Driven Daily » forced induction

s30 l28et engine update

Jesse O'Brien — Fri, 12 Feb 2010 21:09:50 +0000

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 the clutch pedal was not connected.

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.

Two turbo or not two turbo

Jesse O'Brien — Tue, 02 Feb 2010 09:00:31 +0000

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.

Turbocharger Sizing

Jesse O'Brien — Wed, 17 Jun 2009 06:00:36 +0000

Establish a Starting Point

As with any project, the first thing you should do is establish your goals. This is going to require a bit of math, but we’re going to determine the ideal target crank hp gain for your vehicle. A good rule of thumb is that every 10hp you make with a gas engine requires a pound of air per minute delievered into the intake manifold. For example, to transform a 100peak horsepower (php) naturally aspirated engine into a 200php turbo engine, you’re going to need a turbocharger capable of flowing 20lbs of air per minute at a realistic boost pressure. You’ll need to compute the basic engine airflow rate in CFM as follows:

Airflow=(cubic inches of displacement * rotations per mminute * 0.5 * volumetric efficiency(V.E))/1728

The *0.5 is there because a four-stroke engine only breathes every other revolution, while 1728 converts cubic inches to cubic feet per minute

If you were to insert 83 percent for V.E for a typical 2.0L (122CID)Honda engine you would have a total of 247CFM.

122CID * 7000 * 0.5 * .83/1728=247 CFM

At 83 degrees ambient temperature at sea level 247CFM converts to pounds/minute follows:

lbs/min=CFM * .07

Therefore 247CFM * .07 = 17.29 lbs of air per minute.

Using this rule of thumb this 2.0l engine should produce approximately 173 NA HP. Now let’s see what we could do with that number using a compressor…

Verify Target Boost Pressure

On a street car, target boost pressure will be the lesser of the boost needed to make target power or (more likely) the engine’s boost detonation limit. Increase boost enough and A/F mixture in the combustion chambers will begin to explode instead of burning smoothly, which is very bad for the engine. There is no point of having a turbo that can push abnormal amounts of air beyond the point of the engines boost detonation limit if your fuel system cannot deliver the fuel required to safely run your engine at that pressure. Additional boost limiting factors include fuel supply constraints and engine calibration limitations. With premium street gas (typically 93 octane for most and 91 for us Cali folk), assume a maximum of 10 psi of boost without an intercooler and 15 psi of boost with an intercooler. Highest boost pressure will be feasible with pent roof combustion chambers, efficient intercooling, higher octane gas, excellent fuel management with a high quality calibration using the best anti-detonation countermeasures.

Convert Target Boost PSI to pressure ratio

You need a pressure ratio to work with compressor maps that plot air flow at various pressure ratios and compressor speeds. If you’re working with target boost pressure, you’ll need to convert boost pressure to a pressure ratio, which is the percentage of one atmosphere above nothing at all delievered at the compressor’s outlet. For example: 10 psi of boost + 14.7(atmospheric pressure)/14.7=1.68 boost pressure ratio. Which means BPR of 1.68 equals 68 percent higher pressure than NA. On our 2.0l Honda motor running 9.5:1 compression to start with that would be ~16:1 total compression ratio at peak boost.

Convert Pressure Ratio to Density Ratio

Unfortunately, a turbo engine system will not usually flow as many CFM as you’d predict just by multiplying the pressure ratio by the NA airflow of the engine in CFM. Bear in mind that density ratios vary because of turbo’s thermal efficiency and efficiency of the intercooling system. Most street turbos operate in the thermal efficiency range of 55-85 percent.

Let’s go back to the 2.0l Honda engine. If we were to boost that engine to 7.5 psi without an intercooler, the pressure ratio for that engine will be (7.5+14.7)/14.7, which yields a pressure ratio of 1.5. Using the stock airflow of that engine of 17.29lb/min(247 CFM), at a BPR of 1.5, you might expect the airflow under boost would increase to roughly 28lb/min. However, if this particular turbo with no IC is just 75% efficient, the density ratio at sea level is really about 1.3 which equates to 24lb/min of airflow. Bottom line: when turbocharging your engine, you’ll need to start with a slightly oversized turbo to compensate for turbo inefficiency.

Select the RPM range of your engine for maximum compressor efficiency

Contact various manufacturers for a turbo compressor efficiency map for every turbo you’re interested in. You’ll typically want to match your turbo’s maximum compressor efficiency with your engine’s natural powerband. This will require a lot of knowledge about turbos, so you may want to contact the experts at Garret, Precision Turbo, HKS, etc.

Rather than aiming to achieve maximum peak power, think of the areas that will greatly help your vehicle acceleration. 500HP at 10,00rpm is useless compared to a 300hp at 4000-6000rpms in a street application. But if you are trying to maximize your peak power, remember that a forced induction system will always shift peak power to a higher part of the rev range. But with the days of electronic boost controllers, users will be able to pinpoint when the peak boost will be created anywhere on the rev range based on rpm, gear, and other factors. You might place peak boost at lower rev range to amplify torque (helpful with acceleration) but you’ll need to reduce pressure at higher speed to limit peak hp to stay within certain fuel constraints or to protect your drivetrain. For example, dragsters limit boost at lower gears as a form of traction control.

Select a compressor

You’ll notice that a compressor map will resemble a 3d topgraphical contour map of a hill. This map describes the compressor’s efficiency at various combination of airflow rates and boost pressure. To the left of the map also are danger zones at the east and west of the map. This zones illustrates the surge and choke zones of the compressor. Big turbos tend to surge at lower revs with huge turbo lags and usually no streetable power gains. Hybrid turbo is a solution if you are looking for a big compressor but a quicker spool-up time. The t3/4 hybrid is a perfect example which utilizes a smaller turbine but with a bigger compressor to virtually eliminate turbo lag. If your engine has a powerful bottom end, you might choose a big turbo to create big peak power but to accentuate your bottom end as it creates full boost. But with a engine with a weak bottom end and a strong top end (such as a Honda b16 or Mazda 13b), you might want a smaller turbo that spools quickly and build boost as soon as possible to maximize bottom end power and let your engine’s powerful top end take the rest of the way. Either way a small turbo will run out of steam at the upper reach of the rev range and a big turbo will spool slowly but their airflow at higher rev range will eclipse the smaller turbo counterparts.

Some engines also incorporate a second turbine. These can be twin turbos (in which both turbochargers are the same, and increase the gains in their particular rev range) or sequential turbos (in which one turbo is smaller to help the engine wind up, and another to carry it through the upper powerband). Some smaller engines may actually see performance decrease if a second turbo is added because the engine does not produce enough exhaust gas to spool both turbos.

Further Reading

So far, I’ve found one other extremely informative site regarding turbochargers:

http://www.turbominivan.com/tech/turbo101.htm

I feel like I haven’t been looking hard enough, though. What other pages or books should I be aware of?