Backpressure measurement
12-06-2015, 06:38 PM
#23
What size wastegate spring (what rating) is everyone using to combat the backpressure? Are you running a 30psi spring to make 15~psi of intake pressure due to the 2:1 backpressure ratio? Or was backpressure not a consideration when purchasing your wastegates.
12-06-2015, 07:01 PM
#24
The waste gate spring doesn't really combat back pressure. It's more a result of the turbine and compressor. In this case, it takes 2x the pressure on the turbine side to drive the compressor to 1x. A larger diameter turbine wheel would give more leverage over the compressor allowing for a lower back pressure to produce the same boost on the compressor side.
Another way of looking at it is if you vented 1/2 the exhaust pressure through the waste gate, the compressor would produce 1/2 the boost. A waste gate isn't the answer to back pressure issues unless the gate is too small and you're experiencing boost creep.
Another way of looking at it is if you vented 1/2 the exhaust pressure through the waste gate, the compressor would produce 1/2 the boost. A waste gate isn't the answer to back pressure issues unless the gate is too small and you're experiencing boost creep.
12-06-2015, 08:06 PM
#25
The waste gate spring doesn't really combat back pressure. It's more a result of the turbine and compressor. In this case, it takes 2x the pressure on the turbine side to drive the compressor to 1x. A larger diameter turbine wheel would give more leverage over the compressor allowing for a lower back pressure to produce the same boost on the compressor side.
Another way of looking at it is if you vented 1/2 the exhaust pressure through the waste gate, the compressor would produce 1/2 the boost. A waste gate isn't the answer to back pressure issues unless the gate is too small and you're experiencing boost creep.
Another way of looking at it is if you vented 1/2 the exhaust pressure through the waste gate, the compressor would produce 1/2 the boost. A waste gate isn't the answer to back pressure issues unless the gate is too small and you're experiencing boost creep.
Or, would you say that, when ordering your wastegate (spring) you do not take back pressure into consideration at all (you could care less)
12-06-2015, 08:40 PM
#28
I used to think so also, because it references atmospheric pressure, this makes sense. So I've been telling novices to ignore backpressure considerations when looking at which wastegate to buy, focus on the desired boost pressure (15psi? then buy a 15psi spring). Until today, when somebody said that increasing exhaust gas pressure would lower the boost at the intake manifold, requiring a stronger spring. Which makes sense, but I didn't realize HOW much pressure these turbo V8s were producing, some ratios of 2:1 for example. So are people really buying 15psi springs to run 7psi? And 30psi springs to run 15psi? Is there any truth or are they just messing with me.
12-06-2015, 08:55 PM
#29
Dude you're thinking way to much in to this. 8psi spring will give you 9ish psi at the manifold. 14psi spring will net you a little over 15 and so on.
The ONLY time I've seen boost pressure at the manifold lower then what the spring is rated is when guys reference boost pressure for the wastage from a pre intercooler. (Charge pipe, or compressor cover fitting. Referencing boost from there will almost always give you less boost the spring pressure. This is due to pressure drop across the core of the intercooler. I saw one set up with a shitty eBay intercooler showing 6psi less then spring. The dude move his reference signal to the manifold and got spring pressure.
Only time I've seen boost pressure go over spring is if the wastegate is positioned poorly, gate is too small causing boost creep, or a/r is way too small for the motor.
The ONLY time I've seen boost pressure at the manifold lower then what the spring is rated is when guys reference boost pressure for the wastage from a pre intercooler. (Charge pipe, or compressor cover fitting. Referencing boost from there will almost always give you less boost the spring pressure. This is due to pressure drop across the core of the intercooler. I saw one set up with a shitty eBay intercooler showing 6psi less then spring. The dude move his reference signal to the manifold and got spring pressure.
Only time I've seen boost pressure go over spring is if the wastegate is positioned poorly, gate is too small causing boost creep, or a/r is way too small for the motor.
12-06-2015, 09:46 PM
#32
Dude you're thinking way to much in to this. 8psi spring will give you 9ish psi at the manifold. 14psi spring will net you a little over 15 and so on.
The ONLY time I've seen boost pressure at the manifold lower then what the spring is rated is when guys reference boost pressure for the wastage from a pre intercooler. (Charge pipe, or compressor cover fitting. Referencing boost from there will almost always give you less boost the spring pressure. This is due to pressure drop across the core of the intercooler. I saw one set up with a shitty eBay intercooler showing 6psi less then spring. The dude move his reference signal to the manifold and got spring pressure.
Only time I've seen boost pressure go over spring is if the wastegate is positioned poorly, gate is too small causing boost creep, or a/r is way too small for the motor.
The ONLY time I've seen boost pressure at the manifold lower then what the spring is rated is when guys reference boost pressure for the wastage from a pre intercooler. (Charge pipe, or compressor cover fitting. Referencing boost from there will almost always give you less boost the spring pressure. This is due to pressure drop across the core of the intercooler. I saw one set up with a shitty eBay intercooler showing 6psi less then spring. The dude move his reference signal to the manifold and got spring pressure.
Only time I've seen boost pressure go over spring is if the wastegate is positioned poorly, gate is too small causing boost creep, or a/r is way too small for the motor.
12-06-2015, 09:55 PM
#33
The spring is what holds the valve shut in the wastegate. The boost signal to the gate is what actually opening it to allow exhaust gas to bypass the turbo.
Last edited by Busa_rob; 12-06-2015 at 10:35 PM.
12-06-2015, 10:07 PM
#34
Thanks for the attitude. Not all waste gates are the same. Once you start introducing outside references and are not just using exhaust pressure and spring pressure the discussion gets complicated. The discussion started with whether or not back pressure to boost pressure ratios mattered when deciding on a spring to use in the waste gate. If you are not using any other inputs other than exhaust pressure and the spring on a waste gate then you will need a different spring if the ratio is 1:1 as opposed to 2:1. If that is not correct then please correct me.
12-06-2015, 10:40 PM
#35
Not an attitude, just trying to help you understand.
But based off what you said I guess I have no idea what I'm talking about. Someone else can answer your questions.
And btw, the wastegate MUST use a reference signal. It's not just the spring and exhaust pressure that make the gate open. With no reference, the gate will not open, and you will literally get "all the boost".
But based off what you said I guess I have no idea what I'm talking about. Someone else can answer your questions.
And btw, the wastegate MUST use a reference signal. It's not just the spring and exhaust pressure that make the gate open. With no reference, the gate will not open, and you will literally get "all the boost".
12-06-2015, 11:58 PM
#38
A. Spring Rate Controlled Method
If you want to use spring rate to control boost leve
l, install boost signal hose
from the compressor cover
hose barb, to the bottom banjo barb port of the wast
egate can. You will leave th
e top banjo barb port
unused and vented to atmosphere. Secure the hose
connections with either
zip ties or hose clamps,
making sure to route hose away from high heat
sources. Using this method, your boost level will be
determined by the spring/springs used and back pressure.
The above is from page 7 of http://www.precisionturbo.net/tech/i...structions.pdf
Although it does require a boost reference to work, it does mimic the scenario I was referencing. Just need to find a wastegate that does not need the boost reference at all. Getting closer.
If you want to use spring rate to control boost leve
l, install boost signal hose
from the compressor cover
hose barb, to the bottom banjo barb port of the wast
egate can. You will leave th
e top banjo barb port
unused and vented to atmosphere. Secure the hose
connections with either
zip ties or hose clamps,
making sure to route hose away from high heat
sources. Using this method, your boost level will be
determined by the spring/springs used and back pressure.
The above is from page 7 of http://www.precisionturbo.net/tech/i...structions.pdf
Although it does require a boost reference to work, it does mimic the scenario I was referencing. Just need to find a wastegate that does not need the boost reference at all. Getting closer.
12-07-2015, 04:09 AM
#40
A. Spring Rate Controlled Method
If you want to use spring rate to control boost leve
l, install boost signal hose
from the compressor cover
hose barb, to the bottom banjo barb port of the wast
egate can. You will leave th
e top banjo barb port
unused and vented to atmosphere. Secure the hose
connections with either
zip ties or hose clamps,
making sure to route hose away from high heat
sources. Using this method, your boost level will be
determined by the spring/springs used and back pressure.
The above is from page 7 of http://www.precisionturbo.net/tech/i...structions.pdf
Although it does require a boost reference to work, it does mimic the scenario I was referencing. Just need to find a wastegate that does not need the boost reference at all. Getting closer.
If you want to use spring rate to control boost leve
l, install boost signal hose
from the compressor cover
hose barb, to the bottom banjo barb port of the wast
egate can. You will leave th
e top banjo barb port
unused and vented to atmosphere. Secure the hose
connections with either
zip ties or hose clamps,
making sure to route hose away from high heat
sources. Using this method, your boost level will be
determined by the spring/springs used and back pressure.
The above is from page 7 of http://www.precisionturbo.net/tech/i...structions.pdf
Although it does require a boost reference to work, it does mimic the scenario I was referencing. Just need to find a wastegate that does not need the boost reference at all. Getting closer.
Second bold at the bottom...
