I recently picked up a '96 Dodge 2500 with the 12v Cummins diesel engine (178k miles), and I am considering picking up a second diesel truck.  A good friend of mine has an '03 Dodge 2500 with 40k miles they are considering selling, which has the 24v Cummins diesel.  I am not sure if its the standard turbo, or the HO version.  Anyway, the '03 is an automatic, whereas my '96 is a 5-speed.  

Here are my questions.  Which is proving to be a more dependable engine, the 12v or 24v version?  Also, is one more easily modified than the other (with regards to increasing HP/torque numbers)?  Do the 24v engines offer better fuel economy, or are they pretty close to the same?  I know my '96 averages around 17-18mpg, but it is a 4wd model (the '03 is a 2wd).  Also, which would you rather have from a maintence standpoint?  Thanks!

The 12v engine is way more reliable than the 24v because the p7100 pump kicks total ass. The VP44 lift pump blows, its unreliable and unable to make any real power. If you want a good 24v go with a common rail instead. That being said, an aftermarket lift pump is not that expensive and the 24v heads flow much better than the 12v heads. Fuel economy should be similar if the trucks are set up the same, (bed length, both 4x4's, quad cabs, gears, etc.). The 47RE tranny needs help if the truck sees a tuner or much in the way of aftermarket parts. Again, not a deal breaker and something the aftermarket can take care of.

This.

I have seen several people actually do head stud kits and swap a 24v head onto a 12v block and run them. 24v head flows way better and is capable of tons of power. He is also correct with the lift pump sucking @ss. Albeit, if the price is good, that '03 could be a serious ride. If you want to sell either one, shoot me an IM.....

The '03 is a 4-door Laramie loaded model, with the 8' bed.  I believe I can get the truck for under $15k, possibly even cheaper.  I really don't need another truck, but 15k for a 4-door loaded diesel with 40k miles seems like a damn good deal.

FPW

The '03 is a common rail truck, not a 24 valve.  The 24 valve has the VP44 pump which is junk, the new CP3 pumps on the common rail Cummins seem to be pretty good.

Agreed...except for the part about the 47RE. Even if the truck wasn't tuned in any way that transmission literally blew chunks.

My dad has three 12v Cummins engines in three Dodges ('92, '93, '94). Only the 2nd gen '94 is worth much, truck wise. Those 1st gens were really, really awful pickups.

Here's his '94. It has the NV4500 5spd manual with lots of upgrades, including an exhaust brake and a 2spd "splitter."

I've got a 12 valve & love it.  Its stone-simple, reliable, and can be tuned up fairly easily for quite a bit of power.  An '03 should be a common rail engine, which fixes a lot of the reliability problems with the VP44 pump.  In my opinion, nothing can touch the reliability or ease of maintenance on the 12 valves.

Explain this to me, as I am really not understanding what you posted.  

He is right, the common rail was introduced in 2003. I sometimes get confused since Dodge introduced the HD trucks 1 year later than the redesigned Hemi 1/2 tons. Basically, the Common rail motor has fuel rails that are shared by the injectors and injected at a much higher pressure. The P7100 and VP44 trucks used individual fuel lines. The common rail motors are a bit quieter and make really good power with tons of aftermarket support.

PS. on your 12v cummins, remedy the KDP!!!! (Killer Dowel Pin) look it up.

I know, I've read a little about the KDP.  Haven't decided if I want to tackle it yet or not, though, considering the motor already has almost 180k miles on it.

That 2003 is an SO. I had one, and it sucked to tow with because of the auto. It was a 3500 SRW. Traded it in on a '04 6spd with the HO and it's a towing mofo.  But if you can get it for that cheap upgrade the tranny and enjoy.

ETA: Also get an Edge EZ or similar. I put one on the 2003 and it helped a lot unloaded, but towing still sucked. In 2003 they made the auto, 5spd and 6spd. Only the 6spd was an HO.

It always goes at 180,003 miles! - JK.

if you don't want to tackle tabbing the KDP, you can jig it. There's some folks on tdr1.com that have a nifty jig kit that allows you to drill, tap, and put a set screw in front of it provided it hasnt come out to far, in which case you will have to open the gear box and tab it. If you don't, it could lead to some serious catastrophic problems.

IMO, the 12v is more reliable, robust and simple. The 24v can be easily modded with a programmer, but you really need to start any mod program with gauges, then move to air and fuel delivery, exhaust, etc. With an upgraded air filter, a fuel plate, injectors, exhaust, valve springs, turbo boots, and some good gauges, your 12v will be a fire breathing monster.

the 24v also had a few years of problems relating to the block which was made in brazil, I think it cracks or something. it should have a "B" stamped in the side of the motor which will be on the drivers side. I'd stay away if the truck has that. Also the fuel pump(s) kinda suck. the vp44 is OK, but the weak link as I understand it is the transfer pump.

both are good trucks when the main issues are addressed.

Mine: 98 12v 4x4 quad cab longbed, auto. the 5 speeds had higher horsepower pumps in them, but I pretty much have the grail truck other than that.

I took care of the KPD when I bought my 1997 Ram with over 180k. For $60 in parts and a few hours of wrenching, it's criminally stupid to not do it.

I might be picking up a 99 tomorrow.  Also a 24v.

Any tips?

Damn, putting it like that makes me feel like an idiot for not doing it yet!!

Thanks for the explanation Archtaan.

This is correct.  I had an 03 SO also, and I liked it, but after riding in a friend's truck with the 6 speed(IIRC an 05 model) I realized I had basically no power.  It still ran good for the 95k miles I had it, and it got damn good fuel mileage.

03 will get better mileage than 04.5+ , but maybe not as good as your 12v.  The main problem with the CR engine is the injectors.  Stock filtration is not sufficient for fuel passing through at those pressures.  Filtration to 2 micron will fix that.  If a tip cracks they will spill fuel into the combustion chamber and it will take out the engine with it.  Other than that the CR system is good.  A programmer can get you a lot of power.  Auto tranny weakness will need addressed if you up the power.  Even on a stock truck a tranny upgrade will make it feel much stronger and a lot more fun to drive.

12 valve all the way.