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Turbo Kits Explained

We delve into the world of add-on turbo kits with the aid of David Alexander of Silverwater Automotive.

by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images

In a previous article (Designing a Factory Turbo Engine) we looked at how car companies design and implement their turbocharger systems. In this interview, we talk to a leading aftermarket turbo kit designer - David Alexander of Sydney's Silverwater Automotive. David has been the main man behind some excellent Hyundai Excel and Lantra turbo kits (go to the end of Lantra Ball of Fun for our drive report) as well as a few one-offs.

Can Your Car's Engine be Turbocharged?

Pretty well any naturally aspirated petrol engine from the past two or three decades can be turbocharged while maintaining good reliability. According to David, the biggest drama is the compression ratio of the latest engines.

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"The Hyundai Excel that I turbocharged had 10.0:1 compression, the Lantra 10.3:1 and it's not uncommon to have 11.0:1 in some of the more high performance atmo engines," says David. He adds that most of these engines have an efficient combustion chamber design allowing them to tolerate low boost levels.

"You can probably get away with turbocharging more on small bore, long stroke engines. With a larger bore, it takes longer to initiate combustion and you need to retard ignition timing under boost. You start wasting a lot of energy when you have to do that type of thing."

"You definitely need to run an intercooler with turbocharged engines having a static compression ratio above about 9.0:1 - you're shooting yourself in the foot otherwise. Ideally, I wouldn't go about turbocharging a standard type atmo engine without an intercooler."

Which Turbo to Use?

With the widespread availability of brand new turbochargers, many people have no idea what sort of unit to choose.

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David says: "I generally look at what the manufacturers are doing as a guide. Without going into the complexity of compressor maps, you should look at the turbos that manufacturers fit to certain capacity engines and the power output that they work at.

"In the case of the Hyundai Accent kit we used a Garrett T28 turbo based on what Nissan use on their 200SX - the SR20DET is a similar configuration and displacement engine with an output similar to what we wanted to achieve. When choosing a turbo it's also important to pick one that's readily available and there are parts for servicing."

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At the present moment, the turbos most widely available are suited to Nissan 4-bolt turbine patterns. VF and TD series turbochargers are also available to suit the unusually shaped Subaru Liberty/WRX turbine flange.

"You don't want to run a turbocharger that's too small," stresses David. "Exhaust gas temperature goes up along with combustion temps. I think erring on the large side has advantages but, of course, drivability suffers a little. Choosing a turbo is all about compromise."

Turbo Exhaust Manifold - How to Get One

"For the Hyundai Excel kit we designed a new exhaust manifold and had it cast in iron," says David.

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"Quality cast manifolds can support a lot of weight and tend not to crack like some handmade manifolds. I think it's the best approach. The cost involved in a cast iron manifold is mainly in the pattern design. Depending on the complexity and nature of the manifold it costs about AUD$5000 to have a pattern made."

(For another industry expert's view on turbocharger exhaust manifolds, read Buncha Bananas)

Turbocharger Oil and Water Feeds and Return Pipes

All turbochargers require a supply of oil to lubricate the center bearing assembly. Most modern turbochargers (after about 1986) use water-cooling to maintain a stable operating temperature, but some turbochargers are simply air-cooled.

So where should you obtain a turbocharger oil feed from and where should it be returned?

"The oil pressure switch is usually a perfect spot to source the turbocharger's oil feed," says David. "When you're running a ball-bearing turbo you might want to run a restrictor in the line from the oil feed source, because you don't want to tap into a too great an oil supply.

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"For the oil line to the turbo we normally use a Teflon braided hose. You need to have some flexibility for expansion and we've never had any failures with the Teflon braided stuff. An option would probably be to use a hard pipe with a spiral winding.

"The oil from the turbo should drain back into the sump above the oil line. It's good to have a baffle near the return fitting so that oil doesn't splash back up or restrict oil flow out of the turbo. And make sure that the hose you use is rated to the appropriate temperature."

As mentioned, most modern turbochargers have a water-cooled core. Where should the water be sourced from and returned to?

"A lot of cars these days have heated throttle bodies, which are a good place to tap into - you still run the water through the throttle body but then into the turbo and back into the block.

"You've got to be careful tapping into the heater hoses because if you switch the heater on you can change the direction or at least reduce the amount of water flow through the turbocharger. This generally shouldn't be a problem, though. I think the main reason for having water-cooling is to maintain a stable core temperature when you shut the engine down," says David.

Changing the Engine Management to Suit Forced Induction

One you've got the turbocharger hardware sorted out you will need to examine what needs to be done in the area of engine management. Is it possible to retain the factory ECU?

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"When you add a turbo you will overshoot the tables in the ECU - they generally only have a small amount of scope above standard," says David.

"In some cars you can squeeze in about 5 psi of boost and only then you're at the limit of the airflow meter - cars like the V6 Holden Commodore and some Mazdas, for example. The thing is, none of them were designed for force induction so the fuel and timing will be less than ideal.

"There's no easy solution.

"For example, in the early Excel that we turbocharged I ran a larger bodied airflow meter to measure the extra airflow and modified the factory program to suit. I chose that approach because I have the ability to do it and there are advantages in terms of starting and various other areas. In the case of the twin-cam Excel with a standard MAP sensed system, I ended up changing to a 2 Bar MAP sensor and extensively modifying the program to run with that.

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"A lot of people America simply use a rising rate fuel pressure regulator in low boost applications and they seem to get away with it - to an extent. But it's not a great approach from a tuner's point of view. With this set-up, the engine usually drowns in fuel because fuel pressure is raised exponentially and the ignition timing is usually left as it is.

"Of course, with higher fuel rail pressure the less fuel flow your pump can deliver. You really need an upgrade pump as well.

"And there are considerations beyond mixtures and timing. I've turbocharged a 1.8-litre Honda VTEC with a F-CON piggyback computer - the fuel side of things was great, but the cam switchover stage was all wrong with the forced induction.

"At the end of the day you should aim to maintain a usable torque curve. If everything is set up properly I often find that the turbocharged torque curve is fairly similar in shape to the base torque curve - it's just lifted higher," says David.

Take this man's advice. He knows what he's talking about!


Silverwater Automotive Services
02 9748 1300

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