Low Boost, High Boost

[LNah]

Hi all. Just like to ask a silly question. What do you guys mean by a low boost and high boost? Does it refer to boost at low and high rpm respectively or something else? Sorry for the question. First time dealing with a turbo car and in the early learning stages.

[R3N3]

Hi all. Just like to ask a silly question. What do you guys mean by a low boost and high boost? Does it refer to boost at low and high rpm respectively or something else? Sorry for the question. First time dealing with a turbo car and in the early learning stages.

i take it you own a r33?? your car has 2 boost settings, when your under 3000rpm (i cant remember the exact point) it runs at 5psi, when your past 3000rpm it then runs at 7 psi. there is a common and easy mod to earth your boost solenoid so you run high boost all the time.

[89CAL]

4500rpm is the point

Or people have dual stage boost controllers that allow 2 boost levels at the flick of a switch

Or electronic boost controllers (Some) have multiple boost settings, scramble boost (higher boost at the push of a button) etc

Just different levels of Boost

[paulr33]

some cars have two stage boost settings, these are usually referred to as low and high

some are RPM controlled, like in the R33 GTST it runs 5psi (known as low) from 0 to 4500rpm and 7psi (known as high) from 4500rpm to 7000rpm

some have different turbocharger modes or stages - the like the subaru B4 which has a small turbo and a larger turbo which have a changeover around 4400rpm (boost changes as well)

some cars have (aftermarket) boost contollers which let the driver set boost to whatever they like

and often they tune the car for a low boost setting which is safe ie lets say 14psi and have a "high" switch for 18psi

so the driver if he feels like he needs more power or boost can turn the controller to high and get more boost/power

often the high is usaully well over the safe limit and can result in failure

the response i have for high and low is tune and setup your car for the highest safe pressure you can run and control it with the accel pedal

ie having 14 and 18psi is pointless. if your can safely run 18psi, then run it all time and set it up and drive it properly

often you'll hear vl turbo's run xyz PSI and have a magic switch for 22psi etc blah blah

its the same deal, just an electronic controller. if he can safely run 22psi, why not just run it all the time

and there's another "full boost" term which is what most people say the RPM at which the turbo reaches target boost pressure

ie on a skyline if it runs 14psi, the guy will say it reaches full boost at 3500rpm

they mean, it can wind up 14psi by 3500rpm - so they mean the lowest possible engine RPM that reaches target boost

this is subjective to a billion things such as car, engine, turbo, tune, mods etc so its pointless

you might hear guys go

my vl turbo reaches full boost at 2500rpm

it means nothing until you get the facts of....

my vl turbo reaches full boost at 2500rpm

with single overhead cam, std pistons, std diff gears, t04e highflowed, 15psi target, 17" wheels, tune is spot on, larger cams, good intake, good intercooler

[tridentt150v]

Low boost is handy for wet greasy days - otherwise run high boost all the time. Running high boost doesn't mean a thing unless you are boosting. That is, if you are cruising at say 80km/h in 5th then you are not boosting at all so it will make no difference what your boost setting is. Shift bck to third and floor the accelerator and you will be boosting hard, you would generally want all your boost so leave it set at high. On wet greasy days have a low boost setting of say 10psi so that your boost comes on much gentler and doesn't peak hard, you will not spin the wheels as easily and you can drive with more control - whats the use of having high boost and watching all that power go to waste anyway.

BTW your fuel economy will not change much at all unless you are boosting all the time. When you are cruising as above, you are really driving an in line 2.5 litre six and will achieve a fuel economy that reflects this. Of cuase if you boost you will increase fuel consumption proportionally.

[LNah]

Wow... great deal of info. Gives me a good starting point to continue learning more about turbo cars. R3N3, you're right. Mine's a S1 R33. Car's running on stock boost currently, but not intending to do any mods until I can understand more. Thanks, paulr33. You do know your stuff.

Another question. If I were to set it up to run at high boost all the time, does it mean that I will run at 7psi whether below or above 4500rpm?

[paulr33]

yes if you do the std solenoid trick you run 7psi all the time, but that's only when you load the engine up

ie if you plod around in 2nd gear you boost will be -500mmhg which is no boost at all

its only when you load the engine up, the turbocharger builds up speed (the zzzzt noise) and starts to add boost pressure

this is where the guage goes from -500mmhg to 0 and then into the positive +5 boost area - +5 is +500mmhg which is 9psi

so its only until you load the engine up, that the turbocharger starts to build up and "add" boost

so with std setup if you floor it in 2nd gear it goes from -500mmhg to 0 and then to 5psi and stays there until 4500rpm

then just after 4500rpm the solenoid flicks closed and you bleed an extra 2psi so you run 7psi

[LNah]

My boost gauge is similar to the one in the attached image. So I reckon that I'm safe to say that once the needle passes 0, the turbo is boosting up while anywhere before the 0 mark would be a normal vacuum reading?

[LNah]

My boost gauge is similar to the one in the attached image. So I reckon that I'm safe to say that once the needle passes 0, the turbo is boosting up while anywhere before the 0 mark would be a normal vacuum reading?

[R3N3]

My boost gauge is similar to the one in the attached image. So I reckon that I'm safe to say that once the needle passes 0, the turbo is boosting up while anywhere before the 0 mark would be a normal vacuum reading?

yeah thats correct. also once you start doing mods ie. intercooler and exhaust, youll find the boost will increase by itself, because the turbo can flow more freely. while your running your car in stock form you may aswell do the high-boost mod, i did that to mine when i first got it, theres quite a difference that 2 psi makes! and if you get an electronic boost controller do not go above 12psi as your turbo will commit suicide (thats only the stock turbo).

also keep reading on here if you want to learn, its a very good resource

[senilykSkylines]

yeah thats correct. also once you start doing mods ie. intercooler and exhaust, youll find the boost will increase by itself, because the turbo can flow more freely. while your running your car in stock form you may aswell do the high-boost mod, i did that to mine when i first got it, theres quite a difference that 2 psi makes! and if you get an electronic boost controller do not go above 12psi as your turbo will commit suicide (thats only the stock turbo).

also keep reading on here if you want to learn, its a very good resource

I might be talking well over my head about the free boost mod... but wouldn't changing the boost solenoid to run at 7 down low need also to be tuned with the right amount of fuel aswell? Or does the computer adjust the right mixes of fuel so that an imbalance won't damage the engine?

cheers

[ClutchBurndout-:(]

yeah thats correct. also once you start doing mods ie. intercooler and exhaust, youll find the boost will increase by itself, because the turbo can flow more freely. while your running your car in stock form you may aswell do the high-boost mod, i did that to mine when i first got it, theres quite a difference that 2 psi makes! and if you get an electronic boost controller do not go above 12psi as your turbo will commit suicide (thats only the stock turbo).

also keep reading on here if you want to learn, its a very good resource

correction, 12psi is safe, 14 is when you run into issues, that being said, 12psi on stock setup will have so much r&r (rich and retard (over fueling)) that theres no point. 10 psi everyone wins.

[paulr33]

if you do the 7psi boost solenoid mod then the AIRFLOW meter will tell the ECU more air is coming in and it will compensate accordingly

ie; it is an EFI system, so you can just dial in more pressure, and it will compensate accordingly

no carby screws to adjust :-)

[senilykSkylines]

if you do the 7psi boost solenoid mod then the AIRFLOW meter will tell the ECU more air is coming in and it will compensate accordingly

ie; it is an EFI system, so you can just dial in more pressure, and it will compensate accordingly

no carby screws to adjust :-)

Oh ok, so if i wanted to up the boost one day to 10psi then all I would really need is a boost controller instead of taking it to a tuner.

[LNah]

Looks like I'll have to rip the stock exhaust out and put back the bigger one that came with the car. Has a massive 5 inch tip (not sure about the catback size), but thought of keeping the stock on in case cops try to be funny and pull me over for doing 55 on a 60 limit road.

Thanks for the info!

yeah thats correct. also once you start doing mods ie. intercooler and exhaust, youll find the boost will increase by itself, because the turbo can flow more freely. while your running your car in stock form you may aswell do the high-boost mod, i did that to mine when i first got it, theres quite a difference that 2 psi makes! and if you get an electronic boost controller do not go above 12psi as your turbo will commit suicide (thats only the stock turbo).

also keep reading on here if you want to learn, its a very good resource

[paulr33]

yes if you want to run more boost than what the acuator gives you need a controller

a controller basically fakes the pressure signal to the actuator so that it doesnt open

a bit like the old FakeCD for win98

in front of the controller is say 3psi and the controller lies to the actuator and says hey theres only 6psi dont open yet

in front of the controller is say 7psi and the controller lies to the actuator and says hey theres only 6psi dont open yet

in front of the controller is say 9psi and the controller lies to the actuator and says hey theres only 6psi dont open yet

in front of the controller is say 10psi and the controller lies to the actuator and says hey theres only 7psi open now

[LNah]

yes if you want to run more boost than what the acuator gives you need a controller

a controller basically fakes the pressure signal to the actuator so that it doesnt open

a bit like the old FakeCD for win98

in front of the controller is say 3psi and the controller lies to the actuator and says hey theres only 6psi dont open yet

in front of the controller is say 7psi and the controller lies to the actuator and says hey theres only 6psi dont open yet

in front of the controller is say 9psi and the controller lies to the actuator and says hey theres only 6psi dont open yet

in front of the controller is say 10psi and the controller lies to the actuator and says hey theres only 7psi open now

What does the actuator do? Can't get a clear explanation from google.

[JonnoHR31]

opens when it receives boooooost

[defari]

basically regulates the boost pressure

[R3N3]

What does the actuator do? Can't get a clear explanation from google.

the actuator is the small can lookin item that sits next to the turbo (only on internal waste-gate turbos). the actuator is connected to the wastegate flap. if you discoonect the solenoid on your car and run it to the line directly to the waste gate (dont do this, just an eg.), your wastegate will open at 5psi. this is because your wastegate is only rated to 5psi, thus opening when there is 5psi boost. some cars running aftermarket internal wastegate turbos might have say a 18psi wastegate, which will open the wastegate at 18psi. a boost controller bleeds off pressure to the wastegate, effectively tricking the wastegate. this is why when you have a boost controller you can increase you boost pressure above the rating of the wastegate but you cant go below the rating of the actuator.

hope i didnt confuse you

Edited August 12, 2010 by R3N3