I spent a lot of time researching options to control fuel delivery in my l28et for the Sinister s30 project.  Xenon’s website is a great resource overall, and answered the majority of my questions, but I had trouble finding a concise explanation as to what common fuel management choices were available.

Fuel Storage

First off, if you’re putting an l28et into your own s30, you’ll need to decide if you’re going to keep the stock fuel tank or not.  The stock tank is un-baffled, so fuel sloshes around when cornering, accelerating, or braking.  If the tank isn’t full, the fuel pickup will sometimes run dry and won’t deliver fuel to the engine.

If you don’t mind replacing the stock tank, make sure you get a baffled tank.  These essentially have doors that keep a small amount of fuel at the pickup so the fuel pump never runs dry.  Many s30 owners install baffled fuel cells, which are the ideal solution but are time-consuming and require a welder to install.

If you’re keeping the stock tank without modifying it, you’ll need two fuel pumps and a surge tank.  The surge tank is a small container (less than a gallon) that holds fuel.  The first fuel pump feeds the surge tank, and the second pump pulls fuel from the bottom of the fuel tank into the engine.  This is a simple, economical option if your stock tank is in serviceable condition.  I’ll be using an old  1.5liter fire extinguisher as my surge tank, and I’ll post up a diagram of exactly how it works later.  For now, you just get a picture of the extinguisher.

The third, more uncommon option is to fill your stock tank with a sponge-like foam.  The foam holds fuel and keeps it from sloshing.  It reduces lateral weight transfer and is relatively inexpensive, but render conventional fuel gauges useless.

The final option is to keep the stock tank but add baffles.  I can’t come up with a compelling reason to do it unless you’re really into keeping the car looking completely stock.  You’ve gotta be pretty OCD to care what the fuel tank looks like, though.

ECU

280zx-t ecu is pretty much a paperweight that uses electricity.  For most cars, it’s better to unplug the o2 sensor, which feeds information that would be absolutely critical to any other car.  The z31 ECU is pretty much plug-and-play and will improve mileage somewhat.  There are aftermarket ECUs available, such as the Wolf, which come highly recommended, but are expensive ($1000+ USD).

I came to the conclusion that the ideal solution is to install MegaSquirt, but it’s a time-consuming ordeal.  First, you’d have to decide which version of MegaSquirt to purchase.  There’s MS1, MS2, and MS3, and there are various versions of software that can be run on each.  Without getting into too many details, my recommendation is a pre-assembled MS2v3.  It’s worthwhile to purchase a relay board, a cable to connect the two, and another cable to run to the engine itself.  You’ll still have to connect all the wires to the correct sensors and inputs, but it’s a straightforward affair.  You can get away with building the whole thing for around $400 if you don’t value your time very highly and have a moderate amount of experience with soldering, but I highly recommend the pre-assembled kits.

Sensors

The most crucial sensor on for fuel delivery is the air measurement sensor.  The stock AFM (air flow meter, uses a flapper to measure air being sucked/pushed into the engine) is inferior to a MAF (Mass Air Flow sensor, measures air density/velocity), which isn’t quite as good as a MAP (Manifold Absolute Pressure, measures how much pressure is in the intake manifold).  MS2v3 comes with a MAP sensor built-in, and can accurately read up to 15psi of boost.

The second sensor that’s important to note is the o2 sensor.  It measures the amount of unburned oxygen that leaves the engine, and the ECU adjusts the fuel map based on what information the o2 sensor offers.  I’ve heard from several people that the stock 280zx-t ecu goes a little crazy with an o2 sensor plugged in and they recommend removing it for better performance and mileage.  It’s strange and contrary to normal logic, but it’s become common knowledge at this point.  That’s just one more reason for me to dislike the stock ECU even more.

If you’re installing megasquirt or making a major change to your engine configuration, you’ll want to borrow or buy a wideband o2 sensor.  A wideband displays just how rich or lean your fuel/air mixture is.  It’s much more useful than a traditional o2 sensor that essentially only tells you if you’re rich or lean.

The more accurate the information you’re feeding into the ECU, and the more information you’re feeding it, the more accurate it can be.  The faster and smarter the ECU, the more precise the end result will be.  There’s a big difference between accuracy and precision, but you want both, not one or the other.

Conclusion

Fuel management is where you’ll gain almost all the mileage gains on an older efi car.  There can be significant performance increases as well if you end up fine-tuning your setup and spending a respectable amount of time getting it right.

I’m a little frustrated that with all the progress I’ve made I haven’t really finished anything on my to-do list for the s30.  I had it running, but was short one injector and didn’t have a turbo bolted up, so it ran … terribly.  I also had no shifter, and the seats weren’t bolted in so I was pretty surprised when I found out it was in reverse.  Oh right, and no clutch installed.

Note to self:  avoid that kind of excitement in the future.

There has been other progress in the meantime, mostly in the engine bay.

Intake

I bolted up the new intake manifold (from an n47 engine) that’s slightly bulkier than the black (n42) manifold I had, but is complete and a running car with a few extra pounds is better than a non-running car with a few less pounds.  I finished up the installation of the injectors now that I had enough threads to bolt them all in, and hooked up all the wiring.

Fuel

The 280zx-t fuel pump bolted right in to the rear frame like it was made to go there.  I still need to put the stock fuel tank back in (I removed it to clean out a bunch of sediment) and hook up all the lines to it.  Once that’s done, the mechanical portion of my fuel system is complete.  I’m planning to install Megasquirt (the mileage gains pay for the cost of a complete Megasquirt kit in around 4,000 miles) and tune that to replace the stock Nissan l28et ECU, which is notoriously inefficient and unreliable.

Exhaust/Turbo

I’ve finally assembled the turbocharger setup, with the wastegate spacer/flange and 35mm wastegate.  I have a spare wastegate and turbo that I’ll sell off, since I finally decided to use the t3/t04e Turbonetics hybrid turbo.  It should fit this engine perfectly, but I’d still like to get the compressor map for it to confirm.

My intake ductwork is on its way, I’ve decided on slightly oversized 2.5″ piping to the intercooler, then to the throttle body.  I only ordered the piping, since I need to figure out how I’m going to fit it and order an intercooler that’s the right size for the space I have.  Expect an update on that as soon as the intercooler ductwork is in.

The exhaust will happen after the car has been driveable for a bit and I trust everything else.  Exhaust fabrication is relatively quick and straightforward work, so I’m not too worried about it.  I’m much more concerned with the intake ductwork.

DISCLAIMER:

All images are exactly to 1:1 scale, there is no deviation in any of these parts from their real-life counterparts.  I spent months drawing these extremely accurate models, so please point out anything that might be considered even slightly different from factory specifications.  Also, I’m colorblind.  The color scheme is pretty much just so you can tell the different parts from each other.

Since I got so many questions about my l28ett design, I decided I’d write up the basics of how this will work.  Bear in mind, this is different from a standard twin turbo setup, or a sequential turbo setup.  I started writing it up, then quickly decided that words just aren’t adequate to describe this and broke out a pencil and some paper.  I drew up how it would all work, then realized that was just as confusing as words, so I sat down in front of my drawing tablet and I’m gonna walk you through it now.

Base design concerns

Here’s an l28et block and head.  It has 6 cylinders inline with each other (instead of assembled in a v with 3 on each side), and 12 valves (meaning 12 ports).  The 6 holes on top of the head are intake ports, the 6 on the bottom are exhaust.  I was a little creative with the valve cover, and it’s decidedly not to scale, but I don’t really care.  I’m explaining something here, not re-engineering an engine.  This engine is a little abnormal because the status quo of engines is known as ‘crossflow’ meaning that air goes in one side and out the other.  Crossflow designs make turbochargers a little more complex to route, but that’s a solved problem and we aren’t going to worry about comparing the two.  Just understand that the intake and exhaust are on one side of the engine, and the spark plugs are on the other.

Exhaust

Tube steel is the best choice for exhaust routing, since it can withstand heat, is relatively easy to work with (the term is called welding) and doesn’t cost a whole lot.  A mild steel manifold will most likely cost around $100-$150 in supplies for a hobbyist like myself, and makes the front end of the car significantly lighter and also allows exhaust to be routed in an efficient way.  I’m basically taking the front three exhaust ports and collecting them into one, which feeds one turbocharger, and collecting the rear three ports to feed the other turbocharger.  The collectors also have a tube that runs between them, with my wastegate in the middle of that tube.  Let’s explore the wastegate idea a little more, it’s the most important part of any turbocharging setup and often gets ignored.

Wastegate

A wastegate is simply a pneumatic valve that opens to let exhaust gases through.  It’s engaged by air pressure, which is available as soon as the turbochargers start to spin.  When the turbochargers have enough air in the compression turbine side, the wastegate opens allowing exhaust to bypass the turbochargers, and they are no longer powered (exhaust gas is what spins turbochargers).  Without a wastegate, turbochargers would spin out of control and some part(s) of your engine would just explode under the air pressure.

When my wastegate opens, exhaust gas from both halves of the exhaust will be allowed to escape, rather than having to push the turbocharger around before going out the back of the engine.  This allows me to control the air pressure going into my engine, and the cross-pipe keeps both turbos relatively in sync.

Turbos

Normally, both turbochargers would pull air from the front of the engine.  My engine bay is long enough that I can pull air from the rear with the rear turbo, and from the front with the front turbo, and the exhausts of each can merge efficiently and seamlessly between each other.

This is also where the non-crossflow design comes into play.  Instead of having lots of bends and ductwork to get my compressed air to go into the intake manifold, my compressed air points straight up.  If only an intake manifold existed that could take advantage of that…

Intake manifold

I’ll just have to make an intake manifold.  All I need to do is make a plenum, then 6 runners that point toward the ports of the engine, and cut two holes in the bottom of the plenum.  50mm and 60mm throttle bodies are readily available, so I can use two: one for each turbocharger outlet.

This provides instant throttle response.  Turbo lag is slightly present, but pressing on the gas pedal will give a jolt like no other turbocharged vehicle is capable of.

Fuel delivery

Delivering fuel to this is as easy as drilling the correct holes for an injector at each intake port of the engine, then installing a fuel injector there.  I have a great set of injectors from osidetiger, and pallnet has excellent fuel rails available, so this would be a simple process.  However, the stock Nissan electronic control unit would be completely confused by this setup (don’t tell anyone, but it’s confused by pretty much any setup, including the stock setup from the factory).  Megasquirt is a great alternative for controlling fuel electronics and newer versions can control boost levels, so I’d go with that.

Design problems

There are some notable issues that I can see, just looking at this design.  The one that really matters is heat.  A turbocharger generates quite a bit of heat, and throws out compressed, heated air.  Two turbos do … double that.  Normally, a turbocharger is routed into an intercooler (like a radiator, but for cooling air instead of radiator fluid).  This design has no room for an intercooler, so it throws a lot of hot air into the engine (that’s bad).

The proximity of exhaust and intake is always an issue, and that’s compounded even more when there are two turbochargers stuffed directly under the intake manifold.  There isn’t a whole lot that can be done about this.

The main problem with all this heat is called “detonation“.  Detonation occurs when your air and fuel mixture is hot enough that it explodes too early.  If this happens a few times, it’s nothing to worry about, but if it happens as a regular part of driving, you won’t be driving very regularly at all.  To combat detonation, you can add extra fuel to the intake mixture, which is called ‘enrichening the circuit’.  It’s not very efficient, but helps cool down the inside of the engine.

Another option is to run coolant through the intake manifold.  This is a significant amount of work, so I’d suggest settling for the next best thing: running coolant through the throttle body.  The 240sx has a 60mm throttle body that’s perfect for this application, and has coolant lines installed on it from the factory.  Both these techniques will go a long way toward preventing detonation, but let’s take it a step further.

Higher octane fuels are resistant to detonation.  That’s their only advantage.  They don’t make your car faster or burn cleaner or make the car gods love you any more than they already do.  It’s not a bad idea to run higher octane fuels on any high-compression or turbocharged engine.  It costs a bit extra, but if you’re reading about making an exhaust manifold and intake manifold for your two turbochargers… you’d be willing to spend a little extra here and there.

Adding water or a form of alcohol (nitrous oxide or methanol are two popular examples) before the fuel is mixed in will enrich the circuit and drastically reduce detonation.  If you end up going this route, add another injector or two between the throttle bodies and set up megasquirt so they fire alcohol into the compressed air whenever a ‘knock sensor’ is triggered.  You can also add a heat sensor into the intake manifold for this.

One more way to reduce detonation caused by excess heat is to reduce boost.  Opening the wastegate will immediately drop pressure and power in the engine, and will stop the increase in temperatures, but won’t do anything to cool down the engine if it’s already in a dangerous state.  This is best used as a preventative measure, so reduce boost BEFORE your combustion temperatures are excessively high.

The final, and most important thing you can do to prevent detonation is to minimize ‘heat soak’.  The hot air in your exhaust and turbos generates a lot of heat, and that heat wafts up to your intake manifold, making the gases inside even hotter.  An aluminum plate with a fire blanket or another type of insulation as a barrier between the intake and exhaust is a must.

Conclusion

I don’t see the twin turbo setup as being worth the work.  While cool, I won’t really benefit from this design.  I can push as much air into my engine as it can safely burn off with a single t3/t04e turbocharger, and it’s easier to use an intercooler with it as well.  I won’t have the instantaneous throttle response the dual-turbo setup would offer, but I think I’ll be perfectly fine driving across the country with just one turbo.  My goals are only 300hp or so, and that’s very easily attainable with a good turbocharger and an accurate fuel delivery tune.

I’ve been back and forth about the final state of my engine bay for awhile now, and need to make a decision.  I’m looking for your input on which setup you think is the best.

L28et design ideals

The l28et engine is a strange combination of old and new technology, and is the force that will drive the wheels of my Sinister s30 project.  The strange code of the engine breaks down like this:

L – inline (not v-shaped) cylinder configuration

28 – 2.8liters of displacement

E – electronically fuel injected (instead of carburetted)

T – turbocharged from the factory

It’s a well-designed engine that was excellent for its time, but has a few glaring problems that need to be addressed.  Once I’ve finished fixing those, I’ll write up an article, but for today I’m faced with a conundrum: how many turbos should I install on this?

In essence, a turbocharger is an air pump that forces air into the engine, which allows more fuel to be mixed and burned, and therefore more power to be produced.  It has some efficiency gains over a naturally aspirated engine (imagine climbing a mountain with a lightweight oxygen tank that ensures you never get winded, then climbing the same mountain without the oxygen tank) but is generally seen as a power adder.  This particular engine is considered low compression, meaning it compresses air and fuel inside the engine at about a 7.3:1 ratio (as a base of comparison, several Honda Civic engines compress at a ratio of 11:1).  Because that ratio is so low, a turbocharger is necessary to get the most efficiency out of this motor.

So there it is, I’m required to have a turbocharger.  The question becomes, which one(s)?

Stock configuration, upgraded turbo

There are two viable options for a single turbocharger: t3 or t3/t04e hybrid. You can see both sizes here in my collection.  The smallest turbine in the image to the right is the stock t3 that I removed from this engine.  It’s a reasonably sized turbo that provides a fair amount of air into the engine.  Because the l28et is a low-compression engine, larger turbocharger is a good idea in all aspects.  That’s where the t3/t04e comes in, and provides roughly double the air that the stock t3 does.  The t3/t04e is a hybrid between two turbos, using a small t3 turbine to collect exhaust gases, which push a much larger turbine from a t04e and compresses much more air equally fast.

To sum things up: the t3/t04e squishes air more quickly and has the capacity to squeeze more air into my engine.  That means it makes more power more quickly and efficiently, but is extra work to install over the stock configuration of a smaller t3.

Upside:  Inexpensive

Downside:  This is the same setup the l28et came with, and requires the same amount of work as the other options for less power.

Twin t3/t04e Turbochargers

My other option is to install two t3/t04e hybrid turbos, which is cool as ice, but is more work.  I’d need to fabricate an exhaust manifold, similar to a few that I came across on HybridZ.

To effectively install two of these turbochargers, I would want to fabricate an intake manifold.  My design is a little abnormal, with dual throttle bodies facing up from the turbochargers into a plenum, but would work well for everything but cooling.

The hot compressed air would shoot directly up into the engine, rather than flowing through an intercooler.  It’s dangerous to allow hot air into the engine for extended periods of time, but means that the engine responds much more quickly to the throttle pedal.  The car would feel much more powerful, but I’d have to tune the ecu to carefully monitor temperatures and exhaust gases and decrease the amount of boost when it gets too warm.

Upside: Very fast throttle response, lots of power while it’s cool

Downside: Overheats quickly, which decreases power and efficiency on hot days or when driving hard for long periods (such as track days), the most work of all my options

Single turbocharger, external wastegate

In between these two options is a custom manifold for a single t3/t04e hybrid turbo, using an external wastegate.  The external wastegate affords more precise tuning of how much pressure the turbocharger creates before letting exhaust gases skip it.  It’s a big upgrade, and a single well-designed turbo can be just as powerful and efficient as two.

Upside:  Simple, proven setup that’s straightforward to tune, the most amount of power possible while being a ‘safe’ setup

Downside:  Requires fabrication and doesn’t add to the ‘cool factor’

Miscellaneous stuff

Normally there are other considerations to take into account, like how much fuel is available to be delivered, how hot it’s going to get, how quickly your ecu can respond to changes in pressure, and how much pressure your engine can actually withstand before pieces start popping off from the inside, but I’ve taken these things into account (for the most part) and am looking for advice on which configuration sounds the most interesting.  They all make sense, and I have the important supplies to be able to do either.  At this point it’s just a matter of deciding what to go with and putting in the time to finish it.  So what are your thoughts?

Before anyone else mentions it, a twin turbo carburetted engine is a bad idea, for many reasons.  Just because it was on Wangan Midnight doesn’t mean it’s cool or relevant.  Fuel injection is much more efficient and worlds easier to maintain.