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post #1 of (permalink) Old 02-11-2008, 01:38 AM Thread Starter
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12 valve performance overview

This is a revised overview of parts and modifications for the 94-98 12 valve 5.9 liter Cummins motors with the Bosch P7100 fuel pump. For advice as to which upgrade to get and what to do, just post a question. Someone will point you in the right direction.

Lets start with the Achilles Heel of the 12v motor: the Killer Dowel Pin or KDP. It is used in the assembly process of the timing cover, and is simply pressed in. It will eventually fall out and can wreak havoc on your timing gears. Failing that, it will simply drop down into your oil pan in which case your one lucky person. You can fix this several ways: have your dealer do it, do it yourself with a bolt and a fender washer that's been modified (I think there's a how-to in the Tech section), buy a kit from your Cummins Dealer, or buy a kit from a performance site.

The first thing to go about getting power is getting gauges to monitor your engine. A Pyrometer and Boost gauge are necessary for all rigs, while a tranny temp gauge is advised on automatics. You should never let the Pyro exceed 1250* for very long, or you will melt something. With stock headstuds and gaskets, you should not exceed 45 lbs of boost or you will blow a head. You may also want a fuel pressure gauge. They aren't necessary, but they do help in diagnosing some of the problems that come up concerning the fuel system. If you have an auto, you will want to at least get a new torque converter and valve body, if not buy a fully built trans. Suncoast and Goerend are two good brands for strong auto tranny's. If you have a manual, you will need a clutch like one from Southbend or Valair.

Next will be the mods to the pump itself. You will want to grind the fuel plate, or maybe just buy one from a performance shop. Dynomite Diesel Performance www.dynomitediesel.com Banks www.bankspower.com and TST www.tstproducts.com all make aftermarket fuel plates. If you grind your own, these are the instructions: https://www.thedieselgarage.com/forum...ead.php?t=6815 If you decide to change the plate, just replace it instead of grinding it with the same process otherwise.

Another good mod is the governor springs. WARNING: IF YOU RUN THE ENGINE AT MORE THAN 3200 RPM YOU RUN THE RISK OF FLOATING VALVES. You can avoid this by purchasing a set of 60 psi valve springs. The stock setting allows the engine to rev to 2750 RPM, but they start to limit power at 2250 RPM or so. You can tighten down the stock springs 3-4 clicks, or shim the springs as described here: https://www.thedieselgarage.com/forum...ad.php?t=15496 for cheap and get fuel to 3000 with revs to 3300. There are also 3K, 4K, and 5K Governor Spring Kits for sale by performance shops too. A 3K will fuel to 3000 and rev to 3400. A 4K will fuel to 4000 RPM and rev over that. 5K GSK's are for pullers and require extreme modifications to the engine to not be damaged. If you feel like you want the 4K GSK, but don't have the valve springs yet, buy a 4K and leave the smallest spring out. It will run like a 3K. You can use the instructions for shimming the springs to change them.

Another item that could use modification on the pump is the Delivery Valves. Stock DV's on 96-98 autos and 94-95 rigs are 131's. Stock on 96-98 rigs are 181's. There are also 191's, and there has been discussions about using 131/181 hybrids, although the gains are small. Beyond that, there are 022's, 024's, full cuts and lazer cuts. There are some more, but these are the ones you will usually find on most rigs. Lazer cuts don't have shoulder material like the other ones, so they turn off the fuel gradually rather than instantly like most DV's. They smoke more and run hotter, not to mention the loss in economy. DDP and some other performance manufacturers also have their own style of DV's.

Staying on the pump, next will be the Air/Fuel Control or AFC. This unit is set up to give you so much fuel per pound of boost. The Starwheel is located under a hex plug on top of the AFC unit. Tightening it increases the amount of boost to get a certain amount of fuel. Loosening it will give you more power sooner, but at the cost of smoke (if you think of that as a cost). The arm that hangs down can be modified by grinding the foot of it flat. You can also purchase different springs and washers to put in the AFC for adjustments to fueling potential.

After you've modified the Fuel Plate and AFC, you may want to get a 2095 Rack Plug aka Mack Plug. The 2095 plug has a 2mm deeper well than the 2000, allowing the rack to travel further increasing power. You can get one at your Cummins dealer for about $15. They will provide a greater increase in horsepower if you already have more power to begin with. 500hp motors will gain about 20-30hp, while 300hp motors will gain only 10-15hp. Again, this only works if you have an aggresive plate and a modified AFC arm.

One last mod to the pump is timing. Stock timing is 12.5 in 94-95's, 14 in 96-98's. You can adjust it to 16.5 with the stock head gasket. You could go up to 20 with aftermarket headgaskets. Advancing the timing allows better economy and more power, as well as where in the RPM range you get the most power.

Next we'll talk about injectors. Stock 94-95 autos are 160hp. 94-95 manuals are 175hp. 96-98 autos are 180hp. 96-98 manuals are 215hp. There are also 300, 330, and 370 hp injectors from Bosch. But there are lots of choices. Bosch 370's are designed for marine applications and don't have the correct spray pattern. Running them won't hurt your motor, but they haze at idle, smoke a lot, and run warmer than comparable size injectors of other brands. New Era www.neweradiesel.com makes correct spray 370's as well as 435 hp injectors. DDP stage 3's are like 370's, and DDP 4's are like 435's. To get the full horsepower out of 435 injectors, you will need more air. If you add too much fuel without more air, you drown out the fire.

Once you get the pump going and some bigger injectors, you may find that your fuel system can't keep up with the demands. The stock lift pump will only take you to about 500-550hp. One of the more popular options is to purchase a Fuel/Air Separation System or FASS. FASS pumps have higher gallons per hour rating, and they ensure that no air is sneaking into the system through the fuel.

Next on the popular mods are turbos. High Tech Turbo www.htturbo.com Holset www.holset.co.uk Banks and many others make turbos. Stock turbos are Hx35's, but some 94's may have the H1C turbo off of the 89-93 models. For simple adjustments, you can adjust the wastegate for more boost or add a boost elbow or manual boost controller. A boost elbow delays the pressure getting to the wastegate, allowing more boost to build before it opens. A boost controller is a spring loaded valve that can be adjusted to stay shut until a certain psi is made which then lets the pressure go to the wastegate. These are basic mods to a stock turbo.
New turbos are rated by compressor size and exhaust housing size. The stock is called a 54/12 as in 54mm compressor and 12cm exhaust. A common upgrade, the Schwitzer S300, is a 57/14 I believe. Some of the bigger ones are 64/14's, clear up to 72/16's.

To make it breathe, you will want to upgrade your intake and exhaust. You can simply straight pipe it by cutting out the cat and muffler and inserting a piece of pipe. Most people upgrade to a 4" turbo back system. Banks, Flow-Pro, and Aero-Turbine all make low restriction exhaust systems with flow-though mufflers. If you have to have a cat and muffler, you can take them off, cut a hole in the top and gut the insides. Then weld it back in place and put it back in with the weld on top. Some people also go to a 5" system, but things start getting tight. It is also possible to run stacks, which you can get from www.blackclouddiesel.com They also have lots of other performance parts. For intake, don't waste money on a cold air kit. Buy a Big Honking Air Filter, or BHAF. Wix, Napa, and many many more companies all have them in parts #'s. They flow about 3 times the air of a stock box. You will also want to get an Outerwears prefilter for them www.outerwears.com For the big boys, you may want a bigger intercooler but it's not necessary until 550+ horses.

One last thing if your really after the high horsepower is having the pump bench flowed. As far as bench flowing, the shop will hook it up to an electric motor to spin the pump. The "injector lines" run to measuring cups so they can see how much is going throught the pump. Then to increase it, they swap DV's, bore out the fuel passages, change the cam profile, change the plungers, adjusting port closure time, and modify some other stuff until they get the flow rate you want. Most of what came up on Google was places to buy bench flowed P7100's or people talking about it on other forums. This is the most accurate info I could gather, but don't take it as Gospel.

This is the bulk of what you will do for more horsepower on a 94-98 12 valve motor. If you have any more questions, make a post.


1995 Dodge 2500
THE ENGINE: 12v Cummins, the free stuff, 215 Injectors, GSK, boost turned up, 4" strait pipe, BHAF, Turbo Silencer MIA
THE DRIVETRAIN: 13" Luk HD Thermometallic clutch, 5 Speed, 4X4

1998 Dodge 3500 "The Shop That Goes"
THE ENGINE: 24v Cummins, Edge Comp, 4" Flow-Pro, BD exhaust brake, Farmhand Intake
THE DRIVETRAIN: 5 Speed, 4X4 dually, flatbed, and lots of tool boxes and 250 gal fuel tank

Singles Club #71, Outlaw #4
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