how much power does a turbo make

[pete c]

Originally Posted by JETZcorp

I would be curious to know how much horsepower a turbo generates at the turbine shaft.

This is a tricky question. The turbo is generating shaft hp, but, it is using that hp to stuff more air into the intake. If something else is done with that power, the engine will have a substantially reduced power output, which means that turbo won't spin as hard.

The bottom line here is that spinning a turbo to do anything other than stuff air into the intake is kind of dumb. Perhaps taking a small amount of the power off and further reducing the exhaust restriction to compensate may make some sense, but, I kind of doubt it.

[Occasionally6]

Originally Posted by pete c

This is a tricky question. The turbo is generating shaft hp, but, it is using that hp to stuff more air into the intake. If something else is done with that power, the engine will have a substantially reduced power output, which means that turbo won't spin as hard.

The bottom line here is that spinning a turbo to do anything other than stuff air into the intake is kind of dumb. Perhaps taking a small amount of the power off and further reducing the exhaust restriction to compensate may make some sense, but, I kind of doubt it.

At very light loads maybe. Current turbochargers use a waste gate to dump excess exhaust gas around the turbocharger once the desired boost (compressor work) is achieved. There's still plenty of energy available in the exhaust that is being routed around the turbine.

Since about 1/3 of the energy in the fuel goes out the exhaust and ~1/3 ends up available for useful work, in theory there's as much power in the exhaust energy as the engine achieves at the flywheel. At least some of that energy could be used to drive an electrical generator connected to an exhaust gas driven turbine.

Originally Posted by ChazInMT

Yeah, it is true. There is power required to spin the turbo charger, that has to come from the engine. People always think it's just "Waste Gas", but it isn't. There is a load placed on the engine to make the turbo charger spin, if you just let the air blow into the open by not hooking it up to your engines air induction, it would really slow you down. But since it is packing in a lot of air into your engine, the net gain is that it does help, you're MPG increase is due to the turbo allowing you to operate in a better region of the BSFC chart for your engine. This is basic turbo charger stuff.

You don't get something for nothing, but the benefits outweigh the losses in this case. It is understandable for you to think as you do, but it is not accurate.

If you replaced the engine with a combustion chamber that generated exhaust gas with the same temperature and pressure as that past the engine's exhaust valve, the gas would still drive the turbine. The engine isn't driving the turbine by acting solely as a compressor on the exhaust gas.

There is also that the exhaust valve(s) are operating in choked flow at least part of the time. When that is occurring you can do whatever you like downstream of the exhaust valve, even pull it down to a perfect vacuum, and not increase the mass flow rate of the air past the exhaust valve(s).

That means it is possible to increase the exhaust gas pressure between the exhaust valve and turbine, via the restriction caused by the turbine, and not necessarily reduce the flow past the exhaust valve(s).

[Rusty94cx]

What size turbo what psi are you running? A stock mode 90s Volvo was like 110 hp the same motor with a Garret t3-4 well close to it running 7.5 psi boost stock form was like 150 hp. Honda guys turbo the 1.5 1.6 liter motors 110-125 stock and push 400+ hp. So way to many variables. You can tweak the psi to make more power but then there is also spool time little turbo quick spool overall lower psi capability. Big turbo long spool up time but high psi 20+. So run two a little and a big no lag and big top end. Volvo s80 turbos use that set up. So you need to clue us in what the goal is you could also build a jet engine out of a turbo.

[pete c]

Originally Posted by Occasionally6

At very light loads maybe. Current turbochargers use a waste gate to dump excess exhaust gas around the turbocharger once the desired boost (compressor work) is achieved. There's still plenty of energy available in the exhaust that is being routed around the turbine.

I don't have any actual stats, but, I believe that statement is backwards. I believe that a properly sized turbo uses its waste gate only at high loads.

There is one other problem here. How do you harness power from a device that is spinning at crazy rpms and is very hot? You do it with a rather complicated transmission that will cause turbo lag like you've never seen.

The bottom line is that yes, there is some wasted energy here, but harnessing it is gonna be awfully tricky if possible at all.

[pgfpro]

Originally Posted by pete c

I don't have any actual stats, but, I believe that statement is backwards. I believe that a properly sized turbo uses its waste gate only at high loads.

There is one other problem here. How do you harness power from a device that is spinning at crazy rpms and is very hot? You do it with a rather complicated transmission that will cause turbo lag like you've never seen.

The bottom line is that yes, there is some wasted energy here, but harnessing it is gonna be awfully tricky if possible at all.

Sorry Pete he is right. A properly size turbo will run a smaller size turbine then needed to keep turbo lag at a minimum. So the waste-gate will open at lower loads to keep from over boost. If you turn the boost up there will be less waste-gate flow. Check out the MatchBot link and notice the waste-gate flow at 17psi @ 7000rpm then turn it up to 22psi and adjust the turbine expansion ratio to the original turbine phi curve. You will see that a higher boost will have less % waste-gate flow.

As far as the turbine not being able to do anything useful then spin a compressor wheel and add flow. Check out what F1 is doing for the 2014 season.
Renault takes lid off of 2014 F1 turbo engine - F1technical.net

They are using the turbo to make power and taking some of the turbine flow that would normally be dumped out the waste-gate and harness it through a generator unit. The electricity can be used on demand or sent into a battery/capacitor system for later use or to be used to spin the turbo if needed for no-lag.

[oil pan 4]

Originally Posted by ChazInMT

People always think it's just "Waste Gas", but it isn't.

It is waste gas.
Before the turbo went on I was blowing 1,100'F exhaust out the engine, just to maintain speed.
Now that burned fuel that was getting blown out the exhaust is being put to work. When installing a turbocharger on a diesel you are doing no less than adding a second engine under the hood.
That added power and fuel economy isn't what anyone would call "getting something for nothing". You have to buy and install the turbocharger, its expensive, a great deal of work and you are cramming 40 to 80 pounds of extra equipment under the hood.
I rewrote the BSFC chart. Still putting the same load at the same speed on the engine.

[oil pan 4]

Originally Posted by pete c

I don't have any actual stats, but, I believe that statement is backwards. I believe that a properly sized turbo uses its waste gate only at high loads.

Yes this is correct.
I don't not use a waste gate. I limit boost by over sizing the turbo a bit and by fueling then making sure the engine can take the amount of boost it gets fed.
On a gas engine this isn't really an opption.

[mechman600]

Compound turbos have been used a lot. They use the turbine shaft to mechanically drive the load, parallel with the flywheel. Lots of WWII airplane engines used them.
Until recently, Detroit Diesel 15L engines had a compound turbo that drove the gear train, but it seems they have ditched it now. There's probably a good reason for it.

EDIT: The DD16 (600 HP) still uses turbo compounding.
http://www.demanddetroit.com/engines/dd16/default.aspx

[jamesqf]

Originally Posted by pete c

There is one other problem here. How do you harness power from a device that is spinning at crazy rpms and is very hot? You do it with a rather complicated transmission that will cause turbo lag like you've never seen.

How do airplanes harness power from turbojet engines? Which are, after all, basically scaled-up turbochargers pushing bypass air out the back end instead of stuffing it in the cylinders of an IC engine.

Simplest answer is that you don't do it mechanically at all. Turbine shaft is mated to the rotor of an alternator, which generates electricity. By switching the alternator so it only generates at higher exhaust flow, you pretty much eliminate any excess turbo lag. If you happen to have a hybrid, you can store the electricity for later use...

[pete c]

Can an alternator handle the kind of revs it would see bolted directly to a turbo? Perhaps it can, but, I suspect it would be a damn expensive alternator.