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Hello everyone,

First off, a big thanks to all the quality contributors to this forum. None of us could successfully finish these conversions without the help and advice from the members posting positive and helpful information. That said, I wanted to showcase my first “Fummins” build.

Let’s get right down to it. We started with a 4wd Crew Cab Short bed 2000 Ford F250 Superduty with a worn out 7.3L diesel and a ZF6 manual 6 speed.


We named the project “Tom.” That’s for two reasons:

First, we bought the truck from a stylish guy named … you guessed it … Tom. He drove the truck out to us in the Pacific NW all the way from Maryland. Thanks Tom!



And the second reason this truck will forever more be called Tom is this: The school bus that gave up its engine was a Thomas Built Bus (#425 for those keeping track of how to get home after school) which was bought at a GOV deals auction from a local school district. Bus #425 had approximately 9000K hours and 156K miles.


The truck was in surprisingly good condition, considering that the Superduty had north of 300K on the clock and having spent its days in a rust-prone part of the USA. It even made that cross-country drive without issue, other than the expected dirt and wear and tear. The truck ticked all the boxes needed for my first Fummins swap, namely that it was a running, driving truck.

The goal for this build was straight forward: Create a “forever” truck. We decided to tackle this in two phases:

Phase 1
  • Freshen the 24 valve Cummins and boost the power output to approximately 350 HP
  • Install a School Bus ISB 24 valve Cummins out of a 2000 Thomas School Bus
  • Plumb the compressed air system from the School bus to run air bags and air tools as needed
  • Retain the ZF6 manual transmission
  • Install an exhaust brake
  • Repair and stop any rust as needed on the body and or chassis
  • Rewire engine and accessories to ensure the body can be removed easily in case of future repairs.
  • Test drive, test drive, and more test drives
Phase 2
  • Install larger Turbo if more power is needed or if it smokes too much due to the larger injectors
  • Fix anything that need to be replaced after all the testing in Phase 1
  • Repaint Paint exterior body
  • Replace the interior with leather from Leather Seats.com
  • Fabricated and install custom bumpers from MOVE
Because I know everyone wants to see photos, I tried to document the build with the details that would be most interesting and helpful to everyone that reads these posts. Here we go:

We started by dismantling Bus #425 and removing the engine. For any of you considering this, let me just say, it’s a major undertaking requiring a lot of work and equipment. I would never attempt to remove the engine without the use of a suitable forklift or a very big tractor with a loader. Everything on the school bus is big and heavy.

I had excellent help courtesy of a sawsall and a good pack of blades:



While in process, make sure you keep track of the required wires as well as the gauges and the gas pedal. You’re going to need to keep those. Also, if you intend to reuse the bus air system, make sure to keep the governor as well as the dryer and some of the air tanks. We also kept all of the battery cables, fuse holders, and switches. There are a ton of good parts on the bus that we tried to keep for future use.



We finally had both the engine out and the parts we wanted to keep. It was time to send the rest of the bus to the recycler. We were glad that part of the project was over. Working on gravel sucks!!!!

Once we had the engine in the shop, on a workbench, we could really see what we had. Have I mentioned working gravel is the worst? I was so glad to be back in the shop.




In the shop, we first added the SN of the Cummins to Quickserve and unlocked a lot of very useful information, everything from wiring diagrams, service manuals as well as air system diagrams. If you have not set up a quickserve account for your Cummins, I highly recommend you do so.



Our engine is rated at approximately 250 HP, so our plan for 350hp is doable with a set of 100hp injectors and no tuning. We sent the injectors out to our local turbo and injector shop for them to be resized. It appears that our VP44 pump, as well as the lift pump, were recently replaced. Great news for us! One great thing about buying a bus from a big school district is that you can be confident the buses were maintained. As a bonus, the buses aren’t necessarily going to auction because there’s something wrong with them; we learned from the helpful shop manager at the bus depot that most of the auction buses are just old. They just need to make room for new ones.


Our turbo is an HX35W and was in great shape. As a result, our plan is to run it and if the black smoke is bad with the upgraded 100HP injectors, we will swap it with something bigger.


Here you can see the two ECM connectors. Thanks to Quickserve, we have a great wiring diagram for the ECM connector as well as the 23 pin connector that is used for all the power, ground, and switched power connections. Because the School bus engine is modular, the wiring is simpler than it looks. In most cases the harness comes apart in big sections with bulkhead connectors as well as a lot of weather pak connections.

Our engine did have an exhaust leak on the rear cylinder, so we sent the manifold to the machine shop and had it surfaced. The bolt was just loose when we removed the manifold but better to be safe and have it surfaced than to risk an exhaust leak.
 

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We pulled the cylinder head and were very happy with what we found. No ridge, no discoloration and still a clear appearance of the crosshatch pattern on the cylinder walls.

We pulled a couple main bearing caps as well as the rod bearing caps and were again very happy with the condition.



We cleaned up the surface of the cylinder head and inspected all the valves. Finally, we cleaned up the block and got everything ready for new gaskets and head studs. The condition of the engine internals gave me a lot of confidence that this engine has a lot of life left and does not need a rebuild or machining at this time.




Now it was time for ARP head studs and new gaskets.



After everything was torqued up, we sprayed Cummins Beige and topped the engine off with a “Fummins” Valve cover from my friend at Quick Draw.


 

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Now that the engine is ready for install it was time to shift focus to the chassis and get it restored and ready for the fresh 24 Valve. We started by removing the bed and getting the rear chassis restored. You will also notice we bought new wheels and tires for Tom. I could not stand the old crusty wheels it had and the new wheels fit perfectly with the overall theme of the build colors.

After we pulled the bed it was time to clean the chassis and address the rust. Thankfully the rust was limited to surface rust so no significant repair was needed.




After a lot of work and wire wheels, plus some heavy pressure washing, we brushed on rust convertor and then topped it off with SEMS Rust shield in every possible crack and seam. We were very happy with the results.


Now that the rear chassis section was restored it was time to immobilize the truck and pull the cab and the old, tired 7.3L Powerstroke. This turned out to be difficult as almost every mount needed to be torched off. A new poly mount kit from Daystar is on the order list.





After the engine was removed, we moved the chassis so that it could be cleaned, degreased, rust scraped off, wire wheeled and painted with the SEMs rust shield just like the back half of the chassis.


Fast forward, after a ton of work, we have an amazing looking chassis that has all the rust converted stopped and will last for many years to come.

 

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Now that the chassis was restored and ready for the Cummins, it was time to mock up everything and build some mounts. We moved the chassis back over to the lift so that we can test fit the engine positions and build out mounts.




To start the fabrication of the getting the cummins mounted to the Superduty chassis we used 2010 and up Right hand Dodge Cummins engine mounts on both sides. Anchor Part number 3410 Then I measured and cut out some plates on the CNC plasma and test fit everything over and over to make sure I had all the clearance we needed. These engine mounts will be available for purchase on my website Adventure Vehicles NW showcases the vehicles and products of Expedition and Off Road Vehicle Enthusiasts. soon. The transmission was moved back approximately 2 inches; this allowed the use of a mechanical Gen 2 Dodge fan. We also cut out some of the front crossmember so that the high capacity oil pan from the bus could be used. More on engine placement later in the post.






Now that we have the engine mounts fabricated and all the clearances verified, it was time to blow the whole thing apart fishs weld everything and turn the corner and finally start assembling the chassis for good. Before we could do that, we needed to box the front crossmember we cut to have clearance for the large oil pan. This wouldn’t have been necessary if we had used an oil pan from a Dodge truck, but since more oil is better and the Ford crossmember had a huge hole in it to begin with, we decided to cut it out and box it in.



Then we had to touch up the paint.
While the chassis was empty we replaced all the brake lines with a SS set from Dorman. We also mocked up all the air system parts, rear power cables, as well as new Billstein shocks.
 

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Discussion Starter #5
As for mating the Cummins to the ZF6 6 speed transmission, we used the steel adapter plate from Wildhorse MFG as well as a crank spacer and a conversion clutch kit from South Bend. Lastly, we clearanced the block as well as the bellhousing on the transmission to allow the use of the Ford 6.4L Diesel Starter.



After a ton of work we were finally ready to set the engine and transmission back into the chassis and get our custom engine mounts bolted up.


Here are some better photos of the engine mounts we will be selling on our website. If this were a 12 valve, we would have needed offset adapters. This is because the 12 valve does not have the second set of mounting bolt holes in the block.


It was finally time to move the chassis back to the main shop where the Cab was patiently waiting.

Before we finalized the exhaust and installed the turbo, we built a wastegate lock out bar and tack welded the waste gate so that it would build as much boost as possible. Then we mounted up the turbo and finalized the exhaust with a simple 90 degree mandrel bend and a 3-4” transition.



Finally we were ready to set the body back on the chassis. Before we did that, though, we shot a walk-around video.
 

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Appreciate the detailed explanation in the video. Are you planning to develop conversion parts for the GM GMT800/820 trucks/SUVs?
 

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Currently there is not a big enough market for the GMT800 platform for me to justify the expense. That could change but as of now I do not have any plans to support that conversion.
 

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Do you really want to block off the turbo waste gate? You can put a valve in the air line that will allow you to adjust the boost limit. If you're going for 350 HP might want to consider a different turbo. The HE351cw found on 2005 Cummins has been a popular unit to use. It has an electronic boost regulator in the compressor housing but that can be replaced with an aftermarket part that makes the turbo fully manual. That turbo has an HX40 size compressor with a 9cc turbine housing instead of 12cc on the HX35. Boosts quick and has a much larger compressor to feed your bigger power. Main thing is you need at least a 4" exhaust system which was standard with that turbo.
 

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Do you really want to block off the turbo waste gate? You can put a valve in the air line that will allow you to adjust the boost limit. If you're going for 350 HP might want to consider a different turbo. The HE351cw found on 2005 Cummins has been a popular unit to use. It has an electronic boost regulator in the compressor housing but that can be replaced with an aftermarket part that makes the turbo fully manual. That turbo has an HX40 size compressor with a 9cc turbine housing instead of 12cc on the HX35. Boosts quick and has a much larger compressor to feed your bigger power. Main thing is you need at least a 4" exhaust system which was standard with that turbo.
Yup, the OP like most guys is thinking, if you make more boost, you must be making more power. lol
No idea about flow & choke point.
 
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@Nascarmark

Yes, we understand choke point and flow as well an how it relates to PSI. But if you only build 25PSI at 1800RPM with the waste gate and you could be building 35PSI at the same RPM you will have more forced into the engine at 35PSI of boost than you would at 25PSI. We installed 4" exhaust and have clean intercooler as well as good piping and head studs so keeping the waste gate does nothing for us. Regardless, this is not post to be debating flow and PSI characteristics of the stock turbo.

With the 100hp oversized injectors as well as 35 PSI of boost we still get some black smoke under load which we suspected might be the case when we were planning the build. A larger turbo is begin considered for phase 2 of the project. The owner just did not want to spend the money if a larger turbo was not needed so we decided to give the already paid for turbo a try.
 

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Ok, good that you know. Yes, the stock hx35 turbo is 7psi past it's efficiency at this point, so the extra 7psi psi is now only creating more heat, not flow. The extra psi is because of the restriction causing back pressure in this case.
Owner will need to step up to something like a SXE62/68/12 to go along with the 100hp inj's & power programmer that he will be running.
Nice build though.
 

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Discussion Starter #13
After market programmers are not an option because of the original industrial/school bus application. Cummins NW has confirmed we have all the updates as well as the highest HP in their words "allowable" fuel map for that SN engine. Frankly, I'm not a big fan of the aftermarket programmers anyway, I think if they are not used responsibly they sacrifice longevity for seat of the pants performance. I am a believer that the OEM Cummins engineers knew what they were doing.

Currently just from driving the truck with only the injector upgrades and a known too small of turbo it has significantly more power than the 7.3L powerstroke. In my opinion the power numbers that are advertised for these industrial engines are conservative granted I don't have any dyno numbers to back that up. Our goal was to be conservative with all the parts so that we don't lose any of the reliability. Currently The owner is all smiles and he has a lot more money to spend on Phase 2: interior, paint and bumpers. Thanks for all the comments.
 

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Well you can find a programmer for that 029 injection pump. They are out there, just not as common.
You must have some type of a boost fooler on that engine or it would defuel at 21psi.
 

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@Nascarmark

We are continuing to discover there are a lot differences in the Dodge ECM's and the Industrial school bus ECM's. I can't say with 100% certainty what the settings or criteria are for defueling on the industrial ECM. What I can say is that we are not defueling at 21PSI of boost. We hooked a boost gauge up in the school bus before we removed the engine and we were seeing nearly 30PSI so we felt comfortable with our plan of locking out the waste gate and installing the larger injectors. I can only speculate, but If you think about it, defueling an 84 passenger, 18000 LBS school bus at 21psi with an Allison is probably not what Cummins thought would be a good fit for that application. We consistently hit above 30PSI and have no "Codes" or "Alarms" or warning lights.

Again I'm speculating, and basing this on my personal experience, but comparing the school bus 24 Valve to the Dodge 24 valve, the Dodge trucks were heavily de-tuned I assume to save the rest of the drivetrain. That was not as much of a concern for a big Bus like # 425. Also correct me if I am wrong but the infamous "053" Block was never used in the industrial applications. In my opinion the school bus engine and engine controls are a lot more robust than what is found in the light duty truck versions.

There is not much information about the industrial ECM's or tuning them. If you have a source please pass it along. Harvesting these engines out of a retired school bus is a great option if you have the equipment to process it. The problem we ran into is there is just no aftermarket support for them. Not that there necessarily needs to be considering what great results we are seeing with very minor modifications. I might be changing my tune down the road if we start having issues with the VP44 pump but if that happens plan B is to perform a P-Pump swap.
 

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There is not much information about the industrial ECM's or tuning them. If you have a source please pass it along.
Maybe member jr2185 can help you. He did the tuning on Fxsu's ISB170.
 

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In the 99-16 Superduty chassis a 5.9 will usually sit best about 2 inches to the rear of where you have it sitting in that picture. I know sometimes guys get stuck on lining up the shifter in the hole or saving a few bucks on drivelines, but it's worth it to get it in the right spot.
 

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In the 99-16 Superduty chassis a 5.9 will usually sit best about 2 inches to the rear of where you have it sitting in that picture. I know sometimes guys get stuck on lining up the shifter in the hole or saving a few bucks on drivelines, but it's worth it to get it in the right spot.
We moved the transmission back two inches and adjusted the sifter hole as you reference. The photo you have is of a 12 valve which don't have the double set of mouting holes in the block. We used the rear mounting location on the 24 valve and that's why the mounts are farther back on the chassis. For the drivers side we had no choice but to use the rear mount location as the Air Compressor and PS pump would prevent the forward position.

If you keep the transmission in the stock Ford location to avoiding driveline mods then you have to run an electric fan. Moving everything to the rear and running a mechanical fan is the only way to go in my opinion which is how we have the engine positioned.
 

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I was looking at the block in relation to the crossmember. The fwd turbo drain is same location 12/24 valve. The drain hole is on the front edge of the crossmember in your picture, but 2in rearward in mine.

Those air compressors really complicate an install for sure.
 

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I was looking at the block in relation to the crossmember. The fwd turbo drain is same location 12/24 valve. The drain hole is on the front edge of the crossmember in your picture, but 2in rearward in mine.

Those air compressors really complicate an install for sure.
The 24 valves as well as the later 12 valves have two turbo oil drain locations options; front and rear. Ours is positioned in the rear. Take a look at the attached photo that shows both oil drains and the rear engine mount. I assure you our engine is positioned correctly and that the transmission has been moved back the 2" you speak of. You can see the re drilled holes in the frame for the transmission cross member in my video.

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