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Saab Turbos on SBC

11K views 97 replies 10 participants last post by  zildjian4life218 
#1 ·
I went to my local u-pull today and there are two saabs there with turbos on them. They are 2.0 liter engines and my friend said he thought that the flanges were T25. Do u guys think these would work on a twin turbo low rpm sbc. I want to build a low rpm engine that will prolly have a 5000rpm redline on it built primarily for torque.
 
#79 ·
TurboS10 said:
You dont want to use a thick gasket. Quench needs to stay around .040 or under to help with detonation control. I think big block injectors are available for the tbi if you use it with ms.
TPI not TBI. But that would be a great idea if I was using the TBI setup.

bigdog7373 said:
The problem with building a low-rpm turbo motor is the the engine has to rev up the make the turbos spin and make boost, i would go with a supercharger instead.
Exactly what turbos10 said. Different size turbos will make different amounts of boost at different points in the rpm range. So as said if you size the turbos to the engine they will work fine. Thats why when building a turbo engine it is critical to get a hold of the compressor maps for the turbos. This will show how much air measured in cfm, lb/min, or lb/hr the turbo can flow while creating a certain pressure ratio. I imagine these turbos will be all in around 2500rpm by seeing how small they are. I will only really know until I slap it together and see how it runs.
 
#83 ·
TurboS10 said:
It would be a less fab work with one.
Thats true but I don't mind doing the twins. I figured for the fab work im either gonna use center dump manifolds or just flip the stock manifolds around so they face to the front. And then I will weld on some tubing that will point down and weld on a T25 flange. I will just have to keep them above the oil level.
 
#85 ·
I was talking the other day with some friends of mine that are big into turbo charging hondas. They said for injectors the can get a hold of 4 450cc injectors for $50 off of a DSM factory turbo car. Anyway these would work on my tpi intake? I used an online calc and found them to be 42 lb/hr which would be perfect for my build. I was wondering what I would have to worry about fitting properly. I know for the wiring connector I can just get the connectors from that car and splice them onto my harness. Not sure on the intake rail connection or where they go into the intake. Any one have any idea?
 
#87 ·
TurboS10 said:
Either they will fit or they will not. There is no room in between. You will need to know if they are high or low impedence as well.
Alright thanks im gonna go through tonight and play with them and see if it works or not. Ill also post pictures of both injectors. I believe they are low impedance because when my friends use them on their hondas they have me wire in a resistor box that is used to drain off the excess current. Which would make me to believe that the factory injectors are high impedance.
 
#88 ·
zildjian4life218 said:
Alright thanks im gonna go through tonight and play with them and see if it works or not. Ill also post pictures of both injectors. I believe they are low impedance because when my friends use them on their hondas they have me wire in a resistor box that is used to drain off the excess current. Which would make me to believe that the factory injectors are high impedance.
Yes, if you are adding resistors then you are correct. Some ECU's can be set to work with lowZ without the resistors, but some require them. Depends on your end setup.
 
#90 · (Edited)
So I think I might go with some bigger turbos...........

Can someone with turbo knowledge or any knowledge that can help check my math. I bought a book titled "Street Turbocharging" by HP Books. In here is a step by step calculations for plotting turbo compressor maps.

Okay first off you figure out the specs of the engine
305ci
assuming 80% VE
8.5:1 CR
12psi
Redline 5000
IC Eff 60%

Figure out the Pressure Ratio of the compressor
(12+14.7)/14.7 = 1.816

Then the Pressure Ratio of the System assuming a 1 psi drop through the Intercooler
(12-1+14.7)/14.7 = 1.748

Now we figure out the temperature rise after the compressor assuming ideal
Toutideal = [(Tin+460)*PR^0.283]-460
[(85+460)*1.1839]-460]
185*F

Now we find the actual temperature assuming the efficiency of the turbocharger which is 72%.
Toutactual=[(185-85)/.072]+85 = 223.8*F

Now we find the temp of the air coming out of the Intercooler.
TempIC=224-[.60*(224-85)]
140.6*F

The Density Ratio is then figured out by
DR = 1.75*[(85+460)/(140.6+460)] = 1.5869

Then you figure out the VFR which is the volumetric flow rate at redline of the NA engine.
VFR=305*5000*.80/3456= 353cfm

Last step is to find the Mass flow rate which is
MFR=(2.703*14.7*353*1.5869)/85+460 = 41 lb/min

Sorry its so long I want to make sure I have this somewhat right. Thanks! These turbos flow 15 lb/min at a PR of 1.82 so idk if they will quite cut it. I think I will be spinning them way too much and burn them up.

I attached a compressor map for the turbo I am using. The red dot shows where I would be sitting.
 

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#91 ·
Very, very goo grasshoppa....now I show you calcula5tor to do math for you :D:

http://www.turbofast.com.au/javacalc.html

Now that you understand the math you can plug things in to the above listed calculators and actually understand what you are seeing.

There are some points to consider. First, you are only calculating peak RPM. How much are you going to operate at full power? Second if you run those numbers again for the same boost numbers at 3500RPM and I think you will find that it is about perfect. How much time will you spend around this range? Third, the map does continue and if you continue the lines you can see it will be right at the edge, but will in fact still feed the engine sufficiently.

My point in all of this is if it is a street car, it will work very nicely and spool instantly which will make for a very fun ride.

I also dont disagree that they are a little bit small, but not much.....in the end it comes down to what you are wanting to do.
 
#92 ·
TurboS10 said:
Very, very goo grasshoppa....now I show you calcula5tor to do math for you :D:

http://www.turbofast.com.au/javacalc.html

Now that you understand the math you can plug things in to the above listed calculators and actually understand what you are seeing.

There are some points to consider. First, you are only calculating peak RPM. How much are you going to operate at full power? Second if you run those numbers again for the same boost numbers at 3500RPM and I think you will find that it is about perfect. How much time will you spend around this range? Third, the map does continue and if you continue the lines you can see it will be right at the edge, but will in fact still feed the engine sufficiently.

My point in all of this is if it is a street car, it will work very nicely and spool instantly which will make for a very fun ride.

I also dont disagree that they are a little bit small, but not much.....in the end it comes down to what you are wanting to do.
Thanks for the link. I made an excel chart with the same idea as the above link just not written in java script. where on one side you put in the constants and it outputs on the right. Oh well at least i now know what the formulas do. Thanks for all your help everyone. I am waiting to get sometime so i can go down and bore my block. The forged pistons my machinist gave me are .030 or .040 over so gotta punch out the block.
 
#93 ·
Any idea what I should gap the rings too. I got some enginetech El cheapo rings. Just putting some dished stock pistons back in it. I'm having a hard time believing this is gonna make over 400hp with the t25 turbos. Later ill build a 305 with the forged pistons I got and bigger turbos. I put the top ring in and its sitting at about .020. Thanks for all the help and support.
 
#98 ·
The short block is all together. I will be ordering the cam soon hopefully and then I can degree the cam, put the timing cover on, and the oil pan.


For those of you who are observant you probably noticed that piston 1 appears to be in backwards due to the dot on the piston facing the back. It was for the even side but the only piston I had left. I had a pile of pistons from two different 305s. One came apart so most of it was junk. My machinist said the orientation on the pistons doesn't matter for that style heads just the rod orientation does which is correct.
 
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