Trebuchet03's JettKamm (2000 VW Jetta)

[mfor4x4]

I did some more research after I had posted about the fans sucking the car to the ground. I know this would not work in this format for FE, these race cars were using over 20hp to drive these motors/fans.

Here is another option though to get free Horsepower to drive a pump like I am suggesting. I know this may sound crazy so I we need someone to tell me this just to confirm that I am indeed crazy, mounting a turbo on the engine that would not put a single CFM into the engine, it would just put air out the back of the car? Some of the turbos out there put out over 750CFM, if there is no waste gate on this turbo and it developed say 30psi of boost, that is 750CFM going out the back of the car in the dead air zone, I think that it would smooth out the back aero of the car. The added bonus of this would would be the amazing whine the turbo would make going down the road.

[Christ]

There were a few posts about that exact thing somewhere.. I was asking about the Pagani Zonda b/c of its' exhaust routing choice. (Centered exhaust ducts)

The problem with using a turbo in that way is that unless the hot side was "geared" a whole bunch lower than the cold side (think: T3/T4 hybrid, x10) you'd never get that kind of boost w/o being at full throttle.

Turbochargers rely on a feedback loop to spool, hence part of the reason for "turbo lag". Again, you're not going to make free power, and a turbo is no exception. The more work the turbo is doing, the more restrictive it becomes to the exhaust (work load). This adds back pressure, and removes efficiency.

You'd be better off applying that energy to keeping the turbo in a negative pressure range, or "0" boost. That way, any backpressure applied to the exhaust would be nullified by the extra power made from the feedback loop to the turbo, and you'd gain efficiency in the form of less pumping losses.

One exception to this would be to mount a very small hot-side in the intake charge, so that as the engine revved higher, it would spool the turbo, and cause an induction resistance that could still be resolved with the "power-adder turbo", then venting the second turbo's boost side to the atmosphere behind the car.

I'm not sure exactly how well this would work, but I'm sure someone will come up with some math to show that it's not worth the time or effort.

[Christ]

By the way, turbochargers are not actually "free" horsepower. They also induce a parasitic drag on the engine, in the form of exhaust back pressure. The drag is minimal though, so turbos are thought of as "free" as compared to any other forced induction system.

[MissileStick]

I guess the relevant question is "does a turbo increase the thermodynamic efficiency of the engine?" In other words, if you had a generator with a turbo and one without, and you ran them both at full throttle, which one would give you more kWh/gallon?

[Bicycle Bob]

First, let's remember that with a reasonably sized engine at cruising power, there is not much to be recovered by an exhaust turbo, without paying for it in back pressure. However, for an optimised setup operating near full throttle, the Napier Nomad turbo-compound engine hit the magic 50% efficiency forty years before the turbo-charged ship diesels managed it. Napier Nomad - Wikipedia, the free encyclopedia So, if you want to spend a few thousand bucks on a ten-hp. generator for your hybrid, there are fuel savings to be had, assuming that turbos can be scaled down without loosing too much to the square-cube law.

[basslover911]

^^ That engine would be amazing in a car!

Imagine having the efficiency of the diesel during acceleration and the turbine for cruising!

[Bicycle Bob]

That engine has enough power for a train; the mileage would be terrible. I try to imagine this dual mode efficiency you postulate, but it runs my brain off the rails.

[roflwaffle]

Originally Posted by Christ

I'm not sure exactly how well this would work, but I'm sure someone will come up with some math to show that it's not worth the time or effort.

Or they could just use a VGT.

[basslover911]

Originally Posted by Bicycle Bob

That engine has enough power for a train; the mileage would be terrible. I try to imagine this dual mode efficiency you postulate, but it runs my brain off the rails.

Oh no I mean a MUCH smaller engine of course

Maybe a 3 piston diesel coupled through a clutch to be able to couple either the piston engine or the turbine engine to the transmission (kind of like, instead of gears, have engines).

You could even have the diesel in the back of the car and the turbine in the front (or vise versa) that way the packaging would be distributed. And use a hydraulic transmission so no shafts would run up and down.

[MissileStick]

Maybe we should get Trebuchet03 to model that drivetrain.