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855 Cummins big cam 400 question

7379df ยท 2025-09-20 20:51

Getting ready to build a big cam 400 with cpl 625. My question is can I get rid of the original water after cooler and go strictly to a CAC? We done this to a 855 big cam 1 290 hp with no cooling from turbo to intake. To make this work we installed a kenworth t 2000 Radiator and CAC and machined our own aluminum inlet to go from 4" to the rectangular 4 bolt inlet. This truck has been going for quite some time now and seems to be doing really well. We would have to get an intake for a big cam 1. Thanks for any help.

Replies15
  1. #1Simon C2025-09-20 22:11

    Because it would work on one doesn't mean it will work on another guaranteed. Truck Shop would be the best guy to ask as he has a lot of highway Cummins Truck engines. After coolers serve a purpose and what the by pass implications would be , not sure. Maybe too high of air temperature into engine. Maybe something melted. Wait to see if he responds. Simon C

  2. #2Truck Shop2025-09-20 22:11

    You can use any non water jacketed intake, early 250, 335 or N14. 625 cpl below I built a 1.5 years ago now. But use a 3804502 N14 turbo, it spools faster. *

  3. #3Simon C2025-09-20 22:14

    I must of posted 10 seconds before you Truck shop. Lol glad you can help him. Simon C

  4. #4Truck Shop2025-09-20 22:28

    Main thing is don't go over 14 to 15% over fuel with only double nie resist pistons. Spend a few extra and buy a IPD ceramic coated crowned piston/cylinder kit. But if that block has never been machined, which it probably hasn't, any fretting at main cap contact area it will need a line hone, decked, counter bores cut and head bolt holes checked for cracking. And a new set of cam bushings, probably original in it now. Cost of block and 6 con rod machine work around here runs $2,500 plus. Early BCI's had short early head bolts, if it's a late 369 or 393 BCI CPL it will have the longer head bolts. * Time it at .071 injector pushrod travel.

  5. #57379df2025-09-21 22:42

    Thanks a bunch fellas ! I am taking the block in to a machine shop to do just that. Another question I had was timing these. I bought a cheap tool for timing but a little confused on the whole process. I know that you have to shim the rocker boxes but is there a book I could get to help me with this process ? Really appreciate the replies !

  6. #6Truck Shop2025-09-22 00:49

    I just did a run down on it in quick mode without BS in this thread. Post # 15. HeavyEquipmentForums * If you need---I can draw the diagram with step by step instructions.

  7. #77379df2025-09-22 07:23

    Lol... Not rocker box....I meant cam follower.. sorry about that.

  8. #87379df2025-09-22 08:09

    Thank you Truck shop! When the time comes ill give it a try. Greatly appreciate it.

  9. #9Vetech632025-09-22 08:44

    Sell him my tool while you at it!

  10. #10Truck Shop2025-09-22 08:48

    What kind of commission?

  11. #117379df2025-09-22 16:27

    I'm sure Vtechs tool a hell of alot better than my cheap Chinese one I have.

  12. #12Truck Shop2025-09-22 22:02

    You will know when you run back through the procedure, if correct nothing will change at pushrod travel indicator. Stopping at .203 a second time around it should still read .069 for fast, .070 for nominal, .071 for slow. You want it on the slow side. On hotrods I set at .073, throttle response is slightly slower but it gives at little more torque hang time between shifts.

  13. #13Truck Shop2025-09-23 04:46

    Your wife ok with that?

  14. #147379df2025-09-24 11:14

    Oh Hail.... The places we could go with that !!

  15. #157379df2025-09-24 11:15

    Oh Hail.... The places we could go with that !!