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Internal Vs. External

StealthX

By StealthX,
in Engines & Forced Induction

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StealthX Veteran

StealthX

Posted
Posted

Hey forum.

Need some food for thought, I'm trying to weigh up the pros and cons of internal vs external gates.

Problem is, I can't get my boost to ramp up quickly enough, without then creeping up from there. The best I can get is 10psi by just under 3k RPM - which is pretty lazy IMO (.86 disco potato on 2.5L QR25), then slight creep, but any less pretension and it doesn't make 10psi, and more and it makes more boost and creeps more. I've tried boost controller or not, a .5 and 1.0 bar actuator (using .5 bar one now), different pretensions etc... I have two options: put up with the internal gate, or hold the internal gate shut and install an external gate (the manifold I'm using has provisions for the external gate).

Assuming all other variables are the same, what are the general pros and cons of the two types? The way I see it:

External

pros

-finer, more accurate boost control

-boost ramps harder

-better turbine flow

cons

-expensive

-space consuming

-complex (more plumbing, space constraints etc.)

Internal

pros

-cheap

-simple

cons

-prone to creep

-prone to fading (boost dropping off at high RPMs)

-inaccurate (hard to hold a flat line)

Anything else to add? Also, is there any merit at all of running an external gate on my set-up? I seem to think there is...

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StealthX Veteran

StealthX

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  • Author
Posted

IF YOU HAVE A HEAP OF BACK PRESSURE it may help. but thats a pretty small turbo for a rb25.... chances are you have some mad back pressure.

Yeah, hence the creep and retarded ignition. The .86 housing made a huuge difference.

btw its a QR25DE+T i.e. 2.5L 4cyl in my X-Trail...

WYTSKY Veteran

WYTSKY

Posted
Posted

Perhaps Illegal in your state? are you going to plumb it back into the exhaust or screamer?

I had the same issue as you with my old turbo, my current one, with the external gate, the boost line is absolutely flat as- perfect control.

rob82 Mentor

rob82

Posted
Posted

Yeah, hence the creep and retarded ignition. The .86 housing made a huuge difference.

btw its a QR25DE+T i.e. 2.5L 4cyl in my X-Trail...

Have been through these problems before on the XR6T's - ie biggish engine littlish turbo. You will find that most crappy internal gates are not very lineaar if you compare pressure applied to rod extension. We found that some actuators sold as a 8psi actuator would crack around 7psi and be at full extension by 30psi. We went through alot of actuators before finding the right one. you may need to test this for yourself.

The other trick is to change the boost source for the actuator to right at the start of the scroll as you will find that with more flow the pressure at this point goes up when compare to the scroll outlet. On an xr6t if you had 12psi at the outlet at 5000rpm you may have upto 15psi at the start of the scroll. This obviously puts more pressure onto the actuator to open further - hence better boost control.

PS - there is nothing wrong with internal gates in the right applications esspecially if you can get your hands on a dual sided actuator.

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StealthX Veteran

StealthX

Posted
  • Author
Posted

Perhaps Illegal in your state? are you going to plumb it back into the exhaust or screamer?

I had the same issue as you with my old turbo, my current one, with the external gate, the boost line is absolutely flat as- perfect control.

Yeah the screamer would def be illegal in WA, but I was planning to have the exhaust shop make up a screamer pipe, and a recirculation pipe, so few V band clamps and a block off plate later, I'd have a screamer/recirc...

from what i have seen, heard of, read and results etc

external wastegate setups are

more expensive

usually more complex

better response

better control

the two main points are the last two

Thanks man, that helps heaps :) The first two aren't really a problem, there's heaps of space under my manifold, only the cooler piping and an engine mount to doge (easy).

Have been through these problems before on the XR6T's - ie biggish engine littlish turbo. You will find that most crappy internal gates are not very lineaar if you compare pressure applied to rod extension. We found that some actuators sold as a 8psi actuator would crack around 7psi and be at full extension by 30psi. We went through alot of actuators before finding the right one. you may need to test this for yourself.

The other trick is to change the boost source for the actuator to right at the start of the scroll as you will find that with more flow the pressure at this point goes up when compare to the scroll outlet. On an xr6t if you had 12psi at the outlet at 5000rpm you may have upto 15psi at the start of the scroll. This obviously puts more pressure onto the actuator to open further - hence better boost control.

PS - there is nothing wrong with internal gates in the right applications esspecially if you can get your hands on a dual sided actuator.

Yeah I had the same problem with the 1.0 bar actuator, it was making about 12psi with 3mm of pre-tension, when it should make more like 14-15, boost dropped off to about 10 at redline - so clearly didn't want that. The .5bar one I'm using at the moment, has heaps of pretension and makes 10, which it obviously isn't designed for, hence the poor control, I'd imagine it'd work fine at 7psi though. Both were genuine Garrett actuators. My boost source is taken from the cooler pipe closest to the throttle body, and the disco potato has no provision for a nipple located on the comp. housing, thanks bro.

tridentt150v Grand Master

tridentt150v

Posted
Posted

When your pushing the limits, an external handles it better. Nobody [well almost nobody] has a problem with an internal at 7-10psi, but as you wind up the boost and increase the size of the turbo you will find the limits of an internal and an external gate comes into its own. I know that people on here have got their internal to behave, but it cost them several weekends, and a few remove and modifies/tunes etc before they got it [some tinarse will dispute this statement]. All us CBF'eds didn't bother we just strapped on an external and did the set and forget.

I also reckon that an external is better for the future as well - if you end up increasing power/boost etc then the external has the headroom for 'growth'.

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