Extreme Engine Tech: Jim Wolf Technology's Turbo Nissan QR25DE Powerhouse Part 1

The balance shaft assembly is found in the bottom of the oil pan submerged in oil.  It is the weakest link in the chain when the QR25DE is modified.  On 2007 and later QR25DE's, the balance shafts were deleted.

One of the first issues that JWT addressed in our motor is the problems of seizing balance shafts.  Balance shafts work to cancel out a 4 cylinder engines inherent up and down shaking moments and spin at twice the crank rpm.  This means that at 6100 rpm the shafts are zinging at 12200 rpm, it’s a small wonder that they have problems with seizing in their housings. If you raise the rev limit much past the embarrassingly low stock limit of 6100 rpm, the balance shafts seize in their bores creating a chain of events that destroys the engine.  On the QR, the balance shafts are the first failure point.

JWT also felt that the balance shafts helped to contribute to some of the QR25's other problems, excess oil consumption and bearing failure. The balance shafts are submerged in the oil pan and when spinning at 12,000+ rpm they churn the oil to a frothy mixture of oil and air.  This aerated oil, if ingested by the oil pump can cause bearing failures.  The churning balance shafts can also fling oil around inside the block contributing to excess windage and increased oil consumption.

JWT balance shaft eliminator kit removes the problem and also features a pan baffle and windage tray to help control oiling better as well.

JWT removed the balance shaft assembly to address these problems.  On the QR the balance shafts are chain driven from the crank and contained in a separate assembly bolted to the main caps.  JWT used their balance shaft removal kit which has spacers for the main cap bolts, plugs for the oil passages and instructions on how to remove the drive chain for the shafts.  The kit also comes with a windage tray to help speed the return of oil off the crank and free up some power caused by the crank spinning in a cloud of oil.  The kit also includes a pan baffle to help ensure that the oil pump can still be submerged in oil even under hard cornering.  The total oil capacity is increased by a quart as the balance shaft assembly is submerged in oil and its removal makes room for more oil.  Eliminating the balance shafts and the oil demand from their journal bearings increases oil pressure and makes more oil available for the main and rod bearings. The balance shaft removal kit doesn’t seem to cause more perceptible vibration and frees up an additional 8-10 wheel hp.

When compared to the beefy SR20 crank, it is easy to see that the QR totally lacks any overlap of the rod and main bearing journals.  Lack of overlap makes for a much weaker crank.

Nissan probably deemed the balance shafts necessary because they used a lightweight crankshaft with only 4 counterweights probably in an effort to reduce reciprocating weight and windage losses. Unfortunately the crankshaft is weak with no journal overlap and not enough bearing area to support higher loads and revs.  The crankshaft has proven to be failure prone in the RTR World Challenge racer.  JWT addressed this problem by using a 2006 and later crankshaft.  The 2007+ QR crank is from the later model B16 Spec-V QR25DE variant. This engine has a 7000 rpm redline.  This is how the QR25DE should have been from the launch.  The late model engine has a fully counterweighted crankshaft with generous fillets for additional durability.  JWT Deburred and balanced the late model crank , WPC ( read about how WPC works here) treating it to reduce friction and help improve fatigue strength.

The 2007 crank on the bottom features full counterweights and beefier construction.  Note the additional material in the cheek area of the throws.  JWT balanced, mircopolished and WPC treated the crank for strength.