6.2 Civi Vs. Military

[gschooley@gmail.com]

I saw specs somwhere that a civy 6.2 is rated 130HP, and 230 FPT.
A Mil. 6.2 is emissions free, and rated 155 HP, and 255 FPT.
Joe.

Do you know what it takes to convert a GMC 6.2L with the EGR crap
to the military version intake?

 

[gschooley@gmail.com]

Do you know what it takes to convert a 1984 GMC 6.2L with
all the EGR crap to a military style intake manifold?

 

[ODdave]

Iirc the c code had larger intake valves.

 

[patracy]

Do you know what it takes to convert a GMC 6.2L with the EGR crap
to the military version intake?

You'll need the J code intake, and block offs for the exhaust ports.

OR you can cheat and simply unplug the vacuum line going into the EGR valve and place a bolt in the line (from the vacuum side). That'll give you almost the same performance for zero cost.

 

[patracy]

Iirc the c code had larger intake valves.

Other way around. The J code engines had larger intake valves. (4mm larger)

 

[Barrman]

The 1984 civilian engine had a pink wire at the top of the IP and a green wire at the side of the IP. So did the military version. That is all the electronics needed to make a 6.2 from any year work.

Now, switching intakes will mean you have to go over to the military CDR valve. Look at the -20P or -34P manuals to see what all that means and the pieces needed to plumb it.

 

[2deuce]

Has anyone put the serpentine belt on their cucv.? If it had air seems like it could be done on the 6.2.

 

[gschooley@gmail.com]

The 1984 GMC already has a CDR valve up by the radiator. It had 2 inputs for
both sides of the stock intake manifold. The military intake only has 1 connection so I
blocked off one of he ports on the CDR valve. What about the old EGR wiring
to the stock intake manifold, can I just disconnect and pull all the wiring? I'm
sure that wiring connects to the computer under the dash, do I need to ground or
connect any wires together?

 

[gschooley@gmail.com]

The 1984 GMC already has a CDR valve up by the radiator. It had 2 inputs for
both sides of the stock intake manifold. The military intake only has 1 connection so I
blocked off one of he ports on the CDR valve. What about the old EGR wiring
to the stock intake manifold, can I just disconnect and pull all the wiring? I'm
sure that wiring connects to the computer under the dash, do I need to ground or
connect any wires together?

 

[southdave]

I found this interesting...

replacement items and replaced with new parts during assembly/installation.​

Section II. EQUIPMENT DESCRIPTION AND DATA
1-10. DESCRIPTION​

The engine used in the M998 series vehicles is an eight-cylinder, four-cycle, liquid-cooled, naturally
aspirated diesel engine. The 6.2L engine has a compression ratio of 21.5:1 and develops approximately 150
horsepower (112 kW) at 3600 rpm. The 6.5L engine has a compression ratio of 21.5:1 and develops
approximately 160 horsepower (119 kW) at 3400 rpm. For proper orientation, the left and right sides of the
engine are as viewed from the rear.
1990 and above 6.2L and 1994 6.5L engines have the following new and revised parts:​

*Cylinder Heads. ​

​

​

The 1990 cylinder heads have been revised to meet 1990 emissions standards.​

Precombustion Valves. ​

​

​

The 1990 engine is equipped with reverse throat precombustion chambers.​

Exhaust Valves. ​

​

​

The 1990 exhaust valves are coated with chrome to prevent burning and to
increase durability.​

*Exhaust Valve Stem Seal. ​

​

​

The 1990 engine is equipped with a new exhaust valve stem seal that
is not available for previous model engines.
Cylinder Head Gaskets. The 1990 cylinder head gaskets have new circular combustion seals and
are made of a non-asbestos material.​

Fuel Injection Pump. ​

​

​

The 1994 fuel injection pump has a TP sensor and a revised calibration
procedure.​

Fuel Injection Pump. ​

​

​

The 1990 fuel injection pump has a new governor and a revised calibration
procedure.​

*Fuel Injection Nozzles. ​

​

​

The 1990 fuel injection nozzles are shorter and are orientated ten degrees
from the vertical.​

*Fuel Injection Lines. ​

​

​

The 1990 engine is equipped with high pressure fuel injection lines.​

Fuel Injection Line Brackets. ​

​

​

The 1990 fuel injection line brackets have been revised to provide
clearance for the injection nozzles.​

*RPM Sensors. ​

​

​

The 1994 engine is equipped with two rpm sensors. One is for STE-ICE-R and one is
for the engine.​

*Fan Cut-Off Switch. ​

​

​

The 1994 engine is equipped with a fan cut-off switch which replaced the
kick-down switch.
*These 1990 parts are not interchangeable with parts for previous model engines. Differences in
maintenance procedures are identified where applicable. Refer to engine decal number on left rocker
arm cover before ordering replacement parts.​

1-

 

[pitbull]

If it wasn't mentioned earlier, the military glow plugs have a wider spade where the wire connects to it then the civvy models.

 

[Garagefull]

6.2's differences

I have owned many 6.2 and 6.5 engines over the years. And have had good luck out of all of them. Why are these military motor so much louder than the civilian versions? I just helped a friend install a civilian pump and injectors in a 1028. It's still sounds like..a cucv engine does. I understand that the pre combustion chamber size and slot controls the pressure spike inside the cylinder. Has anyone here compared between civilian and mil heads? I am almost at the point of dropping a civilian engine in, or swapping to a 4bt / 4500.I swear this 6.2 sounds like the crankshaft is bouncing around on the front differential. I was worried about how loud mine was until we worked on another of the same vintage.

 

[porkysplace]

I have owned many 6.2 and 6.5 engines over the years. And have had good luck out of all of them. Why are these military motor so much louder than the civilian versions? I just helped a friend install a civilian pump and injectors in a 1028. It's still sounds like..a cucv engine does. I understand that the pre combustion chamber size and slot controls the pressure spike inside the cylinder. Has anyone here compared between civilian and mil heads? I am almost at the point of dropping a civilian engine in, or swapping to a 4bt / 4500.I swear this 6.2 sounds like the crankshaft is bouncing around on the front differential. I was worried about how loud mine was until we worked on another of the same vintage.

The civilian versions have silencer on the air intake that the military didn't use.

 

[Garagefull]

Yes, I have that silencer system on a civilian truck. But I have to pull to exhaust manifold bolts for the support bracket. I've been a little leery to pull them because everything sealed up well.

 

[porkysplace]

Yes, I have that silencer system on a civilian truck. But I have to pull to exhaust manifold bolts for the support bracket. I've been a little leery to pull them because everything sealed up well.

Find a salvage yard with one and get the parts you need ,

http://www.car-part.com/

 

[ken]

The baffle/silencer on the civi engines is a power robber. It restricts the air flow quite a bit. There a few guys on here that ran a dryer hose up to the rad core support opening to make a ram air. Try searching this forum for it. There are some good ideas. I used a air filter housing from a 93 Model 6.2. And I air intake tube from a 85 350 gas motor. It reduced the drone noise a lot.

 

[Mad Texan]

The baffle/silencer on the civi engines is a power robber. It restricts the air flow quite a bit. There a few guys on hereView attachment 752048 that ran a dryer hose up to the rad core support opening to make a ram air. Try searching this forum for it. There are some good ideas. I used a air filter housing from a 93 Model 6.2. And I air intake tube from a 85 350 gas motor. It reduced the drone noise a lot.

I will be on the search for this setup.... there is quite a bit of drone at 45ish that I wouldn't mind quieting down some.

 

[Dock Rocker]

Much of the sound difference has to do with the lack of sound deadening anywhere in the cab. The cabs magnify the sound without any carpet or rubber. Also nothing on the hood to keep it quiet.

Also most of the trucks GM sold had an overdrive. The 3 speed makes the engine rev more thus making more racket.


Sent from my iPhone using Tapatalk

 

[Garagefull]

I was referring more to the injection event noise.Civilian motors are so much quieter. My understanding is that the pre combustion chamber slot size determines how fast the combustion event takes place.these old mechanical pumps just push the fuel out in a big shot pretty much,and the size of that slot determines how much oxygen can transfer and takes the pressure spike out of the injection event. I was hoping that someone had a military head could look at the slot size and see if it is different from civilian.

 

[sandcobra164]

Garagefull, I see where you're going and it makes sense. I installed a new injection pump on my truck that was meant for a newer 6.5L HMMWV. It is much quieter now and sounds a lot less strained going 55 mph. I know everything is turning the same speed and the injection still occurs as a burst. What you're looking for is a timing difference.