sowen
Club Retro Rides Member
Posts: 2,245
Club RR Member Number: 24
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Super charger and turbosowen
@sowen
Club Retro Rides Member 24
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Dec 20, 2013 23:06:36 GMT
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Lots of classic Mini's with the M45 retrofitted have the supercharger between the carb and the head, and they work with no clever stuff, problem is the Eaton's aren't really designed to be compressing a fuel rich mixture, so not ideal. With the throttle after the supercharger, an idle bypass system is required, and available from oem stuff.
That diagram does look like it's got a recirculating valve, I'm sure it would be pre-set at a particular pressure to dump excess air back into the intake of the turbo, more of a safety back-up device to stop the engine over-boosting. The supercharger in the diagram appears to have a bypass, whether it's an idle bypass or supercharger bypass I couldn't say, and also I can't see where the throttle goes.
As an educated guess, I think you would need a large throttle body to make a supercharger bypass system, and a form of controlling it and the switching off of the supercharger clutch.
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froggy
Posted a lot
Posts: 1,099
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Dec 21, 2013 14:20:29 GMT
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sounds like your turbo is a td04 15t from a saab 2.3 so way too big for your engine to start with .i would try a gt17 from a slightly later 2.0 b204 9-3 or 9-5 as your not getting the td04 into the effiecient part of its compressor map at 7psi .
once you work out how much power it takes to drive the supercharger especially with pre compressed air coming into it a correctly sized turbo might be a better option
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Last Edit: Dec 21, 2013 14:23:46 GMT by froggy
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Dec 21, 2013 15:09:00 GMT
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There is certainly more than one way to skin a cat on this, and I agree with most of what Sowen says too, but my own preference is to do it almost exactly in the way as shown in the Lancia diagram... ie, turbo into supercharger.
In that diagram you will notice that there is no means of overboost safety control directly after the turbocharger, only what looks to be a normal remote wastegate (in black) to control the compressor speed. The compressor bypassing is done AFTER both the turbo and supercharger stages, and is routed back to the turbo's compressor intake plumbing.
A lot will depend on where you position your throttle/s, which is an extra complication if you want to keep using carbs. As Sowen mentioned, while it can be done, it probably isn't a great idea to take a fuel-air mixture through either a turbo or supercharger, and if you use carbs downstream of either you will need to think about bypassing them to avoid trying top pressurise air against a closed throttle.
From all of the research I've done so far, Eaton themselves as well as others like Magnusson and Rouse state that when an upstream throttle is closed and a supercharger therefore is not able to pull in normal quantities of air to be compressed, parasitic losses in turning the unit are actually very small.
There is absolutely no need to idle bypass a permanently driven supercharger either if it is downstream of the throttle. Also, with a downstream throttle plate/s, you aren't just bypassing some air to reduce the boost pressure, as Sowen also hinted at you need to be able to bypass ALL of the intake air being drawn through the system at the time, so the valve itself and all associated plumbing has to be quite large.
Up to the point of the turbocharger starting to be able to make significant boost on its own then, I reckon turbo-into-supercharger has to be the best solution. Beyond that point, it might well be of use to disengage the supercharger drive and bypass it and allow the turbo, whos airflow ewill be rising exponentially by now, to do all of the work on its own. I see a few down sides to this though:-
1) There is a greatly increased level of complexity in all of the necessary bypassing and electromagnetic switching controls required, and timing it all to work as intended.
2) For an engine that is driven normally, this will involve the supercharger drive coming in and out under fairly high load, which could produce some quite high inertia loads on the supercharger and its drive system as well as any surge effects this could have on airflow. I think these electromagnetic clutches are generally designed to cut out at low engine speeds rather than at higher speeds well abovethe turbo's boost threshold?
3) In keeping a full-time compound system the turbo and supercharger can compliment each other well, and the loading on both is split in the same proportion as their own relative pressure ratios. Both units therefore only have to partly pressurise the intake air even at full output engine rpm. Taking thermodynamic law into account, this also splits the thermal rise across the two units. If you think about it, the turbo's turbine section normally has to produce sufficient power for its compressor side to be able to bring the engines boosted full airflow rate up to the required boost pressure.
If a downstream supercharger is doing about half of this work for it, the turbine wheel only needs to get enough exhaust gas/ heat energy to do half of this work..... in other words it can be less restrictive to the exhaust side and make the boost pressure to exhaust gas pressure cross-over point come on earlier and easier. This is an important factor for making power easily in turbocharged engines.
I honestly believe that this would be a much simpler proposition if you were to abandon the carburettors first and switch to EFI.
Just for fun though, consider this option. If you think your carbs are 'sealed/ boost fed' enough to work with forced induction, what about locking their throttle plates in the fully open position (or removing the plates completely) and fitting a seperate throttle body upstream of the supercharger? The venturis will still fuel each cylinder as normal, and the throttle upstream of the supercharger will control engine speed while largely reducing supercharger drive losses without the need for any additional controls.
A pair of large bypass valves could be fitted, one between the turbo and its first stage intercooler to open under high total boost pressure (boost control) and another by solenoid valve control at low engine rpm AFTER the first stage intercooler (for turbo compressor and intercooler bypass to reduce intake restriction into the supercharger).
This again is getting very like the Lancia system, except for the addition of an extra bypass valve between the supercharger intake back to the turbo compressors intake side.
Many different things may work, but for any particular use some will surely work better than others.
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Dec 21, 2013 15:20:37 GMT
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sounds like your turbo is a td04 15t from a saab 2.3 so way too big for your engine to start with .i would try a gt17 from a slightly later 2.0 b204 9-3 or 9-5 as your not getting the td04 into the effiecient part of its compressor map at 7psi . once you work out how much power it takes to drive the supercharger especially with pre compressed air coming into it a correctly sized turbo might be a better option I'd agree with that for a normal turbo application, but for use in a compound charged installation you would really need to check out how efficient it was at full airflow but at much lower pressure ratios as the goalposts have moved quite a bit.. It may well be that a hybrid turbo with a large hotside and a smaller compressor can shift a large quantity of air at low pressure while creating lower exhaust restriction? For sure, the compressor flow maps really need to be studied to make the fullest benefit of doing this and to ensure that first stage compression operates at its most efficient.
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pork
Posted a lot
Posts: 1,662
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Dec 21, 2013 16:27:08 GMT
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Wow, great info there people, il take all of it onto account. First hurdles gunna be actually fitting the s/c In a decent place, got couple of ideas for the clutch pulley that I'm trying to figure out. The td04 works ok with the 1.3, comes in at just under 4 k Il admit I've never looked at the map for the turbo, purchased it before I even knew how to read a map....plus it was cheap. I'm up for the challenge,
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RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
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Dec 21, 2013 16:43:07 GMT
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Twin-charging is an idea that keeps coming into my mind as I'm really enjoying my Scirocco being turbo'd, but even with the absolutely tiny turbo on it right now, combined with all the breathing mods you'd expect to help response, the tiny bit of lag there is still really bugs me. Ultimately, I think the added weight and potential for reliability issues mean I'll never attempt it, but I still like looking into it. In fact this has got me thinking about switching the turbo out to an M62 or something all together.
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Dec 21, 2013 18:56:00 GMT
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"even with the absolutely tiny turbo on it right now, combined with all the breathing mods you'd expect to help response, the tiny bit of lag there is still really bugs me." That must surely be the main reason for anyone wanting to do this. There is absolutely no top end power advantage offered by compound charging over a correctly sized turbocharger on its own. For a typical roadcar, 'correctly sized' usually means having its boost threshold at around one third of the engines maximum rpm, so typically at roughly 2000rpm or so. For outright power it could be much higher than this, but more often than not stock factory applications want to reduce lag at the expense of true performance and you often see engines that start to make boost at only 1500rpm or sometimes even as low as 1000rpm. In reality we just have to live with some degree of lag with a 'correctly sized' turbo, as going overly small with a turbo just clogs up the exhaust side at the top end and increases exhaust pressure with many negative results including higher engine component temperatures. Another consideration is drivability, and a really potent turbo engine (especially one with a very low compression ratio) can be a real handful to control in wet conditions....and sometimes even in the dry too! By adding a supercharger we can immediately side step many of the downsides of a turbo on its own. Immediate, proportional boost right off of idle with no lag. If you take the need for the turbocharger to make boost at low to medium engine rpm away altogether in this way, you can then size it to work at its most efficient range only towards the mid to upper rpm range of the engine, and as already mentioned this can be done to work with a much lower pressure ratio. Even at higher RPM, the supercharger then sees a smaller pressure differential across its rotors exactly as it would if operating on its own at a low pressure ratio, which takes less power to drive it as well as being more thermodynamically efficient and producing cooler charge temperatures. This helps get around one of the main down sides of the roots type supercharger. Being greatly assisted by the supercharger downstream, the turbocharger can get on with the job of shifting a lot of air but also only at a lowish pressure ratio. Doing this requires much less energy at the compressor wheel, which translates into both faster spooling and lower exhaust restriction and back pressure even with slightly larger rotating component masses. Other than some added complexity, bulk and weight, it is pretty much a win, win and win situation. Note that if the drive to the supercharger is cut and it is bypassed at higher rpm that some of the important advantages of compound charging are immediately lost. Also that a supercharger on its own can't hope to compete with a correctly sized turbocharger on its own in terms of outright top end efficiency. Using an overly small turbo to try to avoid having lag is like putting grease on a ladders rungs so that you go down it more quickly.... the idea might work up to a point, but the end result isn't going to be very good!
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pork
Posted a lot
Posts: 1,662
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Dec 21, 2013 19:22:26 GMT
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Il draw out a diagram of what I think I need to do later.......then everyone can pick it apart and tell me it's all wrong
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pork
Posted a lot
Posts: 1,662
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Dec 21, 2013 21:32:33 GMT
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So after a couple off tins, I came up with this for my build. Turbo into s/c, 3.5k clutch to s/c is disengaged, bypass opens allowing turbo to take over. Once throttle is closed, vacuum bypass is opened, releasing all pressure into intake pipe before turbo. Idle control circuit to. I have a rev counter with adjustable shift light (max power yo! In my defense, was cheap!), so was gunna set the shift light to come on at 3.5k which would in turn engage the electro clutch and bypass Feel free to pick holes in my plan
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Dec 22, 2013 10:40:51 GMT
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I honestly think you should forgo some of the complexity and just go for a compound setup. The M42 blower is capable of feeding your engine easily within the bounds of the efficiency map, so just plumb it in after the turbocharger and see how it goes. If you still want to run with the supercharger being bypassed at a later date, that can be added. Clutching the supercharger is totally unnecessary, as bypassing it removes 90% of the parasitic losses.
The throttle closing issue can be removed just by running a large bypass valve, something that has 80% the area of your intake pipes will be more than sufficient.
Compound charged with a large bypass valve -
J
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Dec 22, 2013 10:42:21 GMT
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see if this video makes any sense of what your doing this is vw twin charge tsi 1.4
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pork
Posted a lot
Posts: 1,662
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Dec 22, 2013 10:57:26 GMT
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I honestly think you should forgo some of the complexity and just go for a compound setup. The M42 blower is capable of feeding your engine easily within the bounds of the efficiency map, so just plumb it in after the turbocharger and see how it goes. If you still want to run with the supercharger being bypassed at a later date, that can be added. Clutching the supercharger is totally unnecessary, as bypassing it removes 90% of the parasitic losses. The throttle closing issue can be removed just by running a large bypass valve, something that has 80% the area of your intake pipes will be more than sufficient. Compound charged with a large bypass valve - J That's what I plan to do Charger I've got is the m24 from the tsi 1.4, The clutch I bought just coz it was cheap, and like you say May or may not use, depending on how it all goes.
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froggy
Posted a lot
Posts: 1,099
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Dec 22, 2013 11:30:25 GMT
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Leaving the charger running means having to run a much lower wastegate opening point as the ratios are multiplied so 7psi from the turbo and 7psi from the charger is 18psi not 14 .
I rigged up a boost actuated bypass to unload the charger but no matter what level we tried still had a big drop in pressure as we had to up the wastegate pressure on the turbo to get it above 1 bar and fully spooled which meant opening the bypass earlier to stop the pressure going over 2 bar at the manifold
Lancia didn't get their system to work properly either and it was run the charger permanently engaged most of the time .
You can make lots of boost low down but pressure doesn't mean power if the mass of air isn't there .
That lotus has the charger upstream of the throttle
Note that the tsi isn't compound but uses the charger to spool the turbo then switches off as I suggested earlier
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Last Edit: Dec 22, 2013 12:02:02 GMT by froggy
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Dec 22, 2013 13:34:09 GMT
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For a DIY type system like this, I happen to completely agree with Blown-imp, simplicity really is the key. Even with a more basic arrangement though it will be important to select the components well to make the most of the installation as a whole.
Pork, if your current turbo isn't starting to make worthwhile boost until 4000rpm then it really is a good bit on the large side for a general use car. Adding a supercharger would certainly help here, but in reality it may be better to simply swap in a more appropriately sized turbocharger and forget about adding a supercharger altogether... especially if space in your engine bay is already tight. You'd otherwise still have to find space for an extra charge cooler as well, plus some extra plumbing and controls.
From your sketch, personally I'd omit 3, Replace 2 with a compressor bypass valve back to the supercharger intake, and also add either another compressor bypass at the turbo or a first stage blow-off valve just upstream of the supercharger.
It seems crazy to be staying with carbs for simplicity, which is understandable, and then even start to consider anything else like electronic wastegate control or fancy supercharger clutch circuits.
Froggy, some very good points there. I deliberately talked about splitting the loads between the two compressors earlier rather than specific boost pressures from each stage for this reason. You can calculate the pressure ratio for each, but as they act independently I believe that they also really need their boosts controlled independently as well, probably with compressor bypassing after both stages for really good control.
Note that in the VW diagram that once the supercharger bypass valve is opened that there is no pressure differential across the supercharger. In this condition there is very little power required to turn it anyway, and also there will be greatly reduced loading on it when switching the clutch on and off, with it more or less only being the inertia of its own internals. If you really want to cut drive to the supercharger this is the best way to do it, but I think VW only chose this method to be able to eliminate its parasitic losses completely.
Again, as soon as you take the supercharger out of series with the turbocharger in any way it is no longer compound charging and the turbocharger has to provide the full boost pressure. This isn't a problem for a turbocharger at the top end, but it does have a knock on effect in the ratio of intake to exhaust gas pressures (and temperatures) across the engine itself due to the need to provide the extra energy to drive it in doing this.
Also in the VW diagram, in comparison with the energy derived from the exhaust gasses, I am not at all convinced that the supercharger will in fact have much 'spooling' effect on the turbocharger via its compressor wheel. What this arrangement will do though is allow the turbocharger to be better sized for overall efficiency closer to the engines upper operating speeds.
There are some obvious pros and cons to all of these arrangements, but I think some lend themselves to more straightworward DIY installation than others?
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pork
Posted a lot
Posts: 1,662
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Dec 22, 2013 14:24:52 GMT
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I have been looking at EFI, was considering swapping out the cbr600 carbs for the cbr600 itb's, beings they match up to the nice bogg bros manifold I've got.... then megasquirt
But for now, il just build it all up, run it on the carbs beings they work fine still, then sort out injection later
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Dec 22, 2013 16:11:20 GMT
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Finally got pics of the exhaust and bypass valve, i'll put them up later. Just by sheer coincidence, I also happen to have a smaller turbo too lol
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pork
Posted a lot
Posts: 1,662
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Dec 22, 2013 17:06:04 GMT
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Lol nice one!
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froggy
Posted a lot
Posts: 1,099
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The fact that a fairly well funded manufacturer decided against trying to fit the supercharger after the turbo and try and control the transition between compounded boost and pure turbo boost tells me its not a simple feat to accomplish.
If you want to try a smaller turbo I have a mint t25 garret that I don't need , cover the postage and you can have it .
As far as I know only claymore and myself have done this and I'm sure Colin will agree its not a simple conversion with plenty of stuff getting thrown in the bin along the way .
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pork
Posted a lot
Posts: 1,662
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Dec 23, 2013 11:29:35 GMT
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I totally agree, it's not gunna be easy, but I like that sort of thing, my car is just a toy, not a daily driver, just somthing to keep me getting bored, figuring problems out is part of the fun for me
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Dec 23, 2013 11:55:41 GMT
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The fact that a fairly well funded manufacturer decided against trying to fit the supercharger after the turbo and try and control the transition between compounded boost and pure turbo boost tells me its not a simple feat to accomplish. As far as I know only claymore and myself have done this and I'm sure Colin will agree its not a simple conversion with plenty of stuff getting thrown in the bin along the way . That is very true, but on the other hand I also think that VWs objectives in doing it this way, basically for use in a small roadcar where fuel efficiency and drivability would be a major factor, would have been quite a bit different from that of the more performance orientated goals such as would have been the first priority on the Lancia rally cars. VW would also have had to make both the system itself and its various controls long term reliable enough for use in a production car, but would at least have had a much larger R+D budget for doing this. Although the majority of people thinking about doing this by either means will be nowhere near the point of reaching their engines ultimate mechanical/ thermal limits and output, I believe it is in some significant ways better to keep both stages 'in circuit' right up to and including this point. I don't imagine for a second that achieving this would be a straight-off success without a lot of trial and error and experimenting, but I still reckon it should be do-able using only readily available mechanical hardware parts and no other electronics or bypass valves etc controlled by them? In truth, if lower engine speed drivability and flexibility wasn't an issue it would be much better to abandon the supercharger idea altogether and just use a relatively large turbocharger biased towards top end performance that didn't choke up the exhaust. I think that VW's idea is a good half-way house along these sort of lines. The very simplest arrangement might even be a boost-controlled change-over valve of some sort with two completely seperate intake systems using a common single intercooler, but you would then have all the trouble of making it all pressure tight and still either require bypassing of the supercharger or cutting its drive. For my purpose, using the supercharger at all is only a short-term fix until such times as my new twin turbo engine and stronger gearbox can be installed....on their own. I have however specifically been making the new supercharger fitment parts so that both systems could potentially be fitted at the same time. That isn't part of my plan at all, but I've learned never to say never. Do you have a build thread on your own installation? That sounds very interesting indeed and it is always good to get a range of different viewpoints, ideas and thinking on things like this. Pork, in your case I think it would probably be better to forget about the supercharger idea and really look closely into finding a more suitable turbo for your engine. For sure you should be able to make further improvements by swapping in a few different units and choosing one of them, but to get the very best out of your car for minimal effort you really need to do some simple calculations followed by some studying of the compressor flow maps of any that look like they might be approximately right. There is a very good chance that you will find something that will work very well lifted from another car that can be picked up easily and inexpensively.
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