Ultimate L28ET Guide: What You Need for 350+ HP
Original Article by Drax240z
Yes, I'm getting tired of having to answer the same questions over and over again, so here are some common answers, all in one place and easy to find. I hope that those of you with helpful info to add to this will contact us and do so - especially those of you that have been through this a few times.
This is intended to inform the reader of the options which exist in building up a Nissan L-series turbo engine; specifically to give an overall picture of the cost, potential and problems associated with using this engine as a base for a performance application. Much of this info has been used without permission from various turbo websites, books and discussion forums. Bear in mind that this is intended as a guide only - if you follow this to the letter and have a problem, you are the one responsible for your own actions.
Decide on Performance Goals
The first thing you need to do, as with any major project, is to decide what your goal will be. If you're aiming for a 200 HP L-series engine, chances are you won't be needing a turbo. On the other hand, if you're looking to get some more serious power from an L-series, to the tune of 200-500 HP, a turbocharger will more than likely be the most viable option.
So, You Want a Turbo?
Now that you've envisioned your performance goals and decided on the L-series turbo path, it's time to start making that plan a reality. The single most important piece of advice on a build like this, or any other major project for that matter, is this: Research it before you do it! (Reading this guide is a good starting place.) Do yourself a favor and track down the book Maximum Boost, by Corky Bell. (ISBN: 0837601606, Check Half.com for copies if you don't have access to a good used book store.) Read it a few dozen times; by that time, you should have a thorough enough understanding of turbocharger systems to make educated decisions and ask the right questions. Scour the forums and the rest of the Internet to see what others are doing, both what they've done right and what they've done wrong. Take a look at the links at the bottom of this page; some are Nissan-specific and others aren't.
Where Do I Start?
The best place to start would be to find an engine from a 1981-83 280ZX Turbo car. You can either find the engine only, or find an entire donor car. If you're planning on installing the stock turbo engine, getting a whole car is preferable; you'll find yourself in need of a great deal of electronics from the donor - AFM, ECU, wiring harness, fuel pump, etc. I found an engine from a 1982 280ZX Turbo for about $200; this only included the parts physically attached to the engine. The AFM, ECU, and other parts were not included, and were not important due to my choice to use a programmable system to manage my engine.
Get Your Head Checked
Before you head out to call up the local psychiatrist, we're talking about your engine head. As you begin disassembling your engine, take care to put all of the parts into appropriate containers and clearly label them. You'll save yourself a ton of headaches and cursing when it comes time to reassemble it. Once you have the head removed, you'll probably want to locate a machine shop and send off your head. You'll want to find a shop that specializes in import cars, or at least one that has done several before. This step is optional; some people have had great results from unadulterated junkyard motors, however I opted for a complete rebuild.
I sent my P90 head out to a machine shop and received it back in the span of a couple of weeks. Be patient, and allow extra time for the shop to complete the work - if they quote you a 1 week turnaround, expect it to take 2 to 3 weeks. $250 worth of head work included a complete cleaning, a performance valve job and new valve seals, all threads chased and a .010" surface plane.
Remember everything you've heard about putting a hot cam in a performance engine? Forget about them - at least when you're thinking about a turbo engine. Turbo engines have completely different requirements than naturally aspirated motors. For a Nissan L-series motor, the stock turbo cam should be sufficient up to approximately 350-400 HP. You aren't going to get the same results putting a "performance" turbo cam into a turbo engine that you would putting a "performance" natural aspiration cam into a naturally aspirated engine. Turbo camshafts tend to have lower valve overlap than naturally aspirated cams, primarly to prevent exhaust gas reversion. (Occurs when the exhaust manifold pressure between the valve and turbo is greater than the boost pressure. "Hot" naturally aspiration cams tend to have a large valve overlap, and you'll find that these cams would actually wind up hurting your turbo engine performance versus the stock cam. If you're aiming for more than 400 HP, you'll want to contact a camshaft specialist and work out the ideal custom grind for your cam.
Porting and Polishing
If you're aiming for less than 400 HP, porting and polishing is largely unnecessary, though a good cleanup never hurt anything. The way it has been explained to me is that the cash you'd spend on the port and polish could be put towards a better intercooler, turbo, engine management system, or something else and you'll wind up with a bit more "bang" for your bucks. The P90 head already flows well enough. If you're aiming for something over 400 HP, you're going to want to locate a company that specializes in Nissan L-series headwork.
You and Your Bottom End
Moving back to your original goals, the general consensus is that Nissan overbuilt these turbo engines. They ran a very conservative 7 psi of boost, surely to ensure some margin of reliability and durability. I would expect that the stock Nissan shortblock (block, pistons, crank, etc.) can be pushed to a maximum of approximately 350 HP and maintain some measure of reliability. Exceeding that, you're more than likely tossing that reliability factor out the window. If you're looking for a reasonably stout and reliable 300 HP or more, you'll want to give some serious thought to forged pistons. Pre-detination is an engine killer; melting pistons and breaking ring lands in the blink of an eye. A forged piston will give you a bit of a buffer, however you must still be careful setting up your engine and avoid running too lean at all costs. If you're venturing into the realms of 400 or more HP, plan on doing some prep on your connecting rods as well.
Your head gasket is also an area of concern; they rarely blow without some form of detonation occurring. Again, if you're aiming for 400 or more HP, you may want to take extra care and look into block O-ringing or metal head gaskets.
The stock Garrett AIResearch T3 Turbocharger that comes in the 280 ZX Turbo is adequate up to approximately 275 HP. For more serious power, most L28 Turbo engine modifiers use the T3/T04 hybrid turbo. This makes use of the stock exhaust side of the turbocharger and a larger intake impeller, enabling the use of the stock exhaust manifold. There are many turbo shops around the world, and most knowledgeable shops can help you decide on a configuration that will work for you and your goals. Also seek out the advice of people who have done this kind of modification before and learn from their successes and failures.
We'd all love to have a custom-made header for our turbo L-series car, but it's not always necessary to go to the trouble and expense. If you're aiming for anything less than approximately 450 HP, you're fine with keeping the stock exhaust manifold. (If you're planning on anything more than 450 HP, you really should be discussing things with a high-performance engine building expert anyway.) A header for a turbo car can put a serious dent in your wallet, to the tune of $2000 or more for a custom build. They look really good, but that's an awful large chunk of change for looking pretty, when you can easily spend that money on better turbos, better fuel management, etc. Any L-28 series intake will work for this build, however the earlier intakes (1975-78 L-series motors) have far less holes and far less accessories attached to them, which will give your engine compartment a bit of a cleaner appearance with that slight reduction in clutter. Don't panic if you can't find one; it is possible to cut and weld your stock turbo manifold to clean it up a bit.
A popular upgrade option that does provide some benefit is to replace your stock throttle body with a 60mm unit. It doesn't sound like a significant improvement, but the 60mm unit is capable of allowing almost 44% more air to flow than your stock 50mm unit. These 60mm throttle bodies can be found on many fairly recent cars, such as the Nissan 240SX. The 240SX throttle body is almost capable of being a direct bolt-on mod; you may have to make slight adaptations to your linkages. Once you obtain the throttle body, do yourself a favor and hold it up to the intake and smooth out the transition between the two with a die grinder or Dremel tool, otherwise the mod is practically pointless. (Do remove your intake before doing this, if possible. Sending aluminmum shavings into your engine is definitely a bad thing.)
Take a look at the stock downpipe coming off of the turbo. Notice the O2 sensor, then a 90 degree bend, followed by yet another 90 degree bend. This has to be one of the worst designs on this entire engine. You're going to want to look into getting a custom downpipe unless you're satisfied with the performance of this absurd stock layout. A decent design for your new downpipe would be to have it fabricated out of 2.5" mandrel-bent 304 stainless steel with two 45 degree bends. As an alternative, you can have one fabricated out of milled steel and ceramic coated. Be sure to take an account of how much room there is before taking on a custom downpipe; it'd be a waste of money to have a unit built that you don't have room to fit. You can have a 3" downpipe, but it makes getting to the bolts to attach it difficult, and the stock T3 outlet is only 2 1/8".
For the exhaust system itself, 3" mandrel-bent is the only way to go. Press bends are unacceptable. Less restriction of your airflow means your turbo will spool faster and you'll have less lag. The typical concerns of backpressure and loss of torque due to a bigger pipe are meaningless in a turbo system. No restrictions would be perfect, but also very loud indeed. A 3" exhaust system will give you excellent flow when combined with a high-flow muffler. Don't bother using a resonator in this system; the turbo itself will eliminate the exhaust drone that naturally aspirated 6-cylinder motors experience from 2000-2500 rpm. The turbo also quiets the exhaust at approximately 1/3 the rate that a muffler does.
This will be one of your big decisions. If you're planning on running anything over about 275 HP, don't get too attached to the stock system. This is where to spend the money you saved from not porting and polishing, not using a custom header, etc. For about $1000, you can get a fully programmable system to manage your ignition and your fuel delivery. If you anticipate wanting to raise your HP in the future, this is going to become a necessity. The flexibility of this system is almost infinite. If you're planning on sticking with the stock system, you're going to have to sort through countless wiring diagrams to figure out which wires you need where.
This is also one of your areas where you can find yourself using that extra cash you saved. A cheap intercooler will get you nowhere fast. A quality intercooler will run in the neighborhood of $300 or more. This is one of the key components of your turbo system, so do your homework and research thoroughly. Spearco makes some incredible intercoolers, but with the incredible unit comes an incredible price tag. One of the more common performance intercoolers is the Isuzu NPR intercooler, which can be fairly difficult to find, but one can be had used for around $300 if you're lucky and patient. Generally speaking, when it comes to choosing an intercooler for a high performance engine, you want the biggest unit you can find, but I wince saying that, as a good design should be more important than the sheer size of the unit. Do your research and find out what makes a good intercooler, then make an educated choice.
If you're planning on pushing 300 HP, you're more than likely be wanting new fuel lines. A 3/8" feed line should provide enough flow up to about 350 HP, and a 5/16" line should suffice as a return line. A high-pressure fuel pump is also going to be a necessity for your performance engine. Of course new units are very nice, but you can save yourself a few dollars if you try to find a used one from a car with a displacement of greater than 2.8L. (Something along the lines of a BMW 535, 635, 735; possibly a 300 ZX Twin Turbo, Twin Turbo Supra, etc.) The size you need depends on how wild you're planning on going with horsepower. Do your research.
While you're installing your new fuel pump and running the wiring for it (Using a relay, of course) is a good time to do a little bit of anti-theft work. Run a hidden toggle switch on the line that triggers your fuel pump relay. As long as you remember to turn it off every time you get out of the car, it's a pretty decent way to keep your car where you left it.
Your stock injectors will probably only be good to approximately 250 HP, though you can cheat a bit by running a higher fuel pressure through them, which is just a Band-Aid fix for a larger problem. A commonly found OEM injector that can support up to approximately 300 HP is the Ford Merkur/SVO injector. They're considerably cheaper than high-performance injectors, and can fit in your Z with some modifications. If you do go this route, be prepared to shell out for a custom fuel rail, which also has the added benefit of further reducing clutter in your engine compartment.
This is a modification that comes as highly recommended on your turbo L-series car. When the throttle plate closes, air is still being pushed out of the turbocharger. This air hits the throttle plate and reverses direction, heading back towards the turbo impeller. This creates a collision, which slows down the spinning turbo. This will happen every time you switch gears - not good at all. Adding a simple blow-off valve between the turbocharger and the throttle body can help alleviate this problem. Greddy has one available for about $200, or you can prowl the junkyards for a used one from a 1990-94 Talon/Eclipse/Laser Turbo, hopefully in the neighborhood of $20.
Wastegate and Boost Control
The stock wastegate on the T3 turbo is pretty decent. In the pages mentioned below, you can examine two different methods for controlling your boost level. One method entails metering the vacuum signal to the wastegate, and the other involves threading the wastegate rod and changing the length of it. An external wastegate is a superior design to the integrated design, and if you're planning on running anything over 15 psi of boost, you'll more than likely want to investigate designing an external setup. Maximum Boost has a great section on wastegate design.
Choosing the appropriate oil for your turbo engine is a much debated topic. It's strongly recommended to run full synthetic for the life of the engine; it simply stands up better to the high heats often seen in turbocharged engines. If you have something against synthetics and absolutely insist on standard motor oil, try to at least use a straight-weight motor oil. They have an increased stability over the multiweight oils (10W30, 20W50, etc.); this helps to prevent oil "coking", which is one of the leading causes of turbo failure. Even if you do opt for the full syntethic, you'll want to avoid using them during the "break-in" period. They lubricate a little *too* well for that time period, and don't allow the engine to be broken in properly. It's also generally recommended that you change your oil every 500 miles while breaking in your engine, which could be extremely pricey with synthetics.
You'll notice that a good portion of the advice in this article focuses on how to make a high-performance turbo engine without breaking the bank. It's not hard to build a 300 HP engine for about $3500. Be creative and troll the junkyards for OEM parts that might be compatible. Do your homework and research your plans before you spring into action. You'll save yourself time, money, and aggravation if you take the time to find the right items and the right price. Paying top dollar for something you don't need is very frustrating!