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Old 10-17-2008, 08:26 PM   #1
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Re: - Diesel engine questions -

You cant run a diesel too lean.
You can swap parts around on a turbo, or swap out the turbo for more power & air. It's not like a gas engine in that respect, you cant just crank up turbo boost to get more power. In a turbodiesel, it's very simple: more fuel = more power. When you dump more fuel in, the turbo will spool faster, and quicker because of the added heat & load. In a nutshell, you will have to mess with the pump to get more power. If you run too much boost, you can run into surge, where the turbo is trying to cram too much air in & the engine cant flow in enuf. There's a few good turbo books out there to understand mapping and the A/R ratio. Last I remember, the air-fuel ratio on a diesel is around 17:1.
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Old 10-17-2008, 08:47 PM   #2
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Re: - Diesel engine questions -

You don't need an AFR gauge. You, my friend, need an EGT gauge. A rich mixture in a diesel will cause a lot of afterburning in the manifold pushing the EGT's higher and potentially melting down the turbo. Similarly, high load or high RPM's are capable of causing the same problem.

I don't think you're going to get more power by turning up the boost more. Simply put, power is made by burning fuel. Now if you run higher boost the reference signal to the IP should compensate for a slight increase, but you're going to start running lean at some point. All the boost in the world won't do you any good without the fuel to match it. So...the general rule is fuel first, turbo second. You up the fuel until EGT's get uncontrollable, add more boost, rinse, and repeat until something far more expensive and metallic becomes the weak link.

I would suggest getting an EGT and tranny temp gauge no matter what you do if you're planning on modifying the engine at all. Heck, it's not a bad thing to have even if you leave everything stock.
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Old 10-17-2008, 09:04 PM   #3
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Re: - Diesel engine questions -

Well said sirrr, you made better sense of my ramblings.
On your 5.9, a good improvement is to get a smaller exhaust housing on the turbo. The rotary equipped trucks had really big exhaust housings, and the turbo seems pretty lazy. A good place to find a new one is:
http://www.tstproducts.com/16cmturbinehousing.aspx
There are other places to find them, but this has the added info description.
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Old 10-18-2008, 11:07 AM   #4
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Re: - Diesel engine questions -

Something relatively easy would be swapping out the injectors. For a little increase, the 215hp ones would be good, then a little more would be a 300hp injector set, and of course aftermarket ones if that's not enuf. That's the way to get a good gain in power without touching the pump. There's lots of aftermarket support out there for the engine you have. Plus, it's a lot of expense to replace the engine just to gain that little amount(but the 03 & up 5.9s do burn cleaner). The fuel and rpm adjustments wont hurt the pump a bit. Cummins had the 5.9 rated up to 370hp in marine trim.
Str8 piping does help spoolup, and so will fixing the other bends & kinks in the intake. All the back pressure the engine needs is used to drive the turbo. The best result of going non-muffled is to keep EGT down, the noise at the tail pipe is the added bonus . Double check the little line going from the intake manifold to the top/ rear of the pump, many times that line can get worn thru, and not let the pump work to full power. It's a boost reference signal to the AFC diaphram. You should be seeing about 20-22 pounds of boost.
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Old 10-18-2008, 07:36 PM   #5
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Re: - Diesel engine questions -

Yep, basically just pressurize the intake a little & check with soapy water. Normally you wont hear any hiss, unless it's a big leak.
The bigger injector is only flowing a smidge more fuel than your stock ones. That pump has the capability for 600+hp, so it'll carry what you're doing. If you go too big(like the marine 370s or bigger), it can cause a stumble from the sharp pressure drop.
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