So what, exactly, keeps the turbo pressure of 6.2s at 10 psi??

[Knightmare]

I've searched a little (not a lot, don't kill me), and from what I have read, the max boost on a 6.2, safely, is 10 psi. Then they talk about running into physical limitations, without further elaboration.

I have read this in more than one spot.

I'm kinda new to these trucks, but I have a decent understanding of what makes the diesel engine tick. I'm working on my experience level with them.

So, where is the weak point, with boost, exactly?

 

[JAsher45]

there are alot of factors going on when you start adding boost. this is an IDI engine, which means that the fuel is combusted in a combustion chamber in the cylinder head. as the gas expands it shoots out of the chamber... downward and across the piston face causing your power stroke. the opening of the combustion chamber greatly effects the flame speed and desired effect. i have learned this the hard way. as a project that i was on rebuilding 6.5 NA engines. we were giving contracted heads to build the engines. they were reman GM 6.5 cylinder heads.... but they were civi heads from 91-93 from trucks that had the banks turbos system installed according to the casting numbers. the problem came when dyno testing. the engines could not meet HP and TQ. the reason is the precombustion chamber is vastly different. the opening is large and wide, compared to small and narrow. with the larger opening the with no Boost the flame speed was to slow across the piston, and also caused incomplete fuel burn. @ 3600 rpms fuel was actually flowing out and burning in the exhaust.

the real weak part in going above 10 psi. it that the clamping force and gasket can't hold above that... it was not designed or intended to see that much boost. also with the increase of boost you are adding more cylinder temp to the engine.. these engines do not fare well bey adding more heat then they can cool. by adding more boost... you need to add more fuel and timing to make use of the potential. that comes to another weak point of the engine, the IP. there is not much you can relly do unless you have a pump test stand to tweak it just right or send it out to the few who make high proformance 6.2 and 6.5's. i am trying to make this as simpe as possible but it is really just about understanding the thermodynamics of this engine.

 

[3dubs]

The main limitation on the 6.2 is the bottom end. Quick over view of boosting any engine. Air is forced through the air intake into the combustion chamber. Pressure is increased all along the way. The air intake is the easiest to strengthen and most are not a problem. Inside the engine is the problem with boost. It increases pressure in the combustion chamber. The whole engine is about combustion. It increases pressure on the heads. That means valves, rockers, head bolts and so on. The Heads on the diesels are made much stronger than gas engines. While the blocks are stronger than a gas engine they do not have as much reinforcement as the heads. The pressure also goes against the pistons, rods, crank, and block. The weakest point will give first and unfortunately it is the block. Crank, rods, and pistons can be replaced but the block is bad. The caps that hold the crank in the engine have four bolts on every cap. By bolting a piece of harden steel (stud girdle) across the three center caps it distributes the force across all three. The front and rear cap are bolted to the much thicker outer part of the block. While I would stay within the max PSI a stud girdle will reduce the stress on the block. You can make a stud girdle but be sure you temper the steel correctly or just buy one. STUD GIRDLE KIT I am not sure how many people on here have actually been inside the engine but I have and this is the bottom end. If you jack the truck up from the frame the axle should drop down enough for the removal of the oil pan. The kit comes with everything. If you need more information about turbo's I have websites with great info on my other computer. This was just all off the top of my head.

 

[conifercucv]

I just got a banks turbo installed on my m1009 last week. I live in the mountains and it has really helped with my commute. The only thing I noticed is that the EGT climbs pretty quickly and I have to back of the gas on long steep grades. I'm not sure if the turbo needs further adjustment. Any additional info would be appreciated

 

[3dubs]

I just got a banks turbo installed on my m1009 last week. I live in the mountains and it has really helped with my commute. The only thing I noticed is that the EGT climbs pretty quickly and I have to back of the gas on long steep grades. I'm not sure if the turbo needs further adjustment. Any additional info would be appreciated

Put a girdle on it or you will crack the webbing!

 

[Tanner]

Pfffttt.... keep a 6.X NA long enough & you'll crack the main web... or the sides of the block.

We were junking roughly 85% of the 6.X blocks at (unnamed quality engine remanufacturing company) & ended up using new block castings in the remans...

'Tanner

 

[tiger422]

I just got a banks turbo installed on my m1009 last week. I live in the mountains and it has really helped with my commute. The only thing I noticed is that the EGT climbs pretty quickly and I have to back of the gas on long steep grades. I'm not sure if the turbo needs further adjustment. Any additional info would be appreciated

How hot

 

[91W350]

They are not rpm friendly. They will run a long time in a high geared application, but they cannot take the high rpm of the low geared applications. Some of the 2wd Suburbans and pickups with the OD transmission would roll 75 to 80 mph for over 300,000 miles.

My Buddy has the same opinion as Tanner. He says every 6.2 that comes in for a rebuild has a broken crank or block or both. In defense of the 6.2 though, he also admits almost all of them came out of 3/4 ton 4x4 or one ton dually applications.

I was pretty good friends with the Chevrolet mechanic that did all the 6.2 work when they first came out and it did not take him long to recognize the problem...rpm...

Is part of the limit on boost due to the relatively high compression ratio? The Cummins 5.9 for instance is a 16.3 to 17.2 compression ratio, it was designed to run with boost, obviously.

Those main cap girdles look like they should help some with flexing of the block webbing, it would be interesting to see a fleet of them on a long term test. Glen

 

[Tanner]

The newer design 6.5 used in HMMWV and marine applications have a separate lower main 'bedplate' to add strength to the bottom end. This seems to help... another thing that will help it survive is...

STOP USING A 6.X engine to pull loads greater than it was designed to pull...

'Tanner'

 

[3dubs]

Pfffttt.... keep a 6.X NA long enough & you'll crack the main web... or the sides of the block.

We were junking roughly 85% of the 6.X blocks at (unnamed quality engine remanufacturing company) & ended up using new block castings in the remans...

'Tanner

That is why you see a girdle on my engine but not a turbo. While I do plan to add a turbo for when I drive to Denver and higher. But I live at see level so it is not something I need right now. But I put that girdle on fast!

 

[conifercucv]

How hot

It will easily get to its max of 1100 degrees if I don't back off the gas.

 

[3dubs]

It will easily get to its max of 1100 degrees if I don't back off the gas.

Do you run an intercooler?

 

[donalloy1]

abundantly clear that if we stay with stock configuration and do not overload we are ok how gm delivered? m1009 seems to do fine on my end with towed loads under rated tow capacity. wish she did not ping so much when cold. dml2 sends...

 

[3dubs]

My truck is being re-outfitted for a new mission!

 

[2deuce]

I think what limits the boost is the fact that the banks turbo only is capable of 10 lbs boost. There is no waste gate and no intercooler is needed with that low of boost. Correct me if I'm wrong.
I want to add a turbo for economy at higher elevations, and pulling a load. I see alot of 6.2's that have a turbo and a knock on the bottom end. Will the girdle help with crank breakage?along with block cracking?
Also if the fuel isn't turned up with the addition of the turbo will you get better combustion at higher elevs without appreciably increasing stress on the bottom end? Would heat be more under control? It seems to me that turning up the fuel with the additional air to burn it from the turbo would be the big source of heat under a load.
I have noticed the decrease in power and the additional smoke the engine produces with elev. increase. I would think more air in this situation would promote better burning, more power and
economy and temp would be more in line with lower elev.use.
Thanks
Thanks

 

[Tanner]

The crankshafts in the 6.X were cast from the Detroit Diesel - journal surfaces were Nitrided or Tuftrided (surface hardened, but I don't recall which process was used). You can polish a 6.X crank, but cannot cut it, or you'll ruin the surface hardening treatment...

The cranks can break, but it wasn't the main issue we saw in reman world. Most times, the heads or block cracked first.

'Tanner'

 

[Croatan_Kid]

Yes, most of the limitation for boost is the high compression ratio. That's a good 3/4 of the problem right there, the rest is just a matter of self destruction. IIRC, the ratio is 22:1.....wayyyyyy too high to start taking on any more pressure!

It has nothing to do with the turbo itself or any of that setup or whether it's wastegated. The turbo will only put out boost as fuel is increased an the motor is under load. Notice, if you rev a diesel engine with no load, you get no boost. Once it's under a load, the turbo spools and, on a turbo diesel, the boost pressure pushes on a valve of some sort (depends on the kind of motor), which adds more fuel as boost rises. You have to have more fuel to get more air coming into the motor. You can quickly realize that this cycle is perpetual....that's how a diesel engine can run away if turned up too much. On a turbo diesel, the boost pressure controls the amount of fuel that is injected. It seems like on a 6.X motor, you'd just set the fuel rate and it would be the same over the whole RPM range, which would also limit boost pressure.

I'm sure that the Banks turbo would put out close to 20 lbs, but I'm not sure of the size of the compressor wheel, housing or the turbine wheel/housing.

 

[2deuce]

I don't think the Banks turbo adds fuel other than the ability to burn it with more air and if you don't turn up the fuel on the IP then it seems that the turbo wouldn't help much over a NA engine at sea level, but would see gains over a NA engine as the elevation rises. So unless I'm missing something heat wouldn't become a factor because you wouldn't be burning any more fuel unless towing. Can a diesel get too much air causing it to run too lean? or does it only aid in better combustion?
Thanks

 

[2deuce]

It must accelerate faster with a turbo from a stop but that is controlled with your foot. That could cause additional engine strain. I would like to add a turbo for efficiency, but I want my engine to last.
Thanks

 

[Croatan_Kid]

Nope, you can't run a diesel engine lean. They're controlled by the amount of fuel that you put into them, not by how much air comes in.