Turbocharge v. Supercharge

[M.D. Holloway]

One of my students did a great presentation on the two technologies. Made me wonder about supercharging - uses the engine instead of the exhaust, doesn't stress the engine oil to lubricate, seems more reliable. Maybe not as much hp - any other downsides? Anybody ever do it to a 911?

[livi]

Mike,

As I recollect RUF just recently presented a 997 with a supercharged engine. One of the advantages was reliability and less stress on the engine, although it did not gain as much extra hp as with a turbo charger.

I donīt remember the details, but it was in the April issue of one the Porsche magazines.

My first reaction was - WHAT !!!??? Blaspheme !! Supercharge in a Porsche ???

[beepbeep]

Originally posted by LubeMaster77
One of my students did a great presentation on the two technologies. Made me wonder about supercharging - uses the engine instead of the exhaust, doesn't stress the engine oil to lubricate, seems more reliable. Maybe not as much hp - any other downsides? Anybody ever do it to a 911?

Most of traits you pulled higher up are either missconceptions or something your student just made up w/o bothering to do reality check. Most big manufacturers did bother and came to conclusion that superchargers are inferior to turbochargers on almost all points mentioned above save for engine response.

I did this many times before so I won't put much energy into debunking those myths.
Superchargers "seem more reliable" if you ask Joe Sixpack who once owned supercharged V8 with carbs that he run few times up the drag-strip. Joe Sixpack doesn't understand turbocharging and understand the blower. In reality, there are tens of millions of 1.8T VAG engines happilly trundling around the globe every hour. There are hundreds of millions of turbocharged diesels doing the same thing. There are hardly any OEM supercharged cars except few nische-products like Merc AMG's, Koeningsegg (centrifugal blower = half of turbo) etc. If superchargers were so dependable, don't you think manufacturers would use them more often? Turbocharger contains only one moving part: the shaft. If properly cared for, it will last the life of the car. Yes, a friends friends mother had to replace turbo on her _______ (fill in a common turbocharged car) at 70000 miles. But for every friend friedns mother there are thousands of others that didin't have problems. I hate anecdotal evidence but I just can't help say that i recently junked my old SAAB with 240000 miles and original perfectly working oil-cooled turbo beacuse of rust. It was made 1985. Watercooled turbochargers came soon after and don't stress oil as much as early designs do. There is practically no wear on turbo beraings once car is moving. most wear is done while starting the engine with old cooked oil in the turbocharger.

2. "Superchargers use engine instead of exahust". Yes they do. It's not the trait, it's a drawback. Turbochargers are partly driven by entalpi over turbine housing. With other words, some of heat energy in exhaust gases is converted into mechanical motion and exhaust temperature drops accordingly. There is a typical temperature drop of over 300 deg. C before and after the turbine. Yes, there is a increased exhaust backpressure when adding turbocharger but net result is still positive. Supercharger on other hand just draws energy off the crank and heat energy stored in exhaust gases is just wasted. Power levels to drive supercharger off the crank can be quite substantial. We are generally talking about 30-50hp power take in 300-400hp installation. That power id generally transmitted by the belt. Chanelling 40hp trough a rubber belt isn't trivial, isn't cheap and isn't 300000-miles reliable. If we see it from a manufacturers perspective: on one side you have turbocharger with one moving part suspended on a oil-film bearing (no wear and tear while turning), with posibility to use some of wasted heat energy. On other side you have a complex system of hi-torque belts and pulleys, maze of moving lobes (Roots and Lysholm) that need careful machining and sealing, recirculation valves and total draw upwards 10-20% of net power while dumping exhaust heat overboard. Still believe supercharger is more realiable/economic?

If we go further, there are pumping losses inherently connected to supercharger desing when driving on trailing throttle. Being mechanically connected, supercharger will always rotate, wasting power recirculating even when you don't need boost. You can add magnetic clutch and few valves that open when off boost but it will make already bloated system even more complex and expensive.

So it boils to same thing: no, superchargers are not superior in any way except for instant throttle response. Big manufacturers understood this long time ago and pursued/refined turbocharger technology. Reasons why are technical and hard to fathom for ordinary motorist. Ordinary motorist understands a belt and blower but has harder time with entalpi, wastegate and thermodynamics. He will ask you "if superchargers are inferior, why do TopFuel cars use them?". You will tell him "why do TopFuel still use OHC, pushrods and Magneto ignition?" He will tell you "Superchargers are cool, see one of thise Top Fuel cars? Vroooom! They must be better than turbochargers". End of discussion.


These discussions were done decades ago when picton-engined aircrafts roamed the sky. In beggining (created before WWII), they used superchargers (centrifugal, not positive displacement monstruosities as Roots blowers). During the WWII there was a transition towards turbochargers and then towards turbochargers and turbo-compound. After that, whole reciprocitating bussines got killed by jet engines.

You will always find a few persons swearing that their SC installation is dead-reliable and that throttle-response is superb and well worth the hassle. On every one of them there will be ten thousand of persons driving turbocharged cars. I guess it's same with MFI. It's an automotive Mormon-thing.

P.S. Ask Natchamp why he swaped out his blower and replaced it with twin turbochargers

[beepbeep]

P.S. Grandious (part)solution to efficiency problem:

http://www.fastcar.co.uk/New_supercharger_really_shifts.YTW4rnJoa2rmWw.html

While it won't make supercharger car as efficient or cheap/reliable as turbocharged one, this solution will raise the efficiency somewhat. (It was first used on Merlins in Spitfires in late 30's)

[livi]

Very comprehensive. Thanks Göran !

[JohnJL]

Mike,
This is not at all a controversial topic.....;-)

Do a search, lots of people do both with varying degrees of expense, results and enjoyment.

[JohnJL]

And Goran, shouldn't you be busy posting pics of IF2..? We're all waiting!

[dean]

I think one of the main reasons turbos are not on Top Fuel cars is cause NHRA made them illegal in the 50's

[beepbeep]

Originally posted by JohnJL
And Goran, shouldn't you be busy posting pics of IF2..? We're all waiting!

We're done with pictures, it's time to make it move (fast)

[88-diamondblue]

Mercedes Kompressor has made there cars come alive with reliable HP. Superchargers are not the same as a turbo but the effect is more HP. After driving the Ford GT that uses a supercharger I could not imagine a turbo being as smooth as the system Ford put together. But have been proven wrong many a time. Yes I have driven many turbo cars and enjoyed the drive. Also had the chance to talk with the mechanic (Porsche mechanic for 30 years) that installed a super charger on a 95 993 and after driving it he said it was just about as fast as a TT. Heres a shot of of the a SC'd engine. Either work well if designed properly.

[M.D. Holloway]

Goran - Thanks! The student did an interesting selling job to me and sited interviews, hotrod mags and websites for is bib. He go an A for his presentation and report which went strong into the mechanics of both systems and their applications. I guess the thing that brought him over the edge was a cool automated graphic he did show how both worked then had a video clip from a company that manufactures off the shelf super chargers for ricers and what not.

Part of me wishes I asked the question prior to his presnetation and part of me is glad I didn't - it would have jaded my objectivity to grade according to presneting a point of view and backing it up with details and references. It wasn't for his masters thesis or I would have reasearched it out thicker.

Thanks for that great explanation! (I still wonder how a blower would look like sticking out of my engine hatch vents?)

[island911]

Originally posted by beepbeep
. . .So it boils to same thing: no, superchargers are not superior in any way except for instant throttle response. . ..

Just an interesting aside.

In a conversation I had, with another automotively savvy Swede .. . I brought up similar points; regarding turbocharging vs supercharging.

His (very key) point was that supercharging doesn't "back-up the heat" into the engine.

Beeper, do you have any comments on this other metric?

Oh, this Swedes name is Christian Von Koenigsegg -- maybe you know him.

[defcon65]

I've seen a couple pics on Pelican of a Paxton supercharger fitted to a 3.2 engine. It was regarded as reliable and put out about 300HP. It's fair to say that anything that boosts output by 50% is going to stress something, whether it's the engine internals, gearbox or exhaust. I can't understand this compulsion some have for going overboard with horsepower and speed - my stock 3.2 is way more power than I'll ever need...
Feed the beast if you must and be sure to post pics here.

Joe

[Turbo-Mag]

I have to agree with beepbeep. Each has it's good and bad points. I have had both turbo and supercharged cars. An S.C. has great throttle response, but when a turbo spools up...=fun.

With a S.C to change boost levels you need to change pulleys to increase or decrease your pressure. With a turbo you just add a boost contoller and in seconds you can change your pressure. It is that easy as long as you have done your proper tuning. I have a Neon that I built and turboed. Drive it at 8lbs and have a two stage boost controller set to 20lbs of boost. I just flip the switch and wham I'm gone.

As far as reliability I say anytime you add boost to a car you are affecting the life of it. No matter how you boost it, if it is maintained properly it will give you years of enjoyment.

Still I can't help but think of all the trubo charged big trucks, generators, small planes and small cars that are out there. In comparison to S.C's that's gotta tell ya something.

[RarlyL8]

It's all a matter of application.
If I were to purpose build a 911 for street domination it would be supercharged. You simply cannot give away a fraction of a second in hesitation and lag by being caught off guard when the hammer drops.
If that is the ONLY fault that turbos have it is a doosy!

And you can adjust supercharger boost on the fly - the same way you do turbos - with a waste gate and dial-a-death. This ain't the 60's anymore, you don't need a Rat-Fink blown big block hangin' out the engine bay to be supercharged.

[sewell94]

Turbos are alot better than sc, hands down. Sc sound awesome on a v-8 but there nowhere near as efficient. The belt alone takes alot of extra power to run. i've done quite a few of both. Do u care abot about having a ton of tq at 2k rpms, how much time do u actually spend there. Its just fries tires, which makes it harder to drive and if u want to make a turbo have boost at low rpms it really easy, **** u can build 40 lbs from a deadstop so that kills the whole no low end theory on turbos. Turbos are alot more flexible, u can decide where u want the power, u can decide how much boost in each gear for each throttle position. The deciding factor for me is that i haven't see to many F1 cars with SC most had turbos, i'm sure 80's f1 tech is still way ahead most of us. The future will be variable compression ratio engines with variable cam timing with VTN turbos(thats if electric cars don't take over by then )

[kmhemi]

Here is one of our old toys that is long gone now.

[kmhemi]

Sorry those pics are so big.

[M.D. Holloway]

These are some great comments and ideas. I think a better place for this would be on the OT board. I will have to lobby the mod.

Thankx guyz!

[midlife]

At the SEMA show the overwhelming majority of the kits for late model vehicles were superchargers. Including one for the 997.
I think this is not because they are better, but that they are easier to package, and have less impact on the emmisions systems.