UPDATE GMC K2500 SUBURBAN CUMMINS CONVERSION AKA: “SUBRUTUS©”
Well, I’ve been out of pocket for some time now, however, I have been making some progress and decided the need for an ORD SAS conversion w/custom thin spring pack too compliment this conversion.
The Cummins 6BT is installed, the DODGE 47RH 4X4 transmission is finished and ready for install too but I ran into a few issues.
First is that the IFS 9.25” differential needs to be lowered “too close to the Cummins oil pan for my liking” then the case needs to be ground down at the reinforcement ribs to make it fit which in turn reduces the case strength “something I’m not willing to live with.”
Secondly, the Torsion bar cross member would need to be modified & lowered because I’m using the 47RH 4x4 transmission (wide-box) w/clocked NP241 t-case. The amount of drop & fabrication would also require at last a 4” to 6” suspension lift, so instead of going this route an SAS conversion using ORD’s kit and a high pinion D-60 Ford diff is money better spent especially since ORD makes custom thin spring packs for the Cummins conversions.
The Cummins weighs 300+- lbs. more than a 6.5td depending on accessories (increasing sprung weight) and some vendors of conversion motor mounts have stated in their install instructions “to cut out the two diagonals chassis braces attached at the front x-member and to the chassis uprights” for the conversion that is a bad idea as it compromises the chassis designed strength. For my install I’m leaving them as not too compromise the chassis strength, however, I had to cut the passenger side diagonal and weld in a modified bowed section to clear the Cummins, the steel rod used has strength well beyond the hollow unit GM installed during manufacturing.
I haven’t weighed the front 9.25” IFS differential, CV axles, control arm’s, tie rods, center rod, idler bracket & arm, brackets (too be cut off chassis), hardware, torsion bars and t-bar x-member I suspect it will be well beyond the difference of the Cummins to GM 6.5td weight. Selling these items will put a large dent into cost of the SAS conversion.
I’ve found two exhaust down pipe options that work perfectly with the CHEVY/GMC Cummins conversion clearing the firewall, AC accumulator & dual heater lines on later model GMT400 it’s the Cummins center mounted turbo exhaust manifold which places the turbine between # 3 & 4 cylinders (factory or aftermarket).
1st OPTION: Is the 1st gen Ram Cummins 2wd down pipe in 4” diameter for the HX35 & (w) or HX40 & (w) which is available in 4” or stock HX35 turbine outlet size and stainless too.
2nd OPTION: Is the original Cummins Design Cobra Head 4” down pipe (rare) “for utmost exhaust downpipe flow” it hooks up to all HOLSET/CKO HX40 (W) & Super 4” full Marmon turbine outlets then attach a 1st gen Cummins 2wd 4” downpipe trimmed to fit. Both of these options work well with dual HVAC option on the later model GMT400 Cummins conversion all other downpipe options are full custom.
NOTE: Earlier dual HVAC equipped GMT400 use a metal manifold pipe assembly for the heater hoses and does not work, some individuals have used the manifold that places the turbo down low & back between # 5 & 4 cylinders this is OK for stock Cummins tunes however from what I have read from many sources if using this type of exhaust manifold and pouring on the fuel EGTS @ # 5 & 4 cylinders will skyrocket into piston melt-ville……
Pondering exhaust break and/or large mechanical 12”+ t-case yoke disk brake for those steep mountain descents.
Throttle cable to the BOSCH P7100 Injection Pump is an updated Ram Cummins item trimmed to 21” on the pedal side for the GTM400 conversion.
The DODGE 47RH (wide-box) transmission is shifted via the stock late model GMT400 column shifter cable assembly. Normally the GMT400 auto shifter cable is routed towards the back of vehicle then looped through the drivetrain hump to connect to the GM transmission and shifting in a pulling motion, the 47RH shift pattern is opposite to GM so the GMT400 shifter cable is routed through the firewall just left of where it exits the steering column the shifter cable is then looped and routed along the inside of fender well under the ABS lines and module bracket out under the driver side battery tray then looped back and down along the chassis rail then attached to the custom cable bracket I made from the 4L80e shift cable bracket.
The GMT400 shifter cable is looped at about the same angles as it would be for the GM transmission so I expect long life from it, the custom shifter cable bracket (picture in earlier post) is mounted horizontally to the bell housing bolt just under the starter hump on the transmission where the cable is then snapped into place allowing it to shift the Dodge 47RH simple and cheap.
The stock RAM CUMMINS throttle valve cable is used in this application.
I cut the drivetrain hump for the driver’s side NP261 t-case shifter the linkage or NP241 lever will need to be modified. I’m using a three (3) pin shift switch on t-case however a two (2) pin switch will work with the 47RH, NV4500 or NV5600 as well, 40 tooth tone wheel is a must for the speedo.
I’m using the DODGE RAM CUMMINS radiator and charge air cooler aka intercooler the radiator inlet interferes with the driver’s side battery, however I have cut off the outer edge of the tray at the fender well and slightly dented the rear most corner of the driver’s side wheel well where it meets the tray giving the battery room to fit in w/same gap between radiator intake and battery it would have if I was using the GM radiator.
An air-filter canister “water & dust proof” w/5” canister inlet from 6” oval pipe snorkel and 4” outlet to 4” turbocharger compressor inlet will be used.
Mulling the idea of using the 6.5td glow solenoid to engage the Cummins grid heater (s) or just go w/momentary switches leaning towards less electrical accessories even using cable control for fuel run/stop.
I’ve read some individuals have used the 6.5td lift pump in series with the 2nd gen. Cummins mechanical lift pump with good results maybe I’ll try it too.
As usual your thoughts and comments are welcome.
