W202 C230 Kompressor standard boost pressure (and boost curve)???

[StavFC]

As title, anyone know what it is?

Mine doesnt seem down on power, to be honest it feels up on power to how I expected, but after hooking up a boost gauge to check it, I was amazed how low the boost is.

About 3psi at low/mid rpm, 5psi mid/high rpm, and 7psi near the rev limiter (spikes to about double that as you lift the throttle, but thats irrelivant).

That right? I heard 7psi I'm sure, but as you only get that right at the limiter its a bit pointless tbh, lol.

 

[ebo]

did you find out the rates? am wondering if i have a leak! cheers ebo

 

[StavFC]

I haven't, but someone said they thought that was correct.

Im pretty sure peak boost is 7psi, but the way it rises to that level rather than hits and stays pretty much is more the behaviour of a centrafugal supercharger rather then the roots type we have fitted, so I'm still not sure that is correct.

I wouldnt be at all surprised if Merc has it mapped like that, possibly by allowing a controlled air leak through the electronic s/c bypass throttle.
They would do this to control low down torque to limit wheelspin and give a very progressive powerband, something that the car does, but is quite unlike most cars with roots type superchargers.

I may block mine off and see what it does then...

 

[ebo]

keep me posted i was contemplating the something drastick. looking at the speed booster as advertised on the forum to see if that sorts low down power. -3k is said to be economy mode but im not into that idea i want race mode! lol

was it hard to fit your boost gauge? whats involved? where did you mount it in the car?
cheers
ebo

 

[StavFC]

No worries.

Sprint booster you mean?
Complete waste of money IMO, and I've used one in the past.
A gimmick to make your car feel faster when its not any different by making the throttle feel more jumpy. It suits some people who rarely use full throttle as it gives more throttle without them pushing the pedal more, but if you use the full range of throttle, it does owt.

Wouldnt be surprised if Mercedes electronic throttle mapping is preventing us from getting full throttle at all times despite what our foot is doing, but unfortunately SprintBooster don't affect that.

Boost gauge install is a pain in the ****. Well, hooking it up to the inlet system is incredibly easy, but finding a hole/grommet/anything in the bulkhead to run the pipe, well, it's beat me so far! I have just been hooking up the gauge for testing only and running the pipe thru the door, then removing it once im done, 2min job.
I made a tidy A-pillar mount for it that matches the rest of the Sport trim, but until I can find a place to run the pipe it's not much good to me!

 

[ebo]

Get the drill out and a wee 2p 1cm grommet fae maplin job done geezer! lol sound i often (everyday) use the full she bang so you saved me a pretty penny there!

 

[andy27168]

No worries.

Sprint booster you mean?
Complete waste of money IMO, and I've used one in the past.
A gimmick to make your car feel faster when its not any different by making the throttle feel more jumpy. It suits some people who rarely use full throttle as it gives more throttle without them pushing the pedal more, but if you use the full range of throttle, it does owt.

Wouldnt be surprised if Mercedes electronic throttle mapping is preventing us from getting full throttle at all times despite what our foot is doing, but unfortunately SprintBooster don't affect that.

Boost gauge install is a pain in the ****. Well, hooking it up to the inlet system is incredibly easy, but finding a hole/grommet/anything in the bulkhead to run the pipe, well, it's beat me so far! I have just been hooking up the gauge for testing only and running the pipe thru the door, then removing it once im done, 2min job.
I made a tidy A-pillar mount for it that matches the rest of the Sport trim, but until I can find a place to run the pipe it's not much good to me!

Hi,
Utilise a spare grommet in the fuse box, you will have take the top of the fuse box off, and the lower dash trim under the steering wheel.
Can i ask whats the point in fitting a boost gauge?

 

[StavFC]

Hi,
Utilise a spare grommet in the fuse box, you will have take the top of the fuse box off, and the lower dash trim under the steering wheel.
Can i ask whats the point in fitting a boost gauge?

Is there spare ones there? Superb, I was worried about drilling a new hole in case I hit something else on the other side, and praying there was some room under the fuse box was my next hope.

And why? Firstly to check it was running full boost as the majority of older cars wont be for whatever reason, secondly to check what the boost curve actually is on these cars partly out of interest and partly with the intention to improve on it for what I want, and thirdly as I wont be running standard boost for long, 3psi slowly raising to 7psi is silly low for me.

 

[ched999uk]

Firstly to check it was running full boost as the majority of older cars wont be for whatever reason, secondly to check what the boost curve actually is on these cars partly out of interest and partly with the intention to improve on it for what I want, and thirdly as I wont be running standard boost for long, 3psi slowly raising to 7psi is silly low for me.

I haven't tried it yet but I have a cheap (eBay £15 delivered) ODBII to USB reader. On one of the free pieces of software (FreeODB, I think) it does list inlet manifold pressure as one of the parameters. So a cheap easy way to check might be to buy an ODBII reader that connects to a laptop and then you can log the inlet pressure. OK so it wont give you a dash mount gauge but it will help you determine boost curve very accurately as I believe you can also log throttle position and rpm.

 

[Bellow]

OBDKey has what Ched is talking about. Can display on a PDA via Bluetooth or hard-wired.
edit: Also Scangauge. Check model compatibility first though.

Might the boost be kept low in the mid-range to avoid detonation?

 

[StavFC]

I have an OBDII diagnostics machine, but to be honest it didnt even occour to me as I only use it as its main use is as an AFR meter so I use it when tuning.

IMO boost will be kept low simply to keep the power low for ease of driving and to make sure the higher models are worth buying. Same as most cars really.

Compression is only 8.7:1 IIRC, which is very low, with correct fuelling and ignition boost could be double what it currently is with no problem.

It would just be good (for me at least) to know if boost is being held back by other reasons rather than just pulley size, but some simple checks should tell me.

 

[ched999uk]

I have a C230K coupé sport and would be interested in increasing the boost a little but I am guessing there will be all sorts of electronic trickery stopping boost increasing. Although thinking about it in theory boost is directly proportional to compressor speed. Therefore if you are at high altitude then your max boost will be lower, unless you have some sort of bleed off. So by that simple logic we can guess that in the standard configuration boost is limited to a certain degree by some sort off bleed off device. Other wise anyone at high altitude would be getting very low pressure and hence low power.
It may be possible to reduce the bleed off but I doubt it would have any effect as you have a manifold pressure sensor which would probably cause the car to go into limp mode if the pressure got too high.

Anyway keep us informed as this is interesting

 

[StavFC]

From what I have gathered, you can increase boost by a fairly significant margain without any kind of boost cut.

I would go as far as to say MB wouldnt have bothered as unlike with a turbo there is no way of a malfunction ever creating a situation that would increase the boost.

I'm still not convinced the valve stays shut as much as it should though, but only way to find that out is by blocking it to see.

99% sure there is no bleed off thats activated by boost pressure though, thats one thing im pretty damn sure of.

 

[ched999uk]

Interesting StavFC. Have you got any decent inlet system diagrams that show all the sensors and control systems? I would love to have a look
200bhp isnt bad from a 1.8, but it might be nice to have a little more I did have the original development Turbo Tecniques 16valve golf. Which was brilliant but unfortunately I wrote that off at 60mph backwards into a tree Long story. The engine lived and went on to power a mk1 golf GTi campaign and then a mk1 convertible GLi never quite as polished as when it was in the 16v but great fun and was tweekable

 

[StavFC]

Well, just removed the bypass throttle and plugged the hole...

One things for sure, the common internet rumour (as clearly nobody has ever actually tried!) that the bypass is needed to make the car idle, as when the supercharger is de-clutched the supercharger is blocking the inlet air flow, is total and utter ********.
The car idles just perfectly without it, totally normal, id almost go as far as to say it idled better.

BUT! Could I test the car without it? Could I hell! The minute you even lightly tickle the throttle above 1500rpm, the blower pressure was enough to blow the (very tightly jubilee'd in) bung out like a ****** rocket.

No idea if that was on or off throttle (though I never went about about 1/8 throttle, but with a stupid electronic throttle like Mercs have what you are pushing and how much the thottles actually open is often very different), as it MAY be the boost spiking as the throttle shuts as it now has nowhere to escape from, and unlike a turbo its a positive displacment unit so it cant just escape back out the inlet.

Only way of testing that is by fitting a non-ecu controlled escape for the air, a dump valve. They are totally pointless on a turbo car, so I dont think I have any kicking around, but I'll go look...

 

[ched999uk]

Very interesting StavFC. I am loving your investigation. Thanks for keeping us updated

 

[Whitey]

Hi Stav

What's the fit like around the stock release flap ? Does it shut tight ?

Whitey

 

[StavFC]

Hi Stav

What's the fit like around the stock release flap ? Does it shut tight ?

Whitey

Ive not pressure tested it, but I can only presume it must do pretty well, considering its use, BUT as it works just like a conventional throttle butterfly, im a little sceptical it could be fully air tight, especially under pressure.

My main worry is I dont believe its fully shut at all times on purpose (ie the ECU is set to do it), but I'll try and knock up a pressure tester for it soon too, depending what bits I can find lying around to make one from, lol.

 

[Whitey]

Does the ECU throw up any error codes when it is unplugged ?

I know we probably can't increase the boost pressure, but having an excuse to have an atmospheric release valve would be epic !

 

[StavFC]

Does the ECU throw up any error codes when it is unplugged ?

I know we probably can't increase the boost pressure, but having an excuse to have an atmospheric release valve would be epic !

I didnt unplug it yet, I simply left it plugged in but disconected from the inlet pipework.

And you dont need to do anything like unplugging it to have an atmo release valve, the electronic throttle works like that anyhow...

Look at video I made the other week of my car after making a few tweaks, just lightly revving in neutral, can hear the electronic bypass chuff as I let off. Its FAR more noticable when letting off when actually driving.
YouTube - Mercedes C230 Kompressor (W202), custom inlet setup, supercharger whine