[alerno]

Hi,

I have to replace the engine of my car, they broke into the car, tore the wiring harness and they couldn't rewire (JDM). They offer me a 2.5XT engine, another seller sells the full Fozzy JDM STi parts, but I simply dislike the turbo "kick"

I would love to install a 2.5XT or STi engine, run it as 2.5X NA normally, and only apply the boost on demand, like a turbo "button" (without damaging any components)

Possible?

 

[HeyChris]

No.

 

[Yarameme]

NOS.

 

[alerno]

Ok, thanks.

And I guess these "boost controllers" can't be used thus either, right?

 

[adc]

Why are you worried since the engine is built to turbo? Driving normally you only get a few pounds of boost when starting out. I don't understand your train of thought.

 

[OriginalTwoTone]

 

[K675]

Why are you worried since the engine is built to turbo? Driving normally you only get a few pounds of boost when starting out. I don't understand your train of thought.

I don't think OP does either

 

[alerno]

Why are you worried since the engine is built to turbo? Driving normally you only get a few pounds of boost when starting out. I don't understand your train of thought.

I drive very intensely. It always sounds pretentious. Precisely I don't like the sudden onset of boost mid-corner if you are close to grip limit. If Subies allow you one thing is unusually high curve speeds. Driving in the city or on motorway straights or cruising about I don't mind the boost.

I am not "worried" about something, I simply enjoy the linearity of normally aspirated engines, especially around bends.

The reason I would like to keep boost on demand is I live at high altitude, really high (close to 4000 metres above sea, I don't know in miles) so sometimes going uphill with the family or carrying something my NA 2.0 runs out of puff. I normally don't need high torque (or horsepower) at all.

But if it's not doable, too bad.

 

[adc]

I am out..this makes zero sense. You have the power to use how much turbo you want and need. Its not that difficult to use the gas pedal to control acceleration. I have never had turbo until my 18XT. It took about 5 seconds for this 74 year old guy to figure it out. Perhaps someone else can give advice or better yet the mods can close this thread.

 

[alerno]

I am out..this makes zero sense. You have the power to use how much turbo you want and need. Its not that difficult to use the gas pedal to control acceleration. I have never had turbo until my 18XT. It took about 5 seconds for this 74 year old guy to figure it out. Perhaps someone else can give advice or better yet the mods can close this thread.

Sorry mate, I didn't write personally to upset you.

I have the curiosity to see whether this admittedly rare mod could be somehow achieved. I don't see why we have to question each other's intentions or intelligence, instead of seeing if there is any technical possibility. If you think "it makes zero sense" I respect your opinion, but wonder if you have really read what I just wrote. At 41 I have never crashed, not with my old Toyota Starlet turbo either. Yes, I have some humble capability to "control the throttle" I simply LIKE, ENJOY NA's but still would need the boost for the altitude.

Sorry if I angered you (...), but please don't have the thread closed.

 

[Kean]

2.5XT motor less the turbo does not equal a 2.5 NA. I think the turbocharged engines have a compression ratio of somewhere around 8 vs. ~10 in the NA 2.5? Even if it were possible, disabling the turbo would make the car gutless compared to a non-XT Forester.

As mentioned, it's really all about throttle control. Keep your foot out of it and you won't get that "kick". Buy yourself a boost gauge and it will help you learn the behavior of the turbo under various conditions, based on throttle input, etc.

 

[bman400]

Is the OP driving a AT or MT? If it's an MT the keep the revs low ie up shift sooner in the curves. Stay off the go pedal as other have suggested better throttle control will keep the turbo from spooling up. But given how you feel the kick it sounds like you are just mashing the pedal to the floor.

 

[alerno]

2.5XT motor less the turbo does not equal a 2.5 NA. I think the turbocharged engines have a compression ratio of somewhere around 8 vs. ~10 in the NA 2.5? Even if it were possible, disabling the turbo would make the car gutless compared to a non-XT Forester.

As mentioned, it's really all about throttle control. Keep your foot out of it and you won't get that "kick". Buy yourself a boost gauge and it will help you learn the behavior of the turbo under various conditions, based on throttle input, etc.

Thanks. I feared that lower compression of the XT without boost as opposed XS/X. But even that would still be ok. I only need high torque/power when uphill carrying a lot of weight (because of the compression loss here in La Paz)

Again, I have owned a turbo, it's definitely not a problem, or a risk. It's just I don't like it. I humbly don't think it's realistic or pleasant to check a clock if you're on a fast curve at grip limit. I can manage the boost, even on a FWD. Again I just don't like it. There is no problem or risk. Only a matter of subjective preference.

One upside of just getting the 2.5 NA is I could get the lower transfer case eventually.

 

[alerno]

Is the OP driving a AT or MT? If it's an MT the keep the revs low ie up shift sooner in the curves. Stay off the go pedal as other have suggested better throttle control will keep the turbo from spooling up. But given how you feel the kick it sounds like you are just mashing the pedal to the floor.

It hitherto was a JDM 2.0 NA AT (car was my mom's) Definitely no problems. I will defibitely get a manual now (a guy is offering the whole STi drivetrain) Again I understand all of your practical perspective, you are right.

It's just that it is way more pleasant to take curves to their grip limit when torque is linear. No, if you do this it defeats the purpose to simply get off the throttle. I can manage the turbo boost, no problem (it would be if i had 500 hp or so, in RWD or FWD, none of which is the case). It simply is more pleasant.

Sorry for any misunderstanding, I don't really have a problem or risk to solve. It was just a wish I had to have the best of both worlds. I thought you could with a boost controller.

 

[alerno]

Does anyone know if those electronic (multi port solenoid) boost controllers could be used to simply divert all exhaust pressure from the turbo permanently?. If it's all nonsense, sorry

 

[BeatupVR4]

With the way the stock wastegate works (Normally closed) your lowest boost pressure is what the gate spring is set for. Say 8 psi. From here it is possible to raise that with the help of a boost controller. But unless you change something mechanically that 8 is the lowest you can go. You could pull the wastegate rod off and it would not make boost but there is no flick of a switch way to then reattach the wastegate arm.

What you are looking to do is possible with new style normally open wastegates but it would be quite a large project to adapt to your Subaru.

EDIT: Now that you got my gears going it would be possible to have a pressure canister (turbo BMW's use these for vacuum) that could have a valve in it to hold the wastegate open all the time. Then when you flip a switch the valve opens and connects the wastegate back to the intake manifold for a source and the turbo would work as intended. The only caveat would be that every time you "turned the turbo back on" you would have to be in boost and close the valve to hold pressure in the canister.

And if you ever forgot to do that and the valve was closed the wastegate would never open and you would overboost.

2nd EDIT: Oooh you could have a second signal line with a one way valve in it for safety. And then you could just close the valve with the switch and boost once to shut the turbo off.

Here's a quick diagram. The lightning bolt is the engine because that's where the power comes from (Obviously). Thingy on the left is a one way valve, on the right is a 2 way valve in the open position, heart is the canister, smiley face is the turbo (wastegate) because turbos make me happy.

With the valve in this position the turbo will work normally as intended from the factory. With the valve closed building boost once would open the wastegate via the check valve then when you let off the throttle the pressure now trapped in the heart would hold the wastegate open and no boost will be made, or so says the lord. Switch the valve back and blammo, positive pressure above ambient in the intake manifold.
Fun times.

 

[Kean]

One upside of just getting the 2.5 NA is I could get the lower transfer case eventually.

Honestly, if you can just do that, I would say go for it. It will save you all the headaches of trying to do what you propose and likely be more effective / efficient for your needs in the long run.

 

[Dogs]

Many things are possible, if you have the money, inclination, and resources.

You would likely need a variable vane turbo, as a standard turbo would be causing a restriction on the intake. Having the wastegate constantly open on a normal turbo, is likely to have some implications, as well as not likely to produce the best exhaust flow. The variable vane, will still spin with the exhaust flow, so provide less restriction to intake. It will still make boost pressure, as the rpm increases, but won’t come on hard unless you actuate the vanes.

However, were you will have to spend time, effort, and money... is installing a wide band O2 sensor, and ECU tuning.

Alternatively, you could fit a smaller turbo. Boost is on early, so you won’t get that lag and kick so much, and it’s on tap when you need to climb.

 

[2.5x_sleeper]

<snipped>...but I simply dislike the turbo "kick" <snipped>

@alerno curious about that "turbo kick"? On my '07 FSXT the turbo operation is very smooth, no noticeable "turbo kick", boost is slowly addeds as needed in normal driving conditions.

Of course if I want massive turbo boost, I can floor the gas pedal. Then I can get a huge amount of power/torque that I can feel... makes me smile, but that's because I wanted it & caused it to happen.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]

 

[alerno]

With the way the stock wastegate works (Normally closed) your lowest boost pressure is what the gate spring is set for. Say 8 psi. From here it is possible to raise that with the help of a boost controller. But unless you change something mechanically that 8 is the lowest you can go. You could pull the wastegate rod off and it would not make boost but there is no flick of a switch way to then reattach the wastegate arm.

What you are looking to do is possible with new style normally open wastegates but it would be quite a large project to adapt to your Subaru.

EDIT: Now that you got my gears going it would be possible to have a pressure canister (turbo BMW's use these for vacuum) that could have a valve in it to hold the wastegate open all the time. Then when you flip a switch the valve opens and connects the wastegate back to the intake manifold for a source and the turbo would work as intended. The only caveat would be that every time you "turned the turbo back on" you would have to be in boost and close the valve to hold pressure in the canister.

And if you ever forgot to do that and the valve was closed the wastegate would never open and you would overboost.

2nd EDIT: Oooh you could have a second signal line with a one way valve in it for safety. And then you could just close the valve with the switch and boost once to shut the turbo off.

Here's a quick diagram. The lightning bolt is the engine because that's where the power comes from (Obviously). Thingy on the left is a one way valve, on the right is a 2 way valve in the open position, heart is the canister, smiley face is the turbo (wastegate) because turbos make me happy.

With the valve in this position the turbo will work normally as intended from the factory. With the valve closed building boost once would open the wastegate via the check valve then when you let off the throttle the pressure now trapped in the heart would hold the wastegate open and no boost will be made, or so says the lord. Switch the valve back and blammo, positive pressure above ambient in the intake manifold.
Fun times. View attachment 545402

Thanks Thundercat! I'll sit, and devote the afternoon tomorrow to try to grasp it all. I hope you have some more turbos in the meantime