Exhaust only Turbo mod idea

[Phantom]

The STS remote turbo would not have an issue with the suction side as it pulls the air from under the car and being used this way would be easier than using it as forced induction as the pipe does not have to run back to the engine.

On the note of efficiency I have read that the efficiency is not that much different to an in engine non-intercooled turbo since the gases might be moving slower but they are denser (cooler) so it can apply more force. Also that keeps the charge cooler and the piping back to the engine cools it more acting like an intercooler. Most of that does not apply to this situation though.

[DonR]

For the hatch ducting I was picturing tubing welded together in an upside down U shape on the sides & top. The tubing would have a slot milled in the trailing edge for the air to exit. Similar to a stalled rear wing.

I might try just sucking the air in from the underside of the car first. Flexible ducting hose from a race supply shop may help facilitate routing to the suction side of the turbo if you want to bring it from the front of the car.

I would put the turbo directly after the cat, for simplicity sake. If it doesn't work out, you can get a pipe made to put the exhaust back to normal.

[Frank Lee]

I think the question that needs to be asked is, do turbos output more than the input? Otherwise, how can it apply more "thrust" than simply directing the exhaust to the low pressure area(s)?

[bs0u0155]

Frank. That's a relevant point. I think the key is that a turbo charger removes temperature and related pressure from the exhaust... up to 200C. In this case this can be used to move a larger volume of air at low pressure for aerodynamic effect. A bit like a high bypass turbofan engine.

[SoobieOut]

If your car is travelling at 60 MPH, and the frontal area of the car is 2.5 sq. ft. This would work out to be 5280 ft/min * 2.5 = 13200 CFM. I believe turbos are still rated in CFM (Cubic Feet Per Minute) .

Still sounds like a great idea though, removing air from the front and replacing to the rear void.

Maybe a giant conveyor belt under and over the car with embedded vertical plates spaced close together, like the Tesla Turbine.

Well there's my 2 cents...

[Frank Lee]

There ain't a whole lotta pressure there.

Maybe if cooling is an issue a simple heat exchanger would do.

Most little cars are pushing more like 24 sq. ft, not 2.5 sq. ft. of frontal area.

[Phantom]

I do not know if frontal area matters so much with this plan. The reason why is if the car has attached flow till the end of the car then the area that you are trying to fill is only the size of the wake and then you are just trying to push the wake back to remove drag.

[robertwb70]

Agreed about the trailing wake not being 100% of frontal area I'd estimate for most cars it is still about 80% of frontal area though, so lets use a 25 SF frontal area example.
25 SF * 5280 * 0.80 = 105,600 CFM

Since we want to cruise (60 MPH to match above) at a low RPM for FE lets say 2,500 RPM and a fairly average size motor 2.0L (0.0706 CF) we get an exhaust output of roughly 88 CFM so the turbo would have to add 1200% more CFM for 100% fill, I don't think that's even close to being possible.

Considering 100% fill is probably not necessary for a sizable FE gain probably still wouldn't get us anywhere near reality, even at 50% it's still 600% more than engine exhaust needed from the compressor side of the turbo.

[vtec-e]

Agreed on the power requirements if using a turbo etc. to provide high pressure air, but the turbo could be helped with high pressure air already there if the intake is in the right place. F1 cars are using this tech so they must be onto something.
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[bs0u0155]

I think the idea is to not just fill in the wake but to control the attached flow at the edge of the car somewhat. See the Renault experiments with square-backed cars upthread. Also in F1 they're using exhaust "blown diffusers" to keep the flow attached at angles it would normally detach from. Those angles are going to be different at 200mph compared to 50mph though! My thinking is that a relatively small amount of air can be used to "direct" the attached flow inwards minimizing the wake, and filling it a little too. Renault were getting positive results from a small electrically powered system, a turbo is going to be a lot better than that at delivering air.