Author Topic: What's the scoop on older Detroit diesels  (Read 8802 times)

Offline eznuff

  • Newbie
  • *
  • Posts: 4
What's the scoop on older Detroit diesels
« on: October 02, 2007, 07:45:55 PM »
This is a newbie question---

What's the scoop on older Detroit diesels?  I am hearing about 6V92TA, 671, 8V71, 8V92, etc.  What are the life expectancies, horsepower, availability of parts, ease of maintenance, cost to replace with a rebuild, etc.?  I don't know one from the other!

Let me know your thoughts on these.  Also, would someone decode the letters that you see associated with these engines?  DD, DDEC, TA, etc.   There's probably more that I don't know of -- I also saw MUI on a post today -- what does that mean?

Offline white-eagle

  • Hero Member
  • *****
  • Posts: 1184
Re: What's the scoop on older Detroit diesels
« Reply #1 on: October 02, 2007, 08:02:35 PM »
i am not the expert, but i do think i have some of the answers

DD = Detroit Diesel
DDEC = DD electronic computer
T = turbo as in 8V92T

all of them are/were widely used in trucks, buses, off road bulldozers tractor, graders, etc., so many parts still around (I hope).

2 cycle heavy duty engines that will run on almost anything.
1991 Eagle 15 and proud of it.
8V92T, 740, Fulltime working on the road.

Fran was called to a higher duty 12/16/13. I lost my life navigator.

Offline tekebird

  • Hero Member
  • *****
  • Posts: 2264
Re: What's the scoop on older Detroit diesels
« Reply #2 on: October 02, 2007, 08:11:22 PM »
TA= Turbo Aftercooled
MUI= Mechanical Unit Injectors

bigger the engine the more fuel it uses.

First numer is the # of Cyl, second number 71/92 is displacement per cyl will give you an idea on replacement costs.

non electornic engines are the simplest to diagnose and work on for the most part.

electronic engines tend to be a bit more effiecent...but you'll never rack enough mileage to notice.

all are 500K or so engines if maintained properly

Series 40/50/60 are 4 stroke engines and out of your price range unless you go Dina or luck into one of the MCI's that were retrofitted

Offline NJT5047

  • Hero Member
  • *****
  • Posts: 1942
Re: What's the scoop on older Detroit diesels
« Reply #3 on: October 02, 2007, 08:23:44 PM »
The numbers and letters denote what the engine shape and displacement is:  671 is a 6 cylinder, in line, with 71 cubic inches per cylinder.   An 8V71 is: 8 cylinders, "V" shape (V8), with 71 CI displacment per cylinder.  Same for all the rest.  
71s are early style engines and 92 are the next generation.  92s have wet sleeves.  Otherwise, they are similar.  
The "TA" indicates Turbo/Aftercooled.  These are found on most 92 series engines.
Keep in mind that all DD 2 cycles have blowers on them.. the turbo is mounted on top of the blower.  
MUI=Mechanical Unit Injection.  Has mechanical gov and cam operated injectors.  
DDEC=Detroit Diesel Electronic Controls. DDEC engines use electronic injectors.  It is a "fly by wire" system.  An electronically controlled engine. Found on 87 and later 92 series...generally.  
There are plenty of parts to keep these engines running around for years.  They are smooth, cheap to buy, and if in good condition, will outlast most converted bus owners.  
Takeouts are available.  
No diesel is easy to maintain, but DD routine maintenance on DDEC engines is easy enough.  MUIs must have the racks run for optimal performance.  A bit of work at best.  And not something to experiment with.  
250K to 350K miles is common on these engines.  In conversion use, they'll keep going long after they are worn out.  Keep oil and water in them and they'll go.  
Rebuilds are approx $15K for most.  Can range on up if accessories are worn out too.  
We are discussing 2 strokes.  The better engines are the later 4 strokes. But, a coach with a 4 stroke will cost much more than a 2 stroke.  1993 is usually where 4 strokes engines start making appearences in buses.  
The desirability of the engines, IMHO, could be rated from the smallest to the largest....6/71 about 170 HP would be the bottom of the ladder, with 8V71 at 318 HP, 6V92TA at 350 HP,  and an 8V92TA at 400 to 500 HP would be at the top of the 2 stroke list.   Keep in mind that these engines HP range varies.  There were a ton of 270 HP, 6V92TA both DDEC and MUI that were designed for long life and fuel economy (an oxymoron with a 2 stroke) for use in urban coaches.  
The fuel economy ranges from about 9 MPG from a 6/71 to about 4 MPG with a 500 HP 8V92TA.
6 or 7 MPG is the norm.  
JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.”

Ayn Rand

Online TomC

  • Hero Member
  • *****
  • Posts: 8931
Re: What's the scoop on older Detroit diesels
« Reply #4 on: October 02, 2007, 10:07:38 PM »
While Detroit made several million 2 stroke engines, there is an estimate that there are still around 800,000 of them still in use. So for a few more years, there should be parts available for them.  Now finding mechanics that can work on them maybe a reach.  Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.


  • Guest
Re: What's the scoop on older Detroit diesels
« Reply #5 on: October 02, 2007, 10:25:58 PM »
I have an 81 eagle with the 6V92T and it will outlive me, thats all the endorsement I can give, it's a good strong engine that with reasonable maintenance will perform day after day. This is the beauty of a bus conversion, besied the fact that you get to do it your way.