Although they they can punch a huge amount
of air to the engine,why is it that most
auto manufacturer choose turbo,rather than
supercharger? Isn't it true that supes got
few advantages than a turbo? No lag and
less plumbing?

A turbo is a easier kit to setup and install. The most power from a turbo is usually higher in the rev range of the engine, so ask yourself if you want to rev to redline all the time to play with the added power your investing in?

A SC will give you power instantly unlike the turbo which has a bit of lag in accel pedal response. You will also start making power very low in the rev range all the way to mid - high rev range so you have more available power in every day life like on the highway and in the city. Less plumbing is true but there is a big obstacle with SC's and that is intercooling. The SC does its work right above the intake manifold on top of the engine except for a centrifugal type. In order to get the most out of any forced air engine you should cool the compressed air (compression = heat) with a intercooler and that is trickier on a SC because of room. There are intercoolers available for SC's but the Kleemann kit is the only one I am framiliar with and it uses the best kind of Intercooling, air to water with a 4 liter water capacity.

One more consideration and this is a biggy here, how much room do you have to work with in the engine bay? With any V8 W124 room is limited, in my 500E it is VERY tight in there!

To answer another of your questions, many cars are available with Turbo's instead of SC's because they are cheaper to make than SC's. There are many close tolerance moving parts in a Roots type, and Twin screw type SC. The third type, a centrifical is basically the same thing as a turbo but instead of being power via exhaust gas like a turbo it is driven via accessory drive belt. Even though a SC offers more "usable" power, cost is the factor IMHO.

One final question to answer, how long will they last before needing a rebuild? Depends on how well you protect the internal bearings of the device with proper lubrication as they are spinning at very high speeds. When you drive hard and then turn off the car you are stopping oil flow to the bearings and that is the only way they receive cooling. So the oil cooks in there over time and causes the bearings to go south. How long does it take? I don't know but some say a turbo will go 60-100k before needing to be replaced and a SC around the same. Basically technology has not caught up with this issue or they would last much longer.

just some other differences of superchargers vs turbochargers:

a supercharger imposes parasitic losses on the engine all the time, unless there is a clutch that disengages it, like that on the C32.

an exhaust-driven turbocharger uses the energy of the exhaust gases to power the compressor, energy that would otherwise be wasted. But some backpressure results in this, so it is not really "free" energy. But because it has a muffling effect on the exhaust pulses (which have less energy now), a less restrictive exhaust system may be used.

tradeoffs against the exhaust-driven turbocharger are turbo lag and heat/bearing life.

it is interesting to note that an automatic transmission works well with an exhaust-driven turbocharger:
* the slippage of the transmission allows the engine to rev much earlier that one with a manual transmission (where the engine is locked in into a ratio), reducing turbo lag
* when the turbo finally achieves full boost, the torque converter is able to absorb the surge in power, resulting in smoother power delivery.

finally, as a marketing issue, the term "turbo" has more mindshare among the buying public than "supercharged".

Thanks guys,
Its a lot clearer to me now.

Don't want to start a big arguement here, but having designed and installed a variety of both blower and turbo systems, I have to disagree with most of this post.


[QUOTE]Originally posted by roas
A turbo is a easier kit to setup and install. The most power from a turbo is usually higher in the rev range of the engine, so ask yourself if you want to rev to redline all the time to play with the added power your investing in?

Not true. Blowers are easier to install because you only have to modify the intake system. With a turbo, you have to modify both the intake and exhaust. Also, when you work out the engine management on a positive displacement blower, it is essentially a 2D map, whereas a turbo has a full 3D map. With a blower, you have a pretty good idea of the boost at any rpm; with a turbo you don't. Also, a well designed (properly sized) turbo will build boost FASTER than a blower. Check out the Bell website for some comparisons between the M3 blower kits and the turbo kit. Same with the Miata blower vs turbo kits.

A SC will give you power instantly unlike the turbo which has a bit of lag in accel pedal response. You will also start making power very low in the rev range all the way to mid - high rev range so you have more available power in every day life like on the highway and in the city.

Again, not true. As mentioned above, this is one of the most common falacies regarding turbos. I did an NSX TT kit for a friend that has full boost by 3400. The comparable blower kit makes boost 1000 rpm later. No blower could do better, unless you way over spun it and spent most of your time venting through the waste gate. Which, by the way, would make it really inefficient both volumetrically and thermally. A positive displacement blower, especially a twin screw, will come close, but not quite keep up with a small turbo.

[b} Less plumbing is true but there is a big obstacle with SC's and that is intercooling. The SC does its work right above the intake manifold on top of the engine except for a centrifugal type. [/b]

Partially true. Intercooling is trickier, but blowers are more common in low boost applications where intercooling is not as much of an issue. Also, I know of several centrifical blower systems that mount the supercharger right at the throttle body. They are very efficient, although they only give hp at high rpms (unlike a turbo).

There are many close tolerance moving parts in a Roots type, and Twin screw type SC.

No. A turbo spins at over 25,000 rpms or so and have enormous amounts of heat flowing through them. There is no way you can argue that they are easier to build than a Roots blower. In fact, a Roots has the slopiest tolerances of any blower type. If Eaton had decent machine tools, they would be making full twin-screw type blowers instead of Roots type. I agree that the twin screw type blowers have tight tolerances. That is the main reason there are so few companies (all norther European, I believe) that can make them.

Turbos are more efficient, build boost faster, and give more power across a wider power band. Blowers are simpler and cheaper. They often also have packageing (space requirement) advantages over turbos.

My .02.

OZ HAS SPOKEN!!!

Whew, 2 cents? That was more like a couple of dollars! haha Well the only thing I am wondering about is the original post which said that many more cars come with turbos than SCs. To the best of my recollection, the cars that currently come with turbos from the factory are the VW/Audi 1.8T and Audi 2.7TT, and then Volvos and Saabs, and of course the insanely expensive Bentleys and Porsche 911. You don't see too many of the Sweds, the Porsche is too exclusive, the Bentleys WAY too exclusive and rare, so the most mainstream turbo is the 1.8T. But superchargers on the other hand...the new MB AMGs, the GM 3800SC, the Ford Lightning, Ford Mustang Cobra, the Jaguar V8 in their R motors, did I miss any? So I wouldn't say that turbos are that much more common. I would say they are a rather even. It may even lean a little on the SC side because of you leave out the Porsche and the Bentleys on the account of rarity and 6 digit prices and the Sweds on the account of being oddballs, then that leaves you with the two VW/Audi engines. And then that leaves many SC engines, many of which are rather attainable. My 2 cents.

Oh..and I am not including any diesels, because they are another animal.

__________________
'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."

I've driven turbos (Thunderbirds) and supercharged (my Regal GSE) and both are impressive. I like the supercharger better but that's just my opinion based on nothing but my experience. I saw on the Ford website that the 2003 SVT Cobra will produce 390 HP and 390 ft. lbs. torque out of the 4.6 (280 cu ins.). Astounding!!! The only drawback is a broken supercharger belt will make you call the tow truck.

Hmm... oh, yeah, the original question! The ratio of OEM turbos to blowers has varied considerably over time. Blowers were poplular a few years ago becuase:

- they are simple
- they are cheaper
- they require less redesign
- they are more emissions friendly
- easier to retro fit to a car not designed for forced induction

Turbos are popular with OEMs because;

- they are more efficient
- they give better gas milage results
- more total hp

One of the big issues facing OEMs regarding the use of turbos in the U.S. market is the relatively new star-tup emissions requirements. A turbo acts like a pretty efficient heat sink, so the cats take much longer to light off. Some current turbo cars (WRX) solve this by putting a cat ahead of the turbo. They actually use THREE cats on the WRX to make it pass the start-up emissions standard.

Oh yeah...the WRX, forgot about that one. How much extra power do you think can be had by removing 2 of the 3 cats on that car and just leaving the one main cat under the car or even replacing that one with a high flow unit? Just curious. And do you know of the emissions equipment used in the VW/Audi 1.8T and 2.7?

__________________
'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."

Oh yeah...the WRX, forgot about that one. How much extra power do you think can be had by removing 2 of the 3 cats on that car and just leaving the one main cat under the car or even replacing that one with a high flow unit?

Not sure. I would guess a few hp at the wheels (5-10) because the turbo is sized pretty well for that motor and it spools pretty quickly as is. I ran my turbo NSX without a cat for a while and when I put a 3" high flow cat behind the turbo it made absolutely no difference in rwhp.

you know of the emissions equipment used in the VW/Audi 1.8T and 2.7?

Nope. Never worked on those. I believe their emission setup is pretty standard though.

Well....

BTW, you might be interested in the fact that the information I gave above was pulled out from a book by Corky Bell called, "Supercharged!". I generally don't like to pull stuff out of my ass on technical issues. , that is usually reserved for other thing in life.

BTW, you might be interested in the fact that the information I gave above was pulled out from a book by Corky Bell called, "Supercharged!". I generally don't like to pull stuff out of my ass on technical issues. , that is usually reserved for other thing in life.

None of this came out of my ass, either. It came mostly from a lot of experience. And, BTW, from a book by Corky Bell called "Maximum Boost" which is more up to date than his blower book. I know Corky pretty well and I can tell you right now he prefers turbos. Call him and ask. ; )


A SC will give you power instantly unlike the turbo which has a bit of lag in accel pedal response. You will also start making power very low in the rev range all the way to mid - high rev range so you have more available power in every day life like on the highway and in the city.

Again, that is misleading. A good turbo makes more power at high rpm than a blower will, but it can also make more power at low rpms. A good turbo just makes more hp, period. Also, you criticize using smaller turbos that give great low-end power because they 'strangle' at high rpms, but that is more of a factor with blowers. A blower that is efficient at low speed will become extremely inefficient at WOT, both thermally and volumetrically. Blowers have a very narrow range of high efficiency. That is just a matter of physics. This is extremely true of centrifical blowers, but is also true of positive displacement blowers.

The newer vairable vane and ball bearing turbos have made the myth of 'turbo lag' a pretty weak arguement.

What happens every time you step on the pedal at 1k rpm in a turbo?

My cars aren't below 1K unless I'm waiting for the light to change. If you drive at that rpm, you have no need for a turbo or a blower. Maybe a tractor............

However, if you have a properly sized turbo at WOT, it will start building boost very quickly. A blower at the same rpm may build almost as fast if you are willing to give up top end and over-drive it, but then you pay the price higher in the rpm range.

There are 3 types of SC's, roots, twin-screw, and centrifugal. The first two I mention do have big challenges adapting a intercooler but they are out there. The Kleemann for example has a water to air intercooler mounted directly below the twin scew unit, best of both worlds No exhaust plumbing to worry about in my mind equals easier.

WTF? Your original post says "turbos are easier." By the way, I am very familiar with twin screw blowers - Art Whipple is my uncle. He is the guy who got me into modifying cars when I was a kid.

I was not completely accurate in my statement above, what I should have said is the the FEW moving parts inside a Roots and Twin Screw SC are at close tolerances

I stand by my statement that if the folks at Eaton could manufacture to the tolerances required by a twin-screw design, they would do it.

Since you like referencing Corky, here is a blurb from his website;

Also from Corky's site (comparison of NSX systems):

And, finally:


While positive displacement blowers build boost faster than centrifical ones, they suffer even more from the dilema of finding the optimum range to build boost. If you gear them to pull right out of the hole, efficinecy is crap at speed. If you gear them to work at high rpm, you have nothing down low. I have seen a lot of twin-screw superchargers on NSXs. When they are driven to build boost fast, they totally run out of steam at 6K, even on that little 3L motor. If you gear them for boost at high rpm, they have nothing until you wind them out. So, wither way, they are inferior to turbos.

The only real advantgae blowers have is simplicity. Manufaturers like them because they are so much easier to package when you retrofit them (as with the new Cobra). At most, you have to modify the hood line.

Peace.

God D#@&^*ed!!Now I'm really learning from you
guys!!I thank you all but to make things more
complicated,Why do some cars have twin turbos?
One is not enough?If not,then more plumbing,
twin intercooler to?
AYAYAY!!!

cars have twin-turbos for a number of reasons:

* if it is a V or horizontally-opposed engine, it becomes simpler to have a turbo per bank, because of the simpler exhaust plumbing and the resulting shorter runner lengths (=minimal turbo lag)

* an exhaust-driven turbo imposes backpressure on the source cylinders, so it's good to have symmetric backpressure on both banks

* some cars have 1 small turbo for quick response, and a large one for high-rpm output. These are normally arranged "sequentially", where the small turbo operates at low engine rpm and both operate at higher engine rpm