Superchared engines and power delivery

[philharve]

Supercharged engines and power delivery

I was asked for my opinion about MB supercharged engines today but I soon realised I couldn't provide a helpful reply. Despite having driven a kompressor model for just over two months it slowly dawned on me that I couldn't really describe the experience. The problem stems from the fact that, as I understand it, the compressor is not permanently engaged - it has a clutch - and the moment the boost is felt varies according to circumstances which I don't fully appreciate. I believed, until recently, that a supercharger was permanently engaged and continually feeding compressed air to the engine. But it's not like that, at least not with MB, the power delivery 'experience' is more complex. That's the dilemma I am facing! I can drive the same route each day and yet each time the experience somehow feels different. Sometimes the power boost is strong, other times it's only moderate. The result of kickdown, for overtaking (say), can be slightly unpredictable, at least that's how it feels.

Are there any members with wide experience of supercharged engines who can explain to me why the driving experience should feel different? I have this feeling that I cannot reliably predict how the power delivery will change according to road conditions and driving style. It's because I cannot fully appreciate what's happening that I cannot describe the experience to others. Maybe non-MB supercharged engines behave differently.

REGARDS Phil

 

[piestore]

kompressor

HI

I think you will find that your compressor is constantley egaged MB dropped the clutch on the smaller engines a few years ago, the boost pressure is controlled by a throttle body which allows air to leak off from the boost system, although the AMG 55 engines still use a clutch to controll when the compressor is engaged they still use the recirc air flap to control boost pressure

 

[philharve]

Thanks piestore

I am still searching for technical data relating to the engine compressor on the kompressor models but I have yet to encounter anything definitive in print, hence the reason for posting the topic.

I am currently browsing the Internet for information but every reference I've encountered refers to a clutch-driven compressor. I have yet to find any reference to a clutchless system on the smaller engines.

Do you, or have you ever driven a supercharged MB? As this is my first experience of supercharging I have nothing I can compare it to. I always though that supercharging gave big-engine performance from a relatively small cubic capacity. The results I'm getting seem to be a little more complex than that. Cheers.

REGARDS Phil

 

[MSG2004]

I drive the 180k - very quick and no hesitation like a turbo i've been in.

yes you do get a large cpacity from a small engine - mb 1-8 unit = 180/200/230 engines - i think mine is 140 bph - the 200 is about 18- and 230, i don't know - the power on kick down is almost instantly avialable.

Mid range power on the auto is good for the size of the engine and weight of car.

 

[piestore]

compressor

HI

Yes I have driven all of the MB models I think they dropped the clutch system about 3 or 4 years ago the clutch actuated at about 1800 rpm but as i said all the new (small engine) compressors don't have a clutch and they are constantly engaged, as agianst the moden Air conditioning compressors which also no longer have a clutch but are actuated via a wobble plate

 

[SLinKyjoe]

it is my understanding that the modern Kompressors produce the power by squeezing more air into the cylinders. they do this from idle right up to full power therfore you shouldnt notice any difference in power delivery...in other words the engine should have more power than an equivilant size normally aspirated engine and should operate the same..

the turbo engine works on the same priciple but needs a certain number of revs for the exhaust gasses to spin the turbo shaft which into forces more air into the engine therfore the faster your engine spins the more air it can get which in turn means you can get more power..so the faster your engine spins the more power you receive....to stop turbo lag they make the turbos smaller so they spin quicker at less revs but will not produce masses of power...for real power you need big turbos, but they need more exhaust gasses so they revs or more before you feel the power arrive.

both eat fuel.

all the above is known as forced induction for those searching on the net.


you dont need to leave a supercharged engine running when you have drive it like you do a turbo......this is becasue the turbo needs to cool a bit before you stop it......gives longer life to the turbo...

jaguar use a different type of supercharger than mercedes...so you may need to find they type before you read further into it.

 

[GrahamC230K]

Even if you do have a clutch (my 1999 w202 does) the SC becomes active at about 2000rpm (I can hear mine switch in and out thses revs) but in driving, you don't notice it.

it just makes for a more powerful engine comapred to the cc and you have a massice dollop of torque at low revs, similar to a modern turbo diesel, but the Pretol engined Kompressor will the then hold onto that max torque until max revs, unlike a diesel.

In my car over 204 ft lb torque comes in at about 2500rpm and all the way to 5500 rpm approx.

I think SC boost is relative to rpm, bbut MB do have a way of controlling this, so the boost curve is not steep like you woul perhaps imagine. I have a plot of my car on a dyno showing the boost curve agains BHP curve if you would like to see it.

So, image a normally aspirated engine, slight whine from the sc and monster torque.

 

[philharve]

Hi GrahamC230K

I have been doing some more reserch on the Internet today and I have discovered that some Kompressors were indeed fitted with a magnetic clutch and that must be what you can hear, clicking. There's no such 'clicking' in my car so it must be a clutchless installation - one less item to go wrong!

Now I'm trying to ascertain whether I have a Rootes or an Eaton supercharger. Externally they're pretty well identical. Internally the lobes of the rotors are either straight (Rootes) of have a screw-like profile (Eaton). Not that this information is of any real use, it's just that I have an inquiring mind. You can hear the compressor 'whinning' when the engine is cold but it's not really noticeable when warm.

I've also read that superchargers are geared upwards so that they spin typically 1.5 to 3 times the speed of the engine ... 14,000rpm is often quoted for Kompressors. Other makes of vehicle use lighter/smaller compressors which can spin over 100,000rpm. I thought only turbochargers rotated this fast. They need to rotate at this speed to ensure the boost pressure is maintained between 6 - 8PSI (typically) above atmospheric.

As remarked previously by another member, supercharged petrol engines produce torque levels similar to diesel engines but it is maintained over a wider range of engine speed. However, if all this power is used the petrol consumption increases. I've found that using the accelerator gently can produce fuel consumption figures that better a normally aspirated car. So it's not all bad news.

REGARDS Phil

 

[GrahamC230K]

I have done research previously, but didn't find much. I think the pressure on mine is only about 5psi.

I know I was scared when my Kompressor stopped working last year, but it was an ECU fault - everything was fine including the clutch, but the ECU was not sending the signal to activate it!!!!!

Yes, new ECU was almost as much as a new SC! :-x

I have listed to a CLK230K at another forums meeting and that was clutchless.

 

[philharve]

Hi GrahamC230K

I've spent almost 37 years in a profession that is associated with electronics in one form or another. It never ceases to amaze me, the replacement costs of ECUs. I used to design electronic equipment and fix them when they went wrong.

Unless an ECU is seriously damaged, e,g, smashed or burned, the actual cost of repairing the unit can be just a few pounds, if that. The problem in 99 percent of cases are the interface electronics, which means transistors or their equivalent. They can be replaced quite easily and in most cases inexpensively.

People who sell ECUs, new or used or repaired, make a great deal of profit from them. They are mass produced, like DVDs and VHS players, and are argueably less complex. You can buy a top flight DVD player for as little as £70 on Amazon so why are ECUs so expensive to replace? The truth is they are not but why give them away when yor can make a big fat profit.

None of this, of course, has anything to do with air compressors but I thought I would like to have a rant.

REGARDS Phil

 

[suterman]

good point, If you look in the right places you can find ECU's very cheap (£10-£20)