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BubbaBrown

Detroit engines

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Whats the differences between the 71 and 92 series engines, and where would one look for an accurate detail of the V-12 ? Thank you

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Jim is exactly right and Mo'luminum has an excellent 12v-71.

71 series has 71 cubic inches per cylinder, the 92 series has 92 cubic inches per cylinder.

KJ at Double Take Replicas has an excellent set of 8v-92 valve covers.

Early 8v-92's had valve covers similar to the 71's like the GMC General kit.

If you're asking strictly about 12v's, the 12v-71 has 1 long 6-71 style valve cover on each side, and every 12v-92 that I've ever seen has two 6v-92 style valve covers on each side.

You can also source a 12v-71 from the Super Boss KW kit found at Hobby Lobby.

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There are no 12V-92 engines available in our scales so 12V-71 are the only way to go if you want one.

Edited by Force

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How about that. We learn something everyday. Here I thought the difference was that the 92 had a turbo while the 71 didn't.

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The 12v71 had the option of turbo or non turbo, just found that interesting researching a brockway truck build

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Both the 71 & 92 Series engines were offered with & without turbos.

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How about that. We learn something everyday. Here I thought the difference was that the 92 had a turbo while the 71 didn't.

Detroit nomenclature was very clear in the 2 stroke era. Number of cylinders, configuration (- = inline, V = vee) and displacement. They may include a T suffix to indicate turbocharged. All of the 2 stroke Detroits had a supercharger.

4-71 is a 4 cylinder inline displacing 284 cubic inches (4 x 71 cid), 6v53 is a 6 cylinder vee engine displacing 318 cubic inches (6 x 53 cid)  

They moved away from this style of nomenclature when they started producing 4 stoke engines in the late 80s.

 

DD was also rather practical in those days as well, with a lot of common parts shared between engines as Brian points out with the 12V engines using valve covers from the smaller engines. This makes them rather modeler friendly (easy to convert). 

Edited by Aaronw

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A bit of rambling and ranting here on old Detroits....

For what it is worth, external dimension wise the "bare block" on the 71 and 92 are the same. 

The letter after the cylinder/configuration/ci displacement designation reveals a great deal about it as well.  N, T, TT, TTA, etc. There were probably a dozen or more variations.

There were a few rigs that had 92 series 2 strokes with DDEC in the 80's (electronics that were to be the cornerstone of the series 60) but not many as by then the self destruct button had already been pressed within GM.

If you really want to find out about hot rod old Detroits, Johnson and Towers in NJ were THE masters of hopping them up for yachts builders.  They were by far the industry leader in terms reputation and production numbers getting HP and RPM's out of 2 stoke Detroit's that will blow your mind.  Google some engine rooms on yachts in the 40-70 foot range from the 1970's  (Egg Harbor, Post, Viking were but a few of the high end yacht builders sourcing from them).  Impressive numbers and darn good looking and running stuff.   There are lots of forums on these older yachts with great close up pics and info.  Just remember the cooling system is totally different using heat exchangers instead of a radiator.  Most were painted white and kept clean which is great for spotting details on in the pix.

And if you want to get "weird"  look into side by side version of the 12V71.  Basically two 6-71's built Saimese twin style with two cranks.

 

 

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Well if the 6V71's are side by side it's not really a V12 as we know them, the definition of a V12 is that it has a common engine block with 6 cylinders on each side laid out in a V (60 and 90 degree V's are the most common for V engines but 15 are also used by VAG for example), and one crank...an engine with two 6 cylinder blocks mounted side by side with two cranks indeed have 12 cylinders but it's not a V12, it's just two I 6's anyway.

Edited by Force

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In WW2 GM built twin 6-71s for use in tanks. Technically not V-12s but not I-12s either and they were not independent of each other so not really just two I-6s.

 

 

They also built a real monster quad 6-71 with Grey Marine for use in landing craft.

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Detroit also mounted 2 4-71s together in a power pack for greyhound buses before the 8v71.

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These are pictures of a quad-six that was a standby power unit for the Oshawa water works. It was connected directly to an emergency water pump.

DSCN9083.JPG

DSCN9082.JPG

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Well if the 6V71's are side by side it's not really a V12 as we know them, the definition of a V12 is that it has a common engine block with 6 cylinders on each side laid out in a V (60 and 90 degree V's are the most common for V engines but 15 are also used by VAG for example), and one crank...an engine with two 6 cylinder blocks mounted side by side with two cranks indeed have 12 cylinders but it's not a V12, it's just two I 6's anyway.

Just for an understanding, The 12V's and the 16V's were not side by sides. They were bolted crank shaft to crank shaft. The blocks were bolted together with an adapter plate, and opposed each other, Each engine had its own fuel system and its own supercharger. One engine rotation was right hand and the opposing engine ran left hand rotation, in relation to the "Front" of the engine. the cranks used a coupler that made it one crank. Truck applications, the front engine rotated clockwise, (or "Right Hand"), and the rear rotated left. In marine applications were, port side engine rotated one direction and starboard rotated the other. All of the DD two strokes used a lot of swap able components, like front and rear housings cranks and cams. This saved a lot on manufacturing.

 

 

Edited cause I cant type.

Edited by dad vader

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Actually the 12v71 used in trucks was one block and one crank with two 6 71 heads and valve covers. It's a common myth that 12v71s were two 6v71s bolted together maybe in marine duty but not truck use.

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I never worked on an "On highway" V12, However, I worked for a company that specialized in 2 stroke engines, pretty much known in the area, as the best 2 stroke shop. I did work on several V12's in Both 60ton Euclid dump trucks in both mills in this area. These were Equipped with both Detroit 2 stroke V12s 71 series and Cummins 1710 V 12s. These were considered truck engines and were 2 6V blocks. I I will have to get up in the attic and see if I can find my service manuals...... I know for a fact the marine engines were built out of 2 engines, cause I built several of them in tug boats. Even since my army days I never had a real love for 2 strokes. They were very popular, when I was enlisted.

 

 

After looking at several pages on Google images it looks like they were available in both configurations. I just never saw one single block.  I guess I should do a little more research before I spout off at the mouth.

Edited by dad vader

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