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Supercharging my Twin Turbo...

I have a 964 TwinTurbo RS Tuning built engine waiting to go in my 964 Turbo but I have recently been looking at superchargers, something I thought I would never looked at it.
However after some reseach I see that you could use a SC (wipple type) to intially boost at low revs and when the turbos come into play switch over to them.

I see that the Rally Lancia DELTA had it the two and VW are doing one as well. Also BeepBeep posted a Sweed also successfully doing it...

So its been done and I wanted some input from you guys on how in theory it could be done. I think there are enough SCs around on ebay to pick up cheap enough to give the experiement a go.

If it were to be done I though you need to have a bypass system for the SC (on idle and when the turbos are producing more boost than the SC) so some sort of butterfly/solenoid to create a vacum for the SC and the turbos can bring in the air direct from atmosphere whilst the SC just spins with no load and so no HP drain from the engine. i have seen you could also have a magnetic clutch but this would be more complex and not allow the turbos to breath all the air in they want.

Second is the switch to shut of/by pass the SC, an ECU could do it but I thought maybe a mechanical system i.e a vac line from the turbo and one from the SC, when the turbo boost is greater than SC boost the switch happens... Dont know how I can do this...

If anyone has any ideas or theories or what SCs to look at etc I would appriecate it. I understand somepeople will be against it but with respect this is not what I would like the thread to be about. Just about the fact that if you could combine both you would get an amzing steep torque curve and a faster spoil up so you could run bigger turbos as well.

I might never try it but hey its happening out there...


Cheers

Miles
Old 11-22-2006, 06:57 AM
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The parasitic loses because of the supercharger would be subtracted from the turbo gains on boost. Not a good solution, IMHO.
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Old 11-22-2006, 10:46 AM
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The supercharger is on a clutch that would disengage after the turbo spools. The supercharger also has a wastegate that dumps into the tubo inlet and a bypass around it.
There should be very little parasitic drag with that setup. Unfortunately the Turbo/SC combo makes for a very complicated and heavy addition to any engine. It would also need the right EFI and electronic controls to make all the events work together optimally.
Very interesting project. I have thought of doing it myself if it could be justified.
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Old 11-22-2006, 12:06 PM
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I personally don't think it's worth the extra expense. You can get pretty darn good response/spool from a properly matched pair of GT ball bearing turbo's.
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Old 11-22-2006, 03:36 PM
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For a 930 (or 965) I totally agree that you cannot justify the project. Modern turbos with the right combination of headers, fuel, timing, and gearing have zero lag.
As an excersize in experimentation and mechanical creativity it would be an interesting indevor.
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Old 11-22-2006, 07:57 PM
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I think the experiement would be interesting...

But its a good point about the BB tubos with no lag and also the new VTG Turbos on the 997.

However are they really ZERO lag in all gears under all loads? Any charts of a torque curve?
An SC will produce boost at 0 revs...

The cost wouldnt be too extreme if you can do the DIY yourself. There are programmable ECUs out there such as Megasquirt where you can program it yourself. The added weight would be my biggest concern.

I would like to see the boost/torque curves on the BB turbos, if they are that good I would swap them for my two k27s (ex race engine)
Old 11-22-2006, 10:51 PM
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Chris Caroll of TurboKraft has used the GT BB units extensively on TT 3.6L setups. He'd be able to give you accurate performance stats on how they perform on a comparable setup as yours.
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Old 11-23-2006, 01:45 PM
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Thanks but regarding the lag I think that if lag was zero then there would only be one turbo right? Wrong I guess... still the big turbos that can push more air HAVE to have more lag than the smaller ones... also it depends on which gear you are in.. floor it in 6th at low revs it gonna take a lot more time for the boost to come but a SC would build up... man this setup could be something!

So the theory still stands I guess... I didnt really want this thread to be a turbo vs SC debate as its been covered too much and the reason why there is such a big debate is that they both have advantages of their own hence why I wanted to see how possilbe it would be to have both from a perfomace point of view only.

I think it would work- the physics says, if you disconnect the SC when the turbo comes on you wont have any power loss... its just for the low revs and the power to drive the SC at these revs is less than the power gained- yes youll use more fuel as its not so ineffeicent but thats economy... not something im too worried about in my 911... this setup wouldnt work with a set of small Turbos more big ones...

I think tho this is maybe not the best place to discuss. I dont think its hard to do to control the swithcing.

I am going to still look into it, cost wise will farily small to try.

Cheers
Old 11-24-2006, 01:20 AM
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Miles - I found the tread (from a year ago) that has the schematic and information you are looking for.

SSI's with a Supercharged 3.2

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Old 11-26-2006, 10:26 AM
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I did this many years ago on a Toyota MR2 Supercharged with a turbo kit from HKS called a twincharger. Basicaly it added a very large turbo to the factoru SC.

The setup was similar to the above Lancia. An adjustable controller was provided to switch off the SC clutch at a preset turbo boost.

The hardest part is to provide a smooth transition from SC+turbo to just turbo. If you do not get it right when you cutover to just turbos the boost falls below when it was with sc+turbos, then SC kicks back in and you might get this oscillating sensation.

If you ran the turbo on its own you could count to 4 before any sort of acceleration could be felt. However with the SC the response was instantaneous with lots of top end power.
Old 11-26-2006, 05:06 PM
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Fellas, GOD created "lag" to give V8's a chance

IMHO, I think lag is overrated, especially if you've fairly accurately matched the turbo to the engine, for it's intended purposes. The "spool-up"/response you can get from modern day turbo's is amazing. I'm running a GT35R ball bearing turbo on my 3.3 and lag is not an issue (to me). Plant my foot and I get neck snapping acceleration "almost" instantaneously.

Had I gone a slightly smaller GT30R, I really think lag would be eliminated completely.
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Last edited by WydRyd; 11-26-2006 at 05:51 PM..
Old 11-26-2006, 05:47 PM
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Thanks Brain for the pic, thats the one I saw in the Corky Bell Turbo book.

Koenig911... very interesting to hear someone with seat of the pants experience. Its true the modulation of the bypass is key to make it work properely.
I see that all these are setup to have the turbo before the SC, is that because of the compounding of the boost if it was the other way around or what?

if this was to work I really only think its good for a set of BIG turbos GT35R or 40s perhaps that are effcient at high rpm and flow ALOT of power and are not instant response at low rpm. I would of thought this would be no good for less than 650HP engine.

There should be also some hidden tuning in this setup if you match the SC and Turbos together for an optimum combination.
Old 11-27-2006, 12:24 AM
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