James
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| posted on 11/5/06 at 11:42 AM |
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Twin Superchargers.... why?
Was thinking about the extremely cool Koenigsegg on Top Gear and thinking about it's twin supercharger system.
I understand the basics of turboing and supercharging.
I can understand the reason for twin turbos so as to have 2 smaller ones to help prevent lag. Or one small, one large. Or else maybe you want to drive
one off each header bank of a V engine.
But a supercharger is driven off the crank right? And can presumably feed an air box for both inlet manifolds so what's the point of 2 when you
get no lag?
Is it that one is on a clutch mechanism so it kicks in at higher revs so as to reduce the charger's power consumption at low RPM?
Or are they indentical and it's so one feeds each header? What's the benefit of this?
Thanks,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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emsfactory
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| posted on 11/5/06 at 11:53 AM |
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You can use a twin chargers to make a staged system. So one charger will increase pressure by a certain amount and this is then fed into the second
stage charger which ups it again. Dont know if thats what the konniieiengngngnsnsnsgeegegggggg uses though.
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mookaloid
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| posted on 11/5/06 at 11:53 AM |
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A couple of guesses...
Available space under the bonnet? dragsters have them on top of the V8 and they stick up about a foot above the engine and bonnet.
the closer to the inlet ports the better from a response point of view?
if the supercharger is further away from the inlet there might be a (very momentary) lag whilst the air starts to compress up to working pressure, so
1 for each bank of cylinders could work better.
cheers
Mark
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nick205
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| posted on 11/5/06 at 12:04 PM |
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....or possibly just a marketting tactic - 2 always sounds better than 1 doesn't it?
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olv
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| posted on 11/5/06 at 12:16 PM |
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i think 800bhp sounds good whichever way you get it 
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NS Dev
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| posted on 11/5/06 at 12:17 PM |
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I will take a guess and say it's probably using Vortech type centrifugal blowers as they are very compact and small.
With these, their max pumping rate is not really enough for large engines and you need two. (a pretty std conversion on modern small block chevies in
US road cars)
They use a pair of large turbocharger compressor housings driven by an epicyclic gear train and belt driven off the crank, so the problems are not
dissimilar to turbos in terms of airflow, except that the speed constraints of the mechanical drive limit the top end air delivery compared to the
equivalent turbo.
You were thinking along exactly the right lines though, there's not really any technical reason to use two unless you can't get one that
is big enough, or it's difficult to mount one because it is so big!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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NS Dev
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| posted on 11/5/06 at 12:19 PM |
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quote:
Originally posted by olv
i think 800bhp sounds good whichever way you get it
Why the superchargers though?
Ultima have 720hp from a smallblock chevy running a good old carburettor and nowt else, and yep it is road driveable no bother, trying to get my mate
round with the demo car so I can get a ride out with the new engine! Last time out it "only" had 640hp!!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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DaveFJ
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| posted on 11/5/06 at 12:45 PM |
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slightly OT sorry......
Years ago i had a mate who got 700+ bhp out of a ford v6 in a capri....
admittedly he had twin turbos AND a supercharger.. (never quite sure how that worked) and the engine alone cost him over £10,000 to build - thats in
'91.....
he got a 'centre spread' in fast ford (i think)
Dave
"In Support of Help the Heroes" - Always
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rusty
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| posted on 11/5/06 at 01:10 PM |
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The thing is with superchargers they work best at a certian RPM so you can't just spin them faster to get more air so it may even have two for
better boost over the rev range.
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muzchap
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| posted on 11/5/06 at 01:15 PM |
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Best way is as the CAPRI did
Supercharge for low down rev range, then turbo for high end
That must have been some Capri!
How many bags of cement did he have in the boot
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If you believe you're not crazy, whilst everybody is telling you, you are - then they are definitely wrong!
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jono_misfit
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| posted on 11/5/06 at 02:26 PM |
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Run a decent anti lag (or response system as they all call it in WRC now) on a turbo and the super charger doesnt help that much........
Of course the turbo turbine doesnt last that long if you do.
If you doubt the difference an anti lag system makes, you need to look at the torque curve from a wrc car.
jono
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NS Dev
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| posted on 11/5/06 at 02:59 PM |
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Yea, but they only run them to fit with regs, they are a right hotch potch of a system which I would not want on any car I ever work on.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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jono_misfit
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| posted on 11/5/06 at 03:50 PM |
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I dont disagree with you that their not ideal, but making a working anti lag system is a bit easier than compound charging and is lighter in
weight.
Personally i'd rather have a larger displacement than forced induction.
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clutch_kick
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| posted on 11/5/06 at 03:53 PM |
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It's all got to do with Compressor efficiency. First compressor feeds into second, achieving a greater mass flow of air, with a lower relative
increase in air temperature.
This is used in modern jet engines which are generally twin spool ( two concentric shafts ), where the 'Core' of the engine would
generally have 9 stages of compressors to achieve the highest efficiency.
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MikeRJ
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| posted on 11/5/06 at 05:47 PM |
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quote:
Originally posted by jono_misfit
If you doubt the difference an anti lag system makes, you need to look at the torque curve from a wrc car.
jono
Turbo lag is an entirely different issue to the RPM at which useable boost is made. Do WRC actually use anti-lag techniques to spool up the turbo
from very low engine RPM?
[Edited on 11/5/06 by MikeRJ]
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jono_misfit
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| posted on 11/5/06 at 07:47 PM |
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As far as im aware, yes.
Due to the inlet restrictor theres only a very limited power band and the engines dont rev that high so they try to make the most of it.
The response systems are used to have the turbo spooled, so when the throttle is opened its already up to speed and can deliver useable boost
pressure.
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jon_boy
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| posted on 11/5/06 at 10:24 PM |
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Anti Lag. As far as im aware when you come off the juice (vacuum sensor?) the timing gets mucho retarded and goes bang with the exhaust ports open so
it all pops in the exhaust/turbo making it spin up fast off throttle, but ruining half the engine. Hence the flames at the gear changes/off throttle
moments. Not the sort of thing you run if you have any kind of budget.
[Edited on 11/5/06 by jon_boy]
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