I just fitted a gauge (to the fuel reg pressure line)
At full throttle at about 4 to 6k my boost gauge sits hard on 6psi.[]
Has anyone else fitted a boost gauge.
SLK230 1998 with Pulley kit.
I dont know what pressure switch do you talking about Bazzle; Do you have any pic to show me please? Or maybe do you mean vacuum actuator-switch (at the front of the engine under the plastic cover) for cold running (USA and Euro models)? But this is not pressure sensor! Please post some pics if you have them...
P.S Finally i get info about M62 max pressure, flow and revs...: EATON-M62
So now we know that something is leeting out pressure when pressure is larger than 0,6 BAR at the throttle body.
Then if we know that M62 have Flow at Max. Speed @ 1.8 Bar: 810 cubic meters / hour , and if we know that 230kompressor engine pulls arround 700 kg of air/hour at full throttle and full rpms, then it is obviosly that our M62 IS more than 100 % CAPABLE to make 1,8 BAR at full throotle (engine uses only 700 kg of air and M62 pushes 810 cubic meters). So where is missing 1,2 BAR (1,8-0,6)?
If i am not mistaken, than 700 kg of air/ 1 hour is equal 542 cubic meters of air / 1 hour, if we know that 1 cubic meter of air weights 1,29 kg. So our M62 is more than adequat (810 cubic meters/hour at 1,8 BAR) to feed our engine which uses aproximately 542 cubic meters of air/h.
Please some one correct me if i am wrong.
So, now i am 100% sure that something (possibly bypass valve) is letting out all boost which is greater than 0,6 BAR at the manifold. Now the question is how to convince bypass valve that it does not open at 0,6 BAR, but at cca 1 BAR??
So, now i am 100% sure that something (possibly bypass valve) is letting out all boost which is greater than 0,6 BAR at the manifold. Now the question is how to convince bypass valve that it does not open at 0,6 BAR, but at cca 1 BAR??
The one and only reason the bypass valve is there is to control boost pressure.....
As I previously posted....this is done by the ECU by comparing the MAF reading at a particular engine speed and throttle opening
Monitoring the PWM signal to the bypass valve will show its action/position
An Electronics Engineer may be able to design something to modify this PWM signal ........probably easier to take the bypass valve out of the circuit by changing the air inlet plumbing or reducing the bleed by using a restrictor.......with associated risks and ECU problems (P0803 DTC and S/C shutting down)
I dont think Air bypass valve return position control to DME; In otherwords: DME only hopes that bypass flap is where it suppose to be (according to PWM signal); So let say that PWM signal is 50; So flap is open according to that value. So if you at that moment manualy (by hands) move flap for 10 degrees, DME wont know that; But we could not manualy move flap between driving, so we must electronicaly move flap. And possible solution is by resistor as far we understand this thing till now.
So why could we not put resistor between DME and bypass valve? This resistor will make PWM signal for exaple 10% smaller (or bigger?); So if DME send 80% PWM signal, then this resistor will correct this signal to 70% ; so bypass will open for 10% less, so we get more boost. The question is what will hapened when MAF will sense more boost? Maybe then bypass valve will open for another 10 degrees, so at the end we dont have more boost, but same boost as before we changed position of flap...
The feedback loop from the MAF to the ECU, which then adjusts the bypass valve, is going to control the boost to the programmed level ......even with modification of the PCM signal (I'm not an electronics engineer, but I doubt it is as simple as a resistor to change the pulse percentage)
I guess the main factor is how quickly this feedback loop can adjust the boost(some graphs of boost against time when you flatten it would be interesting)
The increased performance noted from the Pulley Kit would be related to this delay.........
So the best way to increase boost during hard accelleration would be to interfere with this feedback loop......
The restrictor in the return pipe slows the bleed and hence lengthens the time taken for the feedback loop to control the boost
..........so the restrictor is a very inexpensive solution......Bazzle has already done the experimenting and posted the dimensions he came up with.......
......at this stage, I can't see any serious risks from restricting the rate of bleed..........but if the ECU calculated boost gets off the map, then it seems you wil get a CEL and P0803 DTC that will eventually cause the S/C cut off with total loss of performance
So does anyone have access to a recording pressure monitor?
No pulley kit for me and 8PSI on Defi boost guage and 10PSI on bloody freezing nights after doing acceleration runs for about 30 mins. 10PSI only for a split second, then shapes back to about 8-9 normally.
its not a good idea to put resistors here and there especialy on sensors/devices which are monitored... it will simply trigger a DTC code and turn off the supercharger as a device is out of operating tolerance paramaters.
the boost map is calculated with input from a combination of sensors and its coded on the cars ECU. i have put a restrictor on the bypass and yes it does boost a tad quicker but it wont increase the boost as the pulley dictates that. a person on another forum has FULL blanked/closed the bypass..... and guess what? sees a big burst of boost at revs its not suppose to (again lookin at boost map) and turns off the supercharger. all safety and to stop engine damage.
the key is the ECU. blank the bypass valve, floor the car hard, watch the boost spike hard and then quickly drop as the supercharger turns off.......
thats why a boost increase of a few psi by pulley kits would seem to work. as its still in the OK tolerances. if you want more PSI its not going to work unless you 1) do something about the ecu 2) and give it more fuel....... this car would give a lot of cars a run for there money running 1bar (14psi)
No pulley kit for me and 8PSI on Defi boost guage and 10PSI on bloody freezing nights after doing acceleration runs for about 30 mins. 10PSI only for a split second, then shapes back to about 8-9 normally.
I would be interested to see more technical information re Boost control in early SLK's...............
Any links to graphs of boost vs time or boost vs rpm in an SLK with clutch and bypass valve control.......
DickB............do you have any technical info .....I see on your site that you have developed electronic performance mods for the Miata..........
..........or are you able to do any analysis of boost control
......... do you have access to chart recorders and sensors
.........if this research led to an easy way to bring on full boost and limit boost loss through the bypass valve, then the standard pulley/kompressor may have some performance left to give an increase in power without pulley changes.............
.........those with pulley kits are probably not getting the full benefit of their mod because of ECU control of boost
Just a thought.....would do it myself if I had access to the appropriate measuring equipment
David, after a long research, we (German SLK forum) discovered that MAF send data to DME to lower the boost (open bypass). So when our MAF detects more bost than cca 10 PSI, than it send that signal to DME and DME open bypass to bleed boost out. So in the end you can do WHATEVER you like with pullyes and bypass control, but BOOST will NEVER be greater than 10PSI, unless you reprogram or fool MAF that it read less boost that it really does. Pullyes do work to some degree, but after cca 10 PSI (i men even larger or double pullyes) there are only loses as far as HP goes.....
According to the Mercedes info at alldatadiy.com, there is a very easy way to get maximum boost - step on the gas pedal:
"The flap is always closed at full throttle (maximum boost pressure)."
The Miata aftermarket supercharger system that I used is different from the SLK system. The same type of Eaton supercharger was used, but in the Miata the throttle is relocated upstream from the supercharger. The supercharger was always engaged (no clutch), but a bypass valve at the supercharger recirculated the output to the input under closed throttle. The bypass valve was actuated by vacuum, not engine electronics
In the SLK, the throttle is downstream from the supercharger. Under closed or partially closed throttle, the supercharger is producing more air than the engine can take in, so the bypass valve is used to recirculate the excess volume back.
The Roots supercharger is a positive displacement device, and although we talk about boost pressure, we should think in terms of air density and volume. It would seem likely that Mercedes engineers designed the system to take the full volume out of the supercharger at WOT - anything less would be a waste and inefficient use. So it seems likely that the Mercedes statement is accurate - anytime you are at WOT, the bypass valve is closed. When you close or partially close the throttle, you are by definition limiting the volume of air into the engine, so the bypass valve is employed to dump the excess volume of air. If you don’t do this, more air will be crammed into the cylinders than desired, and the throttle will become unresponsive in a negative way (the engine won’t slow down in response to a closing throttle the way that you want).
I don't think that there is any advantage to be gained by trying to manipulate the bypass valve control electronics.
I have not made any measurements of this, but it might be a fun project...
.......those with the pulley kits may be the ones that can benefit most if the Mercedes engineers designed the system to take the full volume out of the supercharger at WOT with the standard pulley
.....it would be interesting to see a recording of the PCM signal controlling the bypass to see if infact it remains closed or is adjusted to control maximum boost even under WOT
......a recording with pulley kit for comparison could be even more interesting
Looking forward to some interesting results.....even if it proves the MB Engineers have got the most out of the system
"" Checked gauge against a master from work , same reading, max 7psi.
Originally was picking up reading on "T" fitting on pressure line to fuel regulator. (1998)
Now on aluminium pipe Supercharger side of Intercooler.
New pressure reading of 9lbs, so must be a drop of 2 to 3 across I/C..makes sense.
You other guys, where did you tap into read pressure??
Bazzle ""
I am convinced my reading of 9psi is now OK for pulleyed car at SC output. (pre 2000)
The 7 was at the inlet manifold with a couple of pounds drop across Intercooler.
We fit ICs to turbo vehicles at work and always get a loss across them.
Allowing for visual and calibration error of guage it could be quoted as being around 10psi (forget that bar crap )
I am convinced my reading of 9psi is now OK for pulleyed car at SC output. (pre 2000)
The 7 was at the inlet manifold with a couple of pounds drop across Intercooler.
We fit ICs to turbo vehicles at work and always get a loss across them.
Allowing for visual and calibration error of guage it could be quoted as being around 10psi (forget that bar crap )
You want to measure boost from the intake manifold. That will give you the most accurate reading.
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