Does an OM352A have a wastegate on the turbo? I thought all turbos needed a wastegate but I'll be darned if I see one on my truck. Even turbos with an internal wastegate have an external acuator, right? I know my volkswagen does. Is that just the way the mog is? I searched for "wastegate" but not a whole lot came up concerning the OM352A. Thanks!
No wastegate on the 352A mog turbo's, infact, most big truck diesels don't have a wastegate, they just run to the top of their effiency range... more fuel in, more boost out (well it is a little more complicated than that, but you get my drift).
Cheers,
Ben
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People freak out when I drive into the shop with a perfectly good Mercedes, only to start cutting it up for parts. I just tell them that something has to die inorder to keep all of the other Benz's running.
That's actually kinda neat. I like the simplicity. I thought I was pretty turbo saavy but I learned something new. I custom built the turbo setup in my 92 GTI and in all my reading up on turbos a large part of the discussions are about wastegates. No where was it an option not to have one but I guess this is a totally different beast than a volkswagen!
Well, even though most large trucks don't have a wastegate, they should. I have had large trucks, one a Mack military wrecker with a Continental diesel that I have had 'gated and non 'gated versions and I can tell you that if done properly you get a higher torque rise, less smoke and more boost at a lower rpm. Big trucks like my Autocar with a Cat diesel usually don't have wastegates because the non wastegated turbos are much cheaper and the engines usually spend their time mostly on the highway running in a narrow rpm range and the turbo can be set up to provide a desired amount of boost in that range. The Unimog, however, is a good example of a vehicle that should have a wastegate. Boost could be made much sooner and torque would be much higher starting out and going through the gears and you could still be running nearly without boost at cruise for economy, or even with a small amount to cool the charge down and run a bit lean. Diesels are the opposite of sparkers, lean cools them down, rich makes the cumbustion temps go up. I even made the one on my Continental adjustable so I could adjust how much boost it made and when. I haven't had my Mog long enough to get into this aspect of it, it runs very well now, but I will be sizing a wastegated turbo for it in the future and then getting into the appropriate fuel pump issues as well.
Why change the turbo, MB know ware the boost needs to be or they wouldn’t get the torque they have at higher rpm’s, high torque rise is a fallacy, just as is having high peek torque and high rated hp is if you have blind disregard for what goes on in the intervening RPM’s & the 90% of other systems a dyno doesn’t account for.
I'm not sure what your point is, but if you are happy with what you have, don't change it. I would like to change the amount of peak torque my truck has and where it has it. My truck has high speed axles and 14.5's so "real" gear ratio is not as manufactured and I would like more torque at highway speeds as I go up a hill with a load as well as more torque when starting out without having to wind the engine out to 2700 rpm and use all the gears. I want 10-12 psi at 1200-2000 rpm and after over 30 years of building turbo motors, diesel and si, I know how to get it. I'm fully aware of the engine and ancillaries as a system, so it's not a problem keeping things safe. This is a change that I would like for my truck with me driving it the way I like to drive, and that is to shift as few times as possible, using the lowest rpms possible, as I move from 0mph to any desired speed. High torque at low and broad rpms is the key to doing this. It is not at all hard on the engine if combustion temps at full load and boost are kept reasonable and this may involve addition of an intercooler as well as a waste gate. Winding the engine up as you go through the gears is what is hard and fuel inefficient. High rpms increase mechanical loads on an engine way more than boost and controlled combustion temps would. I have all the respect in the world for Mercedes, but their constraints as a manufacturer are not necessarily mine as a user, hell, I was playing with OM352's 30 years ago and it was considered Mercedes' third world engine even then. Robust and reliable, well proved I think you guys in the UK would say, which mostly means old according to my friends there, it certainly is capable of being improved a bit when one has a clear picture of where one is going and how to get there.
Howdy Troca,
I've thought about a wastegate for my truck also. It would seem to make sense that it would spool up faster for less lag with a different turbo but you'd have to wastegate it not to go over the 10-12psi limit that I'm wanting to stay with.
Chas
Exactly right. A different trim turbo is needed, probably a bit smaller turbine with a decent exit diameter and the wastegate. I'll have to take an afternoon and record some load/temp/boost/ tubine P in and out curves to decide where to go from the factory turbo. Won't be soon, probably later this summer, as I've already got too much to do and the Unimog ain't broke. When I get a game plan together and can explain what I think should be done and why, I'll share with the list for those who might be interested.
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