legacycentral bbs

Well I didnt get a turbo, but I did get a supercharger off of Ebay today for a 4 banger Mercedes. As luck would have it I also won a ZEX nitrous system as well early this morning. Thank God I actually have the money this week.

Here is the link to the supercharger.
http://cgi.ebay.com/ebaymotors/ws/eBayI ... :EOAB:US:6
I plan on either mounting it to the left of the engine where the airbox currently is (seen this done with charger in Australia) or messing with an extra intake I have and seeing if I could do a top mount Eaton style charger.

I got my work cut out for me either way.

I plan on running only 5-6 lbs of boost so I dont make my new rings say "Ouch!".

I might actually have a "fast" car for the first time in my life!

Now I just have to figure out how to hide a large purple bottle and a supercharger from my wife!

try local shopping centres, or outside lawyers offices and doctors surgeries, i'm pretty sure you'll find a badge at one of those places

what are you doing in the way of fuel, timing, and boost control?

run low boost and hope for the best at this point for fuel. Boost on a charger is controled by the size of the pulleys. I will run high octane for the timing problems.

First I just have to get the thing actually working (ok, first I have to pay for it and get in the mail, then I have to get it working).

From what I have read in the forums, low boost should not overtax the system and the computer should accomadate for the increase air flow. Or so I hope. I have the "talent" for the monkeywrenching and metal milling and so forth. I dont have the computer whoo whoo knowledge at all. So we will see what happens.

But first, I just have to actually get the charger to actually work.

well I dont think the fuel system, or the ecu is going to like that at all at the very least you should upgrade the fuel pump and use a rrfpr. Otherwise I'm almost certain you'll run lean, real lean. I'm sure you wouldnt like having to tear apart the engine again to fix some detenation problems so soon

Well I dont belive you. The engine will be fine. I will run 20 psi! I will be Superman!


No, I dont really want to rework the engine again. By the time the charger actually is working I am sure I will be asking a thousand questions. And I know where to go!

Thanks

Here's a few on e-bay

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... me=rvi:1:1

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... me=rvi:1:2

You can also get them at the dealership, but they would cost more than you paid for that S/C.

You could cut the V8 out of this...

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 7907180400

I actually put a watch on the first one, thanks.

But I figured I might as well wait untill it actually works to spend money on one. Please God please, let it all work out.

As I type this I just remembered the biggest obstacle. Which direction does the damn thing turn? If the charger turn the right way (whichever it is) no problems. If it turns opposite, then I will have figure some major problems out.

Go pretend to be interested in a new Benz at a dealership

Look under the hood and you'll know

I'd venture to guess that the shaft spins clockwise.

You might have a better chance if you had found a centrifugal SC. Those are significantly easier to mount (basically the compressor side of the turbo, with the exhaust wheel spun by a belt off of the engine).

I'd say the easiest place to mount the system would be on top of the manifold, but that would require a custom Throttle body setup to bolt to the inlet side of the "k"ompressor (the back). If you've got access to a CNC mill, you could make all the adapters you need in a day.

The only problem would be the stock ECU. It's unlikely that it has ANY maps for positive manifold pressure. In fact, if the ECU sees a positive pressure, then you might run into a big fuel cut issue. Easiest thing to do would be run a piggy-back system that can emulate a boost condition. The downside to this, would be that the stock ECU would learn around the setup.

Now it would seem to me, that you could swap a Turbo Legacy ECU into the car, set up a "boost controller" (basically just leave it plugged into the sensor, but not have anything else connected, just like you'd do with an MBC). That way, you've got an ECU that has a boost map to handle the fuel delivery for the first few psi. That should make things a little easier to handle.

No question though, it's a roots blower, so it should be setup as such. You'll have to cut the shit out of your hood though, to fit it on top of the manifold.

Are you going to have a switch to activate it? The M-B has a clutch like an A/C compressor so it only works under WOT or something like that.

Steve

BAC 5.2
So what is the difference between negative and positive pressure? Where the blower mounts in reference to the throttle body? So if it is mounted on the manifold then it is after the throttle body making it positive and if before then it is negative? Thanks

Steve,

Yeah, since it has an electromagnetic clutch, I would have it so it only comes on via a switch since it is a power eater when not at WOT.

Negative pressure = Vacuum.

Positive Pressure = Boost.

Where you mount the blower doesn't really matter (afterall, a turbo is pre Throttle Body), but that IS a roots style blower, so it should be setup as such.

What is the importance of a "roots" style versus the others?

Roots offers linear power delivery. Instead of having the crank spin a turbine (like with a centrifugal SC, which is basically the compressor side of a turbo spun by the engine), you have 2, 3 bladed "screws" that spin off the crank.

What happens is, air coming in HAS to go through the screws. The air travels into the screw inlet (backside) and the blades of each of the screws (which interlock) compress the air and force it into the manifold.

A Centrifugal setup behaves almost exactly like a turbo, but is independent of engine load, and dependent on engine RPM. This is good because it means that the SC spools exactly as fast as the engine spools (at whatever ratio the pulleys are set to). It's bad, because bottom-gear pulls (like pulling from 3rd gear at 2k) don't make full boost, unlike in a turbo car. It behaves like a turbo, meaning there is some slight lag and some spool time, but there is no exhaust interference.

Roots blowers are a favorite among most in the crowd.

Then they get into whipple style chargers (which are actually banned in some Drag classes because of the insane amounts of boost they make). Whipple blowers are your basic roots setup, but with a twist. Instead of just pressurizing the manifold like a normal roots blower (what you have), it is a compressor, and compresses the air inside the SC, and then again into the manifold. The amount of boost they can make is ridiculous. Imagine, if you will, 60psi as soon as you are on the gas. Fucking insane.

The stock engine management isn't mapped by manifold pressure, so it's not like it'll just cut out like most speed-density cars would...

Running a non-turbo ECU with forced induction in some ways is a lot like running a turbo ECU at ridiculously high boost levels. You're way outside the maps so the ECU has to kind of guess what to do. It does see all the airflow, so it does provide a somewhat reasonable amount of fuel even if airflow is beyond its maps.

The big problem is that with the ridiculously hot air provided by a Roots blower, stock ignition timing will probably be too advanced, and the fueling will probably be a little less rich than you'd want. I don't know so much about engine tuning for supercharged applications, but that seems like the case to me.

I guess then my next ebay purchase will be a intercooler then

I wouldn't really worry about an intercooler at low boost (under 6psi).

6psi isn't really that much boost, and an intercooler would just kill throttle response for not much cooling difference. The heat from a Roots blower at 6psi is almost the same as the heat from our near 9psi Turbo Legacys.

An intercooler wouldn't hurt, but it would add a bit of complexity.