Super Contributor

Re: D 399 speed

Ran into this several years ago on some mechanical drill rigs, I'm assuming this is what you're driving?


By playing with the governor springs we could get a high idle of 1450 and a full load rpm just above 1300.  We ran into problems with valve float, and went with some aftermarket valve springs, there was a shop in Midland TX that had some experience back then in building heads for D399's and 398's for that application, but I can't find any info on them now.


What governor are you using, the CAT hydramechanical, or a Woodward UG8?


What we found back then was that the higher speed horsepower was limited by exhaust port temps, so on the engines we did we made sure they had cylinder pyrometers.  We also had some luck playing with the fuel injection timing (by setting the fuel lifter height) but I can't find any of the info in my files and all they guys I worked with back then are long gone.


The reality these days is you may be better off finding a couple of 3412's rated at 1500 or 1800 RPM to do what yo want, probably save you money on fuel consumption too.


Hope that helps.

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Accepted Solution

D 399 speed

I have two old CAT D-399 engines rated 1,100HP @ 1,200RPM but the torque converters (Twin-Disc) will only efficiently transmit 400HP at the 1,200RPM; so I have two choices

1)  Run the engines at speeds greater than 1,200RPM - I would really like to run at 1,450RPM to get decent and efficient HP transmission through the torque converters - Does anyone know what the upper end of speed I can safely go to and what engine HP loss should I expect at 1,300 and 1,400RPM 

2)  Run at 1,200RPM and push more Horse Power into the converters so that they run in the inefficient part of the torque converters 'curve' but I can then get more HP out of the converters. Problem with doing this is that the torque converters get very hot quickly. Hence my enquiry about option one and what is the safe top limit of run speed I can go to.

Duty load is near continuous for two/three days and then reduced load (40%) for two/three days. It is only the days of continuous running that I need the higher speed. Can I do it?