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Discussion Starter · #1 ·
What’s this turbo thing?

I’m starting to get a little curious about MY turbo!
Could anybody fill me in with a few details?
1) At what engine RPM does the turbo start / stop working?
2) Is it just idling or is it standing still when outside this rev range?
3) How fast does it spin?
4) Is its speed limited or will it just go as fast as the exh gasses?
5) How come the exh doesn’t fill it with carbon?
6) Why cant I just stick bigger turbo, inlet manf & exh to gain power?

I’m sure there are other curious Saabers out there so if there are any other questions please add them to the list.

Pete
 

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Discussion Starter · #3 ·
Re: What’s this turbo thing?

Its a 9-5 1999 3.0 V6 petrol. But haven’t the other lpt 9-5s and 9000s got similar characteristics?

Pete
 

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Re: What’s this turbo thing?

1) At what engine RPM does the turbo start / stop working?

It will start working at around 2000rpm

2) Is it just idling or is it standing still when outside this rev range?

It is not idling, when your engine is idling, it is still producing exhaust pressure, the turbo is spinning, but not enough to produce pressure

3) How fast does it spin?

At max pressure, turbo's can spin over 20.000rpm, the outer parts of the turbine can exceed the speed of sound

4) Is its speed limited or will it just go as fast as the exh gasses?

In theory it is not limited, the more exhaust pressure, the more speed. In the real life, there is a limit to the max speed of a turbo, this depends on the turbo, the inlet and the exhaust system.

5) How come the exh doesn’t fill it with carbon?

Temperature is to high

6) Why cant I just stick bigger turbo, inlet manf & exh to gain power?

You will have to adapt the amount of fuel as well, this will mean bigger carburators or injectors, adapted ecu etc. Off coarse you will need an engine that can cope with the extra power.
 

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Re: What’s this turbo thing?

Actually most smaller turbos can go as fast 150,000 RPM without "overspeeding" ... in reality they will usually hit about 200,000 RPM before the hub "bursts". At that speed the outer edge of a 60 mm compressor will be going 1,406 mph ... or roughly Mach 2.

Here's the flow chart for the turbo found on a C900T 16V:



Dubbya~
 

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Re: What’s this turbo thing?

Pete A - your car is a bit different from the "normal" 4-cylinder Saab turbos in that your engine uses an "asymmetrical" turbo arrangement. What this means is that only one of the two banks of cylinders in the V actually drives the turbo. This means a smaller turbo can be used (and this will generate boost well before 2000 rpm) without the extra mass and thus inertia that a larger turbo would experience.

Not sure of the specifics but it will not stop generating boost towards the top end of the rpm range, it's just that the effect will drop off as the volume of exhaust/intake air approaches the maximum flow of the turbo. The level of boost generated at higher rpm (and indeed any rpm) is also controlled to a large degree by the ECU.

You could probably fit a bigger turbo, and make other mods, but this would be likely to give more lag due to the inertia mentioned above. That's why early 99 turbos don't do much till about 3000 rpm and then suddenly take off like you've been hit up the chuff by a freight train

If you're serious about modding that engine, perhaps an alternative route to explore is a second small turbo on the other bank of the V, however I'm not sure if anyone has done this before, if there is space, or indeed if this engine is strong enough to take the extra performance reliably.
 

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Re: What’s this turbo thing?

I've heard of someone making the V6 twin turbo somewhere over here in the states. Been a while. No online link though, or I'd share it.

Dubbya~
 

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Discussion Starter · #8 ·
Re: What’s this turbo thing?

Thanks for the info. That’s exactly what I wanted. (Saab specific).


While surfing this morning I found these
http://auto.howstuffworks.com/turbo.htm
http://www.turbotechnics.com/
They help with the understanding of the works, whys and wherefores.

Regarding modding the engine:-
It is something I would love to do, but for time, space, expense and not being able to do without if I cock something up.

Years ago I did a bit of work on my own transport:- Head gasket’s. Replacing OHC. Stripping a motorbike gearbox (it took 4 attempts to get that right). S U Carb’s. Brakes. Clutches. And of course the obligatory problems with coil, condenser, points, distributor Etc. THOSE WERE THE DAYS.

Anyway enough waffle. Thanks again for the help and keep it coming because I’m still curious.

Pete
 

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Re: What’s this turbo thing?

What about adding an extra but bigger turbo on the other enine bank? Then it could take over when the orginal small turbo gives up?
 

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Re: What’s this turbo thing?

Guess a better intercooler could also boost output!

Wasnt it basicly the same engine Vaxhaul used for the Lotus Omega = 340 HP twin turbo??
 

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Re: What’s this turbo thing?

For UK purposes it was known as the Lotus Carlton- the Omegas was the EU version. Both were the same body shape.

Spec:
Layout Longitudinal, front ,rear drive
Capacity 3615cc, six cylinders in line
Bore/stroke 95/85mm
Compression ratio 8.2:1
Head/block Aluminium alloy / cast iron
Valve gear DOHC, 4 valves per cylinder
Ignition & fuel Electronic ignition and fuel injection, Delco management system, two Garrett T25 turbochargers
Max power 377bhp/5200rpm
Max torque 419 lb ft/4200rpm
Specific output 104bhp/litre
Power-to-weight ratio 228bhp per tonne

Gearbox
 

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Discussion Starter · #14 ·
Re: What’s this turbo thing?

Thanks for that Soren, how much is 13 500 sek in £?

But as fliptop said:-Is the engine strong enough to maintain reliability?

Then what about the gearbox and running gear?

Wish I could afford two of these! (don’t we all?)
 
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