Nissan Spec-V: Part 15: Making a Motor (Continued)
10/10/2006
When we last left off, Jim Wolf Technology was well on the development path for our motor with new rods, pistons and the removal of the balance shafts. JWT had a few more tricks up their sleeve to improve the motors power and reliability.
QR25’s are known to have problems with spinning rod bearings. The rod bearings are on the small side 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 resolve the problems.
First off as discussed in our last installment, JWT eliminated the balance shafts. This helps ensure that the oil pump gets only un-aerated liquid oil instead of foam. Cutting off the balance shaft’s oil supply means that there is more oil available 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. JWT machined a groove in the main bearing saddle in the block and drilled additional feed holes in the main bearing. This allows the rod bearing to have an uninterrupted flow of oil for nearly 360 degrees of crank rotation.
This groove leads to additional holes in the main bearing to give the rod bearings and crankshaft a more continuous supply of oil.The nozzle sticking into the cylinder on the right is the Honda piston cooler.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 modifications will cure the QR’s penchant for destroying its rod bearings.
The engine was bored 1mm oversize to accommodate the new pistons. During boring, a torque plate was used. A torque plate is a special metal plate that is bolted to the top of the head during machining to simulate the distortion that bolting on a cylinder head will apply to the block when bolts are tightened. The torque plate helps ensure that the cylinder bores will be round when the head is attached to the block.
Turbocharged engines create a lot of internal heat, much more than a typical naturally aspirated engine. This issue is compounded in road racing where an engine is stressed for up to 40 minutes at a time in comparison to mere seconds for a street car or drag car. To help the pistons shed heat JWT installed piston coolers from a Honda B18C engine.
This aluminum plate was used during boring and honing to simulate the distortion that bolting on a cylinder head creates. This way when a head is actually bolted on, the bores will be round.The piston coolers are the copper colored nozzles that squirt oil onto the underside of the pistons.
Piston coolers are nozzles tapped into the engines main oil galley that shoot oil to the undersides of the pistons and help keep them cool. The Honda piston coolers are nice because they have a check valve that only opens at high rpm when there is a surplus of oil flow. At low rpm they close and help reserve idling and low speed oil pressure.
On the cylinder head side, the engine is stock. Flow bench testing showed that the QR benefited from only minor porting. It also showed that a QR head flows over 15% more than an SR20 head. JWT lightly ported the valve bowl and short side radius of the intake and exhaust ports, which was about the only place where the flow bench testing showed a significant difference, could be made. JWT also unshrouded the intake and exhaust valves in the combustion chamber to improve flow as the valves open.
In this photo of the intake port, you can see the porting in the valve bowl and short side radius. Flow bench testing showed that porting the ports entrance did not help.
Likewise, the exhaust port only improved after some light massaging of the bowl and short side radius.
The chamber was also lightly reworked to remove sharp edges, unshroud the intake and exhaust valves. The QR head flows pretty well from the factory and did not need extensive porting to produce some impressive flow numbers, over 20% more than an SR20 in modified form.JWT replaced the cams and valve springs with their S2 cams. The S2 has been proven to make 10-12 more hp at higher rpm and to work well with turbocharged engines. The stock valve springs float at a pretty low rpm and this combo will allow us to safely turn up the rev limiter to 7000 rpm
JWT S2 cams are ground on new billets and can usually be installed without re-shimming for valve clearance.
Here are the JWT valve springs and titanium retainers in place.The engine was assembled using a stock late model head gasket. It is a strong metal head gasket that should hold up well to turbo charging. Early head gaskets were prone to failure but Nissan improved the later gaskets and we made sure that one of these was used. 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.
The stock head gasket is a MLS type (multi layer steel) that should hold up well to boost.We replaced the heavy front pulley with a lightweight billet aluminum one from Unorthodox Racing, which takes about 3 lbs of rotating weight off the front of the engine. We also used an idler pulley and bracket from a non air-conditioned 2003 Altima.
The Unorthodox Racing pulley is machined out of billet aluminum and is 3 lbs lighter than the heavy stock steel part.
An idler pulley from an Altima without air conditioning allowed us to remove the air conditioner compressor.After these modifications, most of which were designed to help reliably, our attention is now turned to the turbo system. Stay tuned, for our next installment.