View Full Version : superchargers VS turbos
05-07-2002, 01:25 PM
interesting fact sheet i found:
one dumb question: If turbos run off exhaust gasses, dosent that filter hot dirty air into the engine?
05-07-2002, 01:43 PM
The turbo has two sets of impellers, one that is driven by the exhaust gas and another one that pumps air into the engine. This separates the exhaust from the fresh air, so that exhaust does not enter the engine.
05-07-2002, 02:16 PM
i just did a speech on the pretty much exact layout of that page! where were your 5 days ago!!!!!!!!!!!
05-07-2002, 02:42 PM
That fact sheet seems to have a drastic slant towards superchargers.
Personally, I always thought a moderate amount of turbo lag was fun. :)
They didn't seem to mention the massive amounts of engine power required to turn a decent supercharger, nor mention that the turbocharger effectively reclaims some energy that would have been wasted out the tailpipe.
Also, there are applications where the high-rpm effectiveness of a turbo would be preferable to a supercharger.
Just my humble opinion.
05-07-2002, 04:39 PM
yeah i agree. its definately slanted towards SC's. And turbos are more efficient for small displacement/high rpm engines never the less. Just thought it might get some general info out there
05-07-2002, 07:20 PM
That is true, the article does seem to be supercharger biased.
the turbocharger effectively reclaims some energy that would have been wasted out the tailpipe.
turbochargers actually create backpressure, forcing the engine to push harder to expel the exhaust gasses. No?
05-07-2002, 11:39 PM
Tubros can be made to be fairly non-restrictive to exhaust by clipping them if needed.
05-07-2002, 11:41 PM
How about some data to back up his claims?
He sources include SAE papers, but what quotes did he use?
Turbocharger is an industry term the correct term is "Turbine Supercharger".
It might be also interesting to note that very few professional race cars use a Belt Driven Supercharger. Most prefer to use the "turbine Supercharger" since it operates well at higher speeds.
05-08-2002, 09:59 PM
You have to understand where they are coming from. From a manufacturing standpoint, superchargers are better. It is easier to match output to the motor, and there are no real concerns about reliability.
Turbo's are certainly more efficient, but that is not the primary concern of the OE. Any form of forced induction is such a huge improvement over NA, that the differences in efficincy is not important.
That is the angle that paper was written from. IMO
05-09-2002, 04:28 AM
"Superchargers do not require aftercooling as outlet temperatures rarely exceed 140 degrees C."
Seeing as I have being playing with turbo'd motors for a few years now, I really noticed the differences of the SC. The turbo feels like a slingshot, the band stretches... and you get snapped into next week! The stock SC feels more like a big block as you start away. The instant torque is awesome, but it flattens out as revs build. The two are sort of opposites as far as how they deliver the power.
05-09-2002, 11:55 AM
Another dumb question.
What would happen if you ran both a turbo and a supercharger on a car at the same time?
Would you get the benefit of instant HP from the line with the supercharger, and then as you built speed the benefit of the Turbo?
05-09-2002, 12:27 PM
my dream project is a SC+TC 3.8
05-09-2002, 12:52 PM
--What would happen if you ran both a turbo and a
--supercharger on a car at the same time?
I have an uncle with just such a beast.
A V8 Detroit diesel with an 8-71 supercharger on it with a HUGE turbocharger sitting on the top of that. Makes 425hp all day long.
It hauls... Gravel that is!
05-09-2002, 01:24 PM
Turbo's and Back pressure - Turbo's are highly efficient compressors with two different sides. The side that is in the exhaust stream is optimized to decrease interference. Any interference that it produces is far outweighted by the boost it can create on the other side.
The ideal design from a wide performance standpoint is a SC that is designed to optimize low RPM performance and cuts out at the same time that a Turbo Charger, optimized for high RPM performance spools up.
Because it is a plumbing nightmare, instead you more often see twin turbo setups where one turbo works well at low exhaust velocities, and the other works well at high exhaust velocities.
The other part that is difficult is that if you build a supercharger that can withstand high RPM's (10,000 crankshaft rpms) it can't give you your good low end boost. So to get good low end bost with an SC yet keep the high end RPM's, you need to be able to do more than just bypass the SC, you need to de-couple it from the crankshaft. Creating a electronically or mechanical coupling that can withstand the TORQUE generated by a good SC has not been easy in the past, and no one has really tried to make one since.
(The MR-2 from Toyota had a A/C type clutch used to decouple it's very small SC plus a bypass valve)
05-09-2002, 01:43 PM
Great assesment Mike.
My SVO turbo only starts making power at 2500-3000 rpm, heck the SC is half way through its powerband by then. By 4000 rpm the smallish turbo on the SVO is capable of over 25psi boost and has to have the exhaust vented off (wastegate) to lower intake and backpressure. Sizing the darned turbo to get low end AND top end is half the black art of turbos. Using a supercharger to fill in the bottom end with a turbo designed for max to end would be a thrill.
Why does the SC need to be disconnected? Use of a one way valve would allow whatever has the most pressure to dominate and block off the other. Food for thought.
A centrifugal SC like the Vortech has many of the advantages of a turbo without the exhust pipe nightmare. What about a compact charger that combines a centrifugal section with a positive displacement section?
05-09-2002, 02:56 PM
I have heard of a beast that used both turbo and SC and the results where not that good. I don';t have any technical data on this, I just heard it doesn't make the power we would expect. Also, the SC's are lossing a good amount of hp (50 or so) due to belt drag. Turbos do not loose that hp and are more effiecient. Steve
05-10-2002, 01:40 AM
There was an article back in 1988 or so about a modified Lamborghini countach. It had a supercharger (don't know what type) and a HUGE twin turbo system. These turbos were gigantic, they didn't even think of making power until about 5000rpm. The particular supercharger I remember was mounted in between the "V" in the V-12 engine, so It might have been a roots blower.
The plumbing looked good but there was alot of it. I think the final #'s were somewhere around 600hp for the whole set up. I don't remember who built it and I don't have the issue anymore. Supposedly they used some sort of bypass valve to recirculate boost through the blower at a certain RPM. I guess they just felt that they could live with the blower drag at 7500rpm.
On the Other Hand the current mercedes SLK 3.2 AMG DOES use a magnetic/electronic decoupler on it's Lysholm (whipple) supercharger. This according to mercedes benz, improves fuel economy like 10%. When Boost isn't being called into action.
Since their 3.2 V-6 is a SOHC 3 valve per cylinder design, it uses a whipple charger and a air to water intercooler. It makes 340hp, stock. Pretty sick little engine.
If you're looking for the instant boost of the supercharger but comparable efficiency of the turbo, then consider the whipple charger. It has an efficiency rating of around 70-80%, but still delivers more low end torque than a conventional centrifugal supercharger.
Lots of expensive OEMs are now using them, like the aforementioned Mercedes and The mazda millenia Miller cycle S engine used a Lysholm. (however the mazda unit was too small for our Supercoupes cu. in wise and quite expensive, around $4000)
05-10-2002, 02:03 AM
Of course the Whipple has more low end torque than a centrifigal supercharger, the Whipple is a roots charger.
600hp from a twin turboed supercharged countach really isn't that impressive. They definitely could have used some more R&D.
05-10-2002, 10:35 AM
The need to decouple the supercharger from the the crankshaft is to avoid blowing it up when the turbo's hit their stride and take you all the way to the 10,000 rpm crankshaft redline.
A supercharger that gives you the most bang for the buck at low RPM's is not going to like high RPM's at all.
The issue with all crankshaft powered superchargers is that they rob more power, the faster they are turned. You could try to make a two stage supercharger, each optimized for a certain power band, but you can get far more power from a turbo, without the loss of crankshaft horsepower at higher RPM's. I.E. a V-6 Taurus SHO with a Vortech is good. A V-6 Taurus SHO with a well designed turbo system is better.
It really comes down to bang for the buck. We are not tryining to build production cars here, so if you think you can get some real bang for low dollars investment, do it whatever way you want. But if money is no option, and time is plentiful, the best bet is a SC + Turbo.
05-11-2002, 12:12 AM
I think that the 1988 article was about a 1987 Countach, or something like that. I think that the stock Countach *only* made around 390-420hp. So 600+HP back in the day with cruder fuel management systems etc.. was pretty impressive.
The majority of these countaches were built for Clients who wanted more zip at the track but wanted to keep it docile for street use.
I don't think that they used a decoupler for the supercharger, or else it could have made more hp.
I wonder how interstesting it would be if it were possible to "build" a decoupler for our engins, then we could "turn it on and off."
Supercharging and Turbocharging at the same time adds alot of weight and complexity to the system. With all of the plumbing etc. it makes it hard to realize that an engine resides underneath. If that is the case, just use a bigger engine.
That is why Big blocks ruled up until the gas crunch. It was just simpler, cheaper and the power gains were very real.
After the fuel crunch, turbos were big, but people didn't know how to take care of them (coking up turbines etc) and stayed away from them. OEM's went back to using N/A engines, tuned intakes/exhausts and DOHC multi-valve engines and even varibale valve timing. This way you can get the economy of a smaller engine, the power of a larger engine and the reliability as well.
Many OEMs who still turbo charge their cars (Audi, VW, Volvo, SAAB) are now using a new generation of "light pressure" turbos. What they have found is that a small turbo charger can be optimized to work well with in a smaller power range. These turbos typically only operate around 6-8psi and they blow boost on a Multi-valve engine anyway. Since they are small, lag time is minimal, giving the engine a real power boost that most people can feel instantaneously. The disadvantage of these turbos??? They are optimized for very low boost levels and do not respond well to "turning up the boost" that some of the older and larger turbos did. (anyone remember how much boost could have been had by a Stock GN turbo? About 18psi)
One of those little Audi/Vw Turbos could probably make about 10psi of boost before they started to heat the air up too much and cause detonation. Still, there are chips and stuff out there, and if you are enterprising you can change out the turbos, but then you loose some lower end grunt.
05-11-2002, 08:23 AM
Mst of the reason for the lower boost was for emissions and responsiveness. Ultimate power can be built with a 7:1 compression engine using 18-25 psi boost but the low compression (needed to survive the high boost) is "dirty" with unburned hydrocarbons at low outputs. At high outputs excess fuel is often used to insure against detonation. More "dirty" emissions.
As well, the low compression engine is totally unresponsive without boost, so turbo lag becomes a big problem.
A 6-10 psi turbocharger can be installed on a more or less stock engine. Sure you can add an oil cooler and intercooler but forged crank and pistons are not especially needed. You can essentially use your EPA certified core engine pretty much as is, making certification and production simpler. There is no optimizing and higher technology, just beancounters at work!
Emissions killed the 2.3 turbo. A lot of that paper was correct for production engines. Hopefully supercharged engines will have a better time of it and we'll see more of them in the future.
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