Allis 301 mods for pickup truck

My brother, my dad, and me have duramax’s and haven’t had too bad of luck.
Mine is a 2004 LB7 (just got it earlier this year) as a non runner (it did run the day before I went to look/ test drive it) and put around 2k-3k into it (failed computer and injector) with a full service and waterpump. Now it needs a power steering pump.
I thought about finding an old 3/4 ton pickup and putting a Allis Chalmers 426 in it but I really like my duramax now.

Back in 1983 I put a 433I from F2 in a 72 Chevy C10. Used a combine flywheel, Ford pressure plate and clutch will bolt right to it, had to make adapter for pilot brg. Ran injection pump like it was set for combine. It had power like a 292 gas engine. used Ford overdrive trans out of F150 with 300 inline 6. In 1984 drove to west coast and back with 10 ft cabover camper, could only run in 3rd, direct gear. pedal to the medal 2450 rpm and 58 mph getting 15.8 mpg. Ther were pictures on here at one time. I called it my "Allisfordolet" truck.

Hate on my 2007 Ram all you want, but it’s given me 19 years of trouble free service. Yep, it’s got a Cummins heart but the rest of the truck has been rock solid for 154k miles. A lot of those miles the truck has had a trailer of some type or 5th wheel camper behind it. I bought it new to pull loads that I needed it to and it has served me well. My XT looks quite nice on my gooseneck going down the road behind it.

Still has the original trans in it. I installed a high capacity oil pan on it. I did replace the AC unit 2 years ago, forgot about that. It receives regular maintenance and I only use OEM filters and oil.

Allis Silver Pony wrote: Heyfound your posts. Hope the project is coming along well. I have a similar one. Oh and the critism never ends does it. Just go with the Cummins, its so much easier...blah blah blah. I get it though. So anyways, let me tell you about my project so far. I have been away from it for a while. But Im slowly working on it. Allis chalmers 301 Ported head Tuned fuel pump 198cc Allison 1000 transmission 2007.5 GMC 3500 The engine is completely apart and has been cleaned. I gave it a acid bath. I was very impressed with how it cleaned up. I painted the block and head red. I know honestly I could only get my hands on red. It looks sharp. New injectors to match the pump flow. I'm going to build a new manifold and working with a shop to put twin turbos on. This will allow me to capture a powerband down low and up top. I ported the head. And its at a shop currently getting new valve seats and planed. The machist ordered aftermarket valve springs. The stock springs were somewhere around 40lbs closed and 80lbs open. Given that its going to have 35psi boost. I needed something closer to 100 lbs closed and 200lbs opened. Anxious to see what he ordered. Its a project I want to focus on, but its gona take some time. Lets get to the allis transmission. Obviously its the transmission that came with the truck. And the transfer case. The transmission is an excellent one. Going to beef it up a little bit. Since it has plenty of miles on it anyways. Lockup converter and its currently a 5 speed. Its possible to go from 5 to 6 on these. I plan to go to the 6. This is exciting and definitely love making progress when I can. Critics will harass us to no end and it makes the end all that more valuable. Trust me digging into this just doeshave the suuport on literature and aftermarket that cummins does. And yeah if we were to take a 5.9 and tune it up we could and get alot more potential out of it. A P7100 on a 5.9 has somewhere around 800cc fuel delivery capability. But thats insane. This DB is tuned to 198cc. Im not really sure off the top of my head what a stock one is for a 7020 tractor. But its significantly more cc. Every part is pretty expensive. The cooling for this bad boy is gona be something. Gona put a intercooler and large oil cooler. Anyways your idea of what I have heard is solid.

A 2003 ZF6 has a high gear ratio of 0.72:1. A stock 1984 K20 could have a 3,42, 3.73, or 4.10 axle ratio. It’s tire size could be 235/85R16. So using those numbers, engine rpms of 2200 & 2400 should yield the following;
84.29 - 91.95 mph @ 3.42 gears,
77.29 - 84.31 mph @ 3.73 gears,
70.31 - 76.7 mph @ 4.10 gears.

Edited by AC7060IL - 19 Jul 2026 at 9:18am

Apears we have similar goals in mind with our builds. I cant answer your questions... if they were directed to me.. Im new to the forum. I haven't put hands on the project for a while. Im hoping to get back to it around September. I also need a damper, which I believe you were researching. I definitely would like to know if you figured out the best course. What are you doing to acheive 300 hp? So far I invested in a a modified fuel injection pump and new injectors. My BAR pressure is set at 262. I will also build a manifold and put compound turbos on to give me a broad powerband. Its going to be a while before the project is completed. I know that ZF6 will be nice. My allison 1000 is gona be much more complicated and its automatic. It might loose alot of the fun factor... but I like its highway manners. I believe you said you would be at 2200 rpm on the highway.. with my Allison I should be closer to 1940 in 5th and 1620 in 6th. 5th gear is .71 and 6th is .61 on my Allison.

Your ZF6 6th gear is .72, 2,120 if you had my 3.73 and tires going 75. I do notice that transmission would be nice if your pulling heavy. I pursued it and honestly didn't want to change the driveline and get a new transfercase and so on. I had a 6 speed Cummings and loved it. Im sure your ahead of me when thinking about the gears. It is fun to throw different combinations and see what the results will be. Im basically building a rig that will have an insulated box on my ranch hand bed. I will utilize it like an open camper concept that I can put on and remove when needed. I will also pull a small trailer with a side by side on it. I have another beast I use to pull a gooseneck around with a backhoe or farm tractor. I may pull the gooseneck from time to time with this build though. Im researching the different radiator/intercooler kits available for a duramax.I will eventually purchase one and most likely have to move it forward alot.... I would like to keep the manual fan. Are you keeping the manual fan? You have a larger engine bay and gour also adapting the transmission brackets. Im anxious to get my hands back on the engine and figure all this out. I really dont eant to go to electric fans. But I will see what I will need to do. For the oil cooler, I was researching upgrades on the market for modern trucks. I haven't really compared the cooling capacity from modern trucks to whats available stock wise for the allis 301. However its pretty significant Im assuming. Of course the cost as well. You spoke about pistons. I also researched increasing the bore. My conclusion was to stick with the stock.I was also going to have forged pistons built. That is expensive. It would of costed at least 3400. However forged pistons, often do not have the top ring that cleans the bore. And the conclusion was that the engine would actually last longer with a stock rebuild kit. Given the build was reasonable. That can be negotiable what that actually is. But south of 400 hp, is what Im thinking. Ive basically concluded that based off cummins builds. There is just alot more info on them. So Im going with cast pistons. And Im shifting my budget to the cooling side of things. Im not really going after as much hp as I can get. I do want to find it where I can. Right now Ive read the stock head flows around 110. That was on this forum.. I ported the head myself... and surprisingly the machinist thinks it will pass.. yeah I was nervous about that one. Curious what the flow increased to. I haven't found anyone else posting bech test results. Apparently tractor pull guys have tuned them up significantly, but them dudes are not posting about it from what I can find. I have owned alot of trucks and a 2001 powerstroke I had plenty of power. Which was around 250hp and 500 lb of torque. At the end of the day, if I acheive that it will be a success. Im highly confident it will be much higher than that.

There is more than one cylinder head casting from 1964 until 1985.  The oldest heads had a "crescent" milled into the intake valve opening trying to start the incoming air swirling around the O.D. of the cylinder sleeve. Pretty sure by the late 1960's they quit doing that. So, they must have felt turbocharger boost was starting the air turbulence good enough. I know IH 400 series engines had a high-swirl cylinder head like on the D-414/436 engines and it was different than a DT-414/436 cylinder head.

Edited by DrAllis - 24 Jul 2026 at 10:42pm