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Old 02-16-2018, 08:06 AM
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Join Date: Feb 2012
Location: Scotland & Indiana
Posts: 231
om603.912 N/A to turbo

So I've opened Pandora's box just by typing that combination of letters and numbers and punctuation.

I'll keep it simple. I've got a 300k+ mile 603.912 n/a in my w124. It's dead slow and uninspiring until you get to 80 then it cruises nicely (aside from the drifting from much needed suspension work...I digress).

I've seen several fellows in Europe modify this motor through various methods: 6.0/7.5+ IP elements (dieselmeken or diy job with Bosch calibration) possibly switching to a turbo pump rather than the stock n/a pump, swap the intake and exhaust manifolds from a turbo 603.9xx with accommodation for the RHD steering box, and I'm sure a few other things and get what I consider a decent result.

I like to fiddle about with this car. I am not currently interested in a swap for another motor 60x or otherwise. This would be one way to fly a bit under the radar with my spouse who would be against me buying all the kit to swap a motor. With bolt on stuff I can fly under the radar.

Plus I just want to see what it will do. I'm not interested in huge hp for drifting or anything other than a modest gain so that I can get up to speed on the motorway and hear the turbo do its thing. I miss my turbo om617.

Useful input is welcomed!!!
1992 W124 300TD Estate RHD 300K miles
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Old 02-17-2018, 10:51 AM
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Join Date: May 2016
Location: Texas Hill Country
Posts: 4,650
I'll preface by saying I'm not an engine building expert, but there are a few differences between the N/A and Turbo 603 that may give you pause for a "simple" upgrade.

The injection pump is of course different, if you just want turbo, there's no reason you need to shell out big bucks for a modified one. The turbo engine has oil cooling jets under the pistons to help with the added heat, it also has enlarged coolant passages in the head, different prechambers (larger), different radiator (larger), an external oil cooler, oil supply and return for the turbo, and injectors with a higher pop pressure.

The early 603's also had heads that were extremely sensitive to overheating resulting in cracks. Not sure if the N/A's suffered the same way, but adding a turbo is going to increase the heat load on the cooling system by a fair margin.

If it were mine, I'd personally think twice about bolting on a turbo and just source a turbo 603. I think it'd be a lot cheaper in the long run since you wouldn't have to source extra parts and worry about the engine being overstressed.
'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'91 350SD - "The Diseasel Jr." 168K
'86 300SDL - "The Diseasel" 189K (Totaled 1/31/19)
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
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