Conversion from a Nissan 2 stage variable camshaft timing system to a fully variable system from a Mazda BP6D engine (page 1).
When Nissan designed the VG30DET and VG30DETT engines in the late 80’s they were fitted with a 2 stage camshaft (cam) timing device for the inlet cams. The cams have a duration of 248 degrees, and open at top dead center (0°). Though this results in a smooth idle, and good top-end power, the mid range power suffers from the late opening and late closing of the cam. Therefore, Nissan installed a cam phaser that could advance the camshaft’s timing by 20° from around 1000rpm up to 5800rpm. These cam phasers work with an internal helical cut gear system. By moving it back and forth the angle changes.The side closest to the camshaft is pressurized by a large spring. On the outer side, an oil chamber can be filled by oil pressure to compress the spring and advance the camshaft.
In order to ‘feed’ oil into the cam phaser, Nissan made the camshaft hollow, with oil pressure supplied through the front camshaft bearing at the front of the head. A channel is cut into the camshaft to widen the area of oil supply. The bolt that holds the cam phaser to the camshaft has a hole straight through it, so that the oil can get to the oil gallery in the front of the cam phaser. At the rear end of the camshaft, a solenoid allows oil pressure to escape on demand of the engine management. By releasing oil pressure at the back of the camshaft, one would expect the cam bearing to run dry, but the solenoid does not allow all oil pressure to escape, just enough to release the spring. The black sections in this section view shows where the oil flows;
My own VG30DET is fitted with high performance Tomei camshafts. These camshafts have a block pin preventing oil flow through the camshaft and delete the cam phaser system all together. The cam phaser is replaced by a standard non-variable gear. But why does the factory phaser need to be deleted for these camshafts? When Nissan designed the phaser, they made the spring strong enough to resist the forces from the standard camshafts. But as more aggressive camshafts are fitted, the spring can’t cope, the phaser starts to rattle and timing inconsistent. But this does not just occur on high performance cams, many older VG30DET(T) engines suffer from springs with lost tension or contaminated oil jamming the helical gear system. Removing the phaser will result in a loss of overall power on both standard and high performance camshaft equipped engines. There are people who cut the phaser open and install a custom stiffer spring, but some have found issue with this a well as these uprated springs require more oil pressure.
Improved cam phaser design.
The helical gear 2 stage camshaft phasers were among the first used to adjust cam timing, Porsche even went as far as going with adjustable timing belt tensioners to change the phasing. But over the 90’s an improved design entered the market, the so called vane style cam phaser;
In this design, no springs are used, yet there are 4 advance and 4 retard chambers. By filling either set of them with oil under pressure, and draining the opposing chambers, the camshaft will advance or retard. By applying oil pressure to both chambers, the cam timing will remain relatively constant. Contrary to the spring and helical gear phaser Nissan used on the VG30DET(T), these type of phasers are continuously adjustable per degree. Not just that, the range is far greater. The Mazda BP6D phaser can adjust up to 49° compared to the 20° for the VG30DET(T). A vane type phaser requires complex electronic control though. On both the crank and camshaft trigger wheels are placed that actuate magnetic sensors on every crank rotation. The engine management can read the angle of the camshaft now, but it needs control over the oil pressure to both chambers. In order to do so, a solenoid is used. The solenoid has a central inlet, with 2 drain ports next to the inlet port. On the other side of the solenoid’s cylinder are the outlet for the both the advance and retard chambers. By moving the piston to the retard side, the advance side is closed from pressurized oil, and the relief chamber allows oil to escape entering the cylinder head (and vice versa).
The solenoid is actuated by the ecu through duty cycle. The duty cycle is a percentage of a voltage, the more is applied the more oil can flow to the advance chamber. An internal spring pushes the piston back to the retard chamber. As soon as a change in rpm or load demands an angle change the solenoid responds immediately. In order to ‘feed’ oil into the cam phaser, the pressure is fed through the front camshaft bearing like the VG30DET(T) has. However, in this case 2 feeds are required, and thus 2 seperate entries in the camshaft itself. The picture below shows the Mazda BP6D bearing cap. Although the pressure points are quite close to each other, the clearance between the cam and cap/head is so small almost no oil can leak into the other.
But converting the Mazda layout over to the VG30DET(T) cam and heads is impossible. There’s simply no room to make 2 feeds next to each other, and additional drilling in the camshaft will seriously compromise it’s strength. Even unmodified cams can break, notice the broken VG30DETT cam pictured below. The cause is shown in the following section view, notice how the oil feed into it not only weakens the shaft, it’s outer radius is also smaller to act as a channel for the oil. Mazda cut these channels into the head and bearing cap surfaces so they only had to drill small oil feed holes.
In order to make 2 pressure feeds into the camshaft, I went out to draw the entire system up in Solidworks. I also bought a BP6D head to study it’s design. There were several limitations to take into account.
1st, the original pressure/inlet point in the VG30DET(T) camshaft can be used, but it may not be shut from oil pressure to avoid the bearing area running dry.
2nd, drilling in the camshaft will weaken it. In particular, there may be no additional holes drilled that further weaken the weakest section at the oil inlet.
3rd, the Mazda cam phaser has a ‘drain’ through the front of the phaser unit. As oil flows through the chambers, some of it will leak along the front and rear surface entering an overflow chamber at the front of the phaser. In this overflow chamber, the mounting bolt to the camshafts sits and Mazda drilled a small hole through this bolt to allow pressure to escape. The oil can then reach the camshaft where another hole allows the oil to drain back into the head. I’m sure this drain system can’t be closed off and it requires a 3rd oil gallery within the cam.
4th, the trigger plate from the BP6D has to be converted (pressed on) to the Nissan camshaft. It then needs to be aligned with the magnetic sensor, limiting the mounting spot to just the rear of the camshaft. Same goes for the crankshaft sensor and trigger plate.
5th, the oil in-and outlets of the solenoid must line up. On the BP6D, the 2 oil return drains from the solenoid are located right above the main oil return gallery back into the sump. But on the Nissan VG30DET(T), being a V6, the oil return galleries are on the exhaust side. The location of the solenoid should therefore be placed as close as possible to a return gallery so that there’s no excess oil circulating inside the head.
6th, the diameter of the oil feed galleries inside the camshaft must match those of the Mazda cam. Bigger is fine, smaller is unacceptable as this will increase the response time of the unit.
Below are pictures of the Mazda phaser taken apart, the red straw in the cam is where the oil can escape back into the head from the overflow chamber. This chamber (described above as 3rd limitation) sits in the middle of the 4 bolts on the lid at the left picture. The other 2 pictures show the oil control housing in which the solenoid sits. The bottom view shows the 2 slot shaped oil returns. The upper view shows the oil pressure inlet.
My first thought was to have new inlet camshafts made up from chromoly, much stronger than the factory cast units. I could then have the BP6D oil galleries cut into it, allowing the BP6D cam phaser to bolt right on. However, doing so would require not just new camshafts, but also a new cap for the front bearing, as it’s too narrow at the sides to accommodate 2 oil channels. This would result in a billet cap that would require the cam bearings in the heads to be align bored, an expensive modification. Apart from the difficulty in finding a trustworthy cam manufacturer, the total costs of these modifications and parts could run up to 2000 euro, way more than the entire budget for this project.
It took me about a month to come up with the following design. In this I use the rear pressure exit hole as a new entry. The original oil feed for the front cam bearing is closed off, in both the head and camshaft. In order to get oil to the cam bearing again, 2 new 1mm holes will be drilled on each side of the closed feed in the head for a permanent oil feed. But there’s still a second pressure feed required, so I designed a housing that sits on the cap of the front cam bearing, and has a passage straight through and drilled into the cap. A new feed through a copper tube and high pressure connections then connects this feed to the solenoid. In order to get the oil to the front of the camshaft, new holes will be drilled and galleries blocked off at some spots.
The following section views show 2 variants for the oil inlets. I came up with a design for both a crush copper washer and O-ring as a seal. The design based on the O-ring was later further worked out. An O-ring is prefered since it can be compressed allowing for +/- 0.10mm tolerance in compression. The picture with the copper ring shows the new oil galleries that need to drilled (and some plugged) into the camshaft. Shown on both pictures are the new 1mm inlets next to the original oil pressure inlet.
The rear inlet is a combination of an aluminium housing and a bronze tube pressed into it. The bronze tube has 0.03mm clearance inside the camshaft. The aluminium housing rests in the cutout at the back of the head. As this cut was align bored with the cam bearings it’s exactly centered. The valve cover presses it down.
The AEM standalone engine management system on my VG30DET is unable to control anything other than the factory on-off VVT solenoids. But controlling the solenoids does not have to be performed by the engine management itself, as there are standalone controllers available capable of controlling the solenoid completely independent of the engine management with just a few inputs; crank angle, camshaft angle, inlet manifold pressure and a 12V source & ground. I choose a VVTuner that’s made by DIYautotune, a company known for producing all kind of engine management parts and accessoires. It is specifically designed for the BP6D engine. Apart from the crank- and camshaft angle inputs this device can also adjust for manifold pressure. This means that the cam timing can be set more retarded for low-load conditions where the engine can run in Atkinson cycle, for smooth operation and lower fuel consumption. As soon as the pedal is pressed and manifold pressure increases the system can advance the camshaft.
The BP6D phaser has an internal lock pin, that locks the camshaft in fully retarded position when the engine is shut off. When starting the engine, to avoid loads to the phaser (that is not yet seeing enough oil pressure) and improve start-up response the cam timing should be retarded to the maximum. The lock pin is released by pressure from the advance side. When I went looking for a cam phaser for my VG30 this was an important consideration, as it ment the engine would have to spin in the same direction (some engine such as Honda’s don’t), otherwise, the lock pin would end up locking at full advance.
After designing the BP6D cam phaser to fit the VG30DETT camshafts in Solidworks and being confident that I could make it work, I ordered 2 VVTuner devices, along with the 3 magentic sensors and 2 solenoids, a crank trigger plate and new connectors and wiring for the sensors. The BPD6 crankshaft trigger plate is the big black plate, with 4 tiny extending trigger points. The camshaft uses a very different type of trigger plate, with 1 point on one side and 2 on the other. The VVTuner is specifically designed to read this ‘profile’ so I must duplicate the exact alignment between crank-and camshaft signal from the BP6D system.
I considered making lightweight aluminium timing belt sprockets, but I was unable to copy the exact toothing shape. So I cut down the original VG30DET(T) cam phaser until only the gear was left, and bolted this up to a brand new hub I made on the milling machine. The hub is made from the strongest aluminium, 7075. The whole assembly is around 210 grams lighter than the factory Nissan phaser, excluding oil.