Nissan Spec-V: Part 17: Details, Details
10/18/2006
After months of slow hand fabrication of multiple custom components, now it’s time to bolt the car together. We are doing the final touches towards installing the engine and transmission and moving to getting the functional parts of the interior done.
QR25’s are known for having weak motor mounts. These soft weak mounts cause wheel hop and allow the engine to beat around in the engine bay. One good drag launch is often all it takes to break the stock motor mounts. We fixed this problem by adding Powertech Imports hard polyurethane motor mount inserts to limit the engines lateral movement. These were a quick and easy install and should help reduce engine lash and wheel hop.
Powertech Import’s motor mounts are made of polyurethane and easily install by slipping into the hollow spaces of the factory motor mount. They can be used to repair factory mounts that have failed.
The Powertech mounts are shown here in place, ready to be installed. They help reduce fore and aft movement of the engine.The QR25’s hammering long stroke is hard on transmissions. Although the Spec-V’s six speed transmission was developed for the powerful and torquey VQ35DE powering the Maxima, the hammering long stroke driven power impulses of the smaller and less powerful QR has caused transmission failure to be an issue with high revving World Challenge cars. Because of this, we did our share of preventive work to reduce the chances of transmission problems. First we cryo treated our gears. Cryo treatment involves subjecting the gears to repeated heating and cooling cycles down to the temperature of liquid nitrogen. Like heat treating, this toughens the transmissions internal parts. Next, we subjected the transmission’s internals to a severe shotpeening with special hardened shot. Shotpeening greatly improves fatigue strength. This treatment worked well in reducing transmission failure in the World Challenge Sentra and it should work for us as well.
Next we used Redline Shockproof heavy gear oil to help protect or transmission internals. This 250 weight oil acts like a liquid cushion between the gears. Finally we used the improved shifter and cables from a 2005 Spec-V. The shifter has a reverse lockout and stiffer cables to give better shift feel and more positive gear engagement which should be easier on the syncros. We think these measures should eliminate any problems we might have had otherwise.
The QR25 also has an extremely heavy dual mass two piece flywheel. This flywheel weighs nearly 30 lbs and really limits throttle response, slows shifts and slows revs. The big mass is very hard on the transmissions syncros as well. We installed JWT’s lightweight flywheel, which weighs a mere 10 lbs. The flywheel is machined from billet aluminum and features a long wearing and replaceable steel ring gear and friction surface for a long service life.
The stock QR flywheel weighs almost 30 lbs and has a cushion between its two main pieces. This absorbs engagement shock and acts like a tensional damper. It works to make things a little smoother and quieter but it’s very hard on syncros and really keeps the engine from revving freely.
The flywheel even has a bearing between the two masses to make things move smoother.The QR25DE has a reputation for running hot. Adding a turbo to this can only make things much worse. The factory cooling system, even for the stock engine, is not up to par for track use on hot days. The QR engine has an odd dual thermostat arrangement that tries to keep the head and block at different temperatures. For racing use it doesn’t work so well. We fixed this by eliminating the thermostat that controls water flow to the block and putting a restrictor in place of the cylinder head thermostat. We also partially blocked off a bypass line that re-circulated water back to the head, not sending it to the radiator.
JWT’s aluminum flywheel is over 18 lbs lighter than stock!
JWT’s Fibertuff disc has these small heat resistant semi metallic pucks. Despite their aggressive look, they are smooth in operation. The sprung hub smoothes engagement shock and cushions the drive train much like the stock QR flywheel did.
JWT’s pressure plate has a lot more clamping force than stock but alters the diaphragm springs motion ratio to keep a light stock like pedal pressure.
Enjuku Racing’s radiator uses C&R’s end tanks and a custom reverse cross flow Visteon core.
The swirl pot was mounted high on the shock tower to help bleed the cooling system of air. The A/N fittings lead to hoses that bleed air from the top of the radiator to the swirl pot.We also added JWT’s heavy duty clutch. Our clutch features a heavy duty pressure plate with 25% more clamping pressure and a sprung hub disc with heat resistant but smooth engaging semi metallic fiber tuff pucks as friction material. Now our clutch should easily be able to withstand our projected power and we have eliminated 18 lbs off our nose. Getting better throttle response to boot is the icing on the cake.
We also turned to Enjuku Racing to design a radiator using C&R end tanks and a Visteon NASCAR core. The Enjuku radiator uses a reverse cross flow design that is 15% more efficient than a regular coolant flow path. The big radiator has over twice the amount of heat rejection capacity as the stock radiator and features an integral fan to keep things cool when idling through the pits.
We also added a high mounted surge tank/swirl pot to the cooling system. This is a high mounted remote tank which serves two functions. One being a high mounted filler, it ensures that the fill point is the highest point in the cooling system. This helps ensure that there are no air pockets or bubbles in the coolant. Second the bleeds in radiator leading to the swirl pot help remove any trapped air from the cooling system as it’s burped out of the engine in normal use. Although few cars have this feature, it is very important to get all the air out of the cooling system in a race car that is being pushed to the limit.
The elements of the cooling system are in place and ready to rock.Our engine is in at last and its time to wire up the instrumentation and get her fired off for the first time!