I've been dabbling in G-Class cars since 2014 when I purchased my 1987 300GD SWB. I loved that truck. It already had an upgraded OM617A turbo so I set out to make it a nice daily driver with a fresh interior, heated seats, and a killer stereo. I learned a lot about G-Wagons and caught the bug big time.
In 2016 I found an Austrian Military Puch-G for sale here in town. My friend and I took it for a quick test drive and fell in love with the spartan nature. Yes, it needed TLC and it was slow but in time I know it would be amazing. Now it is finally as done as any car can be and I gotta tell you - I LOVE IT and find myself driving it more than my G55.
I want to focus on the powertrain choice I made. I'm no stranger to engine swaps, planting a V8 302 in a 1972 Ford Pinto (insert fire joke here) and an LS3 in a 1978 Corvette both with very good results. The LS3 is an exceptional engine, has a great support community for swaps, and once sorted is powerful and reliable. I must admit, I was tempted to drop an LS into my G.
I've seen a lot of early G's get the OM606 engine swapped with a 5-speed transmission. This is a very popular option in Europe, and I've seen some very nice examples make their way to the states. All that being said, I would like to make a strong case for the OM617A engine and Getrag 5-Speed setup.
The early W460/W461 had several engine options that all shared common characteristics: exceptional reliability and a lack of power. Even the wonderful 2.8 DOHC M103 featured in the iconic R107 280SL was detuned somewhat when offered in the 280GE. Anyone who has driven a G-Wagon from the '80s will tell you, they are exceptional off-road and all underpowered!
I've had two G's with the OM617 engine and can tell you, they are amazing engines. Good torque, bulletproof, and super easy to work on. The OM617 has an exceptional reputation bordering on a cult following. Like any powerplant for the early G-Class, the 3.0L 5-cylinder OM617 with 80hp simply did not have enough power for highway driving and without overdrive, top speeds on the early G-Wagons was horrible.
The thing is, when the OM617A was introduced, Mercedes-Benz added a turbo and in early trials was able to squeeze as much as 227hp out of the powerplant -- even more power than a stock OM606. Now that much boost will shorten the life of an engine, but one can get respectable performance and long engine life from an OM617a when coupled with a high-performance injector pump.
To me, the OM617a with Getrag 5-Speed makes the most sense to me for the following reasons:
- OM617a is an easy drop-in for most G-Wagons
- The OM617A is close to the experience provided with the OM617 with more power
- The Getrag 5-Speed was offered on some G-Wagons
- Performance and drivability are exceptional
If starting with the 300GD, don't try and slap a turbo on the original OM617 because the engine was not designed for the boost. You could, however, drop in a high-performance M-Style Injection Pump by Bosch and get 10-15% more performance and call it a day, but why stop there? The high-performance pump with the OM617a turbo engine will upgrade your rig to well over 150hp and provide the best performance. If you already have an OM617a in any car, the high-performance Bosh Injection Pump for the Turbo engine can provide 50-60 additional horsepower.
You will need to find an OM617a from a donor car or an engine rebuilder. Most rebuilders will let you use your old OM617 as a core credit.
Once the engine is sorted you will have the acceleration and power you need for driving around town, but the top-end speed will still be limited by the redline of the engine. I've found that anything over 100 kph or 65 mph requires overdrive. That is where the Getrag or 711 transmission comes in. Do your research because the 711.110 civilian and 711.116 military versions have a top-end 1:1 ratio and do not provide overdrive. For increased top-end, you really want a 711.113 civilian or 711.117 transmission military with overdrive.
These Getrag 5-speed overdrive transmissions are VERY hard to find. If you are looking for one, you are in luck because most folks are spending big bucks and upgrading older G's to OM606 and those modern engines won't really work with the 711.117. I was lucky to find a company in Germany that does swaps that is more than happy to sell old 711.117 transmissions and for a few hundred dollars was able to find one.
Be prepared for some extras. Most likely you will need a new clutch, flywheel, motor mounts, and shaft between the transmission and transfer case. This is a great time to get some new glow plugs. The OM617a also runs hotter so you will want to take this opportunity to recore your radiator or get a new high-performance one. Also, some plumbing for the air intake will be necessary.
Resources:
OM617 Performance Parts Including High-Performance Fuel Injection Pumps
OM617a Used Engine
Basic Rebuilt OM617a Engine
High-Performance Rebuild OM617a Engine
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