I also over boosted w cut out open
May 24, 2013 | 10:26 AM
#11
May 24, 2013 | 10:41 AM
#12
On The Tree
Joined: May 2013
Posts: 121
Likes: 0
From: Jennings LA
Its a Tial 38mm i just mounted it all wrong. 
Its a stock LQ4, it over boosted and i let out at 25#. Im not running any type of BC, just opening the cutout.
Either its the backpressure helping to push open the wastegate or the turbo is just so choked down from the back pressure in the Downpipe-tailpipe. But either way Cutout open = Lots o boost.
Its a stock LQ4, it over boosted and i let out at 25#. Im not running any type of BC, just opening the cutout.
Either its the backpressure helping to push open the wastegate or the turbo is just so choked down from the back pressure in the Downpipe-tailpipe. But either way Cutout open = Lots o boost.
Your in the same situation as the OP, Your exhaust is really restricting the turbo. Back to the boost controller though, That is one of the most critical components on turbo system. You shouldn't run without one, You WILL blow the motor lol
May 24, 2013 | 10:48 AM
#13
Joined: Jan 2006
Posts: 16,282
Likes: 438
From: Huntsville, AL
Turbos dont like anything after the turbine. Their ideal world is a a straight dump to atmosphere after a few inches. I have a 4" full exhaust and a straight through muffler, and with a cutout it makes a large difference even with that. Thats why I went to a 5" dp and 5" cutout. After the cutout, it goes back to 4".
Turbines work off something called expansion ratio. Basically the turbine works better if you can get a very large pressure/heat drop before and after it. So this will be your backpressure from the engine compared to the pressure between the turbo and tailpipe exit. The bigger this ratio the happier the turbo is, meaning it will respond faster to a change in conditions (ie, more throttle), and allow a higher maximum speed (boost). There is a diminishing return here though, thats why backpressure ratio is so important, which is the drive pressure of the turbine divided by the boost pressure from the compressor. Most factory turbo setups are around 2-3, which a good aftermarket kit is between 1.5-2.5, and a pure race setup will be very close to 1. The higher the bp ratio, the more responsive the turbo, but the more choked it is in the upper rpms. The lower the ratio is exactly the opposite, very laggy but extremely efficient at upper rpm.
Now when you free up the turbo with an open exhaust your wastegate will probably have a harder time controlling the turbo because the turbo is much more efficient. Wastegate size and placement have a lot to do with how effective it is.
Case in point, with my setup with a 50mm gate, the least amount of boost I can run with my cutout open is about 18psi, even if the gate is wide open the whole time. This is due to the wastegate location and routing.
Turbines work off something called expansion ratio. Basically the turbine works better if you can get a very large pressure/heat drop before and after it. So this will be your backpressure from the engine compared to the pressure between the turbo and tailpipe exit. The bigger this ratio the happier the turbo is, meaning it will respond faster to a change in conditions (ie, more throttle), and allow a higher maximum speed (boost). There is a diminishing return here though, thats why backpressure ratio is so important, which is the drive pressure of the turbine divided by the boost pressure from the compressor. Most factory turbo setups are around 2-3, which a good aftermarket kit is between 1.5-2.5, and a pure race setup will be very close to 1. The higher the bp ratio, the more responsive the turbo, but the more choked it is in the upper rpms. The lower the ratio is exactly the opposite, very laggy but extremely efficient at upper rpm.
Now when you free up the turbo with an open exhaust your wastegate will probably have a harder time controlling the turbo because the turbo is much more efficient. Wastegate size and placement have a lot to do with how effective it is.
Case in point, with my setup with a 50mm gate, the least amount of boost I can run with my cutout open is about 18psi, even if the gate is wide open the whole time. This is due to the wastegate location and routing.
May 24, 2013 | 11:03 AM
#15
when I had my truck tuned we made two pulls to see what it would do with the cutout open. closed it was 5lbs and with it open it was just a hair over 7.
running a 3lb spring, 3" exhaust and 3" cutout
running a 3lb spring, 3" exhaust and 3" cutout
May 24, 2013 | 12:16 PM
#17
On The Tree
Joined: May 2013
Posts: 121
Likes: 0
From: Jennings LA
Turbos dont like anything after the turbine. Their ideal world is a a straight dump to atmosphere after a few inches. I have a 4" full exhaust and a straight through muffler, and with a cutout it makes a large difference even with that. Thats why I went to a 5" dp and 5" cutout. After the cutout, it goes back to 4".
Turbines work off something called expansion ratio. Basically the turbine works better if you can get a very large pressure/heat drop before and after it. So this will be your backpressure from the engine compared to the pressure between the turbo and tailpipe exit. The bigger this ratio the happier the turbo is, meaning it will respond faster to a change in conditions (ie, more throttle), and allow a higher maximum speed (boost). There is a diminishing return here though, thats why backpressure ratio is so important, which is the drive pressure of the turbine divided by the boost pressure from the compressor. Most factory turbo setups are around 2-3, which a good aftermarket kit is between 1.5-2.5, and a pure race setup will be very close to 1. The higher the bp ratio, the more responsive the turbo, but the more choked it is in the upper rpms. The lower the ratio is exactly the opposite, very laggy but extremely efficient at upper rpm.
Now when you free up the turbo with an open exhaust your wastegate will probably have a harder time controlling the turbo because the turbo is much more efficient. Wastegate size and placement have a lot to do with how effective it is.
Case in point, with my setup with a 50mm gate, the least amount of boost I can run with my cutout open is about 18psi, even if the gate is wide open the whole time. This is due to the wastegate location and routing.
Turbines work off something called expansion ratio. Basically the turbine works better if you can get a very large pressure/heat drop before and after it. So this will be your backpressure from the engine compared to the pressure between the turbo and tailpipe exit. The bigger this ratio the happier the turbo is, meaning it will respond faster to a change in conditions (ie, more throttle), and allow a higher maximum speed (boost). There is a diminishing return here though, thats why backpressure ratio is so important, which is the drive pressure of the turbine divided by the boost pressure from the compressor. Most factory turbo setups are around 2-3, which a good aftermarket kit is between 1.5-2.5, and a pure race setup will be very close to 1. The higher the bp ratio, the more responsive the turbo, but the more choked it is in the upper rpms. The lower the ratio is exactly the opposite, very laggy but extremely efficient at upper rpm.
Now when you free up the turbo with an open exhaust your wastegate will probably have a harder time controlling the turbo because the turbo is much more efficient. Wastegate size and placement have a lot to do with how effective it is.
Case in point, with my setup with a 50mm gate, the least amount of boost I can run with my cutout open is about 18psi, even if the gate is wide open the whole time. This is due to the wastegate location and routing.
May 24, 2013 | 12:30 PM
#18
Boost controller can only work as good as your wastegate can.
I can add 60psi pressure to my wastegate and it will still overboost. Hence my wastegate is too small and its not in the best spot for flow to excape.
I can add 60psi pressure to my wastegate and it will still overboost. Hence my wastegate is too small and its not in the best spot for flow to excape.
