A turbo is MUCH more efficient then a supercharger. At full boost, the sc is using up as much of half of the extra power made, just to turn the darn thing. And the sc heats up the air, as doed ANYTHING that puts air under pressure. The turbo itself only heats up the air in the same method as the sc. The turbo IS spun by the exhaust. This is true. But there is a turbine side of the turbo that is spun by the exhaust. Then there is a shaft that rides in a bearing, that is cooled by oil. Then there is the compressor side of the turbo, which makes the boost. An intercooler can be used by both types of forced induction, to cool down the intake charge. More free power. The turbo doesn't slow the exit of the exhaust much, once it's at boost speed. An engine with a turbo can be more volumetric efficient then an engine with a supercharger. I've had both, and I prefer a turbo. With 2 small turbos instead of 1 big one, turbo lag is nearly eliminated.

 

A little info about turbos and back pressure.
Turbos are NOT free power. Turbos run off of exhaust back pressure, not heat. Turbos are not 100% efficient. Exhaust pressure will always be higher than intake pressure on an turbo engine.
Exhaust back pressure causes power loss. It does not help low end torque like many people think. Exhaust gas velocity creates a scavenging effect to increase torque. You often hear of this on high rpm engines, it has the same effect at low rpms too.
An exhaust system that has good EGV at low rpms is restrictive at high rpms(like stock systems). An exhaust system that has good EGV at high rpms has very little EGV at low rpms(big tube open headers). you can have EGV and no/very little back pressure.
Does this make sense?

I like turbos and Detroits, even better together. 4-71 in an pickup maybe.
Detroits are often more reliable and faster. I don't think that the owner a house thats burning down cares if the fire engine is quiet, sound good, or doesn't leak oil.

 

Daniel. I disagree. It isn't the back pressure that spins the turbo. It is the flow of the exhaust exiting the manifold and passing across the turbine side vanes of the turbo which spins it at very high rpms. The increased back pressure is merely the result of the turbine side of the turbo acting as an obstruction in the path of the flow of the exhaust gases. You are correct that it is not 100% efficient, because of the back pressure that is created. It is however, more efficient then a supercharger.

 

What he said!
AKA right on!

 

I agree with that. Makes sense.
Many people think that turbos cause no prostatic power loss(AKA free power), they do. Thats what i was trying to explain.


Turbos are NOT free power. Turbos are not 100% efficient. Turbos run off the flow of the exhaust gas passing across the turbine side vanes of the turbo. The back pressure is the result of the turbine side of the turbo acting as an obstruction in the path of the flow of the exhaust gases.
Exhaust pressure will always be higher than intake pressure on an turbo engine. Exhaust back pressure causes power loss. It does not help low end torque like many people think. Exhaust gas velocity creates a scavenging effect to increase torque. You often hear of this on high rpm engines, it has the same effect at low rpms too.
An exhaust system that has good EGV at low rpms is restrictive at high rpms(like stock systems). An exhaust system that has good EGV at high rpms has very little EGV at low rpms(big tube open headers). you can have EGV and no/very little back pressure.
Does this make more sense?

 

Efficiency
This is the turbo's biggest advantage. The turbocharger is generally more economical to operate as it as it is driven primarily by potential energy in the exhaust gasses that would otherwise be lost out the exhaust, whereas a supercharger draws power from the crank, which can be used to turn the wheels. The turbocharger's impeller is also powered only under boost conditions, so there is less parasitic drag while the impeller is not spinning. Then once the turbo reaces the maximum desired boost output, the wastegate opens, and the exhaust gase are allowed to flow around the turbine of the turbo. Thus also reducing parasitic drag and increasing efficiency.
I also disagree that the exhaust gas pressure will always be higher then the intakes pressure on a turbo engine. Turbos are often described as exhaust restrictions. The argument is that the increased exhaust backpressure presented by the turbo also robs power from the crankshaft (since it is now harder to push the piston up to expell the exhaust gases. This argument, however, is overstated. Because the intake air is also under pressure (typically greater pressure until the maximum horsepower engine speed), it pushes the piston down. For the majority of the power band, these two forces cancel on another out. Because turbochargers do not use much of the power output of an engine, the highest power levels are possible when using a turbocharger rather than a supercharger. This was more or less quoted from a site "supercharges vs. turbochargers."

 

F150daniel
Posting Guru Join Date: Mar 2003
Location: spartanburg, SC
Posts: 1,026 Signature


I agree with that. Makes sense.
Many people think that turbos cause no prostatic power loss(AKA free power), they do. Thats what i was trying to explain.

What is "prostatic"?
I know that the prostate is a gland.
Was that as in "not a crappy" power loss?

Did you want to say parasitic?

 

"Did you want to say parasitic?"
Yea thats what i was try to say, but i forgot how to spell it at the time and spell checker(rarely use it, not much help) "corrected it" to that. Apparently i got close enough.

 

A few years ago my youngest daughter was shown the spell check, and was hitting learn on all her misspelled words!!!

 

LOL...Now that's funny.

 

Superchargers are great IF you can keep them spinning, turbo's are great if you wanna lug the motor, make it work for a long time. Prolly not many of you will be able to envision this but, think of an old Farmer, now pickture his kid, thats me.

A turbo charged Diesel Motor will run just fine with no boost, with no throttle change at all if you work it, the turbo will boost, work it harder and it boosts more, the rpm's will drop slightly, but it will keep working.

With a supercharged Diesel Motor, if you try to work it down in the lower rpm range it will fall on its face, no lugging abbility.

Now in a truck with 12-18 gears thats great, you can down shift keep the r's up, but in a tractor, which i am using for comparison, there is no down shifting, all you can do is grab more throttle, and by the time a supercharged engine is pulled down its to late, the turbo charged motor will just give more, "pull out of the rut" so to speak. Go to a few tractor pulls, the old two stroke detroits in the Olivers don't stand a chance once they are lugged hard, a turbo motor will just keep blowing till the comprssor stalles from to much boost.

Diesel Rod

 

If you had a blower equiped diesel, it would have to be geared up at all times keeping the engine under boost all the time so it would NEVER fall on it's face, but that would cost lot's of HP to run that way on a 4 stroke, that's why they don't do it and run turbo's only.
The blower on a 2 stroke is the same as atmospheric pressure on a 4 stroke, so it's like a non turbo 4 stroke.
For more power, they turbo before the blower on the 2 strokes.

The only stock blower equiped diesels are the 2 stroke detroits as they have no individual intake stroke, the intake and exhaust motion happens at the same time as the blower blows the air into the cylinder as the piston is moving down, at the same time it also pushes the exhaust out the exhaust valves in the head.
Like this flame smilie guy below, but upside down.
Every time the piston is going down, it's on a power stroke,3/4 of the way through the power stroke, the exhaust valves open and right after that the intake ports are exposed and the pressurized air rushes in pushing the exhaust out the valves, the valves close and the cylinder is pressurized, port is covered by the piston and compression starts, and just before the piston get's to TDC, the fuel is injected.

 

A buddy of mine has an '87 vovlo semi and it has that, a turbo ontop of the blower, I never did know why they did that, learn something everyday.

Yea I know how they work, I have seen many old GM diesels in the oliver tractors, from the 50's those were the two stroke design, same thing, except they only had an intake port, they actualy did have an exhaust valve and they HAD to be kept spinning fast to get any power, louder then H*ll, but still fun to watch.


Diesel Rod

 

I miss the SCREAM of the old 2 stroke Detroit diesels.
Nothing sounds quite like them.

 

as far as belts go you might want to convert it to matbe a twin chain setup.it would use gear pulleys as opposed to the belt style pulleys.also i've worked on various diesels that ranged from non-turbo all the way to quad turbo.2 of the diesels has supers,one had belts for turning,the other had a twin chain.the chain style had better results than the belts-however i would recommend you stick with maybe a solid twin turbo.