I thought I read in a post that one of the turbo companies was limiting the boost output to 11 psi? Anyone else hear anything about this? If this is true, how are they accomplishing this, and why would they do this?

(did a search, but couldn't find it)

 

electronic boost controller via wastegate.


11psi is a bit high. i think companies will sell 5-7psi kits for emissions .. but then you can just up the boost.

 

www.howstuffworks.com

Go there and search for Turbo and find out how they work.

 

I'm well aware of how turbos work. I just hadn't ever heard of being able to set a hard limit as to how much boost the turbo will put out.

 

Well, if you went to the site I gave you, and searched for Turbos, then you'd find out HOW the wastegate is able to limit the amount of air the turbo pushes. Either the stock ECU of a turbo car, a manual boost controller, or aftermarket electronic boost controller controls the wastegate.

The wastegate is essential and required in every turbo system as it stops the turbos from overboosting. Overboosting would/could result in blown turbos and/or blown motor. There are more than just the turbines in a turbo system.

 

There are alot of reasons for limiting boost, but two major ones come to mind that aren't covered really well at howstuffworks. The first reason is heat. Any given turbo has a certain psi/boost range that it is most efficient in. Turbo effeciency refers to the amount of heat generated by compression. For instance, a T-25 turbo is most effecient around 10-14 psi. If had the wastegate completely closed all the time the turbo would probably create up to 23 psi or so, on a 2.0 liter engine. Since 23 psi is way out of the effeciency range the air would be so hot and therefore less dense that you would lose all the benefits of boosting it in the first place. Larger turbos are generally more effecient at higher psi/boost levels because the larger compressor wheel doesn't have to move the air as much to accompish the desired boost, and thereby creating less friction and in turn less heat. One other thing they don't cover very well at howstuffworks is fuel. With more boost, you have more air in the chamber and of course, you'll need more fuel to burn. If you don't have enough fuel the engine will run "lean" which causes high combustion temperatures and can destroy your aluminum pistons easily. 900 degrees is a widely accepted temperature to keep your exhaust limited to. Most stock turbos are sized and limited at their max effeciency rating and the fuel systems are sized to match the power of the engine with that particular turbo running at max effeciency, which is why they limit the boost. There are tons of boost controllers on the market, both manual/spring operated and electronic. I hope I didn't insult your intelligence too much as I don't know how much you already know and I hope this helped you out atleast a little.

 

Just to add, people here in the US seem so fixated on PSi. You have to remember that boost pressure really means nothing. HP is what you want and PSI is irrelative to HP unless you're talking about the same turbo on the same car. Different turbos will produce very different power numbers on the exact same motor at the exact same boost pressure. So are you asking what the HP capacity of the motor is or how much boost pressure a particular turbo will be limited to?

 

There's a little more to efficient boost pressure than just the model of turbo. You can have a turbo that's efficient at 10-14 psi on a 2 liter engine, but that same turbo on a big 5 liter engine will die a horrible death trying to make 10-14 psi.

The bigger the engine the bigger the turbo you need to make the same boost as a smaller turbo on a smaller engine.