convert to turbodiesel or not? - PeachParts Mercedes-Benz Forum

Arzosah · #1 08-20-2003, 03:10 AM

I've been reading all your posts regularly since I bought my 76 300D back in May and have found them interesting, detailed, and informative. However, I have not found anyone talking about differences in the NA diesel and the turbo diesels.

For a while now I've pondered the idea of converting my diesel to turbo. Before my Mercedes was my Diesel Rabbit which was incredibly slow compared to my previous Camaro. That was when it all started. I've discarded the idea of turbocharging the Rabbit and am now just pondering turbocharging the 300D.

There are so many turbos out there I am convinced they work well. Up here in Canada there are enough rusty cars that it would not be too hard to find a good running later model turbo for a good price. Does anyone have any suggestions or ideas that i could consider in making this conversion? What would i have to do?

is the old engine compatible with later hardware? Is it suitable or strong enough to handle some boost? Could i just richen the mixture of the existing pump to compensate for the extra air? would that completly spoil all fuel mileage?would i have to change just the manifolds and plumbing or would i have to change the injector pump too? Or would i have to change over the whole engine; maybe the tranny too?

Any ideas appreciated. the car is in fairly good original condition. it has 119kmiles. I am not totally set on doing this. if the conversion is easy enough, and easy enough to undo, ill do it. otherwise ill just keep it as stock. Thank you.

Arz

sixto · #2 08-20-2003, 03:20 AM

There was a turbodiesel option for the Rabbit though more common on Jettas.

Whether you soup up the 300D or Rabbit, get an engine and transmission from a donor car and replace as a unit. Techincal issues aside, it's easier to do it that way. I'd stick to a MB turbodiesel through 1983. The US (and maybe Canada) got some electronics in 1984 that might complicate the swap.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

#3 08-20-2003, 09:41 AM

whether VW/Audi/Volvo or Mercedes. There are things like oil spray jets aimed to cool the piston crowns from the bottom and stronger designs of the rods etc. Unfortunately, the VW motors also put a much lower compression ratio (17:1) in their turbo models, which leads to hard starting when the rings begin to wear, but Mercedes didn't do this. Back in 1976 there was an article in _Road and Track_ which gave a very detailed analysis of the then-new Mercedes turbo motors, but I don't have access to the exact bibliographical reference from here -- it's all stored at home.

R Leo · #4 08-20-2003, 10:24 AM

Arzosah,
As Sixto says, If you are set on turbocharging, you would be far better off finding a donor 300D Turbo of some sort and swapping out the entire engine. Things like oil spray jets are only part of the equation...the IP for the turbo engine is significantly different from the normally aspirated engine.

Arzosah · #5 08-20-2003, 09:56 PM

Thank you all for responding. I am not set on turbocharging. I've pondered the idea and may want to try something in the future. For now, I am interested in learning more about it and its peculiarities.

I had no idea about the oil sprayers. So that's featured only in the turbo engines? I had a feeling about the IP differences. And I wondered if the trannies had different shift points. I knew that a total changover is the most predictable and safe option. I just wondered if there was an easier, newer and more effective way of doing it with what I already had.

Some people have done some neat stuff with existing turbo systems. I wondered if anyone has done anything with some of the older systems.

kerry · #6 08-20-2003, 10:48 PM

Can you find the info on that Road and Track article? I'd be interested in reading it.

There are people who retrofit a turbo on the 617. There's a company in the UK that specializes in it and adds turbos to a lot of Mercedes motorhomes. I met a guy this summer who had it done and really liked it. It can also be done in the 616.

That being said, I'd just put in a turbo engine and avoid the retrofit.

By the way, I have a turbo and non-turbo. In the Mile High city, the turbo is like adding a second engine.

#7 08-21-2003, 07:56 AM

sixto is offering sound advice. The turbo 617 engines have MANY changes beyond the turbo itself. These changes allow the engine to live with a turbo. Your non turbo engine would not last very long turbo'd. These changes all have to do with increasing engine durability to a level that will withstand the added stress imposed by the addition of a turbo.

Good luck,

#8 08-21-2003, 10:53 AM

Would adding a turbo at mabye 2-3psi hurt much? Ya know, just to improve combustion, scavenging in the cylinders and compensate for ring wear. Even without the extra fuel.

Arzosah · #9 08-21-2003, 08:31 PM

thats a good question about 2-3 psi boost. i suspect the lag would kill any benefit at this boost range. and perhaps the efrot would be better used elsewhere in the engine. but then again. what do i know. i am the student here. Does anyone know if the head can be milled at all to boost compression. or would that put similar stress to turboing.

Larrybible, ty for your input. ive seen your name alot around here. you have good advice. I am sure you are correct again this time. I know some engines need to be built stronger to allow a turbo. i wasnt sure if Mercedes also needed to be. they have a reputation as long lasting engines. i was hoping they were already strong enough. oh well.

Its just as well. i really didnt want to butcher this car. its in decent original condition except for a few things. maybe someday ill restore it. Ive always wanted to restore a car. i just thought it would be some chevy.

rwthomas1 · #10 08-21-2003, 10:35 PM

Hey Finum Fit, you sure that VW lowered the compression on its turbodiesels? I have never heard this before.... It would certainly help durability. Arzosah, yes you can turbo ANY diesel engine and it will make more power provided the pump is adjusted to deliver more fuel. The problem is that some engines don't last very long if you do. Old GM 6.2's and 6.9-7.3IDI Fords responded well to aftermarket turbos provided you keep the boost levels fairly low, less than 10-11psi and the EGT's lower than 1100*F. Yes you could turbo your NA motor but durability is the big question. It would be much easier to just swap in a later model turbo motor and know you did it right. MB's have a history of going bang when you turbo an NA motor. RT

Arzosah · #11 08-22-2003, 12:01 AM

My Rabbit is an 81 NA diesel with a compression ratio of 23:1. the only turbo engine in my manual is an 83 which is also 23:1. it also says that all diesels up to 83 should get 406psi compression minimum. Mercedes 617s are only 21:1 and only 284-327psi compression. It seems like a lot of room for improvement. I guess thats why the engines last so long. Accounts for why nearly twice the displacement only offers 50% more power.

#12 08-22-2003, 11:49 AM

made for them by VW dropped the compression to 17-1 on the turbo versions, but I just assumed that this was what VW was also doing to their 4 and 5 cylinder versions of the same design. Maybe it was not good to assume that, but I thought I had seen it confirmed somewhere else, too.

coachgeo · #13 08-22-2003, 01:30 PM

Might be WAY easier and cheaper to just do Propane fumigation. Will give you same effect as turbo.

psfred · #14 08-22-2003, 07:51 PM

You cannot just drop the later 617 turbo into the W115 chassis -- the oil filter housing is on the wrong end of the block, and interfers with the suspension. I suppose you could make a custom oil filter for it and locate the filter remote (as some 240s are anyway), but stock it just won't go in. You will also have to make the oil cooler hookup work somehow.

I also don't think you can get a turbo in there either -- not enough room between the block and the front suspension. You will have to measure to see.

Too bad, the W115 would be a blast with a turbo 617 in it!

Oh, and by the way, if VW lowered the compression on the deisel with the turbo, Volvo and Audi certainly didn't! Stock compression is 23:1, and it can be as high as 26:1 in production. That's how they get 105 hp and 145 ft/lbs torque out of 2.4L at 10 psi boost.

Peter

grimgaunt · #15 08-23-2003, 07:03 PM

the turbo into a 115 body has been done, albeit with a touch of the universal tool (the big fu****g hammer) and an oil filter adapter plate .
I have swapped many into 123 bodies where it is 'almost' a bolt in.
email me off list if you want to know more.