why turbo not a Supercharger

[jimraelee]

I got to thinking.... superchargers are better for low rpm horsepower, and turbos take some spooling up hence the high end RPM HP numbers... so why are all the diesels made with a turbo, Why not a SC on these for the low rpms they turn.

jim

 

[kcw12]

diesels make plenty of low end, and hardly any up top?

 

[tonkadoctor]

#1 reason manufacturers probably turbocharge vs supercharge is cost.

IMHO a turbo is more efficient than a supercharger as it's taking something that's already there as a waste product (exhaust) and putting it to use.

A properly sized and wastegated turbo spools very fast and will give you more power across the entire RPM band including low RPMs. Take the 3126 or C7 CAT engines as an example. Their torque peaks at 1440 RPM

 

[icanfixall]

As posted, the turbo runs for free. The blower costs the motor about 10% hp to run it. Also building a manifold will be expensive. I saw a BDS blower on a 6.9 and BDS is about 3 miles for my home. They didn't build that manifold but would build an aluminum one for me. The cost was around 18 to 20 thousand buxs because it was a one off design. That is untill everybody has one. Thats a lot of money just to give up 10% of my hp...

 

[Mike]

What is the difference between a turbocharger and a supercharger on a car's engine?

Let's start with the similarities. Both turbochargers and superchargers are called forced induction systems. They compress the air flowing into the engine . The advantage of compressing the air is that it lets the engine stuff more air into a cylinder. More air means that more fuel can be stuffed in, too, so you get more power from each explosion in each cylinder. A turbo/supercharged engine produces more power overall than the same engine without the charging. The typical boost provided by either a turbocharger or a supercharger is 6 to 8 pounds per square inch (psi). Since normal atmospheric pressure is 14.7 psi at sea level, you can see that you are getting about 50-percent more air into the engine. Therefore, you would expect to get 50-percent more power. It's not perfectly efficient, though, so you might get a 30-percent to 40-percent improvement instead.

The key difference between a turbocharger and a supercharger is its power supply. Something has to supply the power to run the air compressor. In a supercharger, there is a belt that connects directly to the engine. It gets its power the same way that the water pump or alternator does. A turbocharger, on the other hand, gets its power from the exhaust stream. The exhaust runs through a turbine, which in turn spins the compressor.

There are tradeoffs in both systems. In theory, a turbocharger is more efficient because it is using the "wasted" energy in the exhaust stream for its power source. On the other hand, a turbocharger causes some amount of back pressure in the exhaust system and tends to provide less boost until the engine is running at higher RPMs. Superchargers are easier to install but tend to be more expensive.

 

[jimraelee]

And yes let me ad one more fact of SC's... they are inherantly inefficent... the SC on my 3800 is only about 75% effecent, with pressure it builds heat, and SC's seem to build more heat the turbos from the results in the Grand Prix world.... Also a N/A engine vs a SC engine only seems to drop about a 1sec to 1.5ssec in the 1/4mi time... as seen in our car club

 

[creighta]

Why not electric superchargers? run for a short burst of power from the battteries and then recharge while cruising. seems like the perfect compromise

 

[Mr_Roboto]

The 12 volt electric motor necessary to run a turbo or supercharger would be very large.

Once cars evolve to have higher voltage systems (48 volts or better) then you may start to see electric boost in factory cars as the motors can be made much smaller if the voltage is higher.

 

[LateApex31]

As posted, the turbo runs for free. T

Turbochargers don't run for free! You are taking thermal and kinetic energy that is going out the tailpipe and using it to drive the turbine. Great, but it isn't free or without cost. The turbine creates a rather large restriction in the exhaust path, so the exhaust doesn't flow as freely and not as much air can move across the engine. Remember, airflow (and torque) is dictated by the pressure ratio between the inlet and exhaust valves. If you measured pre-turbine pressure, you would be surprised to see that it is coupled with intake manifold pressure, and sometimes much higher than IM pressure. This is where a supercharger has an advantage, in exhaust gas scavenging. But even with this drawback, there is still quite strong evidence that turbochargers can make some good power.

 

[argve]

I wonder why then if SC are so much better that all of the diesel world isn't going that way? I mean even the aftermarket does not support superchargers in the diesel world. I wonder is cost is the driving factor but you would think that if it's better then the OEM's would use it and pass the price increases on to the consumers (speaking of commerical trucking as well).

 

[LateApex31]

Superchargers aren't better really. They have packaging constraints, belts to wear and break, relatively narrow operating speed, difficult to intercool, etc. Plus the raw HP that is taken from the crank to spin the blower. A turbo is a better solution for a plethora of reasons. Even with all of it's downsides, a turbocharger is still a great means of increasing HP and torque of an internal combustion engine. IMO, turbo > SC. Plus, turbos sound so dang cool!

 

[sle2115]

Not to mention high SC failure rates. You are turning two rotors and they eventually wear, have bearing failures and such, not good. Personally though, there is NO turbo that sounds any better than a properly setup blower...I haven't heard one for years, but can remember the blower sound like it was yesterday!

 

[dansvan]

Everyone seems to be referring to the roots style positive displacement type sc. There is also the belt driven centrifugal type. Paxton, Vortech, and others. Basically belt driven turbos. Lighter internals, less power to spin. Can be geared to provide boost when you want it.. Easy to mount. I'm wondering why no one has applied these to diesels. One thought is back when the turbo kits were designed and made for our IDI's the centrifugal SC's were still in their infancy.

 

[jimraelee]

Not to mention high SC failure rates. You are turning two rotors and they eventually wear, have bearing failures and such, not good. Personally though, there is NO turbo that sounds any better than a properly setup blower...I haven't heard one for years, but can remember the blower sound like it was yesterday!

REally... I didnt know... there are some 45000 members on the ClubGrandPRix web site and with allthe young wipper snappers winning about everything under the sun, no body mentions SC failures. What "High Failure Rates" are you speaking of?? grand prixs from 97 on have all had SCs on the GTP versions,

 

[LateApex31]

Everyone seems to be referring to the roots style positive displacement type sc. There is also the belt driven centrifugal type. Paxton, Vortech, and others. Basically belt driven turbos. Lighter internals, less power to spin. Can be geared to provide boost when you want it.. Easy to mount. I'm wondering why no one has applied these to diesels. One thought is back when the turbo kits were designed and made for our IDI's the centrifugal SC's were still in their infancy.

Because you can't get a constant boost level from a centrifugal SC, as there is no way to regulate compressor speed (ie. it's coupled to crank speed). You can bleed off boost, but that is doing negative work and very inefficient. Most centrifugal blower dyno plots I've seen make peak HP at redline and the graph has very little area under the curve. A Lysholm blower is relatively efficient from a thermal standpoint, however it still suffers from many of the same drawbacks as a Roots style blower (packaging, belts, etc).

The poster commenting about failure prone superchargers, think about a turbo. A bearing supporting a shaft that sees both radial and axial loads, spins at over 100k RPM, and shares the same oil supply as a diesel engine with one eng of the shaft IN the exhaust stream. Thats a harsh environment and they last a good long while, and a modern supercharger would too given equal engineering.