a diesel is no different than a gasser as far as exhaust systems go.. the less any engine has to work pushing exhaust gasses out, the more power will be available at the flywheel. as for their being no throttle, this means that MORE air will be flowing through a diesel's exhaust than a gassers at all times.
-Bret
By far and away the biggest problem you are going to run into with a diesel is caused by fuel. Keep the fuel filter intervals religiously, if not more often. Use a good NAPA or WIX or other name brand filter, not Wally World or Autozone models. Buy quality fuel at a busy station. They also consume many times the cubic inches of air of a typical gas engine, so keep an eye on the air filter. I always liked having a dual element filter on a diesel.
Diesels are torque machines, but unlike a gas engine, they develop more torque on a less restrictive exhaust. There's really no such thing as not enough back pressure on a diesel. The only problem with a large exhaust is the slower moving exhaust stream causes more carbon buildup. For you that shouldn't be an issue given the load you have to pull. It's only an issue for motors that operate for extended periods in the lower fourth of their powerband.
To imagine why a diesel is so sensitive to a restrictive exhause consider this, a diesel has no throttle plate restriction thus it is always moving "about" the same amount of air that a comperable size gas engine would be moving at the same RPM if the throttle on the gas engine was wide open. Of course this will vary slightly due to fuel flow and heat expansion within the chamber.
You can buy a nice free flowing exhaust from Banks and others or you can use your ingenuity and use the exhaust manifolds from a non turbo 6.5 app like I did. Those and a good free flowing dual setup from a reputable muffler shop. It is worth the search, work and effort.
A non restrictive intake system also helps, noticeably!
The comments about keeping fuel clean are right on the mark. Fuel must be kept clean as that is the life blood of how a diesel works. And of course good clean oil for any engine. I just switched my 6.5 to Rotella SB and it starts easier, runs quieter and hopefully wll last a while longer. The truck has 421,000 plus on it and the engine has somewhere over 251,000 miles. Hoping for an even half million before rebuild.
George Vigner> I am not sure. This is my first diesel vehicle. Does anyone here have
I recommend Baldwin filters..
The stock manifolds have a restrictor ring cast into them, something about emissions I am told. They are far and away the weakest link in the induction/exhaust system. Improving them alone will make a big difference.
No dyno figures, definitely seat of the pants, however I was able to maintain 25 to 30 miles per hour more over the same grades pulling the same 24 foot cabin cruiser. And unloaded the mileage went up 3 mpg or more at the same speed/load.
Later I pulled the injection pump and had it "tricked" at the local diesel house. That helped too, a lot actually. It became fun to drive when loaded instead of being a boring chore.
Possibly not scientific in your book, but definitely demonstrable.
It was an 84 Chevy Sub with a 700R4 automatic.
Celica Dude wrote:
One thing I forgot.
Actually the same amount of air isn't enter> > To imagine why a diesel is so sensitive to a restrictive exhause consider > this,
I am just trying to imagine how *just* an exhaust system makes the thing have more power. It doesn't bring in more air, because the intake is the same.. The same amount of air is entering the engine, as well as the same amount of fuel.
Doesn't compute with me... Do you have actual dyno figures, or just "seat of the pants" dyno figures?
A restrictive exhaust doesn't get as much of the burned air/fuel out the cylinder. The cylinder still has pressure in it on the exhaust stroke. Just because the exhaust valve opens, doesn't mean that the contents just instantly exit. Some is always left behind. By your reasoning, changing the size of the exhaust valve wouldn't matter. But cutting the back pressure in the exhaust is effectively doing the same thing as enlarging the exhaust valve.
Definitely have my interest.. I have an 83 with 700R4...
The only thing I have done (and I can't believe I didn't think of it sooner) was to remove the intake air silencer. It's that big oval muffler-looking thing that's on the bracket beside the air cleaner on the passenger side of the engine. If you remove it, you'll have no more air-horn on the air cleaner.. i'm sure you can figure a way to fashion something. Be sure to tighten the top arch of the bracket back to the bottom part... otherwise, you'll have a terrible rattle (found that one out myself).
You can definitely hear a difference in the intake noise level, but it unrestricts the intake quite a bit. I noticed that I could go faster with a 4000 pound trailer on the highway in overdrive before the tranny wanted to kick down than i could with the silencer in-place. Definitely worth the extra noise for me.
The motor is due for some major service soon... I wonder if i could grind the restrictor out of the manifolds??
I wouldn't think that any more air is getting into the engine because you haven't changed the size of the intake. I can understand the unrestricted exhaust allows more expansion of the gases and the engine doesn't have to fight nearly as much to get the exhaust out.
A 650 cfm carb (although totally unrelated to a diesel) will only flow a maximum of 650 cfm... no mater how much your exhaust system will flow.
If the engine can flow more air out, where is it coming from??? Think of the exhaust/intake system as a whole. The most restrictive element effects the whole system.
Some have doubled the standard air filter elements, (stacked) and then modified the air cleaner housing (made it taller) to hold them, then added a second snorkel slowing the air flow to mitigate the incoming air noise. Not restricting but offering a second path so the overall movement of air is slower with the same volume. Ideally a diesel will have no (zero) vacuum in the intake, however with a clogged or insufficient size air filter that is not the real case. Note on farm tractors there is a device that indicates when the air filter is dirty, it operates on vacuum! Even under high rpms (relatively speaking of course, diesels do not turn really high rpm) with your 6.2 you will find a small amount of vacuum in the intake, indicating the filter and silencer is of insufficient size. Removing the silencer was a good beginning. Try rigging a vacuum gauge and see what you have in the intake of your 6.2 at say about 3,000 rpm. Note throttle setting has little to do with intake restriction on a diesel. Volume of air movement is more related to rpm than throttle setting, unlike a gas engine which is the inverse of this due to the presence of a throttle plate.
As for grinding out the restrictor rings, I think it could be done but not without a lot of effort. If you have lots of time on your hands, a really good set of hearing protectors, good safety glasses, a good air or electric die grinder, and lots (many many) of small sanding drums...... You get the idea! If you can find the 6.5 non turbo manifolds, they flow better and have no restrictor rings. When you compare the two side by side you will instantly see the difference. They are a direct bolt on replacement on a 6.2.
As for your analogy of a 650 cfm carb, it will flow 650 under very specific circumstances. The idea is to approach those circumstances as closely as you can in a field application. Realizing this is only an analogy. The lower you can make the specific air pressure below the carb increases the pressure differential across the venturi and thus more air flows. If you allow more air out the exhaust of a diesel the cylinder is cleaner (more exhaust out, less residual contamination of the incoming air charge) and more incoming charge can enter the cylinder. If the cylinder were to empty into a space with absolutely zero pressure and infinite volume there would be no back pressure. That is not the real world though. To reduce the pressure in the exhaust port is to approach the same situation. Voila, more HP, and better fuel economy. The key to increased horse power and fuel economy is volumetric efficiency (with appologies to Ed Iskenderian, who said it first many years ago).
George Vigner> I wouldn't think that any more air is getting into the engine because you
look at it this way... (using your 650 carb) if your exhaust can only flow 600 CFM in stock form, and you improve it to the point that it flows 700 CFM, you move the most restrictive element (i.e the carb instead of the exhaust) to the intake, which can now flow more air.
-Bret
Okay, you have shown me the light on this topic :oD
Have you heard anything about the topic on this website:
Keep the K&N. Oil soaked cotton is the best air filter on the market today.
transmission
They have prices up there for engine kits...
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