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

Slim Shady

Slim Shady

DEATH BEFORE DISHONOR
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With the advent of the new tunes / new ways to improve our combustion process and other modifications, How much fuel can we actually use. Is there a point at which the effort is futile, based on the combustion restrictions of the IDI process? The 6.5 crew always worries about smoke after our modifications (unacceptable) yet the Dodge and Power Stroke guys (most) don't complain about smoke when they have modified their trucks beyond factory. I understand that we are IDI and the Dodge and Ford Guys are direct injection.

I would also like to hear from the Dmax guys on this. do they worry about smoke as well or just egt temps.

How much egt is to much, the 6.2 diesel in the natural aspirated format runs higher egt's than the turbo model. yes or no ?

The 6.2 gets consistently better mileage for what reason? Less fuel in the program or does the turbo somehow contribute to the fuel economy demise.
 
I've had/have 6.2 n/a and the fleet of 6.5s.
The 6.2 was a 91 k2500LD 3.70 gears 700r4 Banks 3" exhaust and the IP turned up a 1/2 turn Normal driving I got 20-22mpg.Only had smoke if I floored it or was towing heavy. I did get as high as 28mpg on a 400 mile interstate run.I never had a egt guage.
My first 6.5 is the 95 K2500LD in my sig.4L80E and 3.70 gears It has a bit more power than the 6.2 ever could ,when I bought it but can't even get 20 mpg no matter what I do to it. I have put in new injectors, timing chain,4" exhaust GM8 and several different buddy chips. More power but still crappy mpg. I really thought the turbo should have given better mpg than the N/A because it is more efficient.
The turning the fuel up on the 6.2 did give it more power and better mpg. The same doesn't seem to be true on the turbo engine. My theory is that any turbo restricts the exhaust and reduces flow taking away mpg. A turbo isn't free power without a price as I used to think.
 
I agree I have looked at most comparisons between the 6.5 and 6.2 and the only real differences are pre cups turbo / exhaust and fuel program. I have a friend with a 6.2 that gets 24 MPG regularly on the highway, and I wonder why I am happy to get 18 19 mpg, and he is disappointed when getting 22 23.
 
bk95td said:
I've had/have 6.2 n/a and the fleet of 6.5s.
The 6.2 was a 91 k2500LD 3.70 gears 700r4 Banks 3" exhaust and the IP turned up a 1/2 turn Normal driving I got 20-22mpg.Only had smoke if I floored it or was towing heavy. I did get as high as 28mpg on a 400 mile interstate run.I never had a egt guage.
My first 6.5 is the 95 K2500LD in my sig.4L80E and 3.70 gears It has a bit more power than the 6.2 ever could ,when I bought it but can't even get 20 mpg no matter what I do to it. I have put in new injectors, timing chain,4" exhaust GM8 and several different buddy chips. More power but still crappy mpg. I really thought the turbo should have given better mpg than the N/A because it is more efficient.
The turning the fuel up on the 6.2 did give it more power and better mpg. The same doesn't seem to be true on the turbo engine. My theory is that any turbo restricts the exhaust and reduces flow taking away mpg. A turbo isn't free power without a price as I used to think.
Click to expand...
I agree I see alot of people putting in 4bts and different engines to get better MPG's. No matter how hard I try I can't get better than 12-17 mpg. I wonder how good MPG would be if you took the turbo off a 6.5 and put the hummer exhaust on it? Has anyone ever done that? As far as smoke mine will darken the sky if I romp on it with running 10 psi.
 
the common rail Dmax's ECM fuel mapping/tables are so complex(but available to tune) that a good tune with EFI Live along with an intake and exhaust and you can keep even a high h.p. tune virtually smokeless...
 
Slim, my buddy with a 6.2 said his truck ran consistently hotter EGT wise before he put his turbo on. He had the fuel turned up some before, and of course he does after as well, a bit more I think. Him and I get similar mileage sorta, and our trucks do pretty much all town driving. I usually get 15-16 mpg and he gets 16-18. His truck weighs exactly the same as mine, same turbo (VGT) and standard trannies. Of course, he would get slightly better mileage with the 5-speed like I have. He will be swapping soon so we will see.

Anyways he has 3.73s and I have 4.10s. His truck smokes more than mine for sure, but yet his EGTs don't seem as high as mine. Anyways thats pretty much all I can tell ya as far as what I have seen so far.
 
Its not the turbo itself, its the crappy manifolds and tiny turbo. twin GM8s on dual exhaust would likely fetch you better power and much better fuel mileage, even better than the 6.2NA. And youre likely 90% there with some custom headers combing at a T4 flange and larger turbo, or the center mount solution. Then you could extrude hone the manifolds we have and get a little larger turbo and we could be 75% there.

Smoke, is not a good thing climbing a mountain where the air gets thinner and thinner, and the smoke becomes the decision on what gear and how fast youre going, as your EGTs also shoot up. So near sea level, a puff on take-off or when hitting WOT is as much as I would deal with for something that will be good anywhere. Now since the electronics can be programmed with a good amount of flexibility, its not hard to prevent too much smoke off the line. Then having the oxygen to support going 65mph up a mountain depend on the turbos ability to spool enough boost to compensate for thinner air. Thats when an electronically controlled turbo can come in real handy, varying the drive pressure to the turbine to compensate for any situation. However that also means it cannot be as efficient at sea level.

I think the 6.5 will handle plenty more fuel, as long as the oxygen is there to support it, and I think it can handle 30psi of boost without issue if done with the right hardware.
 
our c-5000 dumper has the custom centre mount turbo(351 VGT) the uppipes are 2.5"... at wot, with the 17000lbs truck, and 14000lbs on the trailer, pulling a 2km 7 percent grade, i have to struggle and floor it to hit 950 for egt's.... it has a 2831-5088 IP turned up 1/4 turn past 4911 specs... with the sm-465, i can start out in third empty(17000lbs) and make black smoke for about 200ft and thats it...
 
buddy said:
Its not the turbo itself, its the crappy manifolds and tiny turbo. twin GM8s on dual exhaust would likely fetch you better power and much better fuel mileage, even better than the 6.2NA. And youre likely 90% there with some custom headers combing at a T4 flange and larger turbo, or the center mount solution. Then you could extrude hone the manifolds we have and get a little larger turbo and we could be 75% there.

Smoke, is not a good thing climbing a mountain where the air gets thinner and thinner, and the smoke becomes the decision on what gear and how fast youre going, as your EGTs also shoot up. So near sea level, a puff on take-off or when hitting WOT is as much as I would deal with for something that will be good anywhere. Now since the electronics can be programmed with a good amount of flexibility, its not hard to prevent too much smoke off the line. Then having the oxygen to support going 65mph up a mountain depend on the turbos ability to spool enough boost to compensate for thinner air. Thats when an electronically controlled turbo can come in real handy, varying the drive pressure to the turbine to compensate for any situation. However that also means it cannot be as efficient at sea level.

I think the 6.5 will handle plenty more fuel, as long as the oxygen is there to support it, and I think it can handle 30psi of boost without issue if done with the right hardware.
Click to expand...



I am sure that the innovators here will make it happen, it will be interesting to see how they do it and what ideas they come up with. Anticipation :D
 
buddy said:
Its not the turbo itself, its the crappy manifolds and tiny turbo. twin GM8s on dual exhaust would likely fetch you better power and much better fuel mileage, even better than the 6.2NA. And youre likely 90% there with some custom headers combing at a T4 flange and larger turbo, or the center mount solution. Then you could extrude hone the manifolds we have and get a little larger turbo and we could be 75% there.

Smoke, is not a good thing climbing a mountain where the air gets thinner and thinner, and the smoke becomes the decision on what gear and how fast youre going, as your EGTs also shoot up. So near sea level, a puff on take-off or when hitting WOT is as much as I would deal with for something that will be good anywhere. Now since the electronics can be programmed with a good amount of flexibility, its not hard to prevent too much smoke off the line. Then having the oxygen to support going 65mph up a mountain depend on the turbos ability to spool enough boost to compensate for thinner air. Thats when an electronically controlled turbo can come in real handy, varying the drive pressure to the turbine to compensate for any situation. However that also means it cannot be as efficient at sea level.

I think the 6.5 will handle plenty more fuel, as long as the oxygen is there to support it, and I think it can handle 30psi of boost without issue if done with the right hardware.
Click to expand...

Agreed, I have a question though. Obviously, more fuel=more smoke and higher EGTs. This period of smoky high EGTs can be lengthened with a slow spooling turbo. Now as the turbo starts to spool, the smoke clears and EGTs stabilize. However, I would assume that as the turbo spools to higher and higher boost, IATs increase considerably correct? Would this also raise EGTs? So there is a balance there, and I would assume a better flowing exhaust manifold system and a larger turbo would help this. So which do you guys think has a more significant impact on EGTs?

Am I correct in saying that IATs are just as important to control as fuel? I am just thinking out loud :)

Lots of good threads on here lately....
 
turbonator said:
our c-5000 dumper has the custom centre mount turbo(351 VGT) the uppipes are 2.5"... at wot, with the 17000lbs truck, and 14000lbs on the trailer, pulling a 2km 7 percent grade, i have to struggle and floor it to hit 950 for egt's.... it has a 2831-5088 IP turned up 1/4 turn past 4911 specs... with the sm-465, i can start out in third empty(17000lbs) and make black smoke for about 200ft and thats it...
Click to expand...

Your EGTs just blow my mind every time you mention it ha. Those are very impressive numbers, I'm jealous.
 
vdb11 said:
Agreed, I have a question though. Obviously, more fuel=more smoke and higher EGTs. This period of smoky high EGTs can be lengthened with a slow spooling turbo. Now as the turbo starts to spool, the smoke clears and EGTs stabilize. However, I would assume that as the turbo spools to higher and higher boost, IATs increase considerably correct? Would this also raise EGTs? So there is a balance there, and I would assume a better flowing exhaust manifold system and a larger turbo would help this. So which do you guys think has a more significant impact on EGTs?

Am I correct in saying that IATs are just as important to control as fuel? I am just thinking out loud :)

Lots of good threads on here lately....
Click to expand...

don't forget cylinder pressures...there is a guy in the Dmax world that has done some innovative work to... IIRC "real time monitor cylinder pressures"...

just curious, but has anyone with a 6.5 tried to do this? I'm wondering what you guys would see/find... if no one has yet...
 
It depends on what kind of smoke. Sometimes it's ok, sometimes it's not. when it's heavy dark grey, that is not. Heavy black either. A blast of black at WOT aint so bad. I've turned up a few diesels in my time most recently a 3208t which required a little finess. You have many things to play with. timing, Pre-boost fuel, rack, and governor. When I first cranked her up it was belching a ton of heavy grey and the egts were high. This was because I gave it too much pre boost fuel. Truck ran like a bat out of hell once it leveled out or if I rolled into the throttle slowly...sound familiar to anyone ? I solved it by cutting back my pre boost fuel. The timing could have used a little bump as well but that is a royal PIA on a 3208T so I lived with the little bit that was left. The fuel/boost/advance all has to be in line so to speak. That is why the VGT turbo is such a nice idea. On older mech inj motors it's pretty hard to find a happy spot. Once you increase the fuel it takes alot of tweaking. Those motors had an AFC to help with that. Alot of the big trucks don't have wastegated turbos. it's done through the AFC.
Alot of the Mack guys disconnected them...Ever see a Mack R Model with 6 in it blow some black...Those trucks needed any thing you could do to kick it in the ass...:rof:
Most guys turned em up, disconnected the AFC...Drove by the Pyro and killed old ladys in K cars with the smoke.....
 
buddy said:
More fuel does not mean more EGTs with good combustion.
Click to expand...

That's kinda what I was waiting to hear. I had an idea that was the case. I would assume "good combustion" depends on many things. Like aces said, I would assume timing is a big factor as well. Would increasing fuel and advancing timing be modifications that complement each other? If there is extra fuel being pumped out through the injection line, would there be more injection lag or longer injection duration due to the limitations of the lines and injectors? If that is the case, then I guess advancing it would be beneficial.

I agree with Aces in that the DB2 is very limited in comparison to the DS4 in terms of ability to tune fuel where you want it in the rpm band (I know very little about the DS4), and can be finicky when it come to getting fuel "just right" since like he said, pre boost fuel can be a killer.
 
Is black smoke harder to "pump" out of the exhaust due to larger soot particles that aren't vaporized? That is pump out of cylinder, turbo, and exhaust pipe. I think so. So black smoke would mean ineffecienct drag???? On a big bore long stroke DI engines this is probably not as big deal but with IDI chamber I think it further slows combustion flame propagation speed and pressure rise rate in the cylinder???.

I think black smoke can come from a couple different sources lack of air obviously but also poor balance of flame front expansion/pressure/heat and thus less vaporization.
Can't black smoke be from after the piston is farther down the bore and accelerating as fast or faster than the fuel flame front is expanding? Meaning most of the power is from the initial combusition nearer TDC. Kinda what Kenny was talking about. You have to balance oxygen, fuel, and heat to have good combustion.


I tend towards liking a small puff of black and that is only when I put my foot in it to accelerate above average rate or if romp on it real quick more is ok. If I roll into it I like no visible smoke unless short roll to WOT then some is acceptable but still like for it to clear as more boost spools. NA might be ok to roll coal like a freight train but with a turbo I think its poor tuning.
 
I got 19.5 MPG in the burb (94 6.5) yesterday. Just over a 500 mile trip, still had almost half a tank left.
 
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