Bypassed ALDA switchover-- Why??? - PeachParts Mercedes-Benz Forum

neatokino · #1 03-13-2006, 02:22 AM

I was looking under the hood of a friend's '84 wagon, and I noticed that there were two things different from mine:

1) the Alda switchover valve (the one near the brake cylinder on the firewall) had been bypassed.

2) The black plastic transmission vacuum box on top of the engine (the one that contains the little white levers) had been removed.

Why would someone have done that?

Are those modifications potentially damaging to the engine or transmission?

Is there any reason for my friend not to gather the parts to put those things back the way they should be, and will there be anything particularly difficult about finding the appropriate parts and putting them in?

Thanks in advance,
Michael

Hit Man X · #2 03-13-2006, 02:42 AM

First one was probably plugged up and made the vehicle receive no extra fueling from the IP. Happens often. They're about $35 new and few dollars used if you can find a good one. I need a few more too.

Thing on top is for emissions, you don't "need" it... and it doesn't really do anything. Just had to be there when they were made back in the 80s.

boneheaddoctor · #3 03-13-2006, 08:28 AM

Thats not an Alda "Switchover valve" its an Overboost protection solenoid.

It will save you if something happens that will allow boost to rise above max fact spec.

Its best to fix it...its not expensive to replace and may save your engine.

Brian Carlton · #4 03-13-2006, 08:32 AM

The box with the little white levers is used to control the EGR on that vehicle. Removing it will cause no harm.........however..........the rocket scientist who did the job may.......or may not.......have made the proper vacuum connections after removing that box.

Old300D · #5 03-13-2006, 10:47 AM

Quote:

Originally Posted by boneheaddoctor

Thats not an Alda "Switchover valve" its an Overboost protection solenoid.

It will save you if something happens that will allow boost to rise above max fact spec.

Its best to fix it...its not expensive to replace and may save your engine.

My car was never equipped with one, being a 240D, and I had no inclination to add a piece that would just clog up eventually. With gas engines overboosting can be a problem, I'm not so sure about a 120hp diesel. Maybe long term.

boneheaddoctor · #6 03-13-2006, 10:51 AM

Quote:

Originally Posted by Old300D

My car was never equipped with one, being a 240D, and I had no inclination to add a piece that would just clog up eventually. With gas engines overboosting can be a problem, I'm not so sure about a 120hp diesel. Maybe long term.

well stock boost is 11-13 psi in the benz. The overboost solenoid energizes at roughly 15 psi. A stock Garrett T-3 can push 25 psi easily if the wastegate fales to open. Thats a healthy load to the head gasket , bearings etc.. but for a different reason than a gasser.

Old300D · #7 03-13-2006, 12:38 PM

I don't disagree, however a head gasket designed to withstand 400+ psi static compression plus the peak pressure of burning diesel fuel is not going to notice 10psi more. I hope I've got 10psi margin in my head gasket.

Brian Carlton · #8 03-13-2006, 12:49 PM

Quote:

Originally Posted by Old300D

I don't disagree, however a head gasket designed to withstand 400+ psi static compression plus the peak pressure of burning diesel fuel is not going to notice 10psi more. I hope I've got 10psi margin in my head gasket.

The 400 psi static compression is based upon 14.7 psia.

Raise the pressure to 39.7 psia (25 psi boost) and the 400 psi climbs to an equivalent of 1080 psi.

..............worried yet.................

OMEGAMAN · #9 03-13-2006, 12:51 PM

what kind of power output would that be over stock

Brian Carlton · #10 03-13-2006, 12:58 PM

Quote:

Originally Posted by OMEGAMAN

what kind of power output would that be over stock

Probably nothing........the IP limits the fuel due to it's full load stop........you can't get more power without more fuel.

OMEGAMAN · #11 03-13-2006, 01:33 PM

I wonder what the point of diminishing returns is? I imagine MB left themselves a decent safety margin. I'm only talking about increasing boost pressure not fuel.

Brian Carlton · #12 03-13-2006, 01:42 PM

Quote:

Originally Posted by OMEGAMAN

I wonder what the point of diminishing returns is? I imagine MB left themselves a decent safety margin. I'm only talking about increasing boost pressure not fuel.

As mentioned, I don't believe the ALDA has any more range above 13 psi or so. If you tweak the ALDA, the working range drops even lower.

boneheaddoctor · #13 03-13-2006, 01:52 PM

Point is yeah, there is more power to be had BUT...and this is an important BUT.

You don't make more power without more fuel....and you can't easily turn up the fuel on these whithout fully understanding what you are doing. You can easily render the IP unusible due to ruining the calibration, you can even destroy your engine from a runaway if you don't turn the proper settings the proper way in conjunction together. Settings are very delicate and interaction between different settings plays a key factor.

It will cost you $800 to have an injection shop return your pump to correct settings if you screw it up.

Something to really think about before you start playing with it.

OMEGAMAN · #14 03-13-2006, 01:53 PM

but what happens when you increase boost and nothing else? At what point does it have no more effect on power. If you only had 5psi boost I think you would notice it. In the winter or on cold mountain passes my car has a lot more power than in the hot summer. I just wonder where it ends.

boneheaddoctor · #15 03-13-2006, 01:55 PM

between 11 psi and 25 psi you won't see a difference in power due to delivered fuel limitations.....but above 13 psi intake charge temps start to climb....and the higher you go the more dramaticly they climb.

15psi and up a good intercooler is considered absolutely essential by anyone in the know...