will start this off to go with turbo strip down pic post.
what is a hybrid turbo? usually just a normal turbo that has (mostly) the compressor side modified with parts from a larger turbo, machined housing and lager compressor wheel or sometimes complete larger housing and wheel from a larger turbo.
what do you gain? airflow + reliability
a larger wheel will flow more air at the same shaft rotational speed(needed for more hp) or will flow the same air at a slower rotational speed(=more reliability), it will also be more effecient at your desired rev range if properly sized for your requirements(i went for a 52mm exducer 38.6mm inducer 55trim std was 49mm exducer 34.6mm inducer 48 or 50 trim) i think a 52mm 50 or 52 trim would have made a better daily driver maybe?
trim is best explained low trim (45-50)gives low rev torque, low surge but runs out of breath high rpm.
high trim (55-60) better flow high revs but suffers more with low rev surge
what's the downside?
turbo compressor maps help you choose compressor and trim, unfortunately not much data available for garret gt range compressors(i will post any helpfull data i found)
a larger wheel takes longer to spool up(more weight to get spinning).
too large a compressor wheel for turbine can cause boost creep, overboost etc.(a 1756 hybrid seems popular but i can still get creep on this 1752 even with a 39.5mm exducer turbine so not sure on if necessary for the 56mm comp)
boost creep is where the vnt control is fully open(mine shows 19.99%)and the actual boost keeps rising out of control this is probably too much fuel for set up.
too large a trim size can cause low rev turbo surge(damaging to turbo,)
increase in boost pressure with no turbine mods will increase emp(exhaust manifold pressure)what goes in has to come out.
when turbine becomes choke point or main restriction increase in boost mostly just increases emp and equals extra heat and less effecient.
what can be done to turbine/hot side?
most hybrids ive seen advertised have modified turbine wheel described as cut back, as i understand it this is the machining of the wheel itself on the exducer.
the wheel is cut back o reduce the efficency of the turbine itself, by removing some fin area at the exducer the turbine becomes less restrictive this is helpful to reduce the emp and boost creep described above.
the turbine is now less efficient ,spools slower, spins at a slower shaft speed for same given mass airflow, this is not all doom and gloom as these are vnt turbos.
the ecu can and should recalculate less vnt opening to get back turbo boost presure under control.so say 25% vnt gave 2500mb a cut back wheel may need 35% to get 2500mb, but larger comp wheel is flowing more anyway so vnt % may be not much different.
in my set up i went for a completely larger turbine wheel from another vnt17 turbo, i think it was the largest available exducer 39.5mm with a 43mm inducer.
this required a lot of guesswork, assumptions and machining work which i assume is why turbo builers just do cut back wheels.
i have been holding off for a while till i have run in turbo and tested on the car.im pretty pleased with how it performs, but realistically the time cost and effort put into making this hybrid would have gone a fair way to buying a much better complete turbo aka gtb1756 or gtb2056 or gtb2260 and modifing exhaust manifold and downpipe, oilpipes etc.
i will ask to keep this thread clear for a day or so , so i can finish downloading related pics and data etc.
thanks
what is a hybrid turbo? usually just a normal turbo that has (mostly) the compressor side modified with parts from a larger turbo, machined housing and lager compressor wheel or sometimes complete larger housing and wheel from a larger turbo.
what do you gain? airflow + reliability
a larger wheel will flow more air at the same shaft rotational speed(needed for more hp) or will flow the same air at a slower rotational speed(=more reliability), it will also be more effecient at your desired rev range if properly sized for your requirements(i went for a 52mm exducer 38.6mm inducer 55trim std was 49mm exducer 34.6mm inducer 48 or 50 trim) i think a 52mm 50 or 52 trim would have made a better daily driver maybe?
trim is best explained low trim (45-50)gives low rev torque, low surge but runs out of breath high rpm.
high trim (55-60) better flow high revs but suffers more with low rev surge
what's the downside?
turbo compressor maps help you choose compressor and trim, unfortunately not much data available for garret gt range compressors(i will post any helpfull data i found)
a larger wheel takes longer to spool up(more weight to get spinning).
too large a compressor wheel for turbine can cause boost creep, overboost etc.(a 1756 hybrid seems popular but i can still get creep on this 1752 even with a 39.5mm exducer turbine so not sure on if necessary for the 56mm comp)
boost creep is where the vnt control is fully open(mine shows 19.99%)and the actual boost keeps rising out of control this is probably too much fuel for set up.
too large a trim size can cause low rev turbo surge(damaging to turbo,)
increase in boost pressure with no turbine mods will increase emp(exhaust manifold pressure)what goes in has to come out.
when turbine becomes choke point or main restriction increase in boost mostly just increases emp and equals extra heat and less effecient.
what can be done to turbine/hot side?
most hybrids ive seen advertised have modified turbine wheel described as cut back, as i understand it this is the machining of the wheel itself on the exducer.
the wheel is cut back o reduce the efficency of the turbine itself, by removing some fin area at the exducer the turbine becomes less restrictive this is helpful to reduce the emp and boost creep described above.
the turbine is now less efficient ,spools slower, spins at a slower shaft speed for same given mass airflow, this is not all doom and gloom as these are vnt turbos.
the ecu can and should recalculate less vnt opening to get back turbo boost presure under control.so say 25% vnt gave 2500mb a cut back wheel may need 35% to get 2500mb, but larger comp wheel is flowing more anyway so vnt % may be not much different.
in my set up i went for a completely larger turbine wheel from another vnt17 turbo, i think it was the largest available exducer 39.5mm with a 43mm inducer.
this required a lot of guesswork, assumptions and machining work which i assume is why turbo builers just do cut back wheels.
i have been holding off for a while till i have run in turbo and tested on the car.im pretty pleased with how it performs, but realistically the time cost and effort put into making this hybrid would have gone a fair way to buying a much better complete turbo aka gtb1756 or gtb2056 or gtb2260 and modifing exhaust manifold and downpipe, oilpipes etc.
i will ask to keep this thread clear for a day or so , so i can finish downloading related pics and data etc.
thanks
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