Super- and turbocharging - 'twincharging'
Super- and turbocharging - 'twincharging'
(OP)
Interested in twincharging - where a supercharger assist with boost in low boost situations and the turbocharger taking over once it has spooled in high boost. This can be either in series where the S/C blows into the turbo or in parallel (where surge may be an issue).
Any suggestions on how to do this?
Any suggestions on how to do this?





RE: Super- and turbocharging - 'twincharging'
Blacksmith
RE: Super- and turbocharging - 'twincharging'
your idea for twincharging is to reduce lag or to have more power? Instead of twincharging why not use a variable geometry turbocharger? decision will mostly depend on engine size, though.
RE: Super- and turbocharging - 'twincharging'
RE: Super- and turbocharging - 'twincharging'
Most currently it was tried on the Meguire's Integra Type-R. It was ran the same way using an HKS turbo, and a Jackson racing roots type. It made more power at the wheels at 3,200rpm than it did stock at the crank. 125HP by 2,000rpm. Quite an amazing feat if you ask me. Totalled 424HP with a very fat torque curve for a Honda. If you know Honda's torque isn't something they usually have, but it put down 225lb ft at 2,750. I'd like to take it for a drive.
RE: Super- and turbocharging - 'twincharging'
Rod
RE: Super- and turbocharging - 'twincharging'
http://www.yet2.com/app/insight/techofweek/9609?sid=200
mentions using a variable speed drive for it, answering my own first objection to it.
Cheers
Greg Locock
RE: Super- and turbocharging - 'twincharging'
But as an aerodynamic compressor as a better efficiency than a volumetric one, the best way would be to use 2 centrifugal compressors in series with an intercooler in-between (or an aftercooler for better power but slightly decreased efficiency). They could be driven from the crankshaft by means of a CVT and step-up gears.
Then you install a good and efficient exhaust turbine (maybe a two-stages axial one) on the compressors shaft, so that power can flow in both directions from the turbine to the crankshaft at full load and high revs (instead of discharging the excess exhaust gas with a by-pass valve) and from the crankshaft to the turbomachinery at low revs.
You get a turbocompound engine. If you want to make it simpler you can suppress the valve gear and use a 2-stroke cycle, preferably Diesel because with double stage high pressure supercharging you would have to lower so much the compression ratio of a SI engine that its efficiency would be very low. Such a 2-stroke diesel would have a extremely high power density while being quite efficient.
I developed this idea about 20 years ago. Then I found out that an aircraft engine had been successfully built with that system: the Napier Nomad Nm6 ! A fantastic engine. You can find some photos and cutaway drawings of it on the web; just type its name on Google.
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
RE: Super- and turbocharging - 'twincharging'
According to the data I have the efficiency of Lysholm type compressors doesn't reach more than 75% while centrifugal ones attain about 84% efficiency (overall).
Another point is that you can't drive directly - on the same shaft - a Lysholm compressor with an exhaust turbine since they don't spin at the same revs. Even with a reduction gear between it wouldn't work well because their characteristics maps do not follow the same pattern.
With the Nomad's design, all the turbomachinery lies on the same shaft and the power of the turbine directly drives the compressor, just like in a turbocharger. So, the CVT between the crankshaft and turbocharger never transmit a huge amount of power to or from the crankshaft.
There would be no point in driving a (two stages) volumetric compressor from the crankshaft and then recover the full power of the exhaust turbine by means of a reduction gear and a hydraulic coupling to absorb the torsion vibrations. In addition to the lower compressor efficiency, greater mechanical losses would occur. If the Wright R-3350 Turbocvlone used that scheme (but with a centrifugal compressor) it was probably just to exploit the existing Cyclone basic layout.
Let me get a little bit out of my way now!
For wheels traction purposes an even better concept can be envisaged. Let's call it "Turbocompound High Pressure Differential Supercharging" and let's drive the two-stage centrifugal compressor by means of a planetary differential and a step-up gear train. The crankshaft(s) of the (preferably opposed pistons 2-stroke) Diesel would drive the planet carrier, the ring the compressor while the sun would be on the output shaft. The exhaust turbine is then geared to the output shaft. We get a kind of half gas-generator, an engine working as an integrated torque converter. A problem is the excess of compressed air at vehicle launch. At 6 bars (abs) of intake pressure, about 57% of the crankshaft power goes to drive the compressor and the Diesel can only rev at 57 % of its nominal rpm with the output shaft stalled. But the compressor is spinning at full speed and delivers more air than needed for scavenging and combustion.
There are several solutions. Just 3 :
- The excess air can be by-passed directly to the turbine or to a separate turbine.
- Variable pitch stator blades on the compressor inlet would help.
- A variable compression ratio engine could be used( specific design wanted…)
Of course there would be a heat exchanger and an intercooler between the two compressor stages to lessen the power needed to drive it and decrease the thermal load. With a variable geometry turbine inlet, the efficiency would be quite good from low vehicle speed. A clutch or one way clutch to lock the differential would prevent the crankshaft to rev slower than the output shaft and so avoid stall or even reversion of the compressor rotation. A 4-speed powershift transmission would be all right for up to about 40 tons rigs.
Two locomotives using the concept of Dr Leonhard Geislinger (see CIMAC 1955, "A locomotive with thermo-pneumatic transmission" or something like that) were built and successfully put in regular duty in Sweden in 1955 . The worked about the same way, but with two Hedemora-Pielstick 4-stroke engines and an auxiliary combustion chamber to utilize the excess air. Frank Wallace at Bath University also published several papers about his DCE or "Differential Compound Engine", but he apparently ignored the previous work and practical results of Geislinger.
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
RE: Super- and turbocharging - 'twincharging'
But then again if you are playing around with old T3's and T04's I understand your dilemma!!
RE: Super- and turbocharging - 'twincharging'
kimbo1, are you talking about variable geometry turbine or mostly improvement on impeller design?
RE: Super- and turbocharging - 'twincharging'
As to high boost, a couple of import drag racers using duplx turbos are approaching the 100psi range (Speed Channel). I have no idea how you keep a Honda together at that level. Amazing!
Rod
RE: Super- and turbocharging - 'twincharging'
Yes compressors adiabatic efficiency varies with their size. The overall (adiabatic x mechanical) efficiency figures I gave were for quite large ones used on medium speed Diesels. For smaller compressors they are lower.
For the Lysholm compressor on the Mazda Miller engine:
http://members.rogers.com/sofronov/Cars/Mazda/Room/MillerCycle.html
Lysholm website provides compressors maps (pdf), pictures of beautiful supercharged engines and other info:
http://www.rotor.se/lysholm/en/p_1600.asp
Evelrod,
I also wonder about a boost pressure of 10 bars, especially on an SI engine. At about 8 bars (abs) of intake pressure, the compressor power becomes equal to the engine (2-stroke diesel) power, so that all the crankshaft power is absorbed to drive the compressor. You get a gas-generator: an engine of which all the power is recovered on an exhaust turbine.
The 1983 BMW F1 turbo cars ran a modified M10 block with DOHC and 4 valve head, 1.5 liters displacement, merely 4 bars of boost… and produced about 1400 hp… but no one ever knew exactly because it's said the scale of the test bench went up to 1280hp only… gulp !
http://m10-power.320i.com/E21%20cylinderhead%20modifications.htm
http://www.circlebmw.com/parts/mobile/9423036.htm
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
Rod
RE: Super- and turbocharging - 'twincharging'
RE: Super- and turbocharging - 'twincharging'
My comments may not be directly answering your question, sorry, if I can add my two cents worth - you are thinking of ridding EVO VI technology for a supercharger??
Superchargers are generally low boost units - my understanding is that your turbo will crucify any supercharger you may get your hands on considering your workable rev range and your intent to hillclimb, which is probably why no racing I can think of except dragsters use them. But if you want to pull tractors go for the supercharger.
Spereira, I was talking about improved impeller design and ball bearing units such as Garret and HKS.
RE: Super- and turbocharging - 'twincharging'
I see only few advantages in a volumetric compressor over a turbocharger : no lag, a better boost pressure at very low revs and no exhaust backpressure.
But the power to drive them has to be subtracted from the crankshaft power and so there's a greater load on the pistons and crankgear. Say your engine pumps out 120hp at the crankshaft but 20 are lost in the compressor drive, so you get only 100 hp while your pistons and crankgear are delivering 120.
With a turbocharger you recover some of the exhaust energy that would be otherwise lost and the boost pressure you get is more than the increase of exhaust backpressure. The turbine also acts as a silencer, so that a less restrictive silencer can be fitted.
Another great advantage is that boost pressure is a function of the load while with a supercharger it's more or less a function of rpm and remains the same at low load - unlees the compressor is by-passed and declutched.
Turbocharged engines bmep is limited only by detonation, max combustion pressure and thermal load, so that by lowering the compression ratio the limit is extremely high. With a supercharger the limit is much sooner reached as the efficiency drops more quickly when boost pressure is increased over 0.8 to 1 bar.
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
I am very interested in throttle response, pressure ramp times and packaging for a future project and the mechanical forced induction appears at first glance to have a few advantages. The boost pressure is only a part of the picture for forced induction performance and yet there would also seem to be some tuning advantages for constant boost pressure?
RE: Super- and turbocharging - 'twincharging'
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
I do wonder why some of the higher boost OEMs dont consider a crank driven Centrifugal Supercharger. You would add cost, though I do doubt as much as a Turbo, and have most of the advantages of a Turbocharged engine. Anybody care to elaborate?
RE: Super- and turbocharging - 'twincharging'
A solution would be to drive it by means of a CVT.
Then we get to the idea described on my former posts: why not an exhaust turbine on the compressor shaft? The power transmitted by the CVT would be lowered and some of the exhaust energy could be recovered. No turbo lag and good low revs boost.
It could also be done with a high speed motor-generator on the turbocharger shaft.
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
I do keep trying to get my friend to make his own blower kit for his Talon.... A big 'ol chromed out 8-71 sticking out the hood of a second generation Talon sideways would look very cool indeed.....
-=Whittey=-
RE: Super- and turbocharging - 'twincharging'
aorangi that transient response is very important for me. I agree that given the same boost the turbo engine will produce a greater peak torque (perhaps the torque spread will be over a lower rpm range?)
RE: Super- and turbocharging - 'twincharging'
Whittey, there can be no argument they Centrifugals are louder, though ATI has worked out a reasonably quiet unit, see their SC-1 unit at http://www.procharger.com
There is now more information with regards to long term durability of the Centrifugals, and by and large, I am confident 100 K would not be a problem, as I know of several at the 80-90K mark right now with no maintenance.
Neil I think that would be the thing that kills any large use of supercharging. We now get so much power out of relatively small engines naturally aspirated that the hassle of a superchrger just really isnt worth it for the average joe. Now, take a really small, robust 1.1 L engine, throw 18-20 PSI boost to it in a linear fashion, and you could have a decent sized car that got good mileage, so long as you kept your foot out of it!
RE: Super- and turbocharging - 'twincharging'
RE: Super- and turbocharging - 'twincharging'
I couldn't agree more with what Dan Barnes writes at:
http://www.badz24.com/Cavy%20info/SuperchargerOverview.htm
Excerpt:
"Unfortunately, while lag is not an issue, dynamic characteristics remain a problem, to the extent that some pundits say a centrifugal supercharger combines the weaknesses of a turbocharger with the weaknesses of a supercharger. The mass flow rate of a centrifugal supercharger is roughly proportional to the square of the compressor's rotational speed.
This means that boost rises nonlinearly with rpm, and power is biased strongly toward the top end. This can be seen clearly in the dyno tests we have done on supercharged cars. The most extreme case was a 1.6-liter engine with which the torque curve rose steadily toward redline, the result being 272 hp at the wheels, the last data point before fuel cut. An impressive number to be sure, but completely unusable. The Bosch Automotive Handbook, 4th Edition, states on page 380 that centrifugal compressors "are not suitable" for vehicle engines. This is qualified on page 424, where it is stated that "a transmission unit must be included to vary the rotational speeds if the pressure is to be maintained at a reasonably constant level over a wide range of flow volumes (ie. engine speed)." The accompanying diagram suggests a continuously variable belt-drive transmission."
NOTE: The Mc Cullogh centrifugal of the 50s worked that way.
I found further agreement at:
http://www.jagweb.com/aj6eng/supercharge.html
(BTW,his website has also a very comprehensive and interesting document concerning the history and tech development of the Jaguar V12)
Excerpt:
"The delivery is proportional to the square of the speed of rotation of the impeller, which is fine for an aircraft engine designed to run at a set speed, with the throttle controlled barometrically, but not so useful for a motor vehicle power unit with the usual wide range of operating speeds. The impeller must rotate at very high speed to do anything useful and therefore has a great deal of inertia which can subject a gear or belt drive to very high loads with changes of engine speed. Indeed aircraft engine supercharger drives always incorporated some sort of cushioning device to absorb these loads. A turbocharger gets round these problems by driving the impeller via an exhaust turbine to achieve the necessary high speed of rotation, simply dumping excess exhaust through a waste-gate when the required amount of supercharge is achieved, thus being able to function over an acceptably wide range of engine speeds. Inertia of the impeller and turbine give rise to what is known as turbo-lag which can never be entirely eradicated even though there are ways of making it far less noticeable. Obviously, a centrifugal supercharger driven from the engine will normally only provide useful boost at high engine speeds. For it to make any contribution to mid-range torque, a widely variable ratio drive is needed or the wasteful alternative of dumping excess charge at high speed. One might reasonably conclude that the centrifugal device, despite its appealing compactness and simplicity, is therefore not very promising as a potential supercharger for a motor car. Anyone who doubts this should remind themselves about the V16 BRM engine of the 1950s with its almost uncontrollable power delivery."
I'm not familiar with the big improvement helixed impellers are suposed to provide. If you have any data, I'll be glad.
Neil, I checked from several sources the data for automotive size compressors max. adiabatic efficiency:
Roots (Eaton): 50%
Lysholm : 65%
Centrifugal : 77%
Quote from:
http://www.diy-efi.org/diy_efi/archive/2001-October/msg00417.html
"There are many on the list who _don't_ know that the Lysholms are NOT quite
as efficient as a well selected centrifugal. Lot's of folks seem to think
that because the Lysholms have been described as "much more efficient"
(than Roots blowers) that they must also be much more efficient than good
centrifugals! The numbers you quoted below would have been useful toward
the education of a lot of folks.
Later--
Greg
At 9:35 PM 10/14/01, Stephen Andersen wrote:
>Greg,
>
>I "respectfully" have copies of the Lysholm compressor maps
>in my briefcase, and have done the requisite efficiency
>calculations. While I agree that the lysholm AE is not that
>of a centrifugal compressor, they are still pretty darn
>good (range of 58-64% for my car), compared to 30-50% for
>a new style (Eaton) Roots."
I agree that a volumetric blower is easily and nicely packaged in the V of a car's V engine. The MB AMG 55 has impressive performances and quite a good efficiency with its declutchable Lysholm (yes it's a Lysholm, not a Roots!) compressor blowing at 0.8 bars into an intercooler. The S 55 AMG's got the same performances as the S 600 V12 and has a better fuel economy.
What to chose, then? It all depend what you want, what kind of engine you have, what space and money limitations you have.
For the best torque, power, efficiency, transient response: turbocompounding with 2-stage centrifugal compressor and 2-stage axial turbine and CVT.
For tremendous power, torque and good efficiency: turbocharging.
For transient response, power, torque, efficiency: declutchable Lysholm.
For transient response, some more power and torque: Roots, preferably with a by-pass valve.
For marine power (no torque back-up needed): centrifugal.
For aircraft altitude power: turbocharging or combined centrifugal and turbo.
BTW, a naturaly aspirated engine looses about 12,5 % of its power by 1000 m of elevation. A supercharger one looses some, but less. A turbocharged engine losses none or almost none till the turbocharger rotor and/or wheel blow up.
To answer Doglegracing original question: did we really answer? I think the response was in the first and second answers from Blacksmith and Speirera ļ.
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
RE: Super- and turbocharging - 'twincharging'
http://www.whipplesuperchargers.com/content.asp?PageID=68
-=Whittey=-
RE: Super- and turbocharging - 'twincharging'
Quote from:
http://www.motorsportsdigest.com/forced-whp.htm
"While those who have (or sell) Whipple superchargers swear by their performance, this performance is all too often unproven. Whipple superchargers are rarely, if ever, seen at the track - other than in Top Fuel cars when their only competition is limited by the rules to only roots style blowers. These units are not geared or designed for all-out racing. The ads for Whipples usually make them sound far beyond anything else available. It's a good story, but again is unproven. What sounds good on paper doesn't always work well in the real world. Even though the Whipple is spoken of highly, the centrifugal consistently out performs it in most race applications. I can't blame people for falling for the ads, they really do sound good. I guess you can't always believe what you read. Don't get me wrong, there is a lot of potiential in the Whipple, but it's not exactly what it is said to be."
I was bound to ad it to my last post, but as it was already long as a see snake, I gave up...
Cheers,
Aorangi
RE: Super- and turbocharging - 'twincharging'
For the present, at least in the racing arena, the Turbocharger has a very small Hp advantage, I do believe this year will see that advantage reversed though.
At least from my perspective, the cheapest low tech would be the conventional Roots, followed by a Centrifugal, then a Lysholm, and certainly most expensive, high tech would be a Turbo.
Time will tell
RE: Super- and turbocharging - 'twincharging'
these people are obviously not listening and haven't driven cars with the latest turbo technology!
fixed drive superchargers have poor and non-linear control of boost and are just not as efficient. Further more they are for low boost applications only, where they do perfrom very well such as the merc mentioned. they are not the best for power, racing and high HP applications.
Please no more wipiing the dust off 50 year old turbo and supercharger books everyone!
RE: Super- and turbocharging - 'twincharging'
Aorangi's quote from a motorsport magazine is hardly conclusive evidence apart from the opinion of the author. Such decisions (induction type) are situation specific and the quote he uses has no bearing as far as I can see for the type of motorsport that I am interested in. There is little crossover between motorsport in the USA and that in Australia due to local conditions and also local rules.
The latest book I have read on forced induction (apart from some tech articles) is Bell's Forced Induction Performance Tuning published in 2002. The author states on pg 133 "In motorsport, turbo's are useless in any sort of competition where precise throttle response and low speed torque are required. Therefore they are not for tight circuits, hill climbs, dirt or tarmac rallies (fast tarmac and/or expert drivers are an exception) and other dirt surface events". There is more but perhaps you should read the whole book to take it all into context. Incase you are wondering he details modifications to WRX/EVO and Nissan it the back of the book to show some detail of his arguments.
I appreciate aorangi opinions and his effort to provide information, it has been helpful. However perhaps you should consider that you do not know my level of knowledge or experience before making such a statement.
The unfortunate aspect of the above discussion is that we have hijacked dongleracing's thread.
RE: Super- and turbocharging - 'twincharging'
The unfortunate aspect of the above discussion is that we have hijacked dongleracing's thread"
I second, and promise to not further promulagate this thread. Thanks for the debate all!
RE: Super- and turbocharging - 'twincharging'
^^ So what they are saying is: "In order to race, you have to know how to drive." I thought that was a given? Turbo's do seem to do awfully well in each of those applications where that book says it can't do well.
A directly driver non-displacement type supercharger will always be peaky. Yes, as science progresses that range increases, but you're never going to get full boost down low and full boost up top both with high efficiency. Well, maybe not never, but not anytime soon.
A direct drive positive displacement blower isn't very efficient but offers such a range as to make them useful.
Turbine driven non-displacement superchargers offer a broader range than directly driven non-displacement with similar efficiencies but do not have the throttle response of a directly driven supercharger. They will never have the same response, and so will never please the people that compression-brake then jump on the throttle to measure how much power an engine makes.
A lysholm type directly driven supercharger is an effort to take the good of non-displacement internal compression supercharging (aka, take the centrifugal chargers high(er) efficiency) and couple that with the good aspects of the directly coupled positive displacement blower (broad range). It both compresses internally (which typically gives your higher adiabatic efficiency) and is a positive displacement type to give your broader range.
As with everything, there is a compromise to be made. A positive displacement roots-type blower for that stump pulling torque and great throttle response, yet suffering from heat at high boost. An internal compression cengrifugal supercharger for the high efficiency, boost and throttle response, yet suffers from a lack of range. A lysholm-type positive displacement internal compression blower as a compromise between the two for that lowend punch and broad range of the roots-type, yet with centrifugal-approaching efficiencies. Then you have a gas-driven non-displacement internal compression super(turbo)charger that gives you a broad range with the high efficiency, yet lacking the throttle repsponse that you get with directly coupled and/or N/A high compression engines.
Thats my take on everything i've seen/heard/read about the subject.
-=Whittey=-
P.S. As for the original topic, I think 'twincharging' would be a waste in the end due to complexity and weight.
RE: Super- and turbocharging - 'twincharging'
I have also driven The little WRX, nice car, very little noticable lag in stock form but, as it is modified for 'bigger bang' the lag increased appreciably. Still well within my ability as a race car driver.
As to the "10 bar" deal, sorry boys but that's the way I remember it. I am not a diesel racer but I see in a related thread where 250 psi boost levels are the norm in tractor pull diesels!!!
Now, as a racecar driver with something like 45 years experience in everything from dragracing to TransAm sedans and FIA, I can and have quite easily handled rather sever turbo lag in a Porsche and a Turbo Coupe. It is a matter of timing, that's all. NOT the best for a comfortable drive for sure but, no race car is all THAT comfortable anyway (and definately NOT for the amature). As race car drivers we all borrow from the USMC---"We adapt, we overcome..."!
As to street---The positive displacement blower has it hands down. Grandma doesn't know or care if the engine has a supercharger just that it's power transfer is "linear"!
For the kids in the 'rice rockets' in my neighborhood, the turbo lag is all part of the experience (along with the 'trashcan' exhaust systems currintly in vogue.
Rod
PS to 'doglegracing'---My thoughts are as in Whittey's post except I would say "...complexity and COST."
RE: Super- and turbocharging - 'twincharging'
Sorry, just don't see the point... asif things aren't complex enough already.;)
-Allen
RE: Super- and turbocharging - 'twincharging'
To get back to the original post of Doglegracing, he didn't specify whether the question was related to an aircraft, an 18 wheeler, a locomotive, a supertanker, a motorbike or a drag racing car.
I don't think there's much point in 2-stage turbo and /or supercharging a SI engine, except for high altitude operation. This was done on WW II aircraft engines and is also currently done on some marine diesels.
Turbocharging is universally adopted on diesels nowadays and 2-stage turbocharging or turbocompounding has already come. I don't have in mind any supercharged diesel still in production.
Finally, 250 psi… is that really 17.5 bars ? One would need heavy-duty ducting, intercooler, intake runners and valve springs and…and… no, sorry Rod I can't buy that…
Cheers
Aorangi
RE: Super- and turbocharging - 'twincharging'
It is obvious many who have had their say on this topic aren't end users - or the 50 year old theories would not be popping up constantly - no offence intended to anyone OK! we can all contribute in our own way. Your 2002 book must be quoting other 50 year old books, as turbo cars have been crucifying all forms of racing that I can think of for years(except where they are banned) i.e not abosulutely useless! they have very little lag in most events thanks to anti-lag technology, and even before that the group B derived peugot 206 shocked some people at pikes peak - see that famous video called "climbdance" this is far more exciting than the tommy lee and P. anderson one. As Evelrod mentioned, drivers just get used to the lag and you find yourself getting on the power a bit earlier in the apex to compensate.
On the street, for driveability, give me a mildly supercharged car anyday.
This conclusion is repeated many times above - anyone still confused?
RE: Super- and turbocharging - 'twincharging'
I think I stated above that I was interested in mechanically driven forced induction for some of its specific advantages, and that is still the case. I am not anti-turbo in any way but wanted to find out more information of something that gets less 'press' than turbo's. I have not driven a turbo car on a track in a race. I did speak to a GT3 racer who was frustrated that he was being overtaken by the exiges as he had to be so careful (his thoughts not mine)
In the latest edition of EVO Gordon Murray has answered the question "presumably working on the SLR you've come to embrace the SC as a different way of gaining performance" His reply
"No. Given a totally open choice I'd always go for normal aspiration, for everything: weight, complexity, effecieny, drivability. Supercharging is much better than turbo charging for all the obvious reasons but also has its drawbacks. If you want 500hp, net, you've got to make 700 because 200 goes to driving the SC, and then you've got to cool that power. The small throttle response problem you can get over with byass valves and things. It'll never be normally aspirated but it's certainly a hell of a lot better than turbocharging"
I have not made my mind up which is better for me is this application, but again I am contibuting nothing to dongleracing's thread and will sign off. This is perhaps as discussion item for another thread if anyone has the energy!
RE: Super- and turbocharging - 'twincharging'
kimbo,
Which turbo books do YOU recommend? I still haven't figured it all out, so I'm willing to read and learn. How bout that GT2 class racing... Corvette and Viper aint doing too bad.;)
-Allen
RE: Super- and turbocharging - 'twincharging'
However the claim that they convert lost exhaust gas heat is only partly true, as they also increase blow down pressure on the exhaust stroke, which pushes against the rotation of the crank, thereby creating a relative small parasytic loss.
I did own a Toyota Soarer MZ20 which had the M7GTE motor and automatic transmission. While it was a very comfortable, high performance, reliable, true GT coup, it had two interelated drawbacks.
When pushing hard through corners, that required controlled acceleration for best results, it either kicked down a gear and came strongly onto boost, or it changed up a gear and lost boost, sometimes 2 or 3 times in the one corner.
The option of manual overide of the automatic was not that successfull, as the shifter was vague and the gate design poor, which meant that it was hard to know what gear you were in, and it was to easy to overshift and select neutral.
With a supercharger, I could have squeezed the throttle without a downshift and got controlled, instantainous acceleration.
The technique of allowing for lag, can be usefull on a race track, but it still does catch a driver out occasionaly, such as when moveing through slower traffic, and someone does something unexpected, or the competitive driver deliberately hesitates at a critical time and therefore baulks you.
Turbo's are more efficient, but at times, they do create drivability problems. A positive displacement blower and a turbo compounded could give the best of both, but with relativly high parasitic losses compared to straight turbo.
I doubt if it is worth the extra complexity and weight, but it will give better power than a roots blower and better response than a turbo. It will still suffer somewhat if trying to feather the throttle on an automatic transmission car through a part power corner.
To dogledracing's question, It all depends on exactly what you want to do, and what is the net effect all the compromises for your particular application. Isn't that about the situation with almost every consideration when designing a car, or just about anything else.
Regards
pat
RE: Super- and turbocharging - 'twincharging'
-=Whittey=-
RE: Super- and turbocharging - 'twincharging'
The original question has been answered many times above,so this hijacking has not been wasted. the answer being - no there is no point twincharging. A lot of work and money for very little gain -the Lancia engineers seem to have come to that conclusion too.
Supercharged cars feel much better to drive - no argument about that from anyone
A turbocharged car is the way to go for racing if rules allow it - you don't need calculators or books to see this, but I agree as an engineer myself they will help you understand why. The guy driving the twincharged or supercharged car will be able to console himself that whilst he didn't win at least he had good throttle response.
Progressive racing - I don't recommend any books as I don't read them - my seemingly controversial opinion comes from 3 years of dyno tuning and driving some pretty good machinery myself. The most notable a turbocharged RB25 in a 240Z that made peak power at 7000 rpm, During a test drive I launched it at 2500 rpm with the ability to create huge wheelspin, and a 700 HP 535 BMW with flat torque curve from 3000 rpm which the owners grandmother could drive comfortably - and yes they both had lag, but minimal. That my friends is what I was talking about when I mention the latest technology.
but I'll butt out now anyway!!
RE: Super- and turbocharging - 'twincharging'
I think this thread has been quite informative and I believe we have all learned something, EXCEPT, "doglegracing" who has not logged onto these forums since his original post on March 10,2003 !!!
No argument about street applications and few disagreements about race related blowers. New technology is improving supercharger science and whether mechanicaly or exhaust driven, we can (IMO) look forward to seeing many more OEM applications in the near future.
I also agree that it is possibly time to put this thread to rest.
Rod