, based on the 15-40 motor oil recommendation someone put on the oil fill, that the motor was a bit worked. There is at least one collapsed lifter and it smokes quite a bitÖ Sure, I could easily rebuild it. Probably for cheap. Crate motors are around $1,500. But the 454 gets around 6-8mpg and with the build out inside I feel like it could be more in the range of 5-7mpg.

My thought was if I could increase the mpg to 10-15 that i would save quite a lot of money on fuel. I am a drifter so I do travel quite a bit on my own, however as a photographer, sometimes my work involves traveling cross country. With the amount I drive, I figure I could save around $3,000 a year on fuel with an efficient diesel swap.

My question, what do people think is an ideal candidate for an engine swap? I have heard the 6.5l diesel is a good fit and could mate up to my trans which could make the process easier and cheaper. I feel confident I can do all the work myself. But would like help with brainstorming power plant options.

My budget would be the cost of rebuilding the 454 and around 4 years of fuel savings, which would be in the range of $12,000-14,000.

Thanks you for any insight you can share!!

- Stay Wild -
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Old 11-09-2020, 07:00 PM   #2
Bus Geek
Join Date: May 2009
Location: Columbus Ohio
Posts: 14,687
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
the 6.5 wont give you 10-15.. im not even sure they got that in a pickup truck..

to go diesel not only do you need to think about an engine that fits.. you have the supporting cast too..

what trans is in it? if the bus is a 94 id expect to see a 4L60E which means you need to control that electronic transmission separately sicne the engine computer will be gone.. can your transmission handle the high torque of a diesel engine?

that 454 likely had a top RPM of 4000-4500 so you'll need to examine rear gears .. a diesel typically redlines at 2500-2800 RPM and wont give you 10-15 MPG running there.. it would want to cruise noticeably lower RPM..

a diesel engine is going to be double or triple the weight of that 454.. depending on which engine you use.. can your front axle / suspension / hubs / springs handle it?

other supporting cast you'll need to think about is accesory drives (does the vus have power steering, A/C, etc?

what type of brakes? are there any vacuum operated accessories that wont operate with a diesel (no vacuum)

dashboard gauges - the engine ECM will be gone.. are your gauges tied to the computer or separate?

physical room for your engine of choice?

all thigs to think about which can add cost and effort to the swap.
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Old 11-09-2020, 07:39 PM   #3
Bus Nut
BeNimble's Avatar
Join Date: Jul 2020
Location: Sacramento
Posts: 797
Year: 1999
Swap in a 350 with a turbo if you want better mpg, actually let me edit and say a 383 might be better with the longer stroke more torque at lower rpm. and still a turbo.
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Old 11-09-2020, 08:08 PM   #4
Join Date: Sep 2013
Location: Virginia
Posts: 2,302
Year: None
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Chassis: None
Engine: None
Rated Cap: None
Later 6.2s and 6.5s had TPS in the injector pump for controlling the 4L60E / 4L80E, but the torque converters are typically different from gas to diesel as well. Not to mention the diesel trans will have beefier internals. Not sure a standard 4L60E or even a gasoline version of the 4L80E can handle the torque of the diesel options.

If I were to swap a 454 for diesel, I would likely go with an older 3.9 Isuzu from an NPR truck. I think on a 94 the gauge sensors do pass through the PCM for use in determining fuel and shift points though.
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Old 11-10-2020, 02:20 PM   #5
Bus Nut
Join Date: Feb 2015
Location: Cincinnati, Ohio
Posts: 998
Year: 2000
Coachwork: Blue Bird
Chassis: International
Engine: TE 444
Rated Cap: 12
Your 94 454 is at the end of a long line of smog engines, it's specs are horrible, if you were to rebuild it, you could change the cam and stuff to optimise it for the RPM range you are running and get more power and economy, or you could find a newer GMC based vehicle with the 8.1 engine and swap that drive train into your bus
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