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Project Nissan 300ZX: Part 4

Building the Ultimate Z Engine

Mike Kojima
Sep 26, 2002

In our last foray in the adventure of building the poor man's exotic killer, we did some extensive suspension and brake work to prepare the chassis of Project 300ZXTT to make it worthy for the installation of our anticipated 500-hp-to-the-wheels engine. In this installment we will actually start to dig into the engine, perusing the shiny, trick parts in eager anticipation of their assembly into the beast.

Building an engine with this kind of power is serious business. The power outputs we hope to obtain from our stock-block Nissan will reach levels once only obtainable by all-out race engines. Fortunately, we are starting with a good platform. The Nissan VG30DETT is a robust, sturdy engine right out of the box. The engine, like the rest of the car is overbuilt in stock form, making it an excellent candidate for wringing extreme power levels out of it. It is almost like Nissan designed it to be one of the best sports cars ever produced and then de-tuned it for sale to the public.

The engine is an engineering marvel, featuring four valve aluminum heads with plenty of detonation-fighting quench area, a combustion chamber with a 46 degree included valve angle and two overhead-cams-per-cylinder bank. The ports are positioned for good flow with almost a straight shot to the combustion chamber. The intake cams feature a variable timing device which reduces valve overlap at low engine speeds, smoothes idle, and optimizes overlap throughout the rpm band for better breathing. The rigid iron block features stout construction with a fully girdle-supported main cap system, which makes for a super-stiff and strong bottom end. The crank and rods are forged steel from the factory. The pistons are oil cooled by sprayers located in the block, fed by a standard high-volume oil pump. The engine's specs read like a racing engine build sheet right from the factory.

Even though the VG30DETT is obviously an exceptionally strong engine, we will have to do some in-depth rework of its internals to reliably make this kind of power. Getting an already very powerful engine to double its specific output is asking a lot, even from the most stout of stock units. Our goal is a difficult one--to obtain race car power with stock reliability and reasonable, street useable driveabilty.

Engine Parts
To develop this sort of power, we turned to some of the leading experts in hard-core Nissan performance. Jim Wolf Technology will be lending its expertise in Nissan modification to help us reach our lofty goals. Now let's get to work in prepping the basic bits of our mighty engine, beginning with the block.

The Engine Block
Getting a good block is the basis of building a solid high-performance engine. As we are planning a significant overbore to 89 mm (stock is 87 mm) to bring our displacement up to 3150 cc from the stock 2960 cc, it is important to verify the block can handle such an overbore. Normally, it is not advisable to bore the VG30DETT more than 0.020-inches or 0.50 mm oversize as the VG has relatively thin cylinder walls; however, bigger bores are possible if the block is first checked to make sure there is enough iron to do it safely.

Clark Steppler of JWT checked our block with an ultrasonic thickness gauge to make sure our block had enough meat to support our big-bore intentions. An ultrasonic tester uses reflected ultrasonic waves to measure the thickness of the cylinder walls. Clark measured the block in four places around each bore's circumference at four heights up and down the cylinder walls, for a total of 16 measurements per bore.

After verifying our block was thick enough to safely bore to 89mm, it was sent to Pacific Cryogenics to be cryogenically treated. Cryogenic treating is an extension of the heat treating process where the block is slowly cooled to near absolute zero (-320 degrees F) with liquid nitrogen and allowed to cold soak. The metal parts are then brought up to about 360 degrees (to temper the metal) and slowly chilled again. This is repeated three times or more during a 72 hour or longer total cycle.

Cyro treating completely stress relieves the block and actually strengthens it by increasing the amount of martensite (a hard crystalline variant of steel) carbide inclusions within the metal. It also rearranges the metal's molecular structure into a better symmetrical crystal matrix with more complete molecular bonds that further helps strengthen the block. These microscopic changes also increase abrasion resistance and the lubricity of sliding surfaces, thereby reducing friction. You can expect much longer wear of the cylinder bores as well as improved dimensional stability under all conditions. The improved dimensional stability improves head gasket and piston ring seal. Cryo-treated blocks can make up to 6 percent more power just due to better ring sealing and less internal friction alone.

In many ferrous metal applications, cryo treating can increase wear resistance by over 800 percent, fatigue strength by over 100 percent and tensile strength by up to 25 percent. The typical increase of wear resistance in cast iron like our block is 100 percent. As these improved attributes are all desirable things to increase in a high-performance engine, we are glad to take the time to do it. The price of cryo treating is relatively reasonable, yielding a good return for the money.

Although cyro treating is virtually unheard of in street car engine building, it is one of the secret tricks many top engine builders use to gain improved horsepower and reliability.

Since we will be pumping nearly twice the amount of power the engine is rated for in stock condition, we did a few extra measures to help ensure the engines bulletproofness. JWT filled the block's water jackets about 40 percent with a tough metal-filled epoxy (similar to the fix-it-all JB Weld) to help reinforce and stiffen the block. This block filling can reduce cylinder wall and block flex which can improve ring seal and bearing life. JWT used a metal-filled epoxy because the metal fill gives the plastic epoxy resin a coefficient of expansion very close to that of the iron block. This prevents the epoxy from cracking or separating from the block's interior. Surprisingly, filling the block like this should not have an adverse affect on cooling, at least on this particular engine. Nissan's own VQ30DE engine has much shorter water jackets than our filled ones. Filling the block is a common trick used by NASCAR circle track engine builders to get more strength out of their underbuilt, flexy domestic V8 engines before the advent of factory "Super Duty" racing blocks.

After filling the block, it was checked dimensionally for proper main bore and deck alignment to see if the block required any special secondary operations like align boring or deck milling. Nissan blocks are very strong and almost never need these operations. The block was bored with JWT's torque plates. Torque plates are plates made of thick aluminum bolted to the block's deck before machining. Torque plates simulate the stress and distortion to the block that bolting on the cylinder heads creates. By using torque plates, the cylinder bores will be straight and round once the heads are bolted in place. JWT is the only company in this country to our knowledge that has Nissan torque plates. This extra operation speeds break-in of the engine and ensures good piston ring seal.

After boring, the cylinders were honed using a Sunnen CK-10 automated power hone. The Sunnen has a reputation for being one of the best honing machines; it can create super-round and straight cylinder walls (to tolerances of better than 0.0001-inch) with ease. As a final step, JWT used a proprietary plateau hone process which removes the peaks from the freshly-honed surface and opens up the cross hatch. This reduces oil consumption, speeds break-in and reduces ring wear during break-in.

The Crank
Although the stock Nissan crank is a very strong, heavy-duty forged steel part (which would be the envy of any domestic V8 engine designer) we felt to get the most reliability from our 600 hp monster, we needed to do some massaging to it. Crank failures in even highly-modified Z's are rare but we are careful and would rather spend a little more time and money now than a lot more later.

We sent our crankshaft to out to be cyro treated with our block. It is perhaps the crankshaft more than the block that can most benefit in the increase in wear resistance, lubricity and strength cryo treating can provide. It can improve the wear to the crank's bearing journals and also provide up to 100 percent more fatigue strength. Cryo treating also increases the tensile strength. All of these properties are highly desirable to improve on the crankshaft.

After cryo treating, JWT's fabricator Mike Smith tack welded the bolts of our crankshafts counterweights in place. The VG30DETT crankshaft is unusual; the center counterweight is bolted in place. Under extreme racing use, these have been known to occasionally work loose and fly off, resulting in complete engine destruction. Mike TIG- welded (tungsten electrode, inert gas) the bolt heads of the cap screws, holding the counterweights in place to ensure they will never come loose.

After the cryo treatment and welding, the crank was given a precision dynamic balance job. As a final touch, the crank bearing journals were micropolished to reduce friction and improve bearing wear. This is an extra step late-model Nissan engines have undergone to reduce internal friction on all production engines, but our engine was manufactured before Nissan started doing this.

Normally when building a high powered engine, we would be getting the crankshaft shotpeened. Shotpeening is the bombardment of the part with steel shot at high velocities. This creates a tough microforged skin over the outside of the parts which makes it difficult for cracks to form in the part. Shotpeening usually improves the fatigue strength of a part by over 100 percent. Fortunately for us, Nissan shotpeens both the crank and rods on the VG30DETT straight from the factory, sparing us the time and expense of having to get it done ourselves.

The Rods
Rods are a critical part of the engine. Because they tether the pistons--which move up and down with considerable force--to the crank, the rods are the most highly stressed part of the engine. A rod failure is very catastrophic, usually destroying the entire engine. Although the stock forged steel, bronzed-bushed, floating wrist pin, Nissan rods are very strong and really are akin to many manufacturers' racing rods, we opted to go to an improved real racing rod for peace of mind. The stock rods are very strong and have been used in 600-hp engines with no problem before, but the cost of failure is so high, we do not want to take any chances.

We selected Cunningham rods for our engine. Cunningham rods are forged from billet, then machined to final shape. Most high-performance rods are simply machined from billets of high-quality steel. Cunningham actually forges the rods to near-final shape, then machines the forged blank to final dimensions. This forging process improves the grain structure, making it finer and also aligns the metals grain in the correct orientation with the direction of stress. This means the grain is aligned with the length of the rod. Cunningham uses 4340 high-nickel aircraft chrome moly to make their forging blanks.

This 4340 is much tougher than regular steel and is typically used in racing crankshafts, rods and drivetrain parts. The critical rod bolts are machined from high-strength H11 tool steel. The bolts can take an incredible 296,000 psi of stress before breaking. This is a substantial advantage because most rod failures are directly attributed to the bolts breaking This forging results in a tougher and lighter part than one simply cut from billet. Cunningham also uses a two-piece forging die so the rod cap has the grain flowing around the rod bore. Cunningham is the only rod company to do this. This helps keep the bore from distorting under load and can help improve rod bearing life.

Cunningham rods are machined to very tight tolerances--so tight it is nearly impossible to see the parting line between the cap and the rod body. Every bearing bore is consistent down to 0.0001-inch and all the rods are the same weight down to within one gram, making additional balancing unnecessary.

The rods are also shotpeened with a special two-step process using two different sizes of shot at different velocities with a post-peening, non-directional polishing process. This intensive shotpeening and polishing operation increases fatigue strength an additional 20 percent over regular shot-peening.

Finally, the rods are over 140 grams lighter than the stock rods, reducing reciprocating weight and strain on the rotating parts of the engine. These factors added up will give us a quite a bit of insurance against engine failure. It was money well-spent.

The Pistons
To withstand the stress of 20-plus psi of turbo boost, we selected JWT's forged pistons. Forged pistons are stronger than the stock cast pistons due to the same grain refinement and flow characteristics described with the forged connecting rods. JWT pistons are forged from high-silicon aluminum alloy. Although high-silicon aluminum is not quite as tough and ductile as lower-silicon alloys, it is more dimensionally stable over a wider range of temperature.

Because of this, you can run much tighter cylinder-to-wall clearances with high-silicon pistons. This creates a quieter, longer-lasting engine free of piston slap. Ring life and seal is also improved with these tighter clearances. Road racing engines and high-performance street engines are often assembled with high silicon pistons because long service life is important. Low-silicon pistons are best suited to short-duration, extreme-duty events like drag racing, where life and noise are not important and can be sacrificed for toughness. Typically a high-silicon piston can run clearances as tight as 0.0025-inch where a low-silicon piston runs from 0.0040-0.0060-inch. Even though a high-silicon piston is slightly less ductile and tough than its low- silicon brother, it is still considerably stronger than any OEM-type cast piston.

The inherent strength of forged pistons will help them withstand the rigors of high boost without nearly as much worry about pinching ring lands or fracturing under the pounding of detonation. This will help us gain reliability even with a high power output. The JWT pistons are also about 50 grams lighter than the stock pistons, reducing reciprocating weight and strain on the connecting rods and crankshaft.

JWT pistons are also ground with a tapered barrel shape to the skirts with a slightly offset piston pin to reduce piston slap and the accompanying noise typical of racing forged pistons. These machining tricks also cut down on cylinder wall, piston and ring wear. These pistons are nearly as quiet as OEM- cast pistons in terms of knocking or slapping noise. JWT pistons make use of genuine Nissan or other Japanese OEM-type ring packages. The OEM rings on a typical Japanese piston are low-tension like a racing-type ring for low friction but have several features such as chrome facings that wear much better than your typical moly-faced or iron aftermarket ring domestic engine builders favor.

The pistons feature a tapered, thin wall tool steel piston pin for superior strength and about 60 grams less weight than the stock pin. The pins are also slightly shorter so there is no excess unnecessary metal tied up in the length of the piston pin. The pins are retained with reliable double spirolock retainers. These spring steel retainers can withstand much more side load than the stock wire type retainers and are quite reliable--an important feature as you do not want your piston pin to drift loose into the cylinder wall at high rpm.

The Heads
Our VG30DETT heads and lower intake manifold were ported and polished by JWT to increase flow without loosing velocity. JWT concentrates on keeping the runner volume as low as possible while removing obvious obstructions in the port's flow path. The valve seats were matched to the port walls and combustion chamber to remove the slight mismatch the factory does not bother to correct. The ports are also straightened for a less-obstructed run into the combustion chambers with an emphasis on tumble upon entry into the combustion chambers.

This kind of porting helps keep turbo lag to a minimum and does not sacrifice too much bottom-end power to gain top end. The old-school style of porting where the ports were simply hogged out to be as big as possible often reduced flow velocity to the point of making a car lose much of its bottom-end power. The latest style of porting most good tuners use emphasizes port velocity to maintain good low-end power as well as peak flow. As a final touch, the combustion chambers were polished to get rid of any potential hot spots that could cause detonation.

After replacing the valve guides and valves with new genuine Nissan parts, JWT finished the heads with a multi-angle valve job which includes a 30 degree back cut on the valve face for better low-lift flow. Multi-angle valve jobs work by unshrouding the valve seating surfaces and making a smoother flow path for the incoming air or the outgoing exhaust. These valve jobs commonly consist of a throat cut, a seating cut and a top cut. Stock factory valve jobs usually are just seating cuts, but the stock 300ZX does use a similar three-angle technique on the intake valves and a two-angle cut on the exhaust side. Multi-angle valve jobs create a smooth transition from the port to the cylinder as the intake valve opens. The converse effect is also true on the exhaust side of the engine but the flow is improved as it proceeds from the combustion chamber to the exhaust port. These types of valve jobs increase the flow the most at low lifts where the valves are first opening or about to close. This is important because valves spend more dwell time opening and closing than they do at maximum lift. A proper valve job can contribute up to 50 percent of the total flow gain enjoyed by good headwork.

Since it is impossible to port our complicated, dual-plenum chamber upper manifold without cutting it to gain access to the insides, we sent it to Extrude Hone to have it ported by their patented abrasive-flow method. Extrude Hone uses a unique pump to push a slurry of a special polymer with an abrasive mix of tungsten carbide or aluminum oxide particles mixed into it through the ports at a fairly high velocity. This process can port the insides of even the most complicated part.

While we were at it, we also Extrude Honed the exhaust manifolds, the 02 sensor housings and turbocharger intake and exhaust housings. In testing by Garrett, it was found Extrude Honing can increase turbine efficiency by as much as 3 percent--a sizable difference which reduces the amount of backpressure the turbine creates as it recovers energy from the exhaust stream to spin the compressor.

The Extrude Honing made good work of our lumpy and bumpy exhaust manifold. The stock exhaust manifold is a terrible design. Since it must hug the sides of the block to fit in the Z's tight engine bay, it has all sorts of flow impeding humps, bumps and twists as it snakes its way around bolts and other obstructions. The Extrude Honing really cleaned these parts up, increasing flow by an amazing 40 percent. Since this part of the car is awful to work on while the engine is in the car, we chose not to run headers for the added reliability of the cast iron manifolds. Extrude Honing was the only option to help. The intake manifold's flow was increased by nearly 20 percent with the runner-to-runner variation reduced to 1 cfm; this was over the stock manifold's nearly 20 cfm of variance.

Camshafts & Valvetrain
We opted for JWT's turbo cams. JWT's cams have increased duration and lift for improved high-rpm power. JWT also grinds the cams with a minimum of overlap to reduce the chances of turbo backpressure-induced reversion. Reversion is caused when the high backpressure created by the turbine is more than the boost pressure at high-boost levels and rpm. This causes hot exhaust gasses to back flow through the engine during valve overlap (the point in the four-stroke cycle where both the intake and exhaust valve are open). This back flow causes the internal temperature of the engine to rise, promoting detonation which further increases heat. This can create a vicious circle where the engine has a thermal runaway, overheating to destruction. Excess overlap can also cause charge dilution at idle, resulting in the lopey eight-stroking misfire race-car type of rough idle.

JWT cams are ground on new genuine Nissan billets, so mismatched cam metallurgy with the accompanying excess wear is avoided. Since the cams are ground on new billets, the base circle can be set wherever it is needed. On the 300ZX, high-lift cam lobes can actually contact part of the head, so JWT reduces the base circle about 0.020-inches to prevent clearance problems. This is still within the tolearances of the hydraulic lash adjusters, so the cam is still a direct drop-in. To reduce the chance of valve float at high rpm, JWT installed some of its high-tension valve springs to keep the valvetrain happy.

Summing it Up
In following installments, we will dive into turbochargers, high-performance engine coatings and the assembly process of our mighty engine. We also have some very trick parts, like multiple-map ECUs, computer-controlled Aquamist water injection, special head gaskets and many other parts to test, tune and tweak.

Cunningham Rods
550 W. 172nd st.
Gardena, Ca, 90248
(310) 538-0605

Extrude Hone
8800 {{{Somerset}}} blvd
Paramont, Ca 90723
(562) 531-2976

Jim Wolf Technology
212 Millar
El Cajon, Ca 92020
(619) 442-0680

Pacific Cryogenics
(909) 640-5227
(909) 517-1644 fax
By Mike Kojima
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