Cummins is one of the best-known diesel
engine manufacturers in the world and most automotive enthusiasts know them
for their use in Dodge trucks. The 5.9 Cummins was partially responsible for
the success of diesel engines in pickup trucks and over the years there were a
few different versions of it. Today we're going to talk about 12 valve, 24 valve
and find out which one is better. Before we start this video I would like to
clarify that there are a handful of different versions of the 12 valve and
the 24 valve and for this video we are going to be talking about the 1994 to
1998 12 valve in the 1998 and a half to 2002 24 valve. We're going to ignore the
earlier 12 valve engines and we're going to ignore the later 24 valve engines. For
those who aren't intimately familiar with the 5,9 Cummins let's have a brief
history lesson to get you up to speed. Dodge began offering the 5.9 Cummins engine in their Ram trucks back in 1989. It might have been used in the
outdated Dodge AD Chassis which wasn't selling very well but the addition of
the Cummins engine really reinvigorated sales and put dodge back on the map for
their trucks. Eventually, the competition did catch up and in 1994 dodge had to
revise the comments for more power and to meet stricter emission standards. The
5.9L went pretty much unchanged again all the way up until 1998 and a
half when they introduced a 24 valve version. Eventually the 24 valve was no
longer able to keep up with emission standards and 5.9 was completely
replaced by the 6.7 in 2007. Like I said earlier there are a handful of different
versions of each engine but the versions we're gonna be talking about today are
arguably the most popular. Both engines are very similar and they share the same
bore, stroke, block, architect, and a whole bunch of stuff, but there are a lot of
notable differences. Most of the changes from the 12 valve to the 24 valve revolve
around the fueling system, the valve train, the turbocharger and the
electronics. With that being said, the 12 valve is most famous for its lack of
electronics. It uses a fully mechanical fuel system and does not need any
electronics to run. All the timing is done mechanically. A fully mechanical
fuel system does have its pros and cons with the biggest pro being that it's
super reliable of the specific 12 valve that we're talking about in this video
uses the Bosche P7100 pump also known as the P pump. The P-pump was initially
installed on the 5.9 Cummins with the goal of reducing emissions
output by cutting down on particulate matter produced in cylinder, but it
didn't take long for people to realize that it also had a lot of power benefits.
While the VE-pump on earlier Cummins engines only had one plunger, the P-pump
had six plungers - one for each cylinder. Nearly every internal component of the
p-pump can be modified or upgraded in some way to make the pump flow even more than it already does. With some basic modifications done to the P-Pump, it
increases flow massively and it's able to supply a huge amount of fuel to the 5.9. The 24 valve engine, on the other hand, uses an electronic fuel system so it's
no longer fully mechanical and it relies on a computer to tell it when to fire
the fuel and how much fuel to fire. There are a lot of benefits of using an
electronically controlled injection systems such as better emissions output
and better air/fuel ratios but a lot of Cummins owners do prefer the earlier
p-pump models strictly for reliability sake. The nice thing about the 24 valves
electronically controlled injection system is the fact that you can just
plug a tuner in it to add more power where's the 12 valve you have to modify
something in the pump or upgrade something in the pump the 24 valve you
can just stick a tuner in and crank up the power by cranking up the fueling. Another major change between these two engines is the valve trains. As their
names would suggest the 12 valve is a 12 valve engine and the 24 valve is a 24
valve engine. The four valve head on the 24 valve massively improves air flow and
coolant flow in stock form. The 24 valve head featured 60 pound per inch valve
springs, reshaped exhaust ports for improved exhaust flow, and 6 12mm
head bolts per cylinder. A one-piece valve cover gasket replaced the six
individual valve cover gaskets found on the 12 valve. Interestingly enough even
though the 24 valve head flows more in stock form a lot of sled pullers and
drag racers actually prefer the 12 valve head. With some modifications done to the 12 valve heads such as milling off the
intake shelf and opening up the intake and exhaust ports, as well as a nice
valve job, it actually flows more than 24 valve head and its been proven to be
very reliable and produce a lot of power by drag racers and sled pullers. It
should be noted that there are some other minor changes between these two
cylinder heads such as valve springs, camshafts other small details like that. Both of these engines use the Holset HX35W turbocharger, better known as the HX35. It should be noted that the 2001 and 2002 ISB 24-Valve engines with the automatic
transmission actually used the HX35Y, which is a smaller version of the HX35W and doesn't flow as much air but it should spool up a little bit quicker.
The HX35 has been proven to be a very reliable turbocharger even when it's
pushing twice as much boost pressure as it was initially intended for. Underneath
the cylinder head you'll find that these engines are surprisingly similar. The
pistons are different because they have to be revised differently for the
different injection systems, but they are fairly similar as far as strength. Underneath the pistons you'll find that both of these engines use the same
forged I-beam connecting rods which have been proven to withstand around 800
wheel horsepower upwards of a thousand wheel horsepower with some very light
modifications done to the connecting rods. Unfortunately, every engine does
have its flaws and the 12 and 24 valve are no exception to this rule. The
biggest problem on the 12 valve is known as the killer dowel pin. Now this is a
small pin pressed into the front of the engine during assembly to help align the
front timing cover. Over time this pin can become dislodged from engine
vibrations and if it does it can drop down into the timing gears and
completely blow off the whole timing system. Now if you get lucky the pin
won't actually end up hitting the gears but it will end up popping out over time,
just something to look for on 12 valve engines. Dodge later revised this issue
with the 5.9 For the 24 valve, the biggest problem is the number 53 block
this affects approximately a hundred thousand units which were cast with
slightly thinner jacket walls which can lead to cracking right below the freeze
plugs later down the line. These blocks are easily identifiable by
the large 53 printed on the side of the block near the front. Like I said, these blocks are not guaranteed to crack but it was a big enough problem that Dodge ended up
replacing a lot of these blocks under warranty. Both of these engines have
massive potential whether you want to do drag racing, sled pulling, towing or just
daily driving especially if you were to add a larger turbocharger these engines
can produce huge amounts of power huge amounts of torque very reliably. Deciding
which one is better really depends on what
value most. If you want a super reliable million mile P-pump that's never gonna
break on you with that mechanical injection system then the earlier
12-valve engine is probably the better way to go, but if you want the ease of
just a nice easy daily driver that you can stick a tuner into and just go the
24-valve might be the better engine for you. For those who want to go really
fast and make huge power, the 12v is probably the better engine. The
twenty-four valve might not be as reliable as the twelve valve but it's
still a very reliable engine and will last you a long time. Other than what
we've discussed that's pretty much all the main differences between the twelve
valve and the 24 valve. I want to know down in the comments what you guys think
do you think the twelve valve is better are the 24 valve let me know down below
let's have a little argument be sure to hit that thumbs up and subscribe, and I will see you guys in the next video.
