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Old 01-19-2004, 12:13 AM
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a turbo question.

ok, im doing a little experiment with a little mitsubishi turbo i got off of a 89 daytona. this is my question, how many rpms would a turbo have to spin (not engine rpms) to creat say 5 psi of boost?


thanks

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Old 01-19-2004, 03:29 AM
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first of all it depends on the restrictionon the pressure side.. but i would guess it was in the 90.000 to 110.000 rpm range.n max rpm is arround 120.000 rpm for the small turbos you are tinkering with. a very large unit for a stationary diesel will typically spin 70.000 to 80.000 rpm.

Now if you spin your engine at 6500 rpm and the max rpm fo rthe turbine wheel is 120.000 the drive ratio has to be 18.46:1, if you then have a step up from the crank to the pulley of say 3.5:1, then your internal step up in the blower needs to be 5.27:1 so its not impossible to do your self

i wasnt sure what the experiment was, but i took a wild guess.. was i way off??
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Old 01-19-2004, 04:42 AM
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Turbine speed is not an absolute. It varies by turbo and can be as high as 150,000 max speed. Turbine speed varies constantly to maintain the desired boost level as RPM changes. It may take 60k turbine speed at 3k engine speed and 130k at 5k engine speed. Could be more, could be less. Engine displacement also impacts this number. Tell us what you want to do, and we will tell you if it is doable.

Chris
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Old 01-19-2004, 06:28 AM
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well i got half a turbo from my buddy, its the compressor side and i planned on turning it into a small supercharger running off of my belt system, but now that you guys say its gotta spin in the 100000rpm range im not sure i can safely do it. i would have to make some sort of a gearbox to get the turbine spinning that fast, but it might be a lil dangerous now, everything would have to be super strong.


thanks for the info.
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Old 01-19-2004, 10:03 AM
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actually it doesnt have to be super strong. just super well ballanced, the tourque is equally lower with the gearing ratio.. althougt i would propably rather maunt two small turbos, and fabricate the exhaust instead of engineering a 100000 rpm gearing... but its doable..
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Old 01-19-2004, 04:02 PM
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well i might still try it, see how it goes, my buddy is looking into some gears for me. how do vortech superchargers creat so much boost at like 50000 rpm? turbine design?
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Old 01-20-2004, 02:31 AM
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one answer: turbine diameter, if you look at a vortech the inducer if 3 inches in diameter and the turbine wheel OD is almost 5 inches. so for the vortech to spin the air in the turbine so fast to attain say; 9 pounds of boost it only has to spin half the speed of a smaller turbine.

So either gut a big *** turbo from a stationary or marine diesel turbo with the big turbine, or give the 120000 rpm a try. you might want to look at the turbine flow chart to see if it is even able to flow the amount of air you are requiring at the boost level you are looking for...

perhaps you could post some specifics???
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Old 01-20-2004, 04:29 AM
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Quote:
Originally posted by Super Chevy
well i might still try it, see how it goes, my buddy is looking into some gears for me. how do vortech superchargers creat so much boost at like 50000 rpm? turbine design?
To be technically correct, it is the compressor differences that effect it. Compressor is the cold side and the turbine is the hot side.

Anyway, duece is right about the design. The compressore on the superchargers are much larger. You could use a large unit like I am running for what you are wanting to try, but I think you will find it unsuccessful. Even the major manufacturors have problems keeping bearings in the centrifugal superchargers.

Chris
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Old 01-20-2004, 06:33 AM
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There's one serious problem with what you want to do: bearings. The bearings in the turbo aren't designed to take a side load as a belt would put on it. In some cases they are only bronze bushings that ride on a film of oil. Put a side load and they won't last long -- coupled with the closeness of the turbine to the housing and you have a real problem. Supporting the end of the shaft (opposite side of pulley from turbine housing) might solve the problem, or machining the housing for different bearings. Both have a degree of difficulty.
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Old 01-20-2004, 07:40 PM
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well for the gearbox i planned on using gears that mesh into each other, then i would run a pulley off the gearbox to my belt.
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Old 01-20-2004, 08:23 PM
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I wouldn't spend a whole lot of time on this project, especially since that particular turbo only puts out enough CFM of air to make 150hp at 7 psi in its original application, and less than 300 hp maxed out at around 30 psi. Its really too small for the 2.5L 4 cylinder it came on, and a very basic upgrade on these cars is to go with a larger Garrett factory turbo.
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Old 01-20-2004, 10:27 PM
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oh im not putting this on a v8, its just gonna go on my 2.5 n/a shadow.
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Old 01-21-2004, 02:08 AM
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then leave the turbo alone and fabricate a turbo manifold. youll be way happier with the performance with the turbine driven by the exhaust than if you belt drive it... chech this out
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Old 01-21-2004, 05:29 PM
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Quote:
Originally posted by Super Chevy
oh im not putting this on a v8, its just gonna go on my 2.5 n/a shadow.
In that case, have you considered how your going to get the extra fuel that this is going to require? The TBI unit you have now will in no way keep up.

PM if you need a turbo exhaust manifold, I think I even have one off a 2.5 with the exhaust side of a Mitsu turbo still attached. Maybe we can work something out.
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Old 01-21-2004, 11:16 PM
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thanks for the offer but i would need to do a complete engine and trrany swap if i wanted to go with a turbo. the pistons, connecting rods, cam, distributer, computer and injection system are all different. the trannies out of the turbo cars are much stronger also. so it wouldn't ge worth it to convert my engine over.
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