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Old 09-25-2006
vonTrapp vonTrapp is offline
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Join Date: Nov 2003
Location: Calgary, AB, Canada Eh?
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Default 12 Valve: 1994 thru 1998 Mild Power Upgrades

Note: The following applies to 94-98 12 valve trucks equipped with the P7100 injection pump. 1st gen trucks will need their own separate writeup for the VE series injection pump, but steps 0 to 5 will still apply.

So, you have a second gen 12 valve, and you're looking for a little power increase? Alright, here's the short version of what you can do on a shoestring budget.


READ the forums, RESEARCH the following recommendations, and make up your OWN mind if upgrades are right for you. It's YOUR truck...you can leave it bone stock, or you can make a loud machine spewing black death all over the hiway. Your call.

For a diesel, the formula is simple. More fuel = more power = more heat. A new intake and exhaust will NOT give you HP gains, but they will help keep the Exhaust Gas Temps (EGT's) down to manageable levels (under 1200 deg F is safe).

In short, for a MILD power upgrade (up to a 100HP range):

0) KDP KDP KDP! Regardless if you are going to upgrade the truck or not, the Killer Dowel Pin MUST be addressed first. Trust us on this. Spend a day fixing it yourself now for less than $1.00, or ignore us and spend $1000 to $2000 having a shop fix the mess under your front timing cover at a later date.

1) Brakes, steering joints, suspension, tires, driveline u joints, filters, fuel line check. Seriously...get the rest of the truck in shape first. Suggested things to search are "starter contacts", "fuel heater pre screen", "death wobble".

2) BHAF Big Honkin Air Filter (NAPA 2790 for $60.00 or other suitable intake). Will help lower EGTs and let more air flow. The BHAF fits nicely, looks awesome, is CHEAP and works. The custom intakes from Scotty, AFE etc also work and look great, but cost a little more money.

3) Gut or remove the Catalytic Convertor (IF your state/provincial emmision laws permit it) The stock exhaust will work just fine for the time being. Many users end up straight piping the system by taking off the muffler. Some like the roaring, some don't. Again, it's your call. If you feel you must have a new exhaust, then pick a good quality 4" exhaust with a high flow muffler.

4) Gauges. Pyrometer, boost gauge at a minimum. Add a tranny temp gauge if running an automatic. IN MY MIND, GAUGES ARE REQUIRED for safe and meaningful fueling changes. If you aren't going to be bothered to put the gauges in, then don't read any further or modify the truck's fueling. You've been warned!

5) Timing: bump timing to 15-16.5 degrees. 15 or so if towing, 16 to 16.5 if running empty. Bump it up in 1/2 degree increments.

6A) Fuel Plate. Determine the correct fuel plate profile to put in, depending on your preferances, needs, transmission and fuel pump. A #10 plate is a very common first plate. MAKE SURE YOU UNDERSTAND THE IMPACT ADDITIONAL FUEL MAY HAVE ON YOUR CLUTCH OR TORQUE CONVERTOR.

6B) GSK. A 3000rpm governor spring kit is an excellent add on.

6C) AFC spring kit.

Total mod cost here is between $300 and $400 total...probably less. On a difficulty scale for the average DIY'er, I'd rate the upgrades at 5/10. HP gains will vary, depending on how the plate is positioned and the profile being run, but I don't think 70HP - 100HP is an unreasonable expectation. Actually, HP isn't really where you will feel the change. It's going to be in the torque department, and you're going to love it! Put your foot down, and the motor will just keep on pulling and pulling.


If you have a 12 valve with more than 300,000 miles on the engine, start planning to replace the cylinder head, and the injectors. They both are getting pretty tired around 400,000 miles, and neither is difficult to change out. Injectors can be pop tested to see if they are worn out. A leak down test will tell you how the engine is doing.

Don't worry about the bottom end too much. At 15,000 hours, I tore down our FL70's 5.9L 12 valve, and in spite of all the abuse that engine suffered, you could still see some crosshatch marks on the cylinder walls. Unless the motor has been dusted (run with no air filter in dirty conditions for an extended period) the bottom end should be just fine.

Myth: Running a truck WITHOUT a fuel plate is a cheap way of getting huge HP gains.

Wrong. It's a cheap way to destroy an otherwise indestructable injection pump. We've seen this one a few times, where some "mechanic" claims you'll get huge HP increases by pulling the fuel plate out of the fuel pump. Well, you will get gains...for awhile. There is a technical explanation as to why this is a BAD idea, but for now, just trust us on the matter. Buy (or make) a fuel plate, and run one in the pump.
-2004.5 2500 5.9L QC LB 4x4, Silver, Auto, 3.73 LS, Smarty, Gauges, Alum Slip Tank, Stacks, Dyno'd 385HP 850 ft/lbs and other stuff
-2007 Freightliner M2-106, as below but 300HP, Airbrakes
-2007 Freightliner M2-106, Mercedes MB900 280 HP 800 Ftlbs, Real Jake plus Exhaust Brake, Allison 3000 6 Spd Auto, Espar Heater, 16K Stellar Hooklift
-2005 International 4300 240 HP Allison 2500
-2007 Durango 4x4
-2008 Harley FLHTC

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