Anyone using Variable Geometry Turbos?
12-03-2007, 01:26 PM
#21
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The VG turbo is the high pressure (second in line) compressor. That lets them utilize the higher power potential of the VG turbine at low airflow to spin a small compressor to get initial engine airflow up.
Compared to the single large VG unit used on the 6.0l, shaft speed on the smaller second-stage VG comes up much faster - while it won't support much more than, say, 35% of the engine's airflow needs at max rated, it will come up fast right off the line and get the larger, fixed-geometry low pressure turbo spun up quickly.
A lot of the drive for faster response was driver feel - the off-the-line performance of the Powerstrokes was really poor, especially on the first year models. Tied to that is emissions - without adequate boost, you can't put enough fuel in to get good power without poor emissions (both particulate, smoke; and CO), etc.
BMW used a pair of fixed geometry turbos to do the same thing on the new 3-series - they used a set of control valves to direct exhaust flow and achieve a similar end result without the need for VG (Off the line, all exhaust goes to one tubine to spin it up, then diverts to both as net airflow comes up).
Thanks for the compliment on the bike - rode to Vegas and back this weekend for the Trophy Truck race in Henderson - have almost 20k on it now, still whistling right along.
Compared to the single large VG unit used on the 6.0l, shaft speed on the smaller second-stage VG comes up much faster - while it won't support much more than, say, 35% of the engine's airflow needs at max rated, it will come up fast right off the line and get the larger, fixed-geometry low pressure turbo spun up quickly.
A lot of the drive for faster response was driver feel - the off-the-line performance of the Powerstrokes was really poor, especially on the first year models. Tied to that is emissions - without adequate boost, you can't put enough fuel in to get good power without poor emissions (both particulate, smoke; and CO), etc.
BMW used a pair of fixed geometry turbos to do the same thing on the new 3-series - they used a set of control valves to direct exhaust flow and achieve a similar end result without the need for VG (Off the line, all exhaust goes to one tubine to spin it up, then diverts to both as net airflow comes up).
Thanks for the compliment on the bike - rode to Vegas and back this weekend for the Trophy Truck race in Henderson - have almost 20k on it now, still whistling right along.
Last edited by Big Thumper; 12-03-2007 at 05:15 PM.
12-03-2007, 05:10 PM
#22
Ill vouch for the poor off the line performance of the P Stroke. My work truck is a 05 F450 with the 6.0 and from a dead stop it is dead until it hits 2k rpm. It has also had problems with the VGT vains sticking closed from build up. Along with numerous other problems.
12-03-2007, 05:16 PM
#23
Ill vouch for the poor off the line performance of the P Stroke. My work truck is a 05 F450 with the 6.0 and from a dead stop it is dead until it hits 2k rpm. It has also had problems with the VGT vains sticking closed from build up. Along with numerous other problems.
Also do you notice the power stalling once you get up to higher RPM's and is that what's leading you to say the veins are sticking?
12-03-2007, 05:38 PM
#24
VGT benefits are only utilized when calibrated proplerly...
Besides.. efficiency shouldnt be a reason either.. adding aftermarket parts and typically poor combination of parts eliminates any gains..
And to that point, you can gain huge fuel efficiency points if an electronic bypass is added to a Radix unit..
Besides.. efficiency shouldnt be a reason either.. adding aftermarket parts and typically poor combination of parts eliminates any gains..
And to that point, you can gain huge fuel efficiency points if an electronic bypass is added to a Radix unit..
12-03-2007, 05:41 PM
#25
Absolutely 
I was merely asking for the sake of learning if anyone's done it. I'm not interested in doing it on my set-up in the least bit. More curious as the how people are making them work and their 2 cents on the response time and driving characteristic of their set-up
I was merely asking for the sake of learning if anyone's done it. I'm not interested in doing it on my set-up in the least bit. More curious as the how people are making them work and their 2 cents on the response time and driving characteristic of their set-up
12-03-2007, 06:42 PM
#26
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It's cool porsche is stepping up with the technology. I know the VGT's on diesels have a sweet sound, especially with straight exhaust.
Last edited by Leroy_454; 12-03-2007 at 07:52 PM.
12-03-2007, 06:56 PM
#27
As far as GM having the same problem I am not sure, what I noticed was the Torque curve seemed all screwed up. Power would come and go and odd times under throttle so it went into the dealership. They ran diagnostics and found the problem and showed me the turbo when it was apart. Kinda interesting too bad I did have a camera with me to take some pics of it.
12-03-2007, 07:05 PM
#28
As far as GM having the same problem I am not sure, what I noticed was the Torque curve seemed all screwed up. Power would come and go and odd times under throttle so it went into the dealership. They ran diagnostics and found the problem and showed me the turbo when it was apart. Kinda interesting too bad I did have a camera with me to take some pics of it.
Those woulda been interesting for sure. I remember taking apart a compressor wheel that was 4ft in diameter and didn't have my camera with me at the time. 
12-03-2007, 08:00 PM
#29
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VGT benefits are only utilized when calibrated proplerly...
Besides.. efficiency shouldnt be a reason either.. adding aftermarket parts and typically poor combination of parts eliminates any gains..
And to that point, you can gain huge fuel efficiency points if an electronic bypass is added to a Radix unit..
Besides.. efficiency shouldnt be a reason either.. adding aftermarket parts and typically poor combination of parts eliminates any gains..
And to that point, you can gain huge fuel efficiency points if an electronic bypass is added to a Radix unit..
12-03-2007, 08:07 PM
#30
If I am not mistaken Ford uses oil pressure to operate the VGT on the 6.0 PStroke.. Kinda interesting. Also on a side note after talking with the service manager at the garage he said the the new Diesel fuel that is out is causing problems on the 6.0 powerstrokes. Sticking VGT vains, and premature injector failures due to the fact that the new fuel has less lubricants in it. He said running a Cetane additive helps to prevent this..