In part one of our engine build series, we did a quick overview on the anatomy of our record breaking engine dubbed the SR15VET 20V. Next, we introduced you to the “23 doctor,” Nick Hunter of 5523 Motorsports and then dove into his assembly of the SR15VET 20V’s bottom end. If you’re not up to speed yet, be sure to go back and read up on the Heart of a Record Breaker Series. In this installment, we’ll follow Nick Hunter in the assembly of the coveted “20V” cylinder head and also cover the SR20VE head swap.
Originally, our resident HNIC (head nerd in charge), Mike Kojima, graciously offered up a SR20VE 20V head that he had stashed away in the far reaches of his toy box. Mike’s 20V head was fully ported and had 1 MM larger Super Tech valves installed.
Unfortunately, after our record El Mirage run we’d find out this head’s valve job was questionably performed, which resulted in 40% leak down across three cylinders. We had crushed a land speed record by 30 MPH but now only had a month before Speed Week to resolve our head issues. It was truly bitter sweet.
Without enough time or money to source the parts to repair Mike’s 20V head, Nick and I scoured the earth for another super rare 20V head. Fortunately, Clark Steppler at Jim Wolf Technology always has a good stash of hard to find Nissan and Datsun goodies around. After bartering my first born daughter over some rolled tacos at Sombrero’s, we had ourselves an unmolested SR20VE 20V cylinder head. Thanks Clark.
With only a handful of weeks until Speed Week, Nick Hunter did what he does best and tapped into his Captain Zombie Vampire super powers to repair our head. Forgoing sleep and living on nutrition void fast food, Nick Hunter was able to perform a miracle in record time, barely. How the Captain does this, I’m not sure. It’s just what zombie vampires do I guess.
If you’ve ever compared the dyno charts of an SR20DET and SR20VET, you would notice that it takes a lot more boost on an SR20DET to make the same amount of power as an SR20VET. One of the reasons for this is how much better the SR20VET head flows in comparison to the SR20DET. With a good port and polish job, the SR20VE head can yield flow numbers in the same neighborhood as a ported Honda K series head. (Translation: That’s good, really good.)
Naturally, a port and polish job is where Nick Hunter began the evolution of our replacement 20V cylinder head. On the intake side, the injector area was blended into the port roof and the port entrance gasket matched. Then the port divider was knife edged and the port gradually tapered down towards the bowl. In the exhaust side ports, the nasty short side radius bump was removed, the port divider wall knife edged, and then opened up approximately 15-20% in cross section. In both the intake and exhaust ports, the valve guides were ground near flush to improve flow. To round out the headwork, the seats were cut with a fresh valve job and the area around each valve was de-shrouded.
With the port and polish job complete, there was one last bit of modification that needed to be performed before our SR20VE 20V cylinder head could be assembled. When performing an SR20VE head swap on an SR20DET block, the original oil delivery passage in the head must be blocked. On the SR20VE, this passage aligns with a passage in the block to deliver oil pressure to the VVL solenoids from the oil pump and activate the VVL system. Nick Hunter plugged this passage by drilling a .337″ diameter hole and then threading it with a 1/8″-27 tap. A stainless steel socket head plug was then threaded in place.
Since the VVL system still needs to see oil pressure, we ran an Earl’s Performance Products stainless steel braided line from one of the spare holes in our Tomei remote oil block adapter.
There are two option of where to connect the other end of the Earl’s steel braided line. Probably the more common of the two options is to drill and tap a hole on the square machined boss just below the intake manifold. Nissan was nice enough to have already placed a threaded hole here for us to use as a pilot. Just drill this hole deeper and it will intersect the factory oil passage.
The second option is to drill a hole and weld a bung directly onto the VVL solenoid. This is what we chose to do with the first head. Our second head had both options to give us room to play down the road if we needed to.
If you really want a bolt on solution though, check out Mazworx’s VVL conversion kit. It’s not cheap, but the build quality is good and it makes life a lot easier for the novice wrench.
With the head work complete, Nick Hunter began to focus on the installation of the valves, retainers, and springs. Unlike the SR16VE and first generation SR20VE, the 20V variant uses single valve springs. In this case, more is not necessarily better. The 20V spring is made from a multiple arc (MA) wire which is “ovate” in cross section. This buries spring stress risers further inside of the spring while effectively increasing spring tension. To further reduce the likelihood of stress risers, Nissan also paid special attention to the surface finish of the spring. According to some industry experts, it’s one of the best OEM springs they have seen to date.
While mere mortals would spend hours installing the valve spring retainers, an immortal zombie vampire has a bag of toys to make this stuff look easy. Nick affectionately refers to this one as the “great valve dildo” tool. Whatever it’s really called, it makes installing 16 valve, spring, and retainer assemblies into a painless, 15 minute job. Damn, it’s good to be a gangster zombie vampire.
The next step on the list was installing the rocker arm assembly. Note the larger third journal located in between the two outside journals. What is this voodoo magic? It must be V-TEC, yo. Nope, it’s one of the key elements behind Nissan’s VVL (variable valve lift) system. So how does Nissan’s VVL system actually work?
Remember the steel braided line we routed from the oil pump to the VVL solenoid? That line delivers oil to the VVL solenoid and at a certain RPM, the solenoid opens a passageway. In doing so, oil is sent down the length of a long, hollow rocker arm shaft, which spans the cylinder head. Each rocker arm is mounted to this rocker shaft and oil is delivered to it via the hole inside the bore of the rocker arm.
Oil pressure then acts on the backside of a VVL activation pin which drives it outwards. When the pin moves outwards, it pivots a foot which locks in place underneath the high lobe portion of the rocker arm.
In the locked position, the middle journal of the rocker arm engages the larger cam lobe that is located in between the two small cam lobes. The large cam lobe profile results in increased valve lift. Got it? Now back to the build…
After consulting with Clark Steppler of Jim Wolf Technology, he advised that we should figure out a way to lock the exhaust rockers. The hypothesis was that by locking the exhaust rocker on the big cam lobe we would increase overlap and lift, which would help exhaust flow and ultimately help us spool our herculean Borg Warner EFR 8374 faster.
If we ran the dual solenoid set up which comes on the early model VVL engines, locking out the exhaust rocker would be as easy as using the RPM switching feature of our Turbosmart E-boost Street boost controller. Or, we could have this switching incorporated into our Jim Wolf Technology ECU.
There’s simply not much room for the VVL solenoid when the engine is mounted in a RWD configuration. However, without using a remote solenoid plate, the 20V single solenoid is the only other bolt on option that leaves clearance between the head and firewall. Using the 20V single solenoid set up meant that we gave up the ability to individually control the intake and exhaust VVL switching points.
Instead, we made a longer activation pin which permanently locked the exhaust rocker arm on the high cam lobe. Special thanks to my buddy Julio Solis for machining these up for me.
With the exhaust rocker arm situation figure out, Nick Hunter turned his attention towards shimming each of the valves. Shimming ensures that there is adequate clearance between the valve and the rocker arm and that each valve opens at the same time.
Before I watched Nick Hunter put together this engine, I never really gave the shims in an SR20 too much thought. Back in the days of NASA SE-R cup, if we ever threw our rocker arms, we’d just find which ever ones we could and toss them back into the engine. In other words, no thought was given to shim size or clearances. After seeing 5523 Motorsports’ shim collection and actually giving it some thought, I feel like a personal face palm moment is in order. Excuse me for a second while I dislodge my hand from my face. :::FACE PALM:::
Now that my hand is peeled from my face, I’ll elaborate further on what makes the SR20VE head better than that of a traditional SR20DET cylinder head. The SR20DET has the pesky tendency for its rocker arms to fly off at high RPM. On the SR20DE and SR20DET engines, the rocker arms are basically free floating only being wedged in between the camshaft, hydraulic lash adjuster and valve tip. This is why they fly off at high RPMs and cause all sorts of ruckus. The VVL cylinder head’s rocker arms are solidly mounted to a rocker shaft, making it impossible for them to fly off.
As a side note, those aftermarket thin metal rocker arm stoppers that are made for SR20DET engines are utterly useless. I’ve found that they don’t help prevent the rocker arms from flying off and actually cause more damage to the rocker arms when they do decide to fly off. Instead of just letting the rocker arm fly off, they wedge the rocker arm in place causing them to break. So now, you’re not only searching your engine for shims but you’re also in need of new rocker arms.
Before Nick Hunter could wrap up the assembly for good, he had to first verify piston to valve clearance. This meant assembling the head completely and installing it on to the block only to disassemble it again. It’s a small price to pay to verify that the valve pockets in our JE pistons had enough valve clearance for us to cope with the advanced and retarded camshaft timing settings.
After checking piston to valve clearance, Nick installed an OEM 20V head gasket. Unlike the older variants of the SR20, the SR20VE 20V gasket is constructed from multi-layered steel. The 20V gasket features an embossed fire ring around the bore which is coated in a rubber-like viton to improve micro sealing around the combustion chambers. A similar material is used around the cooling passages to aid in sealing there as well.
Before installing the SR20VE 20V cylinder head for the last time, Nick Hunter removed all of the shims. Without this step, the valve shims would have become dislodged in the nether regions of the cylinder head surely resulting in a profanity filled rant.
Another necessity to swapping the front wheel drive SR20VE VVL head onto a RWD block is the 20V CAS (Crank Angle Sensor). The distributor that is used on the other variants of VVL engines simply won’t clear the S-chassis’ firewall. The 20V CAS isn’t easy to find but if you’re in the market, Greg Vogel at G-Spec Performance usually keeps them in stock.
Nick Hunter installed a pair of Jim Wolf Technology adjustable cam gears onto the end of each of the N1 camshafts. The cam timing was set for 10 degrees advanced and 10 degrees retarded on the intake and exhaust respectively. Although the popular line of thought is to spread the lobe centers on turbo engines, we tightened the lobe centers to increase overlap and reduce back pressure. The idea here was to decrease back pressure and promote “blow down,” which expedites turbo response.
Honestly, we need to spend a lot more time on the dyno to figure out what cam timing this particular engine combination likes; and also, which will result in the best horsepower and torque characteristics for land speed racing.
The last parts needed to complete the SR20VE head swap onto our SR20DET block were a Mazworx water neck and a custom intake manifold.
Since factory SR20VE and SR16VE manifolds would both point the throttle body towards the firewall of our 240SX, we had John Kuchta of Specialty Cars fab up a new manifold for our SR15VET. The intake runners and plenum base were constructed from raw material purchased from Mazworx. Since the OEM SR20VE 20V intake flange is unique and does not share patterns with any of its VVL predecessors, John Kuchta had to use the OEM intake manifold flange and then port it to size.
John Kuchta fabricated the intake manifold plenum by slicing open a 5″ aluminum U-bend that we sourced from Burn’s Stainless. The “U” is what gives the plenum the tapering shape as it nears cylinder four. To top off the plenum, John Kuchta welded an Xcessive Manufacturing SR16VE N1 throttle body flange in place. Yes, we could have gone with a larger throttle body like the Q45. Remember fellas, this is a 1.5L engine!
As a side note, there are a lot of cheap suppliers of aluminum U-bends out there but they often have wrinkles and stretch marks along the bend area. Perhaps the blemishes only have a marginal performance impact, but from an aesthetic point of view they definitely suck. This is why we chose to go with a U-bend from Burn’s Stainless.
Join us next time as we dive into our SR15VET 20V’s turbo system which features a combination of parts from Borg Warner, Turbosmart, and Full Race Motorsports.