Tuning hybrid turbo

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Tuning hybrid turbo

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Oct 21, 2007
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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
 
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this is all based on the garrett gt1749v 777250-1 which is the latest model that replaces others fitted to the jtd 16v (and some alfa's also) i measured up and compared sizes to my turbo when removed and it was all the same dimensionally.

here is a larger 52mm comp wheel next to a 49mm comp wheel, notice the different back design to the new wheel, (to make things easier get the right back design, a spacer sorted it though)
turbo 777250-1 new compressor 002.jpg
turbo 777250-1 new compressor 005.jpg

here is the larger turbine fitted untouched with no cutback(hopefully more flow without loss of turbine efficiency)
turbo 777250-1 new turbine 001.jpg
turbo 777250-1 new turbine 002.jpg
if you look at my old turbine i had a quick go at performing a cut back with a dremel and a stone with turbine rotating at high speed also, you can see the exducer blade angle is much steeper.
there are several pieces that then need machining accurately, i measured up all original parts and came up with around a housing diameter 1.00mm bigger than the comp and turbine wheel diameter, so with wheels in place there is 0.5mm clearance to the housing from the wheel.
i read up a lot about custom turbos being machined to finer tolerances but with a dry new bearing there is a few tenths of a mm movement on the shaft.
im struggling with internet connections and uploading so please bear with me i will upload all relevant pictures or videos i have(eventually)
 
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here is the flow path in the 16v turbo into the vnt area, i found that there is a slight step reducing the actual flow area to less than that of the vnt vane height shown by the height of the vnt ring spacer.
new turbo 2011 before hybrid diy cutback 3 009.jpg
new turbo 2011 before hybrid diy cutback 3 014.jpg
this was opened up to the full height of the vnt spacer (hopefully removing a small restriction)
turbo porting idea.JPG
im not sure what pro turbo tuners do internally to there turbos but most list some internal efficiency mods no idea what they are.
the original manifold and turbine housing was also ported to remove any steps or lips by making a temporary gasket and gasket matching both ports.
the turbine housing is also part of the major restriction, no point putting a bigger turbine in there than what the housing can flow. i think the 8v turbo actually has a higher flowing turbine housing, but smaller vnt vane height.

will try after 6 its taking forever to upload pics
 
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a helpful site to work out what airflow you will need with your hardware and desired outputs is
http://www.turbobygarrett.com/turbobygarrett/webadviser
when inputed my wish list i got a figure of approx 230hp @ 27psi would require 24lbs/min of air. this ultimately gave the go ahead for a hybrid over complete turbo although this value is closer to a 56mm compressor so i dropped my target hp slightly.
heres another online calculator
http://www.not2fast.com/turbo/glossary/turbo_calc.shtml

of course the final part of the rebuild was new bearings (the std turbo already has a 360* thrust bearing, as many hybrids advertise as extra)and assembly and i requested a staggered gap piston seal on turbine(supposed to help on low back pressure exhaust systems) and most important is the turbo balancing. i would not recommend refitting a rebuilt turbo that has not been professionally balanced(just remember it may be spinning at 180,000rpm or more)
 
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i would recomend for the work fitting something like this instead better gtb vnt3 turbos
this guys a regular on tdi forum
http://www.darksidedevelopments.co....6vk-turbochargers-with-vacuum-conversion.html
if you fancy a read and some real turbo p*rn take a look on here
http://forums.tdiclub.com/showthread.php?t=313001
click on ryanp and see more posts
heres a chart i think he knocked up(for tdi engines)
http://i1219.photobucket.com/albums/dd425/euroshack/TDI Club/TurboComparison.jpg
TurboComparison.jpg

http://i1219.photobucket.com/albums/dd425/euroshack/TDI Club/TurboComparison2.jpg
TurboComparison2.jpg
 
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looking through my old data logs this(hopefully) shows pretty clearly, that the std turbos can easily be overspeeded(by overfuelling)and then are in boost creep
std turbo is on the right, just look at the boost curve in the middle brown =desired boost, light blue = actual boost and purple= vnt %
at max desired boost the actual boost just keeps rising, vnt hits min value 19.99% and turbo is out of control , more fuel = more boost = turbo overspeed = ££££
stdturbovshybridturbogr.png

now look at the new turbo, much better control still a small overboost but vnt only hit 30% .also you can see on the off throttle that the boost drops quicker thanks to larger turbine.
 
even managed to find one where i was still just out on new turbo, i have raised boost again from here and raised it higher in the rev range also where it dropped off quickly in desired.
datapic.png

hope this all helps someone in the future.
anyone doing anything like this i would recommend at least a seperate turbo boost gauge, a exhaust temperature gauge , exhaust manifold pressure gauge or at least to log these things properly during set up.
i think a lower trim 52mm wheel and no turbine mods would suffice for 99% of set ups where just a remap is done, and plenty of guys run decent hp with the std turbos anyway.
the whole thing started when i was 99% sure my old turbo was weeping oil on turbine seal(probably due to decat and some massive overboosting over the last few years)i just couldnt do swapping like for like.
lastly it took me a long time to complete, buying a spare, research , buying parts, machining of housings(if i had had to pay for machining id have probably bought one done) ,porting,polishing etc.if tinkering is not your thing buy one done properly(even the turbo guys who balanced my unit could not give any guarantee on the turbo as they had not done all the work plus there was no proof parts would all run o.k together, i understood this and accepted it, there was a few sweaty moments when i ran in anger for the first few times)
i have no idea how long it will last reliability wise, ill post back up if it doesnt
 
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I Wouldn't recommend a vnt on a petrol turbo anyway, I'm not sure they can take the heat(expensive Porsche vnt turbo aside)
Also I wouldnt boost a petrol to 1.8 bar not for long anyway.
This hybrid is fitted to my diesel jtd 16v .The donor turbo was off a Alfa gt coupe ducati(170hp std) but as I said is same size as the latest version of replacement turbo and the jtdm 16v turbo( some early jtd 16v turbos had a smaller vnt vane height of approx 5.5mm compared to the later 6.3mm vane height)
A few Alfa guys were supprised at the std turbo's small compressor inducer of 34.6mm, I think the 8v inducer is 35.xxmm and they assumed the 16v had an inducer of 36mm+
If I were to do it again I would go gtb2056(probably)
 
yes, now upped requested pressure in mapping, last logs were max requested 2800mbar and i think it was overboosting maybe 50mbar and hit 19.99%vnt again so redid map again just raising to 2850mbar max and calculated some afr values from fuelling that required a bit more boost here and there.
no logs recently as still been playing with maps for low rpm mpg.
here were some figures i calculated from one of my later logs to give required airflow/boost to give an afr of 17:1 should be smoke free
revs IQmm3 maf maf temp map temp boost vnt afr maf @ afr17
2360 82.428 1249 23.16 28.36 2484 47.65 18.038 1177
2617 85.725 1248.5 22.66 27.76 2557 42.2 17.33 1224
2887 95.391 1279 21.66 27.56 2557 38.34 15.96 1362
3150 95.412 1316 21.16 27.66 2610 34.89 16.42 1362
3407 95.433 1311.5 21.16 27.96 2658 35.67 16.36 1362
3660 95.523 1338.5 20.66 28.56 2737 35.05 16.68 1364
3901 95.553 1334 19.26 29.66 2760 32.87 16.62 1364
4103 95.523 1295 18.26 30.36 2742 32.05 16.13 1364
4301 95.574 1241.5 17.76 31.36 2713 19.99 15.46 1364
you can see afr started at 18 and went down to 15.46 on these values so more boost was required(for my liking, or less fuel of course if i cant make enough boost).
if i use mm3x0.84 = mg/i and then if i divide maf value in mg/i by IQ in mg/i =afr
if so i can use afr=17 and calculate desired maf value by iq mg/ix17=maf
not sure i got as far as calculating boost from desired maf values, i will just keep upping and logging and seeing what calc afr is.
max power should be around 14.7 afr but i would expect that to be a bit smoky, plus a bit more boost can help keep egt down.most turbo diesel forums dont like to go much below 16:1 for acceptable smoke.
2850mb=26.3psi at sea level, im at altitude meaning sometimes 970mb atmos so i think im running realistic 1880mbar boost =27.3psi at peak maybe more on a low pressure day.
i think std max boost for the jtd 16v was 2350mb or 19.58psi im not sure about the 8v or the 120mj?
 
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