benhart16
Well-known member
Hi,
I'm wondering which of the following turbos would give the best fuel economy for a BEW Golf, automatic transmission, stock or only a mild increase in power, driven in a fairly normal commuter fashion (no hypermiling):
GTC1446VZ
CW : 34,1mm inducer / 46mm exducer
TW : 34,5mm exducer / 39mm inducer
GTC1549VZ
cw - 36/49mm
tw - 37.57/41mm
VNT15
cw-33.7/49mm
tw-36.6/43mm
VNT17
cw-37/49mm
tw-38.2/43mm
GTD1449vz
cw-37/49mm
tw-exducer: 36mm
I think the answer to which turbo is best for efficiency, is going to be the turbo that generates the most boost for the least amount of increase in exhaust backpressure in the operating conditions where the most fuel is consumed throughout the commute. If it's all highway on level ground, then the engine should be producing about a constant 20hp, so the turbo should be sized to be efficient at this speed/power level without choking the engine during acceleration/hills. If it's mixed driving, then the turbo probably should be sized slightly higher as the weighted fuel consumption will be at a higher hp.
I think this above fact points towards going to a smaller turbo, but I've also read that a VNT17 can improve fuel economy over a vnt15 as it reduced exhaust back pressure. Any thoughts on this? Is this true? I'm skeptical, but if someone has real world experience, I'll listen to it.
Back in the 70s and 80s when adding turbos to diesels was becoming mainstream, the literature at the time stated that adding a turbo to a naturally aspirated diesel could improve fuel efficiency. This seems to be the case with the early 1.6 VW diesels. I believe the turbo 1.6D rabbit was EPA rated at 63mpg or something close, while the NA version was around 50mpg. The question is what mechanisms would allow this to occur? Probably the first guess would be the added torque would allow the engine to be operated at higher gears when climbing hills, and thus more efficiently overall (I think the transmissions were identical). Also, adding a turbo effectively increases the (dynamic) compression ratio a little bit. But I think the less obvious contribution is that adding a turbo basically converts the engine to a combined cycle system. The energy scavenged from the exhaust can be used to reduce pumping loses of the engine, and even provide a slight amount of power on the intake stroke as there will be positive pressure on the piston. At the minimum, it will reduce pumping loses, thus improving efficiency. Even if this is small, these small amounts do add up. New generation turbos can generate higher boost pressures than the increase in exhaust backpressure.
I read a thread where a guy had a BRM that he started adjusting the tunes on. He found at normal highway conditions, the variable vanes were kept excessively closed (probably for EGR). When he edited the tune to open them up a bit, his fuel economy went from ~36 to ~42mpg. I can see where a large turbo would have to close the vanes an excessive amount to spool the turbo at the low end of the range would result in poor turbine efficiency, thus requiring excessive backpressure. A smaller turbine operating in the middle of it's range would likely yield much better results. Also, newer generation turbos provide the same boost for less exhaust backpressure than the older designs.
When VW released their TDIe (efficiency or economy) in Europe, they spec'd the GTC1446vz making 130hp. They then installed the GTC1549VZ on the
CR170 and later the GTD1449VZ on the CR184 and 190. As near as I can tell, the Boras with the various engines all are rated at about 53mpg. The GTC1446vz has the smallest turbine housing of any of the turbos. The GTD1449vz has a similar turbine housing as the VNT15, but can flow much much more. That's what 15 years of engineering improvements will do.
I have a manual ALH jetta with a GTD1449vz on it (11mm pump, 0.216 nozzles, FMIC), and my plan is to place a pressure port over the egr port and compare backpressure to boost. I also have an automatic BEW (mostly stock) that is getting a VNT15 at the moment, but will probably be replaced by a GTC1446vz and then a GTC1549vz if I really want to go through the effort to have comparable data. (I'm not putting a GTD1449VZ on the golf, that's too much of a PITA)
Any thoughts? What have you guys noticed on your projects?
I'm wondering which of the following turbos would give the best fuel economy for a BEW Golf, automatic transmission, stock or only a mild increase in power, driven in a fairly normal commuter fashion (no hypermiling):
GTC1446VZ
CW : 34,1mm inducer / 46mm exducer
TW : 34,5mm exducer / 39mm inducer
GTC1549VZ
cw - 36/49mm
tw - 37.57/41mm
VNT15
cw-33.7/49mm
tw-36.6/43mm
VNT17
cw-37/49mm
tw-38.2/43mm
GTD1449vz
cw-37/49mm
tw-exducer: 36mm
I think the answer to which turbo is best for efficiency, is going to be the turbo that generates the most boost for the least amount of increase in exhaust backpressure in the operating conditions where the most fuel is consumed throughout the commute. If it's all highway on level ground, then the engine should be producing about a constant 20hp, so the turbo should be sized to be efficient at this speed/power level without choking the engine during acceleration/hills. If it's mixed driving, then the turbo probably should be sized slightly higher as the weighted fuel consumption will be at a higher hp.
I think this above fact points towards going to a smaller turbo, but I've also read that a VNT17 can improve fuel economy over a vnt15 as it reduced exhaust back pressure. Any thoughts on this? Is this true? I'm skeptical, but if someone has real world experience, I'll listen to it.
Back in the 70s and 80s when adding turbos to diesels was becoming mainstream, the literature at the time stated that adding a turbo to a naturally aspirated diesel could improve fuel efficiency. This seems to be the case with the early 1.6 VW diesels. I believe the turbo 1.6D rabbit was EPA rated at 63mpg or something close, while the NA version was around 50mpg. The question is what mechanisms would allow this to occur? Probably the first guess would be the added torque would allow the engine to be operated at higher gears when climbing hills, and thus more efficiently overall (I think the transmissions were identical). Also, adding a turbo effectively increases the (dynamic) compression ratio a little bit. But I think the less obvious contribution is that adding a turbo basically converts the engine to a combined cycle system. The energy scavenged from the exhaust can be used to reduce pumping loses of the engine, and even provide a slight amount of power on the intake stroke as there will be positive pressure on the piston. At the minimum, it will reduce pumping loses, thus improving efficiency. Even if this is small, these small amounts do add up. New generation turbos can generate higher boost pressures than the increase in exhaust backpressure.
I read a thread where a guy had a BRM that he started adjusting the tunes on. He found at normal highway conditions, the variable vanes were kept excessively closed (probably for EGR). When he edited the tune to open them up a bit, his fuel economy went from ~36 to ~42mpg. I can see where a large turbo would have to close the vanes an excessive amount to spool the turbo at the low end of the range would result in poor turbine efficiency, thus requiring excessive backpressure. A smaller turbine operating in the middle of it's range would likely yield much better results. Also, newer generation turbos provide the same boost for less exhaust backpressure than the older designs.
When VW released their TDIe (efficiency or economy) in Europe, they spec'd the GTC1446vz making 130hp. They then installed the GTC1549VZ on the
CR170 and later the GTD1449VZ on the CR184 and 190. As near as I can tell, the Boras with the various engines all are rated at about 53mpg. The GTC1446vz has the smallest turbine housing of any of the turbos. The GTD1449vz has a similar turbine housing as the VNT15, but can flow much much more. That's what 15 years of engineering improvements will do.
I have a manual ALH jetta with a GTD1449vz on it (11mm pump, 0.216 nozzles, FMIC), and my plan is to place a pressure port over the egr port and compare backpressure to boost. I also have an automatic BEW (mostly stock) that is getting a VNT15 at the moment, but will probably be replaced by a GTC1446vz and then a GTC1549vz if I really want to go through the effort to have comparable data. (I'm not putting a GTD1449VZ on the golf, that's too much of a PITA)
Any thoughts? What have you guys noticed on your projects?