YotaTruck1986

Ok, after hours of researching, I think I may finally be starting to understand exactly how the turbo system works. Please fill me in with any information I may be missing or misunderstanding.


Wastegate?

One thing that has been confusing me is the wastegate. So the wastegate opens under pressure to "waste" some of the exhaust, and thus not spin the turbine faster. (As not to kill your engine.)

The wastegate is connected to the throttle body where the pressure builds, and opens as the pressure exceeds the wastegates set limit?

Does the wastegate have a set factory pressure limit that cannot not be changed, or can it? (Or you could just hook up a bleeder valve and adjust it for more boost, right?)

Can you install a digital device that allows you to control how much the wastegate opens? Is this called a boost controller?


Oil?

Does the engine pump oil in and out of the blower to help keeps things cool and lubricated?


Blowoff valve?

Isn't the blowoff valve mounted somewhere before the throttle body, like on the intake piping?

But does it also have a hose running to the throttle body - like the wastegate - to keep and eye on how much pressure is building?

Once the pressure exceeds the blowoff valves limit, it opens and releases the air, thus lowering the pressure?

Are blowoff valves adjustable?


I drew a crappy diagram to illustrate MY understanding of the turbo system. Nothing is to scale.



I know its a lot to read and answer , but I'd really appreciate it if someone could help me. Thanks for any replies!

X-AWDriver

Actually the wastegate is part of the exhaust housing side of the turbo and yes it regulates boost by opening when the boost pressure is met. To control boost you can use an expensive but nice in car boost controller but on my Eclipse I just ran a manual ball and spring type and it worked great and always was set at 17psi but it would have been nice to just be able to adjust it by a flick of the switch.

The BOV is usually plumbed in after the IC and before the throttle body and yes there is a line running to the intake manifold and that line is the same line that you splice (T valve) the other line of your boost controller while the other connects to the wastegate at least that's how I ran it on my Eclipse.
Some BOVs are adjustable but their main function is to release the turbo's pressure whenever the throttle plate is closed since you don't want that pressure backing into the turbo.

Oil- yes,oil is pumped through the turbo to pull heat from the bearing and most turbos also run coolant lines to further aid in coooling. This is where synthetic oil provides a big edge over dino oil since synthetic can withstand higher temps before coking on the bearings of the turbo plus it's flow is more consistent no matter what the temps are.

YotaTruck1986

Thanks for the reply. I'm still not 100% exact on how the wastegate system, but it's starting to come together... slowly. Thanks.

SLC Punk

To add to what X said.

Toyota's 3sgte and 2jzgte engine's (with the CT26 turbo) also have coolant lines running through the turbo to help cool.

The 3sgte engines (MR2's) have a Bypass valve instead of a blowoff valve, and it is located before the intercooler. The function of this is to put the air that would be released into the atomosphnere on a BOV, back into the intake, since it uses an air flow meter instead of a Mass airflow sensor.

Here is a picture of Toyota's 3SGTE turbo system in the Celica (which doesn't have a BOV or Bypass valve )
I am really bored at work, so that's why I drew it out!

roger

To answer one of your questions-

Yes you can hook up a bleeder valve to fool the computer into letting you run more boost. Check out http://www.xmission.com/~dempsey/ for more info on this mod.

kyle_22r

i think i've seen boost controllers made from fish tank air line gang valves

X-AWDriver

I've also seen several blown motors going this route. You can buy decent $50 ball&spring type controllers from www.boostcontroller.com

SLC Punk

You could. But it doesn't really work well. People experience a lot of boost creep and if you don't watch it, you will blow your engine.


I made one, cost me $20. I have had it on for two years and have experenced NO boost creep. http://www.geocities.com/chmwatson/FAQs/mbc.html

YotaTruck1986

Thanks for the replies, you've been really helpful. Oh, and what is boost creep? Thanks.

YotaTruck1986

Turbo Header Question - Instead of buying custom headers to fit a turbo, could I just run a pipe from my stock headers (or standard performance headers) to the blower? Because a turbos headers curve back up to the blower, but could I just run a pipe around and then back up? It would save a lot of money. Plus, unless I bought a kit, it would be hard to fab my own turbo headers with a place for the O2 sensor to bolt in. Thanks.

Mystickal

On the "hot" side of the turbo, there are two passages for the exhaust gases. One passage spins the blades on the turbo, which spins the blades on the impeller (which is what provides the boost). The other passage is normally closed, but is opened by the wastegate. Once the turbo has spun up and is providing all the boost that it is supposed to, the wastegate opens up. The exhaust gases have a much easier time going through the wastegate then they do through the turbo blades, so while some exhaust does continue to go through the turbine blades (still providing boost), a lot more goes through the wastegate and into the exhaust.

Boost creep can be caused when the wastegate does not dump enough of the gas. The excess exhaust gases spin through the turbo, which increases the boost past the level that it should be.

The purpose of the blow off valve is to prevent the increased pressure in the intake from slamming into the throttle plate when you let off on the gas (for example, during shifting). When the throttle plate closes, the turbo is still producing boost, and the intake is still pressurized. This pressure must go somewhere, and normally it could cause problems with the inlet side of the turbo (picture a fan blowing into a small box, with nowhere for the air in that box to go). So the blow off valve opens and sends the pressure elsewhere. Normally back through the impeller blades of the turbo to help keep it spinning, but also sometimes (illegally) to the atmosphere.

~Bill

YotaTruck1986

Wow, that helped me a lot. THANKS! I really appreciate that. So the bleeder valve helps prevent boost creep. Boost creep can be dangerous because it can hurt your engine. And the blowoff valves empties its pressure back into the blower intake where it would power the turbine or go out the exhaust - thanks to the wastegate. Is that all correct? So blowoff valves that make that loud "trumpet" noise and release the air back into the atmosphere are illegal? I didn't know that. Thanks again, that really cleared up a lot of my confusion. Thanks.

Does anyone have any comments or suggestions on using my stock headers and running a single pipe back up to the blower to power the turbine? Thanks.

Mystickal

No problem.

The bleeder valve tricks stock components into producing more boost than it normally would. Let us suppose that the stock system opens the wastegate at 15 psi of boost. There is a device that senses the 15 psi of boost in the intake and causes the wastegate to actuate. With a bleeder valve, we bleed off some of that 15 psi that is sensed (we're still making 15 psi of boost, but the sensor is only "seeing" 11 psi because we're bleeding off 4 psi that is going to the sensor). Therefore, the system does not open up the wastegate because it does not see 15 psi of boost. By the time the system "sees" 15 psi of boost (and opens the wastegate) we are actually making 20 psi of boost. The bleeder valve does nothing to prevent boost creep. It can cause boost creep (but does not always do so - it depends on the setup and components in question).

Boost creep is dangerous because it can hurt your engine, yes. Look at it like this: If we boost 1 atm (about 14.7 psi) we are effectively doubling the displacement of the engine. So instead of a 2.0L we have an engine that is actually getting 4.0L of air. If boost creep goes up another .5 atm we are then cramming 5.0L of air into an engine that only physically can hold 2.0L. If our injectors cannot inject enough fuel for this amount of air, we can get detonation which will quickly destroy the engine. Even if our injectors can keep up with this fuel demand, the cylinder walls, pistons, rods, etc. must all be strong enough to withstand this additional power with breaking.

You have the first part correct, but I have never seen or heard of a blow off valve plumbed to the exhaust. It would be a bad idea, I would think, because you would have pressurized, relatively cool air from the intake path mixing with the hot exhaust gases. BOVs are normally plumbed back to the turbine or to the atmosphere. When they go back to the turbine, they don't really power the turbine (which is done by exhaust gases on the hot side of the turbo), but they do help keep the blades spinning (on the cool side of the turbo). The BOV routes the intake pressure to the inlet of the cool side of the turbo. It is the BOV that makes the loud PFFFFTTTTT sound during shifting if the BOV is venting to the atmosphere (unless the guy has an electric PFFFTTTT sound maker - talk about a wasteful mod). Venting to the atmosphere is not legal due to emissions. Track and off-road matters are different, of course.

Not a good idea. You want the turbo to be as close as possible the the exhaust pulses. The exhaust gases begin to cool down and slow very rapidly once they leave the engine. Additionally, routing the gases in this way you will likely have a lot of sharp corners, which will also serve to slow down exhaust pulses. You want the exhaust gases to hit those turbine blades as quickly as possible to spin up that turbo, and in that respect you want the turbo hooked up to the headers as close as possible. If anything, route the intake so that it goes down to the turbo - but the turbo will perform best when plumbed right after the headers.

~Bill

YotaTruck1986

Wow Bill, thanks for all that. So I could put the blower down right under stock headers instead of buying new headers that curve up to the blower? Thanks.

Mystickal

Probably not. From a quick search, it appears that there are 2 different exhaust manifolds for 86-87 pickups - one for those with a turbo, another for those without. If you are trying to retro fit a turbo and make the system similar to a factory setup, I'd strongly recommend picking up a factory manual so you can see exactly where they put the turbo and exactly what components are different.

My above explanations and knowledge of turbos are based on my experience with an AWD, turbo-equipped Mitsubishi Eclipse that I used to own. If someone with a non-turbo Eclipse wanted to retro-fit a turbo, it was a very expensive and tricky proposition. Here's a list of items that needed to be replaced when converting a non-turbo Eclipse into a turbo Eclipse. It includes pistons (different compression ratio), transmission (!)(different gear ratios), ECU (controls the opening and closing of the wastegate, among other things), fuel injectors (turbo cars need to flow more), exhaust manifold and nearly the whole exhaust (larger pipe).

For your vehicle, there may not be so many parts. Overboost has a good article on DIY turbo installations, you may want to read through that.

The biggest consideration is how different your truck is from a factory turbo-charged truck.

Best of luck,
~Bill

kyle_22r

you can buy a turbo header from lc engineering or build your own yourself

roger

For a good primer on turbocharging system design, installation, and testing read Maximum Boost by Corky Bell. Vastly informative!

YotaTruck1986

Thanks guys for the posts and links. Very, very informative! I know this may sound like a stupid question but would there be enough pressure in your stock intake to be observed on a PSI gauge? If I had a gauge hooked up, would the needle move at all? Thanks.

SLC Punk

Are you asking if there would be anything registering on the boost gauge on a N/A engine? No, if you had a gauge that had vac on one side and boost on the other, the vac side would move, but it would never get into the boost side.

YotaTruck1986

Thanks. I didn't think the boost gauge would move, just had to make sure. What does a vac gauge measure? Suction? And what is its measurment label? Thanks for the reply.