| What's Going On? |
There are
64 guests on-line
|
|
|
|
|
|
TwinScrew Vs. Centrifugal Superchargers
I would like to know what you forced Induction experts think about each system and why or why not you would go with either a Twinscrew System or a Centrifugal system "Vortech" system.
| | Reply » TwinScrew Vs. Centrifugal Superchargers |
Quote: | I would like to know what you forced Induction experts think about each system and why or why not you would go with either a Twinscrew System or a Centrifugal system "Vortech" system. | The choice was easy for me, I got my Dinan/Vortech sc for zero dollars...
I do have to buy the software (computer headed to NickG. earlier this evening) and as it turns out, I need to redo the compressor's oilfeed line due to fitting an oil cooler that the car I removed the sc system from didn't have.
I do know this about forced induction (admittedly, I have a lot more to learn) but I prefer the linear power delivery of a belt driven supercharger over an exhaust gas driven turbocharger. Granted, the turbo could yield ultimately higher output, but at the expense of real-world driveability.
I would like to learn to learn more about the twinscrew though; perhaps Daniel will let me put one on his car...
| | Reply » TwinScrew Vs. Centrifugal Superchargers |
Randy:
Same here, I was emailed the other day asking what I thought about the twin-screw supercharger system. I replied back with this
Firedwg1@aol.com wrote:
The twin screw SC has one issue... our engines power band is in the high RMP which is a disadvantage when comparing a Votech SC. Twin screws are typically used in low RPM applications because they give the full charge right off the line. Centrifugal Blowers will produce more top end power and tend to be very easy if not better on fuel consumption during normal driving conditions.
I am sure you are already a pro at this but here are all four types of SC's compared
http://www.coloradocobras.com/whippl...son-chart.html
The reply I received back was this
"]your idiot. You dont know Sh!t.
that is why you want the twin screw SC esp in S54 - for the low RPM.
Fuel economy is not event an argument. Get Prius. This is a sports car."[/B]
There are a few major issues why OEM installs are shying away from Roots type blowers. Here are a few quoted from a respectable BMW service shop...
To the best of our knowledge there has never been a twin-screw unit used in an OEM application, it is not even considered as one of the competitive designs. And the cart you linked is obviously biased, as the twin screws are all real loud and don't make good top end power as stated.
(A) Factually speaking:
The Vortech centrifugal unit is an OEM unit just like the Eaton. Toyota (TRD) have kicked Eaton to the sideline 12 months ago in favor of Vortech and soon you will see 5 different OEM vehicles with dealer and soon to be port installed vortech kits. This means they will be EPA approved. Vortech have cast TRDs name onto their units and designed kits for them. Chrysler and Ford are planning to do the same. Right now there are OEM endurance tests going on in Michigan with Vortech units.
Why? Because roots units such as the Eaton, cause higher emissions than centrifugal units such as Vortech, because of load.
Vortech units can run 20 psi with approx 20hp draw. Eaton units become very inefficient when attempting over 10psi and draw upwards of over 40hp at that point on a like for like application.
This info is direct from their respective manufacturers."
I would like to believe the individual that emailed me was just having a bad day or maybe he is right and I am a "YOUR IDIOT" which happened to be misspelled.
If you have an opinion please post it. I would really like to know more about both systems
| | Reply » TwinScrew Vs. Centrifugal Superchargers |
There are three basic supercharger designs.
1. Positive-displacement (such as Roots and twin-screw) herein called PD.
2. Linear-displacement (such as the Latham and most jet engines) herein called LD.
3. Logarithmic-displacement (such as any centrifugal supercharger, turbocharger or not) herein called centrifugal because CD often means "constant displacement.".
Note: "blower" = "supercharger".
Any of the three types can be belt-driven; in theory, any of the types can be driven by exhaust gases, thereby becoming a turbocharger. Lets assume for the moment that all three are belt-driven.
A PD pump (and that's all a supercharger is --- an air pump) puts out the same volume of air every revolution. In a supercharger application that means that the intake manifold pressure (and therefore the cylinder pressure) is highest at low rpms and drops off with increasing engine rpm. This is very good for low-end torque, but the boost fades out at extremely high rpms. The venerable Roots-type blower is a PD unit. The Twin-screw is another, and is somewhat more efficient than the Roots.
An LD pump puts out more air per revolution in direct linear proportion to the rpm of the pump. It produces twice as much air at 2000 rpm than it does at 1000 rpm, and four times as much at 4000rpm. In a supercharger application this means that the intake manifold pressure starts out higher than in a NA engine, higher than in an engine with a centrifugal blower, but less than in an engine with a PD blower. That intake pressure remains pretty constant throughout the engine's rpm range. This is a pretty good idea for an engine with a lack of low rpm torque but which has a very high rpm limit. Unfortunately, they are very expensive to build. The compressor stage of most jet engines is an LD compressor. The only example of an LD blower for automotive use of which I know is the Latham.
A centrifugal pump puts out air in a logarithmic porportion to the rpm of the pump. So you get very little flow at low rpms, a moderate amount at middle rpms, and a high amount at high rpms. In a supercharger application the centrifugal blower produces manifold pressures that are the same as in an NA engine. Pressure quickly rises as rpms rise, and they reach maximum at high rpms. The centrifugal blower does not produce much low-end boost, but it does produce the most high rpm boost. There are many centrifugal blowers on the market, as they are economical to make, easy to mount in most cars, and are easily made in a turbocharger version.
Ah, the almost magical TURBO. The full name is turbosupercharger. It means a surpercharger that is driven by the exhaust gas flow of the engine to which it is mounted. That's all. The nature of a turbine-driven blower is that it starts out at a relatively low rpm and then very quickly goes to a very high rpm. Combine this with the nature of a centrifugal blower and you get gobs of high rpm boost at the cost of low-end torque. You also get the famous "turbo-lag" as the turbine speeds up after you hit the throttle.
Which one is best? That all depends on what kind of engine you have and what you want out of it --- and your pocketbook, of course.
Do you want lots of torque (and hp) off the line? Then you probably want a PD blower. Roots is good, but it looks like twin-screw is better (especially for street cars where the Roots often won't fit under the hood).
Do you want max hp at the cost of low-end torque? Centrifugal is for you --- probably a turbocharger.
Want a little of both? Then you want a LD blower. Good luck finding one.
Our BMW engines like to rev. They could use a little more low-end torque in some cases. That tells me that I would like a twin-screw blower. If I were racing the car and wanted the most hp (and had the driving skill to keep it in the proper rpm range to use that hp) I would look into a centrifugal turbocharger. Other things must be considered too. Will you need to change pistons to keep the static compression ratio down? Possibly, especially with the PD blowers. Will you need to have the engine's computer control reprogrammed? Most likely, yes. Will all that new hp tear your engine apart? Maybe.
| | Reply » TwinScrew Vs. Centrifugal Superchargers |
Mercedes uses a "twin screw" Lysholm design for their higher end superchargers (essentially everything but the C230 kompressor and SLK230). The Miata community went through the Eaton v. Lysholm discussion a while back. Twin screw's increased efficiency means lower intake air temps (versus an Eaton).
As Bob mentioned, the centri units are very similar to a turbo but lack the turbo's strengths because they stay tied to the engine.
| | Reply » TwinScrew Vs. Centrifugal Superchargers |
Quote: ,,,
I do know this about forced induction (admittedly, I have a lot more to learn) but I prefer the linear power delivery of a belt driven supercharger over an exhaust gas driven turbocharger. Granted, the turbo could yield ultimately higher output, but at the expense of real-world driveability. | I'm in the same camp. That steep slope change in the dyno curves of turbocharged cars tuned for max dyno numbers makes them less fun for me on a road course or even on a spirited mountain drive. Of course a lot of it can be tuned away, but at the expense of the top end power. The S54 already has the "comes alive rather quickly at 4000 rpm" character, a turbo tuned for maximum power would make it even more so.
Quote: | I would like to learn to learn more about the twinscrew though; perhaps Daniel will let me put one on his car... | Not gonna happen unless Josh and company decide to tackle the S54, or AA or someone else decides to somehow fit a Whipple to an S54. Right now the only viable off-the-shelf kits for the S54 are the Rotrex-based kits from AA. I haven't seen a Whipple on an S54, and if it takes Josh and company as long to do an S54 kit as it did an S52 kit (assuming they're even considering it), I'll be driving the AC Cobra kit putting down more than enough HP to get me to 60 mph in 3.5 seconds. At that point my interest in going to FI in the M will wane considerably; it'll become a street-only car.
Which is not to say there aren't S54 owners out here wishing Josh and company would do a twinscrew for the S54. I do know that AA helped build a supercharged E46 M3 with 515HP. But Sean Kennedy has been putting down close to 500rwhp for a little while now in his S54 M roadster. Vortec SC, tuned by AA/ICS, built motor w/ Pauter rods, CR reduced to 9.5:1, RMS dual aftercooler, ported/polished head w/ 5-angle valve job, and I forget what else.
I'd say if you want to go with a solution known to work, talk to Sean Kennedy if you're looking for gobs of power from a supercharged S54. Prepare to drain your bank account of a good sum of money. Talk to Karl and company at AA if you want something milder.
|
Page 1 of 16 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
|
|
|
Menu
TwinScrew Vs. Centrifugal Superchargers