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K-jet WUR 350 vs 450SL

  • Racediagnostics
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13 Jul 2020 16:42 #252328 by Racediagnostics 450 SL 107.044 1979
K-jet WUR 350 vs 450SL was created by Racediagnostics
Hi Volker, although EPC has the same part number for both the 350 and 450, the actual Bosch part numbers are different

350SL p/n is 0438140028
450SL p/n is 0438140056

Are you aware of any documentation which explains the differences between the two, or are data sheets available?

Cheers
Jim

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1979 450SL - 2002 XK8 4.2

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  • Dr-DJet
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13 Jul 2020 19:23 #252336 by Dr-DJet 450 SL 107.044 1973 Schweiz
Replied by Dr-DJet on topic K-jet WUR 350 vs 450SL
Hi Jim,

Easy answer: Both Warm Up Regulators (WUR) were used on 350 SL and I will next verify 450 SL Europe.

Long answer:
  • Bosch used 0 438 140 028 WUR till 2/77 and then switched to 0 438 140 056.
  • To make it even more complicated 0 438 140 056 was further modified without change of Bosch no in 1979
  • All 3 types differ in warm full-load control pressure slightly from 2.7 to 3.0 (don't ask me how many stomes per squarefeet :P )
  • They also have slight variations in cold control pressure of 0,1 bar
  • Idle-run warm control pressure is the same in all 3 versions

Okay, now you are down on your knees, begging your fromer accelerator colleague to show mercy in this ;)

I would choose a 1980 WUR 0 438 140 056 and believe that Bosch and Mercedes-Benz were wisest in the latest version. MB obviously has triggered these changes but did not bother to make a big fuzz about it.

And now to 450 SL Europe
  • It started with WUR 0 438 140 010 and then continued with 0 438 140 056 in 9/77
  • 010 behaves ike 028 in cold start but it behaves like early 056 in full-load warm.

Again a late 056 seems to be a good choice. What else do we learn from that? Well Bosch experimented a lot together with Daimler on the right settings for the engine until they finally created the universal 1980 WUR 0 438 140 056 . Maybe it did not matter any more during that last year where they had already launched 450 SLC 5.0 .

And please this all is only vaild for 450 SL Europe. 450 SL US / CAN / JP / AUS is a totally different animal.

Viele Schraubergrüße - best regards, Volker alias Dr-DJet und K-Jet Forscher, Admin und Betreiber dieser Webseite
Alles über D-Jetronic und Zündung auf jetronic.org

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  • Racediagnostics
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13 Jul 2020 20:56 #252346 by Racediagnostics 450 SL 107.044 1979
Replied by Racediagnostics on topic K-jet WUR 350 vs 450SL
Hi Volker, all very interesting to see and understand the history. I had originally planned to cosmetically restore the older unit but will no longer do that, instead I will stay with the 056 (1980) unit. Although my car is a 1979, car the engine is from a 1980 SLC.

As it seems to be working well I will not rebuild, just clean, de-rust and polish.

Cheers
Jim

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