Backpressure - Can big wastegates help?
12-20-2010, 02:31 PM
#1
Backpressure - Can big wastegates help? I would like to keep small exhaust housings on my rear mount because it spools descent.. but my question is can i run larger gates or additional gates to decrease backpressure at high boost? The combo is below in my sig but basically twin Precision 6262's w/T3 .63 exh housings and two Tial 38mm gates. The backpressure ratio is close to 2:1 at around 14 pounds, which i'm happy with, but steadily gets worse with more boost. Any help would be much appreciated!! Thanks
12-20-2010, 03:09 PM
#3
No, with any different combo of engine, heads, turbine, compressor, ect, ect, it takes X amount of drive pressure to support Y amount of manifold pressure
Change anything else in the combo then yes it will change the drive pressure needed for X amount of boost, but not the gates
Change anything else in the combo then yes it will change the drive pressure needed for X amount of boost, but not the gates
12-20-2010, 05:17 PM
#5
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No, with any different combo of engine, heads, turbine, compressor, ect, ect, it takes X amount of drive pressure to support Y amount of manifold pressure
Change anything else in the combo then yes it will change the drive pressure needed for X amount of boost, but not the gates
Change anything else in the combo then yes it will change the drive pressure needed for X amount of boost, but not the gates
But if you are running off the gate, seems like it would make it easier to boost, i know this doesnt sound right, and i cant seem to figure out how to word it.
But a supercharger looses PSI when adding headers and a better cam, Yet makes the same if not more power, at that lower pressure.
If we can evacuate the exhaust easier, wouldnt that kind of do the same thing, allow the cylinders to fill more easily?? or am i really just that stupid and completely way out in left field here??
12-20-2010, 05:19 PM
#6
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Drive pressure is related to boost pressure. To reach a set boost level, drive pressure must be what ever it is, to reach that. A wastegate regulates drive pressure, yes, but it still takes X drive pressure for the compressor to reach X boost level. Decreasing drive pressure by way of wastegate, only decreases boost level.
12-20-2010, 05:29 PM
#7
Drive pressure is related to boost pressure. To reach a set boost level, drive pressure must be what ever it is, to reach that. A wastegate regulates drive pressure, yes, but it still takes X drive pressure for the compressor to reach X boost level. Decreasing drive pressure by way of wastegate, only decreases boost level.
An interesting test... if you could find a larger turbine housing with a comparable cross section at the throat.... but i guess thats easier said than done.
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12-20-2010, 06:48 PM
#8
ok, i see what you are saying about drive pressure (still learning).... but if the motor can spin the turbine hard enough to get 14 pounds of boost with a b/p ratio of 2:1, why does the b/p increase when i crank up the boost? Thanks for the replys! Isn't the excessive backpressure a result of too much exhaust pressure? In other words, at 14 pounds of boost, if i had larger gates or larger exh housings, wouldn't i have less backpressure? Sorry if i'm not making sense!!
x2, the turbine are going to require a specific pressure level to make x amount of boost. Larger wastegate wont change the amount of pressure it takes to generate enough turbine speed to make the set boost level.
An interesting test... if you could find a larger turbine housing with a comparable cross section at the throat.... but i guess thats easier said than done.
An interesting test... if you could find a larger turbine housing with a comparable cross section at the throat.... but i guess thats easier said than done.
12-20-2010, 07:03 PM
#9
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like was said it takes a certain amount of pressure to spin the turbo to overcome the added pressure on the compressor side of it. you cant have more pressure on the compressor side than the exhaust side or the turbo wouldnt function like its supposed to. at minimum you would need atleast a pound or two more on the exhaust side for the turbine to even keep spinning.
12-20-2010, 07:04 PM
#10
Changing the housing yes.... the gates no
the only thing a larger gate will do is allow for a lower boost pressure to be achieved and have better/quicker control of the turbine speed
the only thing a larger gate will do is allow for a lower boost pressure to be achieved and have better/quicker control of the turbine speed
Last edited by rotary1307cc; 12-20-2010 at 07:11 PM.
12-20-2010, 08:52 PM
#11
Ok flow is one thing but too much back pressure is another.. you want to be ex psi to = psi=2-4psi (ex 20 psi = 24psi ex pressure) now if you run a 44mm gate and run 20 psi but have 40psi ex psi a 60mm gate will help but its a baidaid will not cure or fix.. remember the gate is closed till you reach or about reach your target psi so no matter what gate you have will spool the same... there is alot more to this than just gate/ex housing.. ie head flow turbine flow runner size ect..
12-20-2010, 09:32 PM
#12
This is kind of what i was thinking.... yes, it would be the exact same spool because it would be the same small housing but when the larger gates would open it would release more exhaust/backpressure than my current 38mm gates. My thought was to release just enough exhaust to lower the backpressure but not enough to drop the boost pressure..... Instead of a b/p ratio of 3:1 at 20 pounds to a more efficient 2:1 ratio at 20 pounds. If this would be a front mount, i would just install a larger exh housings and be done with it.... But because they are rear mounted, that would hurt spool. I'm not saying i'm correct, just kicking it around in my mind.
Ok flow is one thing but too much back pressure is another.. you want to be ex psi to = psi=2-4psi (ex 20 psi = 24psi ex pressure) now if you run a 44mm gate and run 20 psi but have 40psi ex psi a 60mm gate will help but its a baidaid will not cure or fix.. remember the gate is closed till you reach or about reach your target psi so no matter what gate you have will spool the same.
12-20-2010, 09:38 PM
#13
Backpressure is caused by the smallest point in the system which is the throat where the air sees mach1 or faster air speeds as it hits the turbine wheel. You can do whatever you want before the turbo, the turbine housing controls most if not all of the backpressure.
12-20-2010, 10:12 PM
#14
This is kind of what i was thinking.... yes, it would be the exact same spool because it would be the same small housing but when the larger gates would open it would release more exhaust/backpressure than my current 38mm gates. My thought was to release just enough exhaust to lower the backpressure but not enough to drop the boost pressure..... Instead of a b/p ratio of 3:1 at 20 pounds to a more efficient 2:1 ratio at 20 pounds. If this would be a front mount, i would just install a larger exh housings and be done with it.... But because they are rear mounted, that would hurt spool. I'm not saying i'm correct, just kicking it around in my mind.
12-20-2010, 10:25 PM
#15
I can get my mind around this.... this answers my question. Thanks!
Backpressure is caused by the smallest point in the system which is the throat where the air sees mach1 or faster air speeds as it hits the turbine wheel. You can do whatever you want before the turbo, the turbine housing controls most if not all of the backpressure.
12-21-2010, 07:29 AM
#17
So i should run a 38mm gate then!!! oh wait i can't cause i will get too much back pressure and boost creep!!!!I am not saying it is a cure but its a small factor!! all the other things add up like you said Lou.. if a ex housing flows 70lbs and a motor pushes 100 lbs there will be back pressure. now with a 38mm gate once open lets say it flow 15lbs and a 60 can flow 25lbs its a small factor. cause most run the gate back into the ex..
i guess we can all sell our big gates and run internal gates to save money....
i guess we can all sell our big gates and run internal gates to save money....
12-21-2010, 08:10 AM
#18
So i should run a 38mm gate then!!! oh wait i can't cause i will get too much back pressure and boost creep!!!!I am not saying it is a cure but its a small factor!! can flow 25lbs its a small factor. cause most run the gate back into the ex..
i guess we can all sell our big gates and run internal gates to save money....
i guess we can all sell our big gates and run internal gates to save money....
yes... too small of gate can cause creep
but NO it will not change the drive pressure needed to support X amount of boost....../story
If the gate is too small all it will do is limit how low of boost you can attain, and cause problems with creep
Also there will be problems with spikes because it can't bleed enough exhaust volume fast enough to control turbine speed
12-21-2010, 08:20 AM
#19
So i should run a 38mm gate then!!! oh wait i can't cause i will get too much back pressure and boost creep!!!!I am not saying it is a cure but its a small factor!! all the other things add up like you said Lou.. if a ex housing flows 70lbs and a motor pushes 100 lbs there will be back pressure. now with a 38mm gate once open lets say it flow 15lbs and a 60 can flow 25lbs its a small factor. cause most run the gate back into the ex..
i guess we can all sell our big gates and run internal gates to save money....
i guess we can all sell our big gates and run internal gates to save money....
How about this smart guy, why dont you get 2 44mm wastegates and a backpressure sensor. 1st run your car with a single mm wastegate and see how much backpressure it produces at 20# of boost, than add the lines to the 2nd wastegate and see what backpressure does. ****, lets add 10 wastegates to get rid of all the backpressure. It doesnt work like that.
I dont care how many wastegates you have it will only control how low you can take the boost, at x boost level your going to need a certain amount of pressure on the throat of the turbine to create the cfm of airflow needed to make the boost level.
12-21-2010, 08:30 AM
#20
How about this smart guy, why dont you get 2 44mm wastegates and a backpressure sensor. 1st run your car with a single mm wastegate and see how much backpressure it produces at 20# of boost, than add the lines to the 2nd wastegate and see what backpressure does. ****, lets add 10 wastegates to get rid of all the backpressure. It doesnt work like that.
I dont care how many wastegates you have it will only control how low you can take the boost, at x boost level your going to need a certain amount of pressure on the throat of the turbine to create the cfm of airflow needed to make the boost level.
I dont care how many wastegates you have it will only control how low you can take the boost, at x boost level your going to need a certain amount of pressure on the throat of the turbine to create the cfm of airflow needed to make the boost level.