Well, the little resistor didn't work out to fool the sc clutch as I keep getting an SC malfunction error. So I dug around WIS and found a note that the sc clutch draws 47 watts. Now if I have this right, at 12v this is 3.9 amps at 12v and I need a 3 ohm, 50 watt resistor.

I don't have quick access to one so I'm going to build one with what I can pickup at Fry's.

=

12v / 6.8 ohm = 1.76 amps x2 = 3.52 amps
12v x 1.76 = 21.12 watts so (2) 25 watt - 6.8 ohm resistors should be great

Plus

12v / 30 ohm = .4 amps
12v x .4 = 4.8 watts so (1) 25 watt - 30 ohm resistor

Total draw = 47 watts

I hope that's right as I'm going to solder her up and wire her in soon!

 

Keep in mind, if the sc cltuch draws [dissipates] 47 watts, a circuit with a designed in capacity of approx 50 watts may not last too long. I would add a larger fudge factor .... 47 watts x 200 % would be safer (so two 50 watt resistors in parallel).

also, this difference may seem trivial, but I would consider basing your calcs on running voltage (14) not battery voltage.
As you probably know ... resistance = voltage squared divided by watts .... so the difference between 12 and 14 volts becomes the difference between 144 and 196 in this equation.

keep up the cool work,
Chris

EDIT
if you are limited by Fry's inventory,

you could put two 10 ohm 25 watt resistors and one 30 ohm 25 watt resistor in parallel

for a total of 4.29 ohms

this should create a 3.2 amp load (close enough to the 3.3 amp load that your WIS info suggests) ... your dissipation capacity will not be great (58 watts? ... this is a marginal fudge factor).

Finally, you might want to ask someone to measure the current draw on their sc clutch and work it from that direction.
Chris

 

or ... you could just measure the resistance of the sc clutch (that is, I could have .... : )




I measure (with a very accurate meter) 3.89 ohms (on my slk32) .

At 14volts that is a hair over 50watts. The duty cycle being low, you may be ok with a 4 ohm 50 watt mounted away from anything combustible : )
http://search.digikey.com/us/en/prod...4R0-ND/2020187

EDIT
the manufacturer (of the above power resistor) states the following:
Power rating: Based on 25°C free
air rating.
Overload: 10 times rated wattage
for 5 seconds.

this part seems like it would work fine


EDIT 2

here are some better choices ... priced reasonably and aluminum cased with mounting holes
http://kr.mouser.com/Passive-Compone...sistor&FS=True
Chris

 

I tried my resistor pack and no go. The message came back as P207c supercharger mechanical failure, implausible value.

 

Thanks for the info! It's nice to see someone with some knowledge to share. I'm really thinking that I'm facing a boost pressure issue now but if that doesn't pan out I will see this test through for sure! As well as take your advice on the wiggle room with the resistors!

 

how much boost are you measuring?

my slk32 throws a code near the transition of 20 to 21 psi (this is going off of boost data that makes it through the OBD2 port, so it may be slow). but it throws a "P0108"


so you suspect the car is reacting to the rotrex's non-linear boost?
others have moved on form belt driven turbos for far simpler reasons. You methodical approach to solving each issue as it arises is quite impressive. Looking forward to seeing whatever you come up with next.

Keep up the cool work and happy holidays


Chris

 

Time for an awesome update!

Lots to say and little time. When I first plugged in the SRT-6 ECU it didn't go 100% as planned. First I had the SC clutch error and other little tidbits. Then I conquered the SC Clutch error with the resistor mod I performed. She was running fine but I was getting a sporadic Load limit error (common on modded mercedes from what I read looking for a solution, especially on the Kleeman kit). Partial load pulls resulted in the throttle plate slamming closed like I just dropped the motor through the floor.

I conquered that

Then I had the whole overwriting the developer settings to overcome. Through trial and error and lots of testing I settled that issue.

Then I started getting a couple of new errors; pressure sensor and a supercharger malfunction error.

So I collected lots of data, printed out logs and fault reports. Fried my brain looking at them and decided to take a break and develop my tuning tools and process.

I've had a spreadsheet that I built and used for years that I changed from working with the Toyota FCEdit to the AEM. Basically it is a calculator that accounts for the 21x17 map used by the AEM. It has 4 sections; Base Map, Desired AFR, Achieved AFR, Adjusted Map.

Paste your map, enter the achieved AFR per cell, cut and paste the adjusted map into your AEM tune.



I used to sit for hours mulling through logs in a program called Dataloglabs that provides a great way to manipulate data. I worked through the tune looking for areas with positive throttle input, increasing rpm, etc. I then zeroed in on intersections of RPM and PSI and entered the results in the Achieved AFR section.



So I decided to automate my system. I built a new spreadsheet with Excel 2010 that scans my 225,000+ line logs and dynamically maps the AFR average per cell based on a user definable Throttle Position, RPM window per cell, and PSI window.



So far it has been working great and helping me dial in the fuel in minutes versus hours per tune.

That out of the way, I turned my attention back to the nagging CELs and BAS/ESP errors I was getting with the SRT-6 ECU. Understandable due to the fact that my Rotrex SC doesn't have the exact same boost characteristics of the stock SC and the Mercedes ECU is a living, breathing ***!

It is amazing sometimes how you take a break from something and come back to it and the answer is right there in front of you. I guess I had been working towards the solution one step at a time so it didn't exactly happen over night. Then WHAM the result of hundreds of experiments culminated into an answer. I sat down at my computer, mapped out a plan that I thought would tell me if I was at least on the right track (fully expecting I would have to tweak things further one way or another), implemented and boom.

Six test drives later of 45 minutes or more and NO CELs OR BAS/ESP Lights, no stumbling, no jerking, just smooth sailing (although with lots of extra fuel). Each drive was with progressively deeper and longer pulls, and finally today FIVE WOT pulls in 3rd gear. All confirm that I am finally in the POWER TUNING PHASE and working towards my ultimate number!



My fuel is pretty rich for now but this graphs shows I was making 10 PSI at 4,500 RPM. Right on target to make my desired 12 -13! Next up, more pulls, and tweaking fuel of and spark to find the best combo for power in pursuit of my top end goal of 400+ BHP.

 

Man, can anyone spell rocket scientst

 

Honestly!!! lol. Great job Web.

 

That's an insane amount of diligence and research.

Major, major props to you good sir

 

Awesome !

is 13 psi the limit of this project, or a step? (sorry if you have already answered this in one of the 500+ posts of this thread)

Chris

 

Well, I should probably tweak that statement a bit. The Rotrex offers a few more variables to consider when planning boost. First the top end number is max boost at max rpm. It isn't sustained for very long and changing pulleys to lower the number reduces the entire boost curve. So you plan a little higher than the sweet spot of where you will spend most of your time and tune around the top end with spark and fuel to keep from detonating.

The numbers tend to throw people off a bit as it isn't the exact same conversation as running 13 psi with a turbo or twin screw.

But to answer your question, my current thinking is that 13 psi is the TOP end of where I want to be. It really all depends on how this car reacts with its inherent idiosyncrasies and where its sweet spot lies.

The great news here is that I have spark and fuel control via the AEM = ability to tune for boost. Unlike the "Base Kit" strategy that some employ to save cost and complexity by adding fuel via an RRFPR and low boost so they can run stock timing. In those setups, 13 psi would blow them sky high therefore the typical 8psi for stock compression you see as common.

I still wish I had a full ECU replacement but at least I get to use my cool "Auto Tuning" Spreadsheet to dial in fuel so I'm stoked!

 

Thanks for the kudos btw! They are very much appreciated!

 

I'm glad to report that the tuning is going very wonderful! In the very limited time I have had, she is dialing in nicely with less than a dozen WOT pulls. I'm making a firm 13psi, no knock, and slowly moving the torque drop off further into the power band with each pass.

I'm at 240 RWHP and 270 RWTQ to date. Well on target for the 300+ RWHP I am looking for on the stock motor. So far so Good! Now if it will ever stop raining. I should see my mark before the weekend is over. Also, no CELs!!!!!!!!!!

 

Any new updates Web? Curious as to how things are holding up.
Gord

 

WEB3.0, you are the new generation of tuner young man. In my day, it was a lot of trial and error with not many ways to measure success. It is amazing to me just how precise we can be today with tuning. Pretty amazing stuff. Sure explains why our old muscle cars would get less than 10mph...lol... Most was going out the exhaust I am sure...great work, and an interesting read.

 

Thanks all! I've been pretty busy as usual but still managing to get some time in on tuning. That said, the Mercedes Demons did decide to raise their ugly head one last time. While I wasn't getting any persistent CEL's, under certain conditions my AFR would go insanely rich to the tune of 9:1. It took a little while to massage it and find the right settings to make it stop that symptom without simultaneously creating a CEL.

It was a lot of work, but I did it! Now that I have that fixed, tuning is pretty much the same as it is with any car. I have highway cruise perfect, and am now working on WOT pulls and tweaking the tune for max power. Although the latter was on hiatus for a while, as I got side tracked trying to end my dependence on the SPD for data collection and dyno tuning. The AEM datalogs at a much faster rate which makes for better resolution all the way around. However, it doesn’t monitor vehicle speed. It looks like I can buy an analog converter to convert the GPS speed pulse to an analog voltage (0-5v) that I can log with the AEM. However, the mini project I started was taking too much time so I decided to move forward with what I had and keep the ball rolling. I should in fact be able to post some numbers in the next week or so!

It is actually pretty amazing. The AEM FIC works very well with the SRT tune once you compensate for the differences between the SRT twin screw supercharger and the Rotrex. I've picked up a ton of tips and tricks to make things run smoothly and I have to say, the end result is very nice. In fact, building on what I have done so far, you could use the AEM to tune pretty much any type of forced induction for the NA without much fuss in my book. Not that it wasn’t without fuss getting here, but now that I have the nut cracked, the door is wide open!

 

Tuning is coming along very well. I'm making a nice, solid, 260 RWHP which is about 340 at the crank (or roughly +80 HP at the rear wheels) at a little over 11 psi. I'm calculating this based on 16% drive-line loss as displayed on the crossfire dynos I've found plus the roughly 30 HP required to drive the Rotrex at this boost.

For the record, that is 340 HP and counting on a stock NA motor and they said it couldn't be done!

If you take a look at my logs, I've managed to smooth out my boost signal and my A/F is shaping up into a thing of beauty. I think there is a little more on the bottom end as I can lean her out from where she is at now, but not much left on top at this boost level.

By the way, I just passed the 5,000 mile mark with this rotrex bolted on my car in its current form. The mounting bracket and overall design are finalized and I can now turn my attention towards making her pretty! Everything is holding up very, very well.

That said, the one tweak I do have in mind is to build a box around the inlet to the Rotrex so that I can re-position the inlet to put a much larger air filter on it. The filter I have now is definitely choking it off a bit and I would love to put another few pounds of boost through her.

 

Thats awesome... Is there a possibility of a video showing a walk around and a drive with the beast!?????

 

Very, very good. I'm sure it is impressive in person. would love to take a ride in it someday. What do you calculate RWHP at 14 psi boost? Do you think it would hold together at that PSI? Maybe have to put an SRT6 crank, rods, and pistons in to stand up long term, of course that would require buying them low cost.