Super- and turbocharging - 'twincharging'

[doglegracing]

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?

 

[aorangi]

It looks like the return of the Roots blower has to do with transient response and is also a fashion, like V10 and V12 engines. It looks good under the hood. The turbo lag, even short with current small diameter rotors and variable turbine intake vanes is still not appreciated at all by the customers-drivers. An instantaneous throttle response makes you feel the car's performing very well, and even if the turbocharged one has the best performances it will be less valued.

Cheers
Aorangi

 

[patdaly]

I think the current Supercharged fad uses Roots style blowers simply for the simplicity of packaging and ease of assembly. Typically, these are quite low boost applications, as as such do not justify taking the "engineer" approach. Just for example, the 3 people I know who own 3.8L GM supercharged V6 cars havent the foggiest notion of how, or why they work, they just wanted some extra oomph.
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?

 

[aorangi]

Patdaly, you wouldn't have the advantages of a turbocharger, but instead a boost pressure growing with the engine revs in a propeller law curve. It means no boost at low revs, very little boost at mid-range and too much boost at high revs, perhaps also compressor surge if you try to increase the overdrive ratio of its drive. It's OK for an aircraft or marine engine, but not for an automotive engine. BRM tried it on their F1 1.5 liters 135° V16 but it was a total failure.

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

 

[Whittey]

Centrifugal superchargers are also generally louder than both turbo's and roots-type blowers. Also, will a centrifugal supercharger last 100k miles (160k kilometers) with little to no maintenance?

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=-

 

[NeilRoshier]

patdaly I agree with the packaging issues, having had a look under the bonnet of the new amg55 merc I could not see how they could have made a turbo or twin turbo fit (mind you they probably could!) and few people can argue with the 350kW and 700nm that the engine produces with a rootes blower on PULP fuel.
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?)

 

[patdaly]

Aorangi, I dont know how current you are with Centrifugal development, but they have made great strides in the past several years. Looking at datalogs on my current toy, I have 18 PSI of boost from approximately 3000 to the 7200 RPM redline. This could certainly be shifted down in the RPM range by a greater step up gear, so say you would be able to build a fairly flat boost curve from say 1500 to 5500. The biggest thing I see has been in the advancement of Helixed Impellers, which are very agressive. What you need to do is combine it with a BOV, which below ( and above with a decent management system) the boost targets helps flatten the curve. So long as the BOV releases air prior to the MAF, you would have no ill effects in regards to engine management.

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.
LOL The Talon would indeed be there! I do know 1 person that has done the same thing with a Saturn,though with an Eaton M62, fire me a mail off list if you want the URL for pictures. Addy is patdaly@crtelco.com

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!

 

[NeilRoshier]

Pat I think that with the demands for weight and packaging plus the ability to cater for different market fuel requirements forced induction has a place, especially given the increasing dependance of driver on the comforts afforded in new cars.

 

[aorangi]

Patdaly, I had a look at the link you gave (procharger website), but I couldn't find out how they obtain a flat boost curve from 3200 to 7200 rpm. I understand the excess compressed air is blown off at high revs, as you speak of a BOV (blow off valve?). That may work for a drag racing car but it's certainly not a good means to increase engine efficiency and fuel economy !

I couldn't agree more with what Dan Barnes writes at:

http://www.badz24.com/Cavy info/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

 

[NeilRoshier]

Ah but the other factor is cost! IHI Lysholm less than $200 USD (admittedly used but with a warranty) and turbo?..well was quoted $1720USD for BB turbo for WRX upgrade. Perhaps this will be the deciding factor? (yes I know that it is an unfair comparison, but the rebuild cost for a similar turbo was $400USD for expected parts)

 

[Whittey]

Whipple claims 70-80% efficiency and a guy on another forum claims sprintex has a lysholm-type supercharger with up to 95% efficiency but he gets very defensive when you ask for proof.

http://www.whipplesuperchargers.com/content.asp?PageID=68

-=Whittey=-

 

[aorangi]

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

 

[patdaly]

Aorangi, the Centrifugal companies are very protective of their Impeller designs, and other than the CFM ratings they publish, I highly doubt you will get any other data. They are locked in a fierce battle for supremancy ( ATI Vs Vortech ) What I can say is I just inspected one of the major manufacturers Impellers, and not only could I not figure out just how you could whittle such a helixed piece of art with a CNC, I could not understand what the principle of the secondary helix was. What I do know is it moves a bunch of air, and not only at high impeller speeds. From what I could gather from the sources you provided, they are either reasonably outdated, or have not followed the past year or so in development. Perhaps it would not match the efficency of a Turbo, but I would hardly call it a poor choice for an OEM, especially with ECM control of Boost. Would it not closely emulate a Centrifugal compressor, simply partially unloading the Intake would reduce the drive losses?
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 ;-)

 

[kimbo1]

I would give up aorangi,
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!

 

[NeilRoshier]

Kimbo I am surprised that you would make such a statement! How would you know what I have or have not driven? Perhaps EVO 6, WRX 2002STI and Nissan R33 would change your mind? (I take it that you are familiar with such cars?)
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.

 

[patdaly]

"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"

I second, and promise to not further promulagate this thread. Thanks for the debate all!

 

[Whittey]

"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"


^^ 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.

 

[evelrod]

Well, I have been reading along and it seems that all of us "have a piece of the elephant"!
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."

 

[ProgressiveRacing]

When you consider what guys like Kenny Duttweiler and other turbo notables are doing performance wise (drag race here), it doesn't make much sense to twincharge. There are guys trying it right now... Mike Moran comes to mind... but he's still trying to get where the conventional set-up guys (Rod Saboury, Chuck Samuel etc.) are already at.

Sorry, just don't see the point... asif things aren't complex enough already.

-Allen

 

[aorangi]

Hi guys !

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

 

[kimbo1]

Neilroshier,
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?