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twincharger project
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Cédric  



Joined: 27 Aug 2004
Posts: 1973
Location: Sweden

PostPosted: Tue May 08, 2012 9:52 pm    Post subject: Reply with quote

Hm, pushing through a supercharger, Will be interesting to see how it works at high rpm high boost. There is some serious work put down in this car !

I drive a car with the system above (1.4l 180hp) evry day, and the character is so darn nice, I hope you will get similar but much more HP of course. Its possible to spin wheels almost from idle thanks to the little eaton charger
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Wed May 09, 2012 4:00 am    Post subject: Reply with quote

I'm curious why you would put the turbocharger before the supercharger. It seems like it would be better to have it the other way around...positive displacement S/C providing boost right from idle with no lag, forcing the T/C to spool up sooner, and allowing it to take over the higher RPM range...
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simsport  



Joined: 06 Nov 2002
Posts: 573
Location: UK Warrington

PostPosted: Wed May 09, 2012 4:46 am    Post subject: Twincharger Reply with quote

I am always ready to consider new approaches to things and this idea of not using the bypass valve is interesting if a risk. The risk of course being that the resistance to flow provided by the supercharger kills the efforts of the turbo. Clearly a supercharger is a PD pump (not really an effective PD pump unless its internaly compressing) whulst a tubo is effectivly a centrifugal pump converting velocity to pressure via a scrole or volute curve.

Where a supercharger can cope with back pressure (not too much of course due to bleedback and reworking the air and raising temps) the Turbo doesnt seem to cope very well.

I think on balance the supercharger first technique is the one I would go for. Even then this throws up a few issues , for example the turbo exhaust manifold has an exit that encourages the velocity of the exhaust gasflow, but that would also provide backpressure to the superchager and that can lead to elevated temps for the reasons above.

Biggest issue has to be the 'K' valve design and the fuel control when that is operating as the transition between supercharger and blower has to be smooth and not slow acceleration of the system as that all adds up to rough/hesitant running, a criticism I have read about some poorer twincharger projects.

Its all a bit complicated!

Cheers
Simon
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morghen  



Joined: 21 Jan 2005
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PostPosted: Wed May 09, 2012 6:26 am    Post subject: Reply with quote

interesting stuff.

i'm a systems engineer...have been working in automotive for 5 years. here are my thoughts

I'd go for the VW route too...why? i could use a smaller SC that could blow trough the turbo at lower RPMs...and at higher RMPs i'd switch the valve and turn off the SC. With the VW setup the valve does not have to be such a complicated thing...the systems are linked but at the same time independent....the only thing that has to work "backwards" is the turbo for low RPMs

for your route...the SC pulls trough the turbo at lower RPM and at one point the roles reverse...the turbo blows trough the SC.
for this..you need a big capacity high flow SC...otherwise the system will choke. btw, do you plan to dissconnect the SC at high RPMS using a magnetic clutch?

What will be interesting from my point of view..is the balance points of the switching from master to slave between the SC and the turbo...and how those balance points move and behave during shift ups and downs....furthermore..how does that balance point affect the driveability, reliability and performance of the whole system.

All this hastle going on would put some stress on some parts that..perhaps were not designed to be exploited in that way...so you have to consider all this stuff.
i.e. when blowing trough the SC (if you dont dissconect it) the energy transfer might reverse and you might find stress in the belt and tensioner coming from the SC and going to the crank pulley.

i havent studied the VW route very well...but yours seems like it wastes alot of energy, starting from the fact that for high rpms you would have to keep the magnetic clutch (if you use one) open to dissconnect the SC, both SC and turbo work both ways (blow trough and be blown/pulled trough).

i dont like the fact that you are somehow restricted to a higher volume SC.
i dont like all that dual dependency...from my point of view..thats a nightmare to control.
the only thing i like about your aproach is the fact that the SC feeds pressure directly into the intake while the vw aproach feeds pressure into the turbo.

cheers!
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leadfoot  



Joined: 11 Dec 2002
Posts: 2222
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PostPosted: Wed May 09, 2012 11:51 am    Post subject: Reply with quote

Not sure where you're all getting your info from? I'm no expert in these systems but i'm drawing from a couple of pricipals, a pd sc has no internal compression but can pass compressed air right? It then moves with enough rotations to further compress this trapped air between it an the manifold thereby compounding the pressure, albeit with more heat. So how would it be a restriction?
As to backpressure build up of a turbo, a turbo spools to build up gas in a plenum, normal operation right? Excess pressure read as psi of a gauge that cant be ingested by the motor until the wastegate sees its spring release pressure and prevents the turbo from outputting any more pressure right? So is this not the same situation whereby the turbo builds up pressure but between turbo and sc until wastegate releases?
One issue might be scavenging enough air from a turbo that hasn't spooled enough to flow the required cfm, but im only chasing about 3 psi before the turbo should take over, have to calculate require cfm based on the compressor map,
Hope this explains where im coming from,
Stu
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Cédric  



Joined: 27 Aug 2004
Posts: 1973
Location: Sweden

PostPosted: Wed May 09, 2012 3:43 pm    Post subject: Reply with quote

If you want to read more specific details about the VW system, check out this pdf:
http://www.volkspage.net/technik/ssp/ssp/SSP_359.pdf

How does a supercharger seals work when the intake air is boosted? Havent worked with any superchargers so I dont have them fully under cotrol.
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morghen  



Joined: 21 Jan 2005
Posts: 8164
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PostPosted: Wed May 09, 2012 5:54 pm    Post subject: Reply with quote

The air does not stay compressed once compressed...if it finds a bigger volume in the "next door" it will decompress.

While accelerating...the SC's efficiency might be lowered due to the breatheing restriction caused by the turbo at lower RPMs.
Then, for higher RPM's the turbo's efficiency might be lowered due to the restricion caused by the breatheing restriction induced by the SC.

I think VW guys are not that stupid...you have to keep this in mind



All in all...the system you want to build seems to me a system that will create tensions...and tension will bend the weakest links of the system.
Due to the design my guess is that air will be the main damping element...however it will heat up more.
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leadfoot  



Joined: 11 Dec 2002
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PostPosted: Wed May 09, 2012 10:20 pm    Post subject: Reply with quote

yep it's all a bit of an experiment at the moment,
once I get some data back I can work out any mods required... the systems flexible enough at the moment to play around with.
thanks for all the input so far guys...
Stu[/b]
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leadfoot  



Joined: 11 Dec 2002
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PostPosted: Thu May 10, 2012 5:20 pm    Post subject: Reply with quote

possible revisions, ultilising a one way 63mm valve utilising a pressure actuator from a wastegate and cam arrangement, depending what the sc makes peak I'll set the spring around the same pressure, and a vac controlled 1" bypass valve to allow direct air from the fuel dissy into the blower,
Stu



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RC  



Joined: 25 Mar 2007
Posts: 2634
Location: Australia

PostPosted: Sat May 12, 2012 5:50 am    Post subject: Reply with quote

leadfoot wrote:
yep it's all a bit of an experiment at the moment,
once I get some data back I can work out any mods required... the systems flexible enough at the moment to play around with.
thanks for all the input so far guys...
Stu[/b]


Oh yeah, but what a bloody great & innovative experiment it is! Hats off again to you Stu for thinking way outside the box.

Think that some of the critics are failing to understand the dual stage compressor theory however. Clearly not scuba divers for example, and seen a multistage compressor at work. Large volume of air is initially compressed in large cylinder (piston pump) then in to a second stage at HP to be further compressed, (smaller displacement pump required) then a 3rd or even 4th stage to arrive at <4000PSI.

Personally perceive the CIS to be the weak link and probable issues with temp rise, detonation and ignition control, but am fully open minded and happy to offer any support while watching the bar being raised again. Need to start reading from the beginning but did I guess SC14? Constant drive above idle? The blown commy boys put the upper limit of the teflon melting at 17-21 PSI but that`s with such a massive overdrive to get into 3.8L

Likewise with the transfer tube, both innovative and well done. Be interesting to see the results and even more so if we as a community can gather some quantitative data. Also have some to offer myself, such as an 8mm orifice for permanent bypass results in more detonation damage/ melted pistons to #3 than #4.

Looks like the climate control system may also be on the cards again soon too eh?
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Allan @ DTA wrote:
I have no issue with superchargers, they are for guys who want to drive a car rather than talk about horsepower with their baseball cap on backwards
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leadfoot  



Joined: 11 Dec 2002
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PostPosted: Sat May 12, 2012 12:19 pm    Post subject: Reply with quote

Thanks RC,
I'm obviously new to the twincharging concept like many of us, thankyou for the info as I managed to find a few more sites with calculations from this approach,
interesting to note that in most multistage compression cycles the cylinders get smaller, translating this into pipe size vs throttle size assuming would equate to a safe reduction in piping and throttle under 2.5" and not overly effect the system.
If anyone wants to contribute some helpful calculations then this would be appreciated... I'm quite open to conversation and don't feel abashed to add in some flow calcs or efficiency calculations...

The CIS outlet orifice for the fuel dissy is 60mm, I guess this is inline with the size of the stock throttle body diameter. the turbo inlet I have is approx 70-75mm and then it's pretty much a 2.5" run all the way to sc apart from the turbo comp outlet which is 2" to the first interccoler.

So by my maths an outlet size on the dissy should theoretically be able to flow
.76 x cfm@bhp/pipe rsquared and stay under 440cfsec and not have excess drag right? pulling this calc from corky's book...
I have heard the 400hp limit of the CIS system bandied around previously, take that with a grain of salt... lets say it can do 400hp for the moment and then make assumptions on what it could reasonably do...
.76 x 600cfm@400bhp/60mm pipe = 326 cf/sec approx
or lowering the hp and flow
.76 x 450cfm@250bhp/60mm pipe = 245 cf/sec approx

The extra fueling can be taken car of by my 5th injector driver. This is map based and can do duty cycle for the injector as well. I didn't even use it for 10psi worth of air flowing from the turbo previously, it's there as a contingency and should easily support another 20-30hp above what I make now... I can always swap injectors if needed or add the second one I have as it will drive up to four in total...


I'm using the sc12 again, I have a spreadsheet that I plotted all the flow characteristics and pulley sizes on, so can have a good idea of where I can go in regards to pulleys. I am using a frequency based controller, it's the Jaycar kit with internal relay that can drive 4A. Running this off the ignition dissy and using the start trimpot to control on rpm and the hysterisis of the circuit will control the range of on to off rpm. If I need to I can alway add in a pressure based switch or microswitch off the bypass valve to disengage the clutch circuit on top of this.
At the moment sc drive calculation is between 2.78 and 3.78 psi based on efficiencies and intercooler loss... Always assuming it makes less than my highest figure.
I added an extra "loss" integer into my equations after I got my data logging software and boost figure back at various stages last build, so this should give me some more acuracy although i'm using 2 intercoolers I haven't used before.

A bypass valve would certainly add in efficiency from freeing up drive loss from the sc and reduce the heat buildup, it would lower overall boost and I'd have to have another t valve on the wastegate top port to overcome the 10psi wastegate limit, question is would this benefit be worth the extra effort.
hmmm decisions decisions....
Stu
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leadfoot  



Joined: 11 Dec 2002
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PostPosted: Wed May 16, 2012 7:33 pm    Post subject: Reply with quote

made from a ford throttle body and a vaccum actuator, 2.5" single butterfly,
the actuator is pre loaded in reverse and when boost is applied it opens up the airway... on the cam I have cut a few notches to allow for the spring rate to be changed too
Now I have no idea if the actuator diaphragm will last, I got a full manifold, 6 x injectors, fuel rail, throttle body and vaccum actuator for $20... thought I'd utilise what I had and see if I could make something to experiment with...
So far it's doing what it should, but I need to do a bit more testing to work out the opening pressure as my compressor only has 1/2bar incriments.
Stu


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Joes924Racer  



Joined: 03 Nov 2002
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PostPosted: Tue May 22, 2012 1:20 am    Post subject: Reply with quote

Hello, Its a bit complicated. Your doing great work. Would love 2
you see a
engine bay running vid.
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leadfoot  



Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia

PostPosted: Mon May 28, 2012 12:22 pm    Post subject: Reply with quote

a link to a three part youtube clip on twincharging design, no affiliation...

http://www.youtube.com/watch?v=1arORukm_S8
http://www.youtube.com/watch?v=hDm0g5xA8No
http://www.youtube.com/watch?v=zWu0uTFESg4

Finished new shift rod modifications and engine bay wiring... got the torque tube and engine back in yesterday, making a start on some hookups... still need to get tranny back in and make a start on rad/intercooler and piping back in place,

saw this on ebay, any thoughts?? thinking this could be easily sleeved and a small water intercooler setup could be achieved, might not worth be the weight effort though...
http://www.ebay.com.au/itm/110829448749?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648
Stu
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musicalannette  



Joined: 21 Feb 2012
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PostPosted: Sat Jun 02, 2012 5:58 pm    Post subject: Reply with quote

Just reading through the thread, I think you going the right way with it. Turbo first then supercharging makes sense. Its impressive bang for the bucks.

It really does have to be turbo first, as the turbo boost is more or less exponential with rpm the supercharger is going to be pretty linear. so the turbo can help the blower out when it gets up to speed. if it were the other way round, the blower might have to be huge or be geared up as the rpm increases, so it can spin faster than you would expect at the higher rpm to stop the turbo from being strangled, particulally if you going for high boost/rpm values. I think the VW one was another technical exercise. Impressive but not the first best choice. having a bypass valve in circuit because your turbo i wanting more air than the blower can provide really is polishing a turd territory.
Looks like the VW/audi guys got a bit of a shine though.

Hope this helps.good luck.

ps here is a link to a page on the lancia s4. they use turbo first, supercharger second. last word in drivability and power. There is a drawing about half way down. it's probably worth the hunt.
Under the user greg gordon.
http://www.alfabb.com/bb/forums/engine-conversions/78130-8v-2l-twin-charged-my-little-project-3.html

pps Iwas told as a rule of thumb that you need 2.2cfm of air per hp in a petrol engine (thats at atmosphere though), best book i have found is "turbocharging and supercharging " by allan allard, he did a lot of land rovers back in the seventies. worth £5 from amazon
http://www.amazon.co.uk/Turbocharging-Supercharging-Alan-Allard/dp/0850594944
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