coyoteboy
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| posted on 3/3/14 at 12:31 AM |
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Curious as to the choice of the rotrex, why that over a positive displacement?
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Mr C
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| posted on 3/3/14 at 09:11 AM |
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quote:
Originally posted by coyoteboy
Curious as to the choice of the rotrex, why that over a positive displacement?
No real reason, right price, compact installation, self contained lubrication system, liked the power figures.
Girl walks into a bar and asks for a double entendre, so the barman gave her one
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jeffw
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| posted on 3/3/14 at 09:30 AM |
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Why would you use Positive Displacement over a Rotrex ? Roots blowers tend to be only 40–50% efficient at high boost levels; by contrast centrifugal
(dynamic) superchargers are 70–85% efficient at high boost
[Edited on 3/3/14 by jeffw]
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big-vee-twin
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| posted on 3/3/14 at 01:17 PM |
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I designed my inlet manifold to make allowance for the TPS, it was manufactured by Fast Dan
[img]
 
Focus Pulley
[/img]
The GSXR TPS (2001) is a variable resistor so doesn't act like an on/off switch.
[Edited on 3/3/14 by big-vee-twin]
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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coyoteboy
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| posted on 3/3/14 at 01:35 PM |
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quote:
Why would you use Positive Displacement over a Rotrex ? Roots blowers tend to be only 40–50% efficient at high boost levels; by contrast centrifugal
(dynamic) superchargers are 70–85% efficient at high boost
Same reason all the OEMs use them, reliability, boost off idle, self contained lube. I was just curious what caused the choice as I'm currently
twincharging my tin top and decided to go with a posi displacement (with the turbo operating at max efficiency blowing into the super operating at max
efficiency) (naturally they multiply efficiencies so some drop but worth it for the off-idle boost.
Point me to a supercharger that's 85% efficient at 21psi on a 2 litre engine and doesn't have the hole at the bottom end please, I need
one! FWIW in a reasonable boost level it's no problem for a posi to hit 65% efficient.
[Edited on 3/3/14 by coyoteboy]
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jeffw
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| posted on 3/3/14 at 02:05 PM |
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The Rotrex produces maximum boost at maximum revs. It is effectively a belt driven turbo. The 9.49:1 planetary gear system get the turbine upto 100K
rpm and it produces 16PSI (in my C30/94). Not sure any of the Rotrex C series will do 21PSI.
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coyoteboy
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| posted on 3/3/14 at 08:34 PM |
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Yup, so not high boost or off idle, which defeats the point of a supercharger to me in my app but everyone has their own target so it's not
"wrong". I just wondered what the reasoning was genuinely. Posi disp are heavy and hard to mount so I was hoping to be convinced the other
way lol.
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coyoteboy
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| posted on 3/3/14 at 08:46 PM |
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Fwiw the rotrex range never gets above 72% efficient at any boost level. Compared to the Eaton which sits around 68-65% in the range I want to work,
the difference is about 10 degrees in outlet temp and my intercooler will deal with that just fine! (Thread jack over, sorry! )
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Mr C
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| posted on 3/3/14 at 09:10 PM |
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quote:
Originally posted by coyoteboy
Fwiw the rotrex range never gets above 72% efficient at any boost level. Compared to the Eaton which sits around 68-65% in the range I want to work,
the difference is about 10 degrees in outlet temp and my intercooler will deal with that just fine! (Thread jack over, sorry! )
No problem Coyote, I'll leave you two girls to argue over efficiency charge temps etc etc, not my style, moved on from the playground a good few
years ago.. 
As you say its not wrong,..there's more than one way to skin a cat, I'm not that clued up from a technical point of view, can't be
arsed with the finer detail, if it works it works, though I understood that power delivery is pretty linear without the wallop a turbo gives you, so
you can get on the loud pedal earlier exiting the bendy bits. The engine can also run higher compression 10:1, 10.5:1 at a push, so the engine
isn't too sluggish at low revs. The spec isn't too far from the 620R which has the same blower and seems to go pretty well.
I didn't want the hassle of running a turbo after my last kit car which was scooby engined. I had every intention of keeping it simple but sadly
I can't help myself, if its good enough for a caterham its good enough for me.
BTW I quite like the idea of a roots type blower mad max style just for the shear hell of it Looking forward to seeing how your system works, sounds
mega, similar to the systems used in some group B cars Lancia, if I remember correctly. All the best with it and the build.
Girl walks into a bar and asks for a double entendre, so the barman gave her one
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coyoteboy
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| posted on 3/3/14 at 09:16 PM |
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No playground arguments involved, just technical detail tradeoffs which is just engineering. I'm an engineer, it's my job to identify
the best possible solution given constraints and requirements. Can't help but apply that to normal life! It makes a fundamental difference to
the power delivery and method.
I will open up a thread when I figure out where to jam the Eaton lol
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Mr C
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| posted on 3/3/14 at 10:01 PM |
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Best put it on an engine, why waste a good supercharger,  l look forward to your build thread.
Girl walks into a bar and asks for a double entendre, so the barman gave her one
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jeffw
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| posted on 3/3/14 at 10:07 PM |
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The linear nature of the Rotrex package suits lightweight cars better, in my opinion, that either a Turbo with its torque spike at 3-4K rpm or a
conventional, high torque at low rpm, superchargers. They specifically work well with high compression engines and make them drive like
'Super' NA engines and not a boosted engine.
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Mr C
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| posted on 9/3/14 at 10:00 PM |
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Managed to fit the gearbox to the engine this afternoon, a Mazda 3 MPS box to a Ford Duratec. Clutch needs a little work but no big deal. The standard
ford boxes self destruct after 200bhp this should be good for double that.
[Edited on 9/3/14 by Mr C]
Girl walks into a bar and asks for a double entendre, so the barman gave her one
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