Diesel Geeks

Things to know if you want to know everything about the world of diesel performance

Published in the August 2010 Issue August 2010 Feature

turbine wheel

It's hard to measure the importance of building an engine right. If something goes wrong inside the cylinder, you run the risk of taking out turbocharger parts-like this turbine wheel-along with engine internals.

cut piston

When you hear the term "cut pistons," it refers to the lip around the bowl being machined off. The lip, which is on factory Duramax pistons, can create a hot spot and a melting point on the piston of a heavily-fueled engine.

turbocracked manifold

Early drop-in replacement upgrade Garrett turbos for Duramax engines had an extra bolt boss from the casting process. When the turbo is tightened down to the engine block, the boss would compress against the intake manifold and crack the manifold.

T3 vs. T4T3 vs. T4

Can you tell the difference between these two turbo pedestals just by looking at the first picture? How about in the second picture? The pedestal on the right is a T4; the one on the left is a T3. The up-pipe inlets are about the same, but the openings feeding the turbine housing are much larger on the T4.

LLY vs. LLB/LMM inlets

When GM updated the Duramax from the LLY to the LBZ one goal was to lower EGTs. Duramax engineers addressed the air intake side of things, including the turbo inlet (shown), the air intake runners and the intake bridge, along with a new air intake design. LLY owners can replace their turbo inlet (the smaller one in the picture) with an LBZ (or LMM) inlet and get noticeable improvements in EGT temps and throttle response.

stock clutch

Remember how great your truck ran with just a hot programmer installed? Yeah, your transmission doesn't feel so great now, does it? It doesn't take very much extra horsepower to overcome the holding strength of a stock transmission. The clutches and steels of the higher gears are the first to succumb to heat, but everything in your transmission will experience excessive wear.

Blocking the EGR on a 6.0L Power Stroke was a day-long process. Blocking the EGR on the 6.4L Power Stroke takes half an hour. Make sure you get the blocker plates that are slotted so that the bolts do not need to be removed completely. For the exhaust manifold blocker plate install, loosen the two bolts so that the heads are about 3/8-inch out. Then put a pry bar between the sensor bun and the top flange bolt and spread the flanges apart far enough to slip the EGR blocker plate into place.

cracked pistoncracked piston

One primary concern for any engine builder shooting for high horsepower is the strength of the core engine components. Horsepower at the wheels means stress in the cylinders. Factory rods will be the first component to fail usually (shrunk in this case), followed by piston failures.

stock vs. aFe's boost tubes

Some turbochargers designed for Duramax diesels sit a little taller in the valley than the stock charger, making the stock charge tube too short for a good fit. Strangely enough, the different bend of AFE's Boost Tube (which is designed for stock applications) works perfectly for turbos that sit higher than stock.

LLY vs. LBZ cp3

This is a stock LLY CP3 pump's fuel pressure regulator (left) and a modified LBZ CP3 pump's FPR. The LBZ FPR and pump can command higher rail pressures than the LLY pump. Modifying the FPR lets it send that much more fuel to the rails.

head studs

If you're installing head studs, the proper way to get a good seat and the correct torque is to tighten the studs and bolts to spec, warm up the engine, let it cool completely, loosen the bolts and studs, and re-torque to spec-repeating the process two or three times. But there is a trick. ARP sells something called Fastener Assembly Lubricant, which basically eliminates the friction between the fastener and the part it's threading into. You can get the correct and final torque spec the first time instead of after three or four re-torques.

compressor wheel damage

Stuffing a big compressor wheel into a small housing is a little like embezzling. You might get away with a little extra, but take too much and someone's going to notice quickly. In this case the shaft bearings blew the whistle, and the oversized wheel-spinning at 60,000 rpm or so-wobbled and hit the compressor housing. Oops.


How much nitrous is too much nitrous? When your pistons look like this, you need to back off just a touch.

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