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Go Back   Dodge Cummins Diesel Forum > 2nd Gen. Dodge Cummins 98.5-02 24V Forums > 98.5-02 Powertrain
98.5-02 Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect..NO ADVERTISING .

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Old 06-10-2012, 09:07 PM   #1 (permalink)
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Bigger injectors = More Power = Better fuel economy? Explain.

So I keep hearing about mileage improvements with larger injectors. This doesn't make sense to me.

Bigger injectors result in more power. To make more power you must burn more fuel. How does this result in LESS fuel being burned?

Is this magic? Witchcraft? Voodoo?
Will I need to take up some form of religion for this to work?

Or are people really dreaming and/or faking their numbers?

Can someone please explain how this works?
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Old 06-10-2012, 09:31 PM   #2 (permalink)
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A more powerful motor doesn't have to work as hard. The increased power means that you won't have to press the throttle as hard in situations where you may have had it floored. Not pressing the throttle as much means you're not throwing as much fuel at the motor. All a motor is is a big air pump. The more air you can move, the more efficient the motor is operating. Also, the more air you move, the more fuel you can throw in there, and the more power the motor makes.

Having said that, there is only so far that you can increase the power before fuel economy does start suffering, but in general the "beginner" (again for lack of a better term) mods will help with fuel economy because they are removing stock restrictions and/or increasing the efficiency of the motor by making it more powerful, thereby making not work as hard as it would have had to had it been left unmolested


It seems counter intuitive, but by increasing the power, you also increase the efficiency. By increasing the efficiency, you reduce the amount of throttle needed in any given situation because the motor is operating more efficiently at a higher power level for a given rpm. By reducing the amount of throttle you need to use, you reduce the amount of fuel you need to use.

Hope that helps, I'm not too good at explaining things in writing lol.
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Old 06-10-2012, 09:37 PM   #3 (permalink)
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Simple...

Stock to RV275's... Really easy to explain the gain it not some much that you capable of spraying more fuel in for more power but during normal driving you spraying a shorter burst of fuel in the cylinder giving the illusion of timing advancement.

So say for example it takes 5ms to get stock injectors to fire but RV275's need 3ms now to fire. I know these are random time numbers but the duration of injection event are shorter with larger injectors.

But once you exceed 75-100 HP injectors the spray tend to get screwed up and the MPG's start to fall some.
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Old 06-10-2012, 09:50 PM   #4 (permalink)
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Sounds like we're in the same book, just on a different page lol. You're still increasing the power and thus the efficiency. By increasing efficiency, you don't have to use as much fuel to get the same results. You have a better way of explaining it lol.
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Old 06-11-2012, 01:17 PM   #5 (permalink)
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Quote:
Originally Posted by 94Blackbird View Post
The more air you can move, the more efficient the motor is operating. Also, the more air you move, the more fuel you can throw in there, and the more power the motor makes.

removing stock restrictions and/or increasing the efficiency of the motor by making it more powerful, thereby making not work as hard as it would have had to had it been left unmolested
This would make sense on a gasoline engine, but there is no throttle in a Diesel engine. There are no pumping losses.

This is why my truck with the 5.9L Diesel gets 17 MPG while the same Dodge 2500 with a 5.9L Gasoline engine will get significantly less...


However, if I have a stock truck and I add the injectors ONLY. I haven't really removed any restrictions... Same HY35 turbo. Same air horn. Same intercooler and charge pipes. Same air box...

The ONLY thing I've added is more fuel.


Quote:
Originally Posted by Mopar1973Man View Post
Simple...

Stock to RV275's... Really easy to explain the gain it not some much that you capable of spraying more fuel in for more power but during normal driving you spraying a shorter burst of fuel in the cylinder giving the illusion of timing advancement.

So say for example it takes 5ms to get stock injectors to fire but RV275's need 3ms now to fire. I know these are random time numbers but the duration of injection event are shorter with larger injectors.

But once you exceed 75-100 HP injectors the spray tend to get screwed up and the MPG's start to fall some.
Now this makes sense... Bigger injectors = shorter duration for the same volume of fuel.

Now, how does this affect other things like towing? When I got my Smarty tuner, it has a setting that allows for higher fuel economy, but warns not to tow with it because timing is far advanced.

Also, RV275, I assume are 275 HP injectors out of an RV engine?
That'd make them 50 HP injectors over the stock 235?
Am I right?
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Old 06-11-2012, 01:50 PM   #6 (permalink)
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Quote:
Originally Posted by Pele View Post
This would make sense on a gasoline engine, but there is no throttle in a Diesel engine. There are no pumping losses.
Diesel engines do still have throttles. How else would you control speed and engine rpm? It is true that diesel engines don't have throttle bodies, but ANY engine of any kind has to have some kind of throttle/control device to keep it from destroying itself and to make it useful.

Quote:
Originally Posted by Pele View Post
This is why my truck with the 5.9L Diesel gets 17 MPG while the same Dodge 2500 with a 5.9L Gasoline engine will get significantly less...
Diesel fuel has a higher energy content per gallon than gasoline does, and the fact that diesels are compression ignition motors means that the reaction is going create a greater amount of energy. The reason diesel engines generally have higher fuel efficiency than a gasoline engine is because diesel engines themselves are far more thermally efficient than a gas engine of any kind.

Quote:
Originally Posted by Pele View Post
However, if I have a stock truck and I add the injectors ONLY. I haven't really removed any restrictions... Same HY35 turbo. Same air horn. Same intercooler and charge pipes. Same air box...

The ONLY thing I've added is more fuel.




Now this makes sense... Bigger injectors = shorter duration for the same volume of fuel.
correct. An injector would be considered a restriction in a stock truck, especially a diesel, as the throttling on these trucks is done through the fuel system.

Quote:
Originally Posted by Pele View Post
Now, how does this affect other things like towing? When I got my Smarty tuner, it has a setting that allows for higher fuel economy, but warns not to tow with it because timing is far advanced.
From my understanding, advancing the timing allows the motor to run a little hotter, increasing the efficiency of the combustion. If you place the extra strain of towing at increased rpm on top of the advanced timing, that may put too much strain on the stock head gaskets and/or stock head bolts and be likely to cause a blown gasket or damage internal components. I'm sure someone with more experience with programmers will chime in sooner or later, that's just a guess based on what I've read and my own experience.


Quote:
Originally Posted by Pele View Post
Also, RV275, I assume are 275 HP injectors out of an RV engine?
That'd make them 50 HP injectors over the stock 235?
Am I right?
40hp over stock.


I've got to say I do enjoy discussions like this. Right or wrong, I always come away having learned something new.
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Old 06-11-2012, 02:51 PM   #7 (permalink)
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What would get better fuel efficiency a f-150 v6 4.2l or a f-150 v8 4.6l same exact truck, most would say the smaller engine cause it would burn less fuel but actually the v8 does better because it has more power/efficiency at a certain weight/load/power lvl. Have experience with both of these vehicles, it goes a little deeper than just more availble fuel = less MPGs.
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Old 06-11-2012, 04:04 PM   #8 (permalink)
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Quote:
Originally Posted by 94Blackbird View Post
Diesel engines do still have throttles. How else would you control speed and engine rpm? It is true that diesel engines don't have throttle bodies, but ANY engine of any kind has to have some kind of throttle/control device to keep it from destroying itself and to make it useful.



Diesel fuel has a higher energy content per gallon than gasoline does, and the fact that diesels are compression ignition motors means that the reaction is going create a greater amount of energy. The reason diesel engines generally have higher fuel efficiency than a gasoline engine is because diesel engines themselves are far more thermally efficient than a gas engine of any kind.

the compression dosent really create more energy. the other 2 are pretty dead on

correct. An injector would be considered a restriction in a stock truck, especially a diesel, as the throttling on these trucks is done through the fuel system.



From my understanding, advancing the timing allows the motor to run a little hotter, increasing the efficiency of the combustion. If you place the extra strain of towing at increased rpm on top of the advanced timing, that may put too much strain on the stock head gaskets and/or stock head bolts and be likely to cause a blown gasket or damage internal components. I'm sure someone with more experience with programmers will chime in sooner or later, that's just a guess based on what I've read and my own experience.




40hp over stock.


I've got to say I do enjoy discussions like this. Right or wrong, I always come away having learned something new.
added some info
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Old 06-11-2012, 04:23 PM   #9 (permalink)
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One thing often overlooked is that new injectors (regardless of size) may be replacing old injectors with carboned-up tips spraying nasty patterns hurting fuel mileage.

Just about anything is going to be an improvement at that point.
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Old 06-11-2012, 06:25 PM   #10 (permalink)
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As for empty truck running I can pull 22-23 MPG towing the 30 foot Jayco I'm getting 13-14 MPG.

* Edge Comp (Set for kill on 5x5)
* RV275 injectors
* AirDog 150 (17 @ WOT - 19 @ Idle)
* BHAF
* Straight Pipe 3" exhaust (Don't need no stinking 4" pipe )
* IAT fooler set for 143*F

With these mods I've got zero problem keep good MPGs and good power with very controllable EGT's no over heat issues either.

As for injectors I'm making a plan to just pull them out and clean them every so often...
Mopar1973Man's Dodge Cummins Articles - Injector Cleaning
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Old 06-11-2012, 07:50 PM   #11 (permalink)
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Molar how did you do the temp fooler for intake temp?
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Old 06-11-2012, 07:59 PM   #12 (permalink)
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Molar how did you do the temp fooler for intake temp?
Currently I've got a rheostat jammed in mine for adjustable temperature. I can just watch the ScanGauge II and adjust what I want for temp. As for a permanent fix you can create a IAT fooler like the ECT fooler in the high idle kit and set your resistor value for the temp you want so you'll still keep normal IAT function for starting (grid heaters) and be able to flip the switch after your started.

As for the IAT sensor in the head there nothing hooked to it any longer... Been unplugged now for 2 years!
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