Boost Controllers And How They Work?

[abc123omg]

hey,

i searched around, but wasnt exactly sure of what words to search on this question.

i have a sr t25 on my ka-t and wanted to run 10psi instead of the 8psi i have right now. (yes, i finally gave in and want to run more boost now, you guys were right). so im deciding to just get a manual boost controller. (with a boost gauge and any other needed stuff of course)

now my question is this. If i want to achieve 10psi, and i have a 8psi internal wastegate on my sr t25, do i:

1) dial my manual boost controller to 10psior2) dial my manual boost controller to 2psi, so i get 8psi wastegate + 2psi boost controller = 10psi overall?

I have a Emance tune and was also wondering how people run different boost levels. like how people say they run 8psi diaily, but run it a lil higher when they "Race" or whatnot.

are these people able to crank up the boost because:1) the tune can compensate for it and itll run leaner?or 2) because they have 2 seperate tunes, an activate one of the other when needed?

i also ask this because im not sure if i need to send my ecu to emance again to have it retuned...

thanks guys!

[coolbone28]

Just get a manual boost controller and just turn it up until you reach your desired boost level. Technically it will be at 10 psi.

Second, if it is a good tune you should be able to run a range of boost levels. say 7-14psi with no problems, because the computer will compensate with the use of your sensors (just as long as your a/f is good. You are going to be pumping alot of hot air with that t25 tho). Most people that switch boost levels either have a EBC or a dual-stage MBC.

You shouldn't have to send in your tune, but if you have any reservations, just send him an email and ask him.

[abc123omg]

IIRC, a sr t25 maxes at 12psi, and i have a giant intercooler, so i gues 10psi will be ok? correct me if im wrong.

i also asked jason of emance to let me know about running 10psi.

i think im planning to run 10psi daily now...

anybody think ill have issues with my t25?

[WDRacing]

There are two parts to this answer.

I'll start with increasing boost and how wastegates actually work.

The wastegate, be it internal or external, has a spring or diaphragm inside that has a certain amount of tension/resistance. For instance, the wastegate you currently have will open once it see's 8psi of pressure because the resistance/tension on the diaphragm won't hold any more. Just think of a spring with 6 lbs of weight on it, it can hold up the 6 lbs of weight easily without collapsing. Add another 2 lbs and the spring collapses. Same principle is applied with all wastegates.

So how does a boost controller stop them from opening until a preset amount?All boost controllers either stop the vacuum signal from reaching the wastegate or bleed off part of the signal so the wastegate never actually see's the 8psi until the turbo is actually putting out whatever amount of boost you decide to run.

Electronic type boost controllers are basically just a solenoid valve and a pressure switch. The pressure switch is adjustable, when it see's the amount of boost you set it to, it sends an electrical signal to the solenoid causing it to open. These are controlled by a box that's usually mounted in the cabin and it will have settings or a knob to determine how much boost you want to run.

Manual types just have a spring and ball that can be adjusted via knob, screw or nut. As you increase the spring tension by turning the knob etc you increase the amount of pressure exerted on the ball. The ball is just a ball bearing sitting over a hole. It allows air to escape, hence the term bleeder. Bleeding off some air will keep the wastegate from seeing the full 8 psi. Once the turbo is putting out more air then the bleeder can release the wastegate will see the full 8 psi and then open. The bleeder type is set by slowly increasing spring pressure until you reach the desired amount of boost. This is dangerous because you can adjust it to much and cause detonation. So just take it slowly, adjust it in 1/2 turn increments and you'll be fine.

Now, how much boost can you actually run?

This is determined more by injector size then turbo. Yes the turbo is a high priority in the equation, but if you only have 270cc injectors then even the 8 psi of stock boost is to much.

With that said, determine what injector size you have and what hp level they will be good for prior to reaching 100% duty cycle.

There is a calculator here to help you determine what power rating your injector is good for. I plugged in 370's at 90% duty cycle and got 230hp.

Then you have to figure out how much psi the turbo is good for before it becomes nothing but a heat pump. The T25 is also a big restriction on exhaust flow...but that's a whole different topic. Suffice it to say that it also limits the amount of boost and power you can make because it's choking the exhaust flow, often to the point that you can get exhaust gas reversion. Reversion is simply the exhaust gases momentarily flowing backwards during the overlap phase of the camshaft at low cycling rates.

Anyway, the compressor on the T25 is very small. So anything more then 10 psi is going to create an intake charge that is extremely hot.

If the ecu is programmed for your injector size then it will increase fuel flow as boost rises because it's receiving the signal from the MAF saying it's ingesting more air, therefore needing more fuel.

So the keys are to not max out your injectors and to make sure your turbo isn't going to be a heat pump

Hope this helps...becareful, boost is more addictive then heroin

WD