why turbo not a Supercharger

[swampdigger]

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.

Consider that when the power stroke has completed, and the exhaust valve opens, the cylinder pressure is still pretty high. It's also very hot, and rushes to cool low pressure atmosphere. This is the wasted energy that powers the turbine.

There is drag put on the piston as it reaches the top of the exhaust stroke, however. When the piston is actually pushing the exhaust out.

For the most part, a turbo runs for free.

 

[LateApex31]

You lose that low pressure area when you choke the exhaust stream with a turbocharger. This reduces the ability of the engine to rid itself of exhaust, causing reversion, slowing the evacuation of exhaust gasses(some of which remain in the cylinder and displace intake charge that would otherwise fill the cylinder) and other nasties not to mention lessening the pressure differential between the exhaust and intake valves. It isn't free energy, but it is fairly efficient. This is because that drawback comes with the benefit of positive intake manifold pressure which is obviously beneficial. If it was free energy, the engine could achieve a 100% or greater efficiency, which, as we all know, is impossible.

Put it this way, if you run a turbo at 1 or 2 PSI, it will make less power than the exact same engine naturally aspirated. Why? Because it takes some energy to push that turbine.

I spend every day on a chassis or engine dyno developing engine control strategies, hardware, and software so I've seen 1 or 2 internal combustion engines

 

[Russ]

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!

Just a FYI... The sound made from a roots type blower comes from the air escaping from between the cog type belt and the pulley. If you were to drill holes in the grooves of the pulley the whine would go away.

 

[swampdigger]

You lose that low pressure area when you choke the exhaust stream with a turbocharger. This reduces the ability of the engine to rid itself of exhaust, causing reversion, slowing the evacuation of exhaust gasses(some of which remain in the cylinder and displace intake charge that would otherwise fill the cylinder) and other nasties not to mention lessening the pressure differential between the exhaust and intake valves. It isn't free energy, but it is fairly efficient. This is because that drawback comes with the benefit of positive intake manifold pressure which is obviously beneficial. If it was free energy, the engine could achieve a 100% or greater efficiency, which, as we all know, is impossible.

Put it this way, if you run a turbo at 1 or 2 PSI, it will make less power than the exact same engine naturally aspirated. Why? Because it takes some energy to push that turbine.

I spend every day on a chassis or engine dyno developing engine control strategies, hardware, and software so I've seen 1 or 2 internal combustion engines

Haha, of course it's never *free* energy that comes out of a worm hole is space, but it's energy that would have otherwise been wasted. Entropy sucks. Turbos are your friend.

Interesting about reversion though. I only read about this fact recently, about how the right size headers can leave a cylinder with negative pressure at the right RPMS, pulling in more air on the intake stroke, and achieving an amazing volumetric efficiency.

Any thoughts on an exhaust header before the turbo?

 

[sle2115]

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,

I am speaking more along the lines of high performance stuff. Lifted blowers were and are common. Not really the blowers fault, but none the less, a high failure rate. A friend of mine had a pulling truck. He is a Ford fanatic and wanted to run a 460 Ford with a blower. He pulls in only state sanctioned events and in 2 or 3 years, lifted SEVERAL blowers. His unit was broken in by the builder using an small block Chevy and a direct drive unit hooked up via a coupler to the back of a TH350 tranny. And by the way, there was no belt and a BUNCH of SC whine. In any event, he finally ran into a guy that had been using a similar setup, the guy told him (I was standing there when he said it) to tighted up the gap on his spark plugs. He said the blower he was using was making so much boost that it was "unlighting" the spark, then the cylinder would ignite as the intake opened causing all that pressure to go into the intake. Anyway, he did as was told and had gone 4 years without lifting a blower...seems strange I know.

Anyway, when I used to race, SC's were very prone to failures. Many improvements have been made such as teflon liners, etc. In any event, anthing with moving parts if prone to failure, more moving parts means more prone.