HOW MUCH FUEL IS TO MUCH? Smoke is acceptable or not acceptable, EGT discussion

[WarWagon]

If they made the DB2 with an AFC...Now that would be a little easier but then most would disconnect it anyway...:rof:

:crazy: Some of the Oldsmobile diesels do have an AFC on them it is in the docs I posted up.

Smoke has to clear up. Light haze is about all you can get away with without being phoned in in emissions states. Smoke at altitude means you have choked your GMx turbo where it is putting out heat not airflow/boost.

I have always felt a 6.2 needed a turbo simply to clear up the smoke going over Eisenhower tunnel in CO. So my vote is less smoke than a NA 6.2. Smoke is wasted fuel to the 6.2/6.5 economy crowd. Smokers buy a different rig usually... A 1988 4x4 suburban we had would get 18 MPG driven hard and the 2wd was said to get 24 by people we talked to back in the day. My 6.5 turbo is lucky to get 14 unloaded.

However getting 6 PSI of boost from simply hitting the rev limiter in neutral from the factory turbo is too small. It needs boost from load/heat NOT simply airflow. I wonder is a belt drive supercharger would get better results for no smoke with the same MPG as the small GM turbo?

Interesting: Turning up the fuel and boost on my 1993 did not change the MPG under load, just the MPH/power was better up hills.

 

[turbonator]

so who has messed with the precups for better combustion?

we have a set of diamond pre-cups that we had machined, not the "mouths" so much, but the actual insides.... enough that they drop the compression one point... later today i will post up pics of a t-cup beside a modified diamond one....

 

[Acesneights1]

My burb runs 10 psi with the factory setup before the pcm drops it off a little. I was towing with the truck yesterday.

 

[vdb11]

What year is your burb aces?

For the sake of this thread not being lost I will add some. Just as a quick story I was towing a wagon load of straw a couple weeks ago and like I said, I am overboosting right now. I was running up a slight grade in fourth gear, and it was running 15 psi all the way up the hill, which apparently is too much for my intake set up right now because near the top of the hill I hear a big BANG, boost goes to 0, black smoke starts a pourin out, and the truck sounds way different, I limp it off to the side (luckily there was a large shoulder). I was about to have a heart attack at this point. Pop the hood, and it blew the silicone hose off the piece of straight pipe in my cobbled together intake. Man was I happy to see thats all it was. Turns out the pipe I have in there is just a bit too short and its pulling on the silicone hose I have and wants to pull off.

Anyways thats my boost story and it scared the you know what outta me. It will be getting a longer piece soon with a bead welded around the ends for a ridge

As for fuel, I got my rotor and plungers back, I went with .390 inch plungers. They look HUGE next to the factory plungers. This weekend I will get pics, and maybe if time permits and my pump seal kit comes in time, some running experiences.

 

[Acesneights1]

98. Sometimes I question if it has the rumored 210 hp tune as it was a special use vehicle from the factory. I guess I would have to read fuel rates to know.

 

[vdb11]

Hmm, interesting, I have never heard of that before. Does your 6.5 have a sticker on the valve cover with the HP on it?

I know on mine it has the horsepower, 200 @ 3400 rpm, as well as the idle rpms and fuel rate at advertised hp. IIRC it says 59.5 mm^3. My dads 95 says 195 for HP but I don't remember it saying anything about fuel rate.

 

[Slim Shady]

So has there or is there a consensus that there is a limit to the amount of fuel that we can effectively burn in the 6.5. Adding more air increases the ability to burn more fuel but can we get the fuel into the pre cup and out of the pre cup during the piston position that is most favorable. So the question is how do we get the "fuel burn" to happen when we want at the lower torque rpms 1200 to 1700 rpm and still effectively burn more fuel quicker at the higher rpm and unlock the potential for our 6.5 to breath better at higher rpm?

Quandaries and right now I can tell you that from my observations the rpm band of 1300 to 1700 is the place where our motors have the least power / torque with some of the modifications I have made. But most modifications to the pre cup seem to affect this area the most along with raising EGT across the board. One caveat is that the engine runs cooler with some modifications to the pre cups strictly because of the modification (less heat transfer to the head)

 

[Acesneights1]

Hmm, interesting, I have never heard of that before. Does your 6.5 have a sticker on the valve cover with the HP on it?

I know on mine it has the horsepower, 200 @ 3400 rpm, as well as the idle rpms and fuel rate at advertised hp. IIRC it says 59.5 mm^3. My dads 95 says 195 for HP but I don't remember it saying anything about fuel rate.

It's only rumored. Never confirmed.

 

[Acesneights1]

I asked for a better explanation of what i was trying to say about AFC and the effect on smoke. This was from a Heavy Truck site. Our DB2 equipped trucks do not have this feature. As far as DS4 I do not know if the ecm attempts to perform this function, but I believe so.

AFC=Air Fuel Control
It is a device that is used on turbocharged engine that will limit the amount of fuel that can be injected by the injection pump until there is enough air/boost to burn more fuel.

Most use a spring controlled system that limits the fuel rack and it's ability to travel to full open, this will have a diaphragm of sorts on the opposite side o the spring that will be connected to the intake manifold when the engine builds boost/manifold pressure it will override the spring pressure and allow full rack travel.

 

[Missy Good Wench]

Every 6.5 turbo I have ever owned has struggled to break the 20 MPG mark.

Usually 17-18 tops with the average at around 16

The huge cloud of BLACK smoke is unburned fuel, whicj equals MPG and $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ out the tail pipe.

The small puff of smoke on the Turbo enignes is not a biggy as long as it clears when the turbo spools up.

The larger precups in the turbo engines (larger port) reduces the swirl effect of the gasses in the cylinder and this was the real key to to great MPG's on the 6.2's of the 80's

As the velocity of the gasses exiting the precup port drops (larger port) the thorough mixing of the air fuel mixture also goes away to some extent.

Retarded timing will cause a marked drop in MPG and an increase in EGT's

If you can get the burn done in the cylinder and all done before it's shoved out the exhaust, the results are a much cooler exhaust flow.

Running the timing a tad more advanced will cool things off some, just dont get crazy with the advance.

As the IP wears out the advance piston (DB2 pumps) wears out and the advance stops working correctly and or fails to advance.

Also the POP pressure of the injectors can really make a bunch of difference in the power levels as well as the smoke.

When the injectors are new and the spray pattern and the POP are right up to snuff the fuel spray is a very fine MIST and this allows for a very clean and efficient burn.

When the POP falls off (read this as worn out injectors) the fuel delivry takes on more of a pee stream instead of a nice cone of mist.

Large droplets of fuel ignite slowly and take far longer to burn completely.
This situation basically results in a lot of black smoke and High EGT's and a loss of power.

As the power fall off the foot presses harder on the pedal to get more seat of the pants and with the seat of the pants feel come even higher EGT'S and more BLACK SMOKE.

Its not always just getting fuel into the thing that makes Power and mileage.
Timing is very important as is the length of time that the fuel is being injected.

If the pop pressure is LOW and the fuel slobbers into the precup the ignition is poor and takes far longer before the "fire" is burning good. When this happens the optimal crank angle is gone before the fuel is all used up and then the exhaust cycle is begining even with unburned or partially burned fuel still in the cylinder.

The "Fuel Map" is a very complex issue for sure. The common rail stuff thats all controlled with the computer and the timing, delivery amounts and such are extremely accurate makes things a completely different game than we have on the older engines with a mechanical pump (even the DS4 is mechaincal as far as the actual injection goes)

The extremely high pressures that are used on the DMAX, Strokes and the cummins makes this a whole different ball game.

The one big disadvantage of the IDI engine is the fact that the precup soaks up a huge amount of heat right in the head, where we really dont want it.

Back in the old days of 160 HP maximum 6.2 engines this was not an issue as these engines were designed to get good mileage and not to make huge amounts of power.

As the power levels rose so did the issues with heat and the tendency to self destruct.

The 6.5 TD, the way it left the factory is a compromise engine, sort of in between the 6.2 N/A and the Dmax

Getting a 6.5 TD up to around 225 HP is about the best you can hope for and have good reliability.

The mileage is going to suffer as the reason for the great mileage (small precups and little fuel) is gone, replaced by larger cups/ports and far more fuel.

The Banks Kits offered a great compromise for the 6.2 in that they put some much needed extra air into the engine and a tad more fuel, all while keeping the precups with small ports.

Using a set of precups with the smaller ports can improve the mileage in a 6.5 TD but with a loss of some power.

When we step over into the land of the Dmax and the others DI engines the game is totally different. The cumbustion all takes place in a little bowl in the top of the piston and the flame propagation is totally different.

The transfer of combustion heat is mostly absorbed by the water jacket around the cylinders and not the head.

The piston on the DI engines does take a bit more heat, but they are designed to shed this heat readily.

The Dmax engine uses aluminum heads which also helps transfer more of the waste heat into the coolant flow.

Just some thoughts on a very complex issue

Missy

 

[Pepperidge]

a great explanation Missy...