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  #11  
Old 11th September 2017, 12:49 PM
MikkiJayne MikkiJayne is online now
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SQ7 Electric bi-turbo



TT Clubsport Electric bi-turbo



Both of these use a separate 48V electrical system for the turbo IIRC.

I saw a precursor to this about 15 years ago. It was the compressor side of a Powerdyne supercharger (ie turbo compressor) built on to a small but powerful 3-phase motor. It had an inverter the size of a car battery and power cables as thick as your thumb It was originally intended for truck engines I think.

Magnetti Marelli showed a potential OEM version of the heat recovery system used in F1 at the Autosport show a couple of years ago:

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  #12  
Old 11th September 2017, 03:54 PM
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Excellent
Now we just have to wait for some used SQ7 turbos to start appearing on ebay.
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  #13  
Old 12th September 2017, 10:08 AM
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Looks like SQ7 has a 48v battery? For all electric systems?
https://www.youtube.com/watch?v=sHZjo0e5aGg

So this is very interesting, if this can be made to work for under 1000 then I am seriously interested lol.

So how would the coding work? Can it all be kept separate form the engine ECU? I assume the DC permanent magnet motor has its own dedicated chip and software, would it need a sensor attached to the throttle pedal or something to know when to switch on? I am guessing if its similar to an rc plane electro-ducted-fan then it can simply go to full throttle when its on no need to modulate motor speed.
Would it need to be manually switched off completely when its emptied the capacitors to allow them to recharge?

If in our applications it runs off a dedicated capacitor bank, we could have some cool charging state LEDs to display when its fully charged to go again?

Would it go after the air filter but before the MAF, and would it need to be in a butterfly valve controlled by pass tube so that its not blocking the airflow when its not in use?

And is the D2 ECU software adaptive enough for that much extra airflow or would it need a custom map?

Last edited by Goran; 12th September 2017 at 10:12 AM.
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  #14  
Old 18th September 2017, 10:46 AM
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Run a reserve of compressed air in a tank for charge purposes using the existing 12v system.
Then either drive a turbo with compressed air, or pump the air directly into the manifold (driving a turbo is probably more efficient use of the air reserves). Audi are already doing something like this to cancel out turbo lag in some models.

Then: Extra air = extra fuel.
You'd need a dedicated injector, like a throttle body injector or something and a standalone ecu to drive it. The stock ECU and injectors won't have the adjustment range to cope with intermittent pressure spikes.
All a bit complicated.

Wet shot of NOS is much simpler!

Also, where would you use this intermittent power surge?
Drag strip? Traffic light grand prix? It wouldn't be of much use up through the windies on a mountain climb.
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  #15  
Old 19th September 2017, 04:07 PM
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Agreed about where you would use a compressed air shot on the streets, and NOS for that matter.
Hence why electric turbo seems more convenient and a milder boost that could be available often as it keeps charging as you drive.

Not sure why compressed air should be different from a NOS shot, surely in the cylinder the result is the same, increase O2 density requiring more fuel to burn to produce more powerful bang. If stock injectors can cope with a certain level of NOS they can cope with air compressed to similar O2 density as the NOS surely?

Last edited by Goran; 19th September 2017 at 04:09 PM.
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  #16  
Old 19th September 2017, 07:27 PM
MikkiJayne MikkiJayne is online now
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Apply some beermatematics to the compressed air idea:

The V8 consumes 2.1 litres per revolution. Lets work on 0.5 bar of boost, making that 3.15 litres per revolution. A 0-60 dash in an S8 with 500hp would be sub-5 seconds. We'll use 5 seconds for simplicity, and lets assume an average of 4000 rpm (1000-7000 range)

4000rpm for 5 seconds would consume 1050 litres of air. A standard scuba tank holds 2300 litres, so would be good for two 0-60 runs, or 10 seconds. The second run might not be quite so good as the pressure in the tank reduces significantly, but the gearbox would have blown up after the first run anyway so that probably doesn't matter
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  #17  
Old 19th September 2017, 10:52 PM
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Delivering 7psi boost on 11:1 compression with indirect injection is asking for trouble anyway.
My idea with an air tank is to use a relatively small one and drive an air drill/die grinder type arrangement with it to spin a turbine.
10-15 thousand rpm with high torque should get some decent boost.
You'd need high pressure in the tank though (100_150psi) which I'm not convinced a 12 volt compressor could deliver, which means a mechanically driven compressor, which results in mechanical losses at which point you may as well supercharge it...
(How's that for a circular argument!)

As for delivering extra air, that's only half the story.
Air in and of itself will not give you power.
What it gives you is the ability to burn more fuel.
Providing as little as 10% more air to an engine will go beyond the ability of the injectors (and ECU map) to provide sufficient fuel to burn at the ideal stoichiometric ratio of 14.7:1 (minimum air:fuel ratio at which complete combustion occurs and therefore provides maximum efficiency).

So without adding more fuel you're wasting your time.

You end up with a lean burn which beyond being a waste of all this air you've gone to the trouble of generating, actually burns hot, thereby reducing engine efficiency too.

Similarly with NOS. NOS in and of itself does not provide power. It provides a very rich and dense oxygen mixture with a lower stoichiometric ratio than that of regular air - the same volume of NOS can burn about 30% more fuel than that of air and achieve complete combustion. It's stable and won't explode like pure oxygen might.
But it still needs fuel.
Most NOS comes as a 'Wet Shot', which contains fuel at the correct ratio to burn. That's why they call it "power in a bottle".

One idea I have been playing with is some sort of water injection. They use it in turbocharging to create a cooler denser charge in the cylinder, but beyond that steam has a higher expansion ratio than air and won't affect air fuel ratios. So adding a small volume of water (we're talking droplets here!) might improve the energy of expanding gases during combustion as it flashes to steam and might slightly improve engine efficiency as it absorbs some of the heat energy.
Though like most things, if there was something in it someone would already be doing it!
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Current:
2001 Audi S8 - Brilliant Black with Black interior, Solar Sunroof, Tinted side and rear glass, RNS-D, XCarLink, Bose, clunky old phone in arm rest!
2002 Audi S8 - Project
Replacement head coming thanks to MJ
Avus Silver with Black interior. All features as the '01, with the 'S' mode auto shifter. Dodgey rear tint (need to find a way to get rid of that).
Family:
2009 Volvo XC90 V8 R Design
- has a louder more obnoxious exhaust than the S8, sounds great! Love this thing - Q7 was double the price, and certainly not double the car!

Sold:
1997 Audi A4
- Hamilton's Club Sport, Achat Grey (will miss the old girl)
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