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Old 12th September 2007
SteveTheFolkie's Avatar
SteveTheFolkie SteveTheFolkie is offline
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Exclamation Can I add a turbo to my NA

This topic has been flogged to within an inch of life. There are numerous threads covering it in this forum. The answer is yes. For details, I suggest you search the existing forums rather than start yet another redundant thread.

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Old 13th September 2007
gorper gorper is offline
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Default A Little Information About Turbocharging a Non-turbo

Tens of thousands of enthusiasts around the world have turbocharged their non-turbo cars, from complete, professionally-engineered bolt-on kits to ultra-low-buck DIY affairs with parts sourced from the nearest pull-a-part. Naysayers who admonish people not to try it on a Saab 900 are misinformed: it’s been done before, many times, and there are many who’ve done it to engines that aren’t half as stout as Saab’s slant-4 variants. And, yes, with similar compression ratios to the B2x2i's 10.1:1.

The guys shelling out big money for bolt-on kits have it pretty easy: just lay down the Visa. But for the DIY’er, turbo conversions usually require extensive custom work: exhaust manifold and muffler system; oil/water plumbing (often including drilling into the block or oil pan!); intercooler fitment and plumbing; fueling and timing; and more.

However, turbocharging a non-turbo Saab 900 requires no custom work at all: every single part bolts on, and was designed and manufactured by Saab themselves. Further, the Saab engine is extremely tough, so the bottom end requires nothing. And that is the beauty of the conversion.

The only differences between non-turbo and turbo 16V engines are the intake camshaft and the pistons. The intake cam on the turbo closes later than on the non-turbo cam, which helps to decrease the trapped compression ratio. The pistons on the non-turbo have less dish; this is how Saab increases the static compression ratio.

Can I Do It?
The conversion requires decent mechanical ability and experience. If you have, say, changed a clutch, then you can probably turbocharge your NA. However, more important than your experience is your knowledge. If you do not understand how turbochargers work and how they affect your engine’s performance, then you probably should skip this project until you do. Or, at least, first learn more about turbos. “Street Turbocharging” is, in my opinion, currently the best-written, most useful book about turbocharging on the market. There are others, yes, but if you’re going to buy just one, buy this one.

Where are the Step-by-Step Instructions?
Sorry, not here. If you require a laundry list of parts, step-by-step instructions, and photos, then this project is probably not for you.

Won’t I Blow Up My Engine?
If you do your homework and don’t try to push things, no. Can it happen? You bet. Will it be my fault if you do? Nope. Life’s hard in the big city – you’re on your own. It’s up to you to learn about a turbocharged engine’s timing, fueling, and knock protection requirements.

What Do I Need?
You basically need a donor 900 Turbo. On Craigslist, find one with a bad transmission for a couple hundred dollars. You want a car that’s got the same head as yours; for example, you need a 16V Turbo to convert a 16V NA. From it you’ll need the entire intake tract, beginning with the intake snorkel, and, depending on your car, ending with the throttle. You’ll also need everything from the exhaust manifold back to the tail-pipe (in the U.S., you can get a brand-new cat-back exhaust for about $150 from You’ll need any associated water and oil plumbing, too, including the oil cooler, lines, and filter boss.

Note that, for water-cooled turbos (88+), you’ll need the lower radiator hose. Also note that the hard-line from this hose to the turbo is different for manuals and automatics. A line from a manual is incompatible with an automatic--I don't know if it works the other way around--and there is no part number on them that I have found, which makes it hard to find one unless you are able to hold it. Therefore, if possible, find a donor with the same transmission type.

Add the donor Turbo’s fuel/temp/boost gauge to your dash to see what’s what with your boost pressure.

Sheesh, You’re Not Too Helpful…
You can do a lot of damage with a little bit of information and not enough knowledge. Sorry, but I won’t facilitate the demise of your engine by giving instructions when you don’t know why you’re doing what you’re doing. Nonetheless, following are some details that will help you do this right, and run stock Turbo (11 psi) boost levels.
  • Premium fuel only
  • Turbo ECU (91-93 conversions will require retrofit to LH2.4). If you have an LH2.2 car, you'll need an LH2.2 Turbo ECU. Got LH2.4? You'll need an LH2.4 Turbo ECU. There are no LH2.4.2 Turbo ECUs, which is why 91-93 will need to convert to LH2.4**. (As you can see, it's helpful to have a donor car with the same version of Jetronic. It is not critical, though: you can find the proper ECU easily at (U.S./Canada).
  • Turbo injectors (In the U.S., you can have them cleaned inexpensively at
  • Non-turbo 3 bar fuel pressure regulator, that is, your stock regulartor
  • Intercooler – stock is plenty good for this project
  • APC system (It is basically standalone, requiring 12V and tach signal only – converting to a Turbo harness is unnecessary.)
  • Turbo distributor with advance defeated (For details, search my old posts from summer 2007.)
  • Turbo intake camshaft (lowers trapped compression a little)
For a simpler conversion, you can run ~5 psi of boost without the Turbo ECU, intercooler, APC, and distributor. You’ll still want to use premium fuel.

Disclaimer, Blah Blah
It bears repeating that it’s your responsibility to ensure your engine is adequately fueled and has properly timed spark. It’s also worth noting that there are myriad details that you will need to chase down. That is part of the fun, in my opinion. Others may post those details if they want to. As Mom would say, “bless their little hearts.”

Importantly, I am just an anonymous person on the internet (only DanComden knows that I'm not a complete moron, and even he may disagree with that, not that I could blame him...). You would be foolish to take my advice without being able to determine whether it’s sound. If you’re wondering, yes, I have successfully turbocharged a non-turbo car ('86) and know of a bunch of others. But I’m neither a professional mechanic nor an engineer, and I don’t claim to have all the answers.

Others' Input
Someone who is seriously considering this project can find lots of information on the web, including this and other Saab forums. It's a good idea to take the time to read up. My only advice here is to question whether the people whose posts you are reading have actually done a conversion. If they have not, then I would say keep looking: if I had a nickel for every forum post by someone who's not done it that says, "don't do it, you'll blow up your engine," I'd have enough money to put gas in my turbo'd NA car for a year.

**I have not converted an LH2.4.2 car to LH2.4 (my conversion was on an '86, with LH2.2). I have been told that there are some challenges to it but I don't know what they are. In other words, you're on your own, just you and the Bentley manual wire diagrams.

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Last edited by gorper; 13th September 2007 at 12:23 PM.
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Old 18th September 2007
gorper gorper is offline
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Default More on NA --> Turbo

Can a mod add this to what I wrote in the NA --> Turbo sticky, then delete this?


Appendix A: Modifying a Turbo Distributor for Use With a Turbocharged NA

You can get boost retard by using a Turbo distributor with the advance portion of the capsule defeated. People who turbocharge NA cars that aren't Saabs have to buy an MSD BTM or re-program their computer-contolled ignition system, if that's possible.

Using the Turbo distributor is a somewhat crude solution, but it is cheap and easy to do. It seems to work well on my car.

Modification Overview
The Turbo distributor has a crude vacuum advance and boost retard system atop it. What you do is modify this capsule so that it will NOT advance under vacuum any more–the EZK will do this for youbut leave it so the boost retard still functions.

Following is a photo of an unmodified capsule. Note the notch in the arm just above the base of the capsule. During high vacuum conditions, the arm is pulled up against the base, its travel limited by the notch:

To keep the capsule from advancing while the EZK is trying to do the same thing (which is does better), remove the capsule from the distributor, then, take a small washer and grind a slot in it perpindicular to the edge and through to the center, like taking a bite out of a donut. This is done so that the washer may be slid behind the arm:

Next, grind the edges of the washer so it will press-fit up under the base of the capsule:

The thickness of the washer needs to be the exact distance between the base of the capsule and the notch in the “arm” that moves in/out under vac/boost:

Setting Base Timing
For '86-'87 NA 16V owners, you're used to the 14* BTDC base timing setting. Owners of newer cars with crank-mounted sensors don't have a base setting, as EZK sets it for you. If you use a Turbo distributor, you'll need to manually set the base timing to 14* BTDC.

Miscellaneous Details

'86 and '87 non-turbo cars have a distributor with the Hall sensor inside; 88+ cars have a crank-mounted hall sensor. If you are turbochargin g an '86-'87, then you have a plug-and-play situation if you buy a Turbo distributor from 85-88, as those years have the same oval connector plug as your car. You can use an 89+ Turbo distributor, but you'll need to re-wire the plug, as it's different (square).

For 88+ NA cars with LH2.4, you can use any c900 Turbo distributor, but you'll need to customize the Hall sensor wiring to connect it. You do NOT use the crank-mounted sensor; you use the sensor in the Turbo distributor.

LH2.4 distributors have a slightly more robust plug than the earlier style; however, they are both somewhat fragile.

Before you modify the capsule, make sure that its diaphragm is not torn and that it holds pressure applied with your MityVac tool or similar.

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Last edited by gorper; 18th September 2007 at 11:40 PM.
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Old 10th October 2009
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Alex Alex is offline
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Extra information supplied by Gorper.

Originally Posted by gorper


A Turbo ECU cannot be installed on a 16V turbo conversion without also running a Turbo ignition system because Turbo ECUs do not output a load signal to the EZK, without which the EZK cannot function properly (it will start/run the car, but not modify timing to engine conditions). So if you want to run a bunch of boost, you'll need to ditch the EZK.

When I first planned my conversion, a very knowledgeable and experienced Saab enthusiast with whom I spoke recommended keeping the EZK ignition control system with the addition of a Turbo distributor. The idea was to defeat the Turbo distributor’s ability to control timing advance – letting the EZK do it – but allow the distributor to retard timing under boost conditions. This is a good idea in theory, but, without a load signal, DOES NOT WORK in practice and is only worth pursuing if you are running modest boost levels with the car’s ORIGINAL, NON-TURBO ECU, which has the necessary load signal.

Unfortunately, this took me several years to discover. Up until a few weeks ago, I had been using a Volvo Turbo Jetronic ECU in my car, along with EZK and a Turbo distributor with advance defeated. Like Saab non-turbo ECUs, Volvo Turbo ECUs also have the load signal that the EZK must have to run properly so I never knew about the issue.

Recently, because of what I had concluded were wiring issues with my Volvo set-up (a Volvo injector harness must be used to accommodate the injectors' resistor pack), I swapped it out and put in a 1986 Saab Turbo Jetronic box and associated components. I immediately got a flashing Check Engine light, which the Bentley manual revealed to be a No Load Signal error. The EZK will start/run the car like this, but, according to posts on, it will not change the timing.

Finally, a word about NA Jetronic ECUs. When I first got my conversion on the road, I ran the stock NA Jetronic ECU. However, using a wideband oxygen sensor, I discovered that the NA box does not sufficiently fuel the engine at higher boost levels (it kept the mixture pretty close to stoich.). So I wouldn't push things with an NA ECU.
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