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Discussion Starter · #1 ·
Just wondering what waste gate actuators will fit the mamba 18g from opening prematurely? As the mamba one wont stay shut 2500 revs and have a 30 psi spring in it and I can’t get any more tension out of it
 

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Discussion Starter · #5 ·
To the point where it stays shut but doesn’t open it makes 37 psi at that point but I really only need 27 😂 I really think it’s just the mamba actuator that’s the problem, I really don’t want to bin the turbo it works great it makes 30psi by 2000 rpm it just can’t hold it and I can hear the the gate open after 2500 rpm
 

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nissan
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I've seen this a number of times with Mamba 18g turbos that have 6cm exhaust housings and modified injector pumps.. I'm guessing the housings are on the tight side and provide too much restriction generating excessively high Exhaust Manifold Pressure. It doesn't seem to be the same problem with stock pumps so I'm guessing it is caused by the extra exhaust gas and extra EMP generated by the bigger pump. The problem does not seem to exist with the 8cm housing but naturally it doesn't spool as quickly.
 

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Discussion Starter · #7 ·
I've seen this a number of times with Mamba 18g turbos that have 6cm exhaust housings and modified injector pumps.. I'm guessing the housings are on the tight side and provide too much restriction generating excessively high Exhaust Manifold Pressure. It doesn't seem to be the same problem with stock pumps so I'm guessing it is caused by the extra exhaust gas and extra EMP generated by the bigger pump. The problem does not seem to exist with the 8cm housing but naturally it doesn't spool as quickly.
Yeah I have the 6cm housing and I’m sure your spot on with the problem but surely someone would have come up with a fix , cause I really don’t want to deal with the lag of the 8cm as them drivability with the 6 work with the low down spool.. welding the gate shut would work and going an external gate would do the job but really don’t want to go down that road
 

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I'm pretty sure that others here have used a different actuator for this exact reason. Maybe a search of older threads might help if nothing pops up here.
 

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You need a bigger diameter actuator. They have a stiffer spring for the same boost level. The Garretts work well but are a sealed unit and the spring cant be changed. Turbo smart aren't quite as big in diameter as a Garrett but bigger than a Mamba and can be pulled apart to change boost springs. I think you can change shaft lengths too. Cost is about $200.

Someone here thinks a Garrett will fit.
 

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You need a bigger diameter actuator. They have a stiffer spring for the same boost level. The Garretts work well but are a sealed unit and the spring cant be changed. Turbo smart aren't quite as big in diameter as a Garrett but bigger than a Mamba and can be pulled apart to change boost springs. I think you can change shaft lengths too. Cost is about $200.

Someone here thinks a Garrett will fit.
You actually need to clip the turbine wheel to reduce your emp. The actuator is a band-aid at best
 

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Clipping the wheel is a solution but only just as its still a band-aid as well, and can only do so much. Small housing with turbine wheel design is the issue. It depends on blade count, angle, and weight. for the gas flow quantity, or how much fuel/ air you are pushing with respect to housing and turbine wheel size.

You probably need to see or test what EMP you have first. If its over 2:1 then there isn't anything you can do, short of fitting a larger AR housing for that size turbine wheel for your fueling tune level.

This stuff is a science, trial and error will only go so far. A 18G is a small turbo for a TD42 with a 12mm IP. You have stated you have full spool value by 2000rpm, which suggests you have fueling to reach the volume gas capacity well before 2000rpm so you have reached the capacity of the turbine wheel well before 1800rpm. So you are trying to gate off that excess after 1800 rpm but by 2500 rpm you have reached the limit of what the gate size and actuator travel design will allow to flow. Yes you can play around with springs and get a slightly better result but still you are restricted by the spring and gate flap design.

I will try and explain this concept best i can. Say we have a 30psi spring or a spring with 30psi suggested tension for a actuator. we have set the actuator so it has a tension on the gate flap to crack open at a boost pressure of 30 psi but our EMP at 30 psi boost pressure is 60 psi. So if our gate flat hole is 20mm dia we have a surface area of about .5 inch so we have 45 psi acting on the spring if mechanical advantage on the gate leaver is 1:1 which it isn't the flap arm is about half the length of actuator leaver, so we have a extra mechanical advantage on the spring so 60 psi acting on the spring to hold it closed. But soon as the gate opens that EMP pressure acting on the spring is reduced so the gate will open an amount that is in a equilibrium position with EMP and spring actuator tension. So as more exhaust gas is increased with rpm the higher the EMP will go. The point is here the housing /gate sizing with turbine wheel has a set amount of gas it can flow or PHI so playing with gate settings and tension can only do so much. You have to change the housing or turbine wheel size or design to get control back on the gate.

As a side note boost pressure isn't a measure of a turbo and its flow capacity. This is where design comes into play, it is possible to have a turbo that can flow better volumes in spool with a lot less boost pressure so you get a higher torque rise, air quality or density with fuel is what makes power/torque. By the same token super fast boost rise isn't a measure of driveability or torque. For most of us drivability is the single key to a nice engine. Sometimes or mostly you have to compromise some very low torque to get flexibly in the rpm range. Its usually a engine that can develop its power at a constant rise all the way through its rpm range is the nicest to drive. Torque is a big factor on how you get that power curve, as power is a product of torque, not the other way around. You measure torque to calculate power, power is a math calculated value.

EMP above say a suggested 2:1 EMP:IMP will kill driveability it reduces power development after peak torque. Too small of a turbo will show up on a dyno with that characteristic power flattening off and even dropping off after 3000 rpm.

I find for a good powered sub 200rwkw TD42 you need a comp wheel size of about 67mm trim dependent and a turbine wheel size of about 58mm trim dependent to get enough flow to get gate control and more respectable EMP:IMP ratio. But this EMP stuff isn't the be all to end all either its just a big consideration in the big picture, as is everything else in the turbo sizing game.
 

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Discussion Starter · #14 ·
Clipping the wheel is a solution but only just as its still a band-aid as well, and can only do so much. Small housing with turbine wheel design is the issue. It depends on blade count, angle, and weight. for the gas flow quantity, or how much fuel/ air you are pushing with respect to housing and turbine wheel size.

You probably need to see or test what EMP you have first. If its over 2:1 then there isn't anything you can do, short of fitting a larger AR housing for that size turbine wheel for your fueling tune level.

This stuff is a science, trial and error will only go so far. A 18G is a small turbo for a TD42 with a 12mm IP. You have stated you have full spool value by 2000rpm, which suggests you have fueling to reach the volume gas capacity well before 2000rpm so you have reached the capacity of the turbine wheel well before 1800rpm. So you are trying to gate off that excess after 1800 rpm but by 2500 rpm you have reached the limit of what the gate size and actuator travel design will allow to flow. Yes you can play around with springs and get a slightly better result but still you are restricted by the spring and gate flap design.

I will try and explain this concept best i can. Say we have a 30psi spring or a spring with 30psi suggested tension for a actuator. we have set the actuator so it has a tension on the gate flap to crack open at a boost pressure of 30 psi but our EMP at 30 psi boost pressure is 60 psi. So if our gate flat hole is 20mm dia we have a surface area of about .5 inch so we have 45 psi acting on the spring if mechanical advantage on the gate leaver is 1:1 which it isn't the flap arm is about half the length of actuator leaver, so we have a extra mechanical advantage on the spring so 60 psi acting on the spring to hold it closed. But soon as the gate opens that EMP pressure acting on the spring is reduced so the gate will open an amount that is in a equilibrium position with EMP and spring actuator tension. So as more exhaust gas is increased with rpm the higher the EMP will go. The point is here the housing /gate sizing with turbine wheel has a set amount of gas it can flow or PHI so playing with gate settings and tension can only do so much. You have to change the housing or turbine wheel size or design to get control back on the gate.

As a side note boost pressure isn't a measure of a turbo and its flow capacity. This is where design comes into play, it is possible to have a turbo that can flow better volumes in spool with a lot less boost pressure so you get a higher torque rise, air quality or density with fuel is what makes power/torque. By the same token super fast boost rise isn't a measure of driveability or torque. For most of us drivability is the single key to a nice engine. Sometimes or mostly you have to compromise some very low torque to get flexibly in the rpm range. Its usually a engine that can develop its power at a constant rise all the way through its rpm range is the nicest to drive. Torque is a big factor on how you get that power curve, as power is a product of torque, not the other way around. You measure torque to calculate power, power is a math calculated value.

EMP above say a suggested 2:1 EMP:IMP will kill driveability it reduces power development after peak torque. Too small of a turbo will show up on a dyno with that characteristic power flattening off and even dropping off after 3000 rpm.

I find for a good powered sub 200rwkw TD42 you need a comp wheel size of about 67mm trim dependent and a turbine wheel size of about 58mm trim dependent to get enough flow to get gate control and more respectable EMP:IMP ratio. But this EMP stuff isn't the be all to end all either its just a big consideration in the big picture, as is everything else in the turbo sizing game.
Way to much science for me lol , thanks for the info guys , but I even had issues with it when it was running a stock 11mm running 18 psi it would still blow the gate open. I don’t know I guess I’ll change out the turbo
 

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I had this problem when I first fitted my mamba 18g. Had to run a heap of preload on the gate & it held 20 psi without to much problem. Fitted a 12mm pump a few months ago, now no matter what I do it wont stop humping! I fitted a washer in the piston in the mamba actuator, made no differance. Fitted more washers, it did stop humping, but thats because the gate was closed solid!. That saw like you 30 plus PSI! I then fitted a garret 20psi actuator. Made no difference. Wound that much preload on that, it to didn't open. So now I'm going to turf the Mamba & either fit a RMS or P4x4 turbo.
 
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