Two turbo or not two turbo
Posted on February 2, 2010 by Jesse O'Brien in In the Garage
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.
Cool site man. My vote is for an externally gated single T3/T04E setup. The twin turbo setup does have the wow factor, but its' pretty risky if you're not planning on using an intercooler, not to mention it would probably be harder to tune. Of course you could also incorporate water/methanol injection to aid with the cooling, but I'm not sure if you want to go down that route.As you said, a single turbo setup can be just as efficient and powerful as a dual and will allow you to use an intercooler. The external wastegate will let you fine tune boost as well. Lag shouldn't be too much of a problem with the T3/T04E since you'll have decent off-boost performance from the 2.8L of displacement. And since you'll be using an intercooler, there will be less worries about detonation. Provided you have adequate fuel delivery, you can just crank up the boost since your compression ratio is already low. A nice clean setup for a DD (after all the fab work required for the exhaust manifold/downpipe/exhaust that is).
I've got a few ways around cooling the intake charge, since I'm already planning megasquirt:1 – water/*anol injection through the 7th injector port at the throttle body that's on the intake manifold from the factory, when the intake charge is too hot2 – modifying the fuel curve when the intake charge is too hot3 – modifying the timing when the intake charge is too hot4 – decreasing the wastegate boost controller solenoid setting when the intake charge is too hotFor a daily driver, it's actually not such a terrible idea since I won't be driving it hard for extended periods, except the occasional track day. I'm really not leaning toward the twin turbo setup, since it represents the most work of all the options. Right now, I'm a little biased toward the Turbonetics t3/t04e externally wastegated with a nice big intercooler on the front (and possibly water/*anol injection and other temp. control methods on top of that, since I'm doing megasquirt either way).Thanks for coming by though, I needed someone to offer a little validation for all the work I'm planning to do.
Cool site man. My vote is for an externally gated single T3/T04E setup. The twin turbo setup does have the wow factor, but its' pretty risky if you're not planning on using an intercooler, not to mention it would probably be harder to tune. Of course you could also incorporate water/methanol injection to aid with the cooling, but I'm not sure if you want to go down that route.As you said, a single turbo setup can be just as efficient and powerful as a dual and will allow you to use an intercooler. The external wastegate will let you fine tune boost as well. Lag shouldn't be too much of a problem with the T3/T04E since you'll have decent off-boost performance from the 2.8L of displacement. And since you'll be using an intercooler, there will be less worries about detonation. Provided you have adequate fuel delivery, you can just crank up the boost since your compression ratio is already low. A nice clean setup for a DD (after all the fab work required for the exhaust manifold/downpipe/exhaust that is).
I've got a few ways around cooling the intake charge, since I'm already planning megasquirt:1 – water/*anol injection through the 7th injector port at the throttle body that's on the intake manifold from the factory, when the intake charge is too hot2 – modifying the fuel curve when the intake charge is too hot3 – modifying the timing when the intake charge is too hot4 – decreasing the wastegate boost controller solenoid setting when the intake charge is too hotFor a daily driver, it's actually not such a terrible idea since I won't be driving it hard for extended periods, except the occasional track day. I'm really not leaning toward the twin turbo setup, since it represents the most work of all the options. Right now, I'm a little biased toward the Turbonetics t3/t04e externally wastegated with a nice big intercooler on the front (and possibly water/*anol injection and other temp. control methods on top of that, since I'm doing megasquirt either way).Thanks for coming by though, I needed someone to offer a little validation for all the work I'm planning to do.