Question for Doktor Bert - PeachParts Mercedes-Benz Forum

kestreltom · #1 01-08-2013, 12:19 AM

Hello

Until now, I have been a silent admirer of the work you have done on your 300sd, and have gone about tuning my 671 based on much of what I learned from you

I have a 1984 300d. I am planning to remove the turbo and rebuild it myself. I have a machine shop and am handy with port & polish tools. I would like to recreate as much as possible of what you did to your turbo including adapting a larger exhaust turbine and upgrading the compressor wheel.

I have seen a few Buick GN turbos on ebay, but they seem few and far between. Do you know of a source for GN turbines, or something else that will work? How did you go about deciding to use the GN turbine? Did you open up the exhaust housing in the vicinity of the exducer? Was the inducer the same as stock? Did you use the stock bearings and shaft? Where did you acquire the upgraded compressor wheel with the double blades? Were the compressor trim the same as stock?

Would something like this work?

http://www.ebay.com/itm/T3-Stage-1-Performance-Turbo-turbine-wheel-Turbocharger-Best-Money-Can-Buy-/400381045582?_trksid=p3284.m263&_trkparms=algo%3DSI%26its%3DI%26itu%3DUCI%252BRTU%252BUA%252BFICS%26otn%3D21%26pmod%3D150960600027%2 6ps%3D54

Any help would be much appreciated.

Thank you in advance for considering my questions,
Tom

charmalu · #2 01-10-2013, 10:47 AM

Bump

Charlie

Doktor Bert · #3 01-18-2013, 12:31 PM

Sorry, fellows...

I've been tied up. Let me work on a detailed response....

Stretch · #4 01-20-2013, 04:38 AM

Quote:

Originally Posted by Doktor Bert

...
I've been tied up...

Lucky chap.

moon161 · #5 01-20-2013, 08:22 AM

Quote:

Originally Posted by Stretch

Lucky chap.

It is called 'la malaise anglaise' isn't it ;-)

Stretch · #6 01-20-2013, 12:28 PM

Quote:

Originally Posted by moon161

It is called 'la malaise anglaise' isn't it ;-)

It could very well be - though the internet suggests it isn't just a habit of a single nation.

Doktor Bert · #7 01-18-2013, 12:32 PM

Short version:

The Buick GN turbine isn't really worth the work. Instead, you will find better gains from an improved compressor wheel...FWIW

kestreltom · #8 01-23-2013, 10:44 AM

Quote:

Originally Posted by Doktor Bert

Short version:

The Buick GN turbine isn't really worth the work. Instead, you will find better gains from an improved compressor wheel...FWIW

Since I was not able to find an affordable GN turbine, I bought a Stage I turbine wheel and shaft from an ebay seller. This wheel has the same inducer/exducer diameters as the GN turbine ( I eventually found these dimensions online).

I will tear into the car's turbo next week and report my findings here. I will have no problem modifying the turbine housing if needed.

Bert: Would you recommend sticking with the original 45 trim compressor wheel, or go to a 50 trim with a slightly large inducer diameter?

Thanks!
Tom

Doktor Bert · #9 03-12-2013, 12:37 PM

I like to try different trims...Sometimes the results conflict with theory.

Updates????

kestreltom · #10 03-12-2013, 09:50 PM

Quote:

Originally Posted by Doktor Bert

I like to try different trims...Sometimes the results conflict with theory.

Updates????

Hmmm... That is interesting, makes me wonder if I should order a 50 or 60 trim compressor wheel and get it installed pronto.
But before I get ahead of myself - let me fill you in on what I have done to my turbo so far.
I ordered a stage II turbine wheel and machined out the cast iron housing so it would fit the wheel. The stage II wheel inducer (large diameter) is the same as the original, but the exducer is substantially bigger and the exit vanes are not as bent over as the original. The stage II blades are cupped and wider than the original and I think they will be more efficient at extracting power from the exhaust. Here is a shot of the original and stage II wheels side by side:
https://picasaweb.google.com/lh/photo/FvqphZAN5jjauW4MBFJmxdMTjNZETYmyPJy0liipFm0?feat=directlink
Here is a youtube video of the machining operation:
Maching the OM617a turbine housing - YouTube
Then I rebuilt the turbo using a gapless oil control ring on the turbine side and a new 45 trim (stock) compressor wheel. I also painted the turbine housing with a high temp silicone paint.
I am currently installing a custom air/water intercooler and am in the middle of modifying the original intake manifold with a rear intake fitting in order to simpify the tube routing. I already installed an MW IP that has had the governor tweaks outlined by OM616 on the ST website and is drip-timed at 26 btdc, installed a woodruff key for about 2 degrees of cam advance over factory, and have a nice electric fuel pump from a Powerstroke 6.0 installed.
Unlike a lot of guys on the ST website, I don't want a mega turbo with monster boost and awesome lag. I want what Doktor Bert has: namely faster spoolup and better torque down low. I also don't want the IP governor de-dueling at the usual 3000-3500 point, which I think is reasonable given that the new turbine wheel has a more open blade pattern that should flow better and keep the drive pressures in check as boost builds up to 17 psi or so. I will be monitoring boost, egt, and drive pressure. Wish me luck!

Silber Adler · #11 03-12-2013, 10:07 PM

Hi Tom
I have been trying to get a handle on turbo technology. I saw your video of you hogging out the housing, impressive machine work

Why would you just not get a bigger turbo unit? I hope it isn't an ignorant question. Maybe you said but it went over the top.

kestreltom · #12 03-12-2013, 10:59 PM

Quote:

Originally Posted by Silber Adler

Hi Tom
I have been trying to get a handle on turbo technology. I saw your video of you hogging out the housing, impressive machine work

Why would you just not get a bigger turbo unit? I hope it isn't an ignorant question. Maybe you said but it went over the top.

Hello Silber,
The eternal question, eh? (Thanks for the kudos...)
Keep in mind that the following information is theoretical and has yet to bear results that I can demonstrate. But the results will be coming soon...
My take is that the larger the compressor/turbine/shaft, the more energy it takes to spin it up to the point where you start making boost that you can feel. The original Garrett T3 in my '84 300D was sized well for that engine and above 2500 rpm, it can make way more boost than the injection pump can feed with fuel, consequently it has a very conservative wastegate setting (My stock wastegate was set to 9 psi !?!). The problem is that with the technology at that time, the turbine design was slow to build boost.
The newer Stage II and III turbine (exhaust) wheels are better designed and can extract more energy from the exhaust stream down low - so if you can adapt your exhaust housing for them, you can fix the slow spooling nature of that T3 turbo design.
Doktor Bert has suggested that adding a larger 50 or 60 trim compressor wheel might also help. But I have heard stories of 60 trim wheels causing turbo lag.
Keep in mind that my goal is to improve low end torque and turbo response - not create a coal rolling, tire shredding drift machine. I feel that the factory set the IP governor on these engines a little too conservatively for my taste, so I will be adjusting the governor to try and increase the low to mid range fueling to match the hoped for improvement in boost response.
To be honest, not everyone has their own machine shop or access to one - so many try to adapt later design turbos to their 617a engines, which for me is way more work than I wanted to get into. A variable vane turbo like the one outfitted in the new Mercedes Sprinter vans is a good example.