Yacht Master

Our supercharger operates in an "on demand" mode, governed by many parameters. The question I have is a simple one for anybody that has a boost gage installed. At what speed over 40 mph is the supercharger engaged full time? I have no gage and can't tell at highway speeds. At low speeds accelerating with a little throttle I can feel the S/C comes on @1200, if I go easy it will come on @2200. After the initial acceleration and load on engine is reduced S/C goes off line. What I am after here is highest zero boost (non supercharged) constant highway speed.

jangy

I think I want a boost gauge mounted somewhere in my car, because I always wonder if the SC is on or off. I'm more curious to know what conditions (if any) allow for max boost.

Yacht Master

Jangy,
I don't know why they did not put a boost/vacuum gage in.
I could wire a led light to the S/C clutch to tell when it engages, but that may or may not tell me the position of the By-pass valve. Anyone know if the S/C clutch is on the same circuit as the S/C by-pass valve? My first thought is that the by-pass valve is operated by a small stepper motor and since the butterfly valve is or looks to be balanced they could be using this to modulate boost pressure too.

All I want to do is find highest cruise speed before S/C comes on.

tigerlam92

I bet according to Mercedes Benz in deep market research LOL, they probably found that most of their potential customer will probably not care as much of the boost gauge and further their manufacturing cost is probably way to high as it is. Like you guys, I won't mind having one. I found it to be very useful as well as the fuel pressure in my other car.

If you can find an intake manifold pressure source, you can hook it up to a boost gauge pretty easily by running a small vacuum line into the cockpit.

If you hook that source up to an intake manifold sensor then hook that up to some light source (thinking something like a TRCII by Crane) then the light comes on when you have boost.

I doubt it is purely by RPM, at the minimum it should be RPM in conjuction with throttle position or manifold pressure.

stevebez

S/C engagement is largely dependant on throttle position and possibly gear selected or gear changing mode.... not necesarily road speed.

If you are at 1/5th throttle almost certainly S/C will be disengaged regardless of speed - but lets say your in Manual mode in 2nd at 2500rpm and just trailing the throttle ("ready to run mode") it will probably be engaged.

If you are anywhere past 1/2 throttle and beyond it will be engaged in my experience. What is not clear for me is how long it remains enaged or if the bypass valve just opens up on a trailing throttle ... the thing is the S/C is such hard work for the engine to run - I think as soon as you go off throttle I think it disengages... or the S/C is starved - not sure which ...

Finny

Just found this awesome gauge to solve all our problems.

VEI Systems: http://www.veisystems.com/vbm-m.html

Video of gauge in action: http://video.google.com/videoplay?do...70552140848505

Page with details of group discount: http://www.veisystems.com/gb_details.html

What do you guys think?

mfissel

there are a couple of vacuum/boost gage options out there. Has anyone found a good spot to mount a gage in the E55? What is the best spot to get vacuum/boost from the manifold - i.e. any current connections not used or can be t'd-off from?

vrus

I use this one.

http://www.dakotadigital.com/index.c...rod/prd377.htm

vrus

The guage that I bought is very compact.. I am making a custom mounting bezel to fit into the ashtray area.. The boost guage along with some other electronics will live in there.

There is no place on the car to T into for boost.. all the hoses are all PRE-S/C which means they will only read vacuum.. You need to drill & tap a 1/8" NPT fitting into one of the surge tanks and put your boost hose on that.

mfissel

Will the surge tank tap also give you an accurate vacuum reading?

ChicagoX

The only downside I see to that unit is the necessity to run a vacuum line from the surge tank all the way to the gauge.

Looks pretty cool, though.

ChicagoX

Nice. I see these gauges on the custom rods all the time.


Are you using the teal or the blue?

dsc

I have a surge tank tap in my car. It doesn't show actual full boost. I remember Cory saying the boost off the surge tank will be less, I think due to being down stream after the intercooler. You lose a couple of psi across the IC. I have K2 and my highest boost was at 4600 rpm at about 10.4 psi. Does anyone know what the boost curve should look like?

Finny

Apparently this is due to "vacuum/pressure transducer" temperature sensitivity.

The unit recalibrates to ambient temperature after each start which gives a more accurate reading.

For me though, its all about the cool animation...

Yacht Master

DSC
Location Location Location, the easy part is to tap the surge tank. No matter where on the surge tank you tap there will still be an influence of one of the intake runners. The best location is almost impossible to get to with the S/C installed. It stands to reason the Intercooler would shrink charge and cause pressure drop. I find it interesting that your maximum boost of 10.4 topped out at 4600, did it remain at 10+ on up to red-line? A boost curve or boost parameters would be some great information.

I would still like to know at what highway cruise speed will the S/C remain off line until, or is it always on?

dsc

I was on a dyno Dynamics so red-line isn't possible. During the pull the S/C kicked in at about 2400 rpmto about 10 psi, drop to about 8psi at 3500rpm and prgressed up to 10.4psi at 4500rpmcame down to 10psi at500 cut off was about 6000rpm for the pull.

My tap in on the neck of the surge tank on the passenger side. For all I know the drivers side could (shouldn't) be different.

I want to get it done on a dyno jet soon.