Extreme Engine Tech: Jim Wolf Technology’s Turbo Nissan QR25DE Powerhouse Part 2

Extreme Engine Tech: Jim Wolf Technology’s Turbo Nissan QR25DE Powerhouse Part 2

By Mike Kojima

When we last left off on our QR25DE project, Jim Wolf Technology was well on the development path for our motor with new rods, pistons and the removal of the balance shafts.  JWT still had a few more tricks up their sleeves to help the motor make more power and to improve its reliability that we will get into in this installment.

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This groove leads to additional holes in the main bearing to give the rod bearings and crankshaft a more continuous supply of oil.  The bearing has been polished and WPC treated as well.

QR25’s are known to have problems with spinning rod bearings.  The rod bearings are on the small side in diameter and width and don’t have much surface area to bear load and to support full hydrodynamic lubrication.  JWT did several things to improve this situation and hopefully cure the problems.

The rod bearings were polished and WPC treated.  Tests show that WPC treatment can increase the bearing load capacity by as much as 25%.

First off as discussed in our last installment, JWT eliminated the balance shafts.  This helps ensure that the oil pump gets only unaerated liquid oil instead of foam.  Cutting off the balance shafts’ oil supply means that there is more oil available to be fed to the rod and main bearings.  Next JWT modified the oil passages feeding the main bearings.  As the rod bearings are fed via passages in the crank from the main bearings, oil flow from the main bearings is critical.  In stock form, oil is fed from a single hole in the main bearing to the hole in the crank that feeds the rod bearing. We also used the late model rod bearings.  The quality of the rod bearings was upgraded after a rash of failures of stock motors under warranty.

These grooves in the main saddles help feed those additional holes in the main bearing over more degrees of crank rotation.  This gives the rod bearings much more oil.

JWT machined a groove in the main bearing saddle in the block and drilled additional feed holes in the main bearing so the rod bearing can have an uninterrupted flow of oil to it for nearly 360 degrees of crank rotation. Next the rod bearing feed hole in the crank was chamfered and tear dropped.  This helps ensure that oil can find its way into the hole instead of getting squeezed out of the sides of the main bearing.  Hopefully these mods will cure the QR’s penchant for destroying its rod bearings.