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Discussion Starter · #1 ·
i was just wondering why all the high power deisels are turboed?can thay not make power with out FI?you can find NA gas motors putting out 500 hp and tourqe.so why not deisels
 

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I'm not understanding your question, FI(fuel injection) doesn't really have anything to do with weather a Diesel is turbo or NA. But all Diesel are fuel injected.
 

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Um, I think he wants to know why NA diesels can't make the same power an NA gas engine could. And I'm sure someone here could get rel technical and explain it to him, but I can't.
I think its because diesels don't make as much vacuum as gas motors, so they're very sluggish and ususally not too powerful if they are NA. So they use turbos (or sometimes superchargers) to get more air in the cylinders.
The reason it's so easy to make a diesel go fast is because all you need to do is increase the turbo pressure and increase the ammount fuel and you add a lot of power. With a gas engine its not as easy.
 

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Discussion Starter · #4 ·
MoparMurdoc said:
Um, I think he wants to know why NA diesels can't make the same power an NA gas engine could. And I'm sure someone here could get rel technical and explain it to him, but I can't.
I think its because diesels don't make as much vacuum as gas motors, so they're very sluggish and ususally not too powerful if they are NA. So they use turbos (or sometimes superchargers) to get more air in the cylinders.
The reason it's so easy to make a diesel go fast is because all you need to do is increase the turbo pressure and increase the ammount fuel and you add a lot of power. With a gas engine its not as easy.
that just what i want to know.and by FI i ment forced induction
 

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Since Diesel draw no vacuum the turbo is used to fill the cylinders fast enough to make decent power. But you are right, you don't see many if any strong NA Diesels.
 

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new84 said:
i was just wondering why all the high power deisels are turboed?can thay not make power with out FI?
Even though diesels use the same basic, piston driven, four stroke design as a gas engine, a diesel is a completely different animal.

The short answer to your question is yes. Without forced induction, diesels do not do as well at all, especially as compared to gas engines. By their design, light truck diesels are built to work. They have heavier reciprocating and rotating mass that takes longer to put into motion. However there were some light diesels that run as good as gas engines of similar displacement such as the small 4 cylinder VW diesels due to light mass.

you can find NA gas motors putting out 500 hp and tourqe.so why not deisels
The simple answer is they can't without some help. The fuel itself is more powerful than gas, but without alot of air, it can't make power. Gas engines take advantage of their higher rpm nature to draw in alot of air to make power, but diesels are low rpm engines.

The solution to making power in a diesel is to turbocharge them. So heres where it gets good for turbodiesels. Take your 500 hp gas engine. It has to make this power at high rpm, say over 3000rpm. They also make most of their torque at higher rpms. The diesel makes most of it's power around 1500rpms.

When you consider pulling loads or expect high demands on the engine, with the gas engines, you need to stick your foot in the throttle alot because you have to get the rpms up to make torque. The turbodiesel begins pulling hard just above idle.

Compare a 1967 440 to an 89 5.9 Cummins. The 440 has more torque at 480ft-lb @ 3200rpm, but the 89 Cummins makes it's 400ft-lb @ 1500rpms The difference? The Cummins begins to pull hard at less than half the rpms of the 440. Now think of this, say you are pulling a load up an incline. Your rpms are dropping and you have the 440. When the engine lugs down to 1500 rpms the 440 will not be making peak torque to continue the pull, you either have to downshift to put the engine in a higher rpm or lug. The turbodiesel doesn't need to rev fast to keep pulling, it's chugging along happily.

Ed
 

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A diesel engine is not suitable for high revs, so a propper camshaft and timing are adjusted so that the peak torque is at low rpms.
Diesel fuel needs more energy to combust, and hence produces more energy. If you compare two identical engines, one running on gas and one on diesel, the diesel will produce more torque per stroke than the gas engine. The problem is, at a higher rpm the gas engine produces more torque strokes.
Besides, often, when building a sport engine HP is more important than torque, and HP is usualy more linked with high revs... Its power=work/time, the higher the revs, the smaller the time, the higher the power. In a utility vehicle, its exactcly the opposite, torque is more important. You need torque for moving heavy loads, and hp to move fast... With exceptions.
 
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