OK I could make this long and complex, but there’s no real need to make things complicated, ideally youll have a long discussion with your turbo manufacturer BEFORE buying a turbo that exactly matches your intended rpm, horsepower and engine displacement, and youll install a blow off valve with an adjustable pressure level and an ignition that has a rev limiter and has the option of adjustable ignition advance as the boost pressure increases.
obviously youll want to maximize your results with parts selected to match your rpm and hp goals.
BTW there’s a good deal more info in this thread
viewtopic.php?f=86&t=1215
Ok first you need to understand how a turbocharger works
http://www.squirrelpf.com/turbocalc/
So read this
http://auto.howstuffworks.com/turbo2.htm
Ill assume you’ve got the basic idea, a turbo uses exhaust flow to spin a turbine on the same axle that spins a matched compressor turbine that sucks in and compresses air to which fuel is added as its stuffed into the engine, the compressed fuel air mix burns and produces an even larger volume of exhaust spinning the exhaust driven turbine even faster so a power loop of rapidly increased pressure on the intake side, or BOOST is created, it will eventually reach the point where no more air can be compressed due to he flow rates and resistance on the intake compressor matching the pressure on the driven turbine or roughly equal pressure on one side being matched with resistance to flow, on both sides of the axle the turbines are spinning on, the turbine housings and impellers size and design on each end of the axle can be changed but they come as a matched set from the factory for a set flow, rpm, and displacement band.
This force generated by the high pressure exhaust on the exhaust turbine shaft generates torque at the compressor end as they are physically connected. Remember that part as its important, because getting things matched incorrectly breaks parts.
the turbocharger is compressing air, forcing it into the engine, the engine is burning it.. And expelling the exhaust and your turbine housing pressure goes up accordingly, the torque applied at the exhaust turbine wheel increases, increasing the spin speed and compressor efficiency at the other end.
End Result? Boost is produced and it climbs rapidly
Ok,
Now imagine this, The turbo begins to spin, as above, but the intake compressor wheel is generating more air than the engine can flow thru its cylinders due to both compressor efficiency and engine component flow capacity and the torque required to spin that intake compressor is not being matched, or exceeded on the exhaust, flow and pressure rates, will equalize or fall.? keeping in mind that unless the air is flowing thru the engine, and exhaust flow into the exhaust turbine housing, our turbine shaft torque will not increase to spin the compressor faster, the compressor is slowing, due too the compressed air resistance eventually equaling the force generated by the exhaust and increase..... youve also got potential detonation damage,to deal with if the pressure spikes to rapidly.
Result? Compressor starts to slow its rate of acceleration a little.. (beginings of a compressor stall)
So what?
The engine is still rotating and forcing high pressure air, thru the cylinders but the turbo has stopped producing enough exhaust to increase boost, so our engine slows temporarily, once the boost pressure drops a bit, as the engine has now had chance to burn what excess was available and the inlet pressure is now dropped, the exhaust turbine torque is now increasing again...
VERY IMPORTANT:
Remember also that at same time, compressor resistance to spin has also dropped due to housing no longer being as pressurized and as a result, the torque required to spin it has dropped rapidly, a rapid repetitive cycle of speed up, stall, drop off, speed up, stall drop off, etc...
So we get: Fast, slow, fast, slow, or in other words: The turbo is Surging.
http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html
In a quickly closed throttle condition (assume no blowoff valve), your compressor flow
The whole thing to understand is the way to stop surge is to throw FLOW to the compressor. FLOW may result in stonewall, but that won't break things.
This is why bypass valves should open on partial throttle IMMEDIATELY! Even LIGHT lifts of the throttle should result in a 'sigh' from the turbo piping. This drops pressure on the intake side of the engine
On hard closed throttle the bypass should open and let that flow off. If You set the blowoff valve spring resistance too high you’ll induce surge , that blowoff valve is there to limit or prevent surge, when you hear that woosh the blowoff valve opened for an instant, doing what it was SUPPOSED TO DO: PREVENT SURGE!
They will keep in this condition for as long as it takes to let flow stabilize, and then close the blowoff valve
obviously youll want to maximize your results with parts selected to match your rpm and hp goals.
BTW there’s a good deal more info in this thread
viewtopic.php?f=86&t=1215
Ok first you need to understand how a turbocharger works
http://www.squirrelpf.com/turbocalc/
So read this
http://auto.howstuffworks.com/turbo2.htm
Ill assume you’ve got the basic idea, a turbo uses exhaust flow to spin a turbine on the same axle that spins a matched compressor turbine that sucks in and compresses air to which fuel is added as its stuffed into the engine, the compressed fuel air mix burns and produces an even larger volume of exhaust spinning the exhaust driven turbine even faster so a power loop of rapidly increased pressure on the intake side, or BOOST is created, it will eventually reach the point where no more air can be compressed due to he flow rates and resistance on the intake compressor matching the pressure on the driven turbine or roughly equal pressure on one side being matched with resistance to flow, on both sides of the axle the turbines are spinning on, the turbine housings and impellers size and design on each end of the axle can be changed but they come as a matched set from the factory for a set flow, rpm, and displacement band.
This force generated by the high pressure exhaust on the exhaust turbine shaft generates torque at the compressor end as they are physically connected. Remember that part as its important, because getting things matched incorrectly breaks parts.
the turbocharger is compressing air, forcing it into the engine, the engine is burning it.. And expelling the exhaust and your turbine housing pressure goes up accordingly, the torque applied at the exhaust turbine wheel increases, increasing the spin speed and compressor efficiency at the other end.
End Result? Boost is produced and it climbs rapidly
Ok,
Now imagine this, The turbo begins to spin, as above, but the intake compressor wheel is generating more air than the engine can flow thru its cylinders due to both compressor efficiency and engine component flow capacity and the torque required to spin that intake compressor is not being matched, or exceeded on the exhaust, flow and pressure rates, will equalize or fall.? keeping in mind that unless the air is flowing thru the engine, and exhaust flow into the exhaust turbine housing, our turbine shaft torque will not increase to spin the compressor faster, the compressor is slowing, due too the compressed air resistance eventually equaling the force generated by the exhaust and increase..... youve also got potential detonation damage,to deal with if the pressure spikes to rapidly.
Result? Compressor starts to slow its rate of acceleration a little.. (beginings of a compressor stall)
So what?
The engine is still rotating and forcing high pressure air, thru the cylinders but the turbo has stopped producing enough exhaust to increase boost, so our engine slows temporarily, once the boost pressure drops a bit, as the engine has now had chance to burn what excess was available and the inlet pressure is now dropped, the exhaust turbine torque is now increasing again...
VERY IMPORTANT:
Remember also that at same time, compressor resistance to spin has also dropped due to housing no longer being as pressurized and as a result, the torque required to spin it has dropped rapidly, a rapid repetitive cycle of speed up, stall, drop off, speed up, stall drop off, etc...
So we get: Fast, slow, fast, slow, or in other words: The turbo is Surging.
http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html
In a quickly closed throttle condition (assume no blowoff valve), your compressor flow
The whole thing to understand is the way to stop surge is to throw FLOW to the compressor. FLOW may result in stonewall, but that won't break things.
This is why bypass valves should open on partial throttle IMMEDIATELY! Even LIGHT lifts of the throttle should result in a 'sigh' from the turbo piping. This drops pressure on the intake side of the engine
On hard closed throttle the bypass should open and let that flow off. If You set the blowoff valve spring resistance too high you’ll induce surge , that blowoff valve is there to limit or prevent surge, when you hear that woosh the blowoff valve opened for an instant, doing what it was SUPPOSED TO DO: PREVENT SURGE!
They will keep in this condition for as long as it takes to let flow stabilize, and then close the blowoff valve