I just don't understand

[minigts]

Ok, so I'm pretty familiar how a turbo works. I don't get too technical when I talk about them as to not sound like an idiot or say something wrong, but I am just NOT understanding one aspect; that is, how in the world do you NOT build boost when you aren't moving? I mean, I have thought about this, maybe not enough, but with just the mechanics of it, why wouldn't it build boost when you aren't moving? I have driven my car with the speed sensor disconnected, the factory solenoids disconnected and just the lines from the manifold to the wastegate which is all "mechanical", no sensors or anything involved and was still producing boost when driving.

I asked a friend who is relatively savvy with cars and his only suggestion is that there is resistance being applied at the motor and that somehow has something to do with it. But I'm just not understanding because in essence, gases are flowing through the exhaust the exact same way when you are sitting there vs. when you are moving, correct? So what is controlling it? I mean, if that were the case, would you build boost going down a very steep hill where there was little or no resistance from the transmission?

There, I have admitted I don't understand how it works. Make fun, but at the very least explain this please.

[contraption22]

When under load, more exhaust gas and heat is created, providing enouigh volume to spin the turbine.

[minigts]

Do exhaust temps rise with RPM or only under load? I guess with RPM, you are just increasing the frequency with which the gases leave, not the temps? That kinda makes sense, just surprised the volume isn't changed enough to affect boost levels when not moving. If it's that simple, I guess I will just be in awe every time I am at a light revving the motor and it just spikes at 0 on the gauge. :\

[contraption22]

EGT rise with load. Like you said, they will not rise with RPM.

[turbovanman²]

The size of the wheel plays a huge part in the process. Listen to big rigs, there turbo's are spooling at idle. Turbo's are driven by the heat and volume of the exhaust gas, so couple that with turbine wheel and housing size, is how the turbo is spooled. If you have a large turbine wheel and housing, its going to take alot of exhaust to get it started whereas stock turbo's and my example of rigs, are designed to spool with very little exhaust flow.

Hope that makes sense?

[overlordsshadow]

I've been able to make standing boost before, giving it the gas. I think it just has to do with getting enough air and heat through there, which at normal idle won't create boost. Drive in any gear and then try to stay at 0psi. Your bov is shut, your wastegate is closed, and your throttle is part way. That is how much gases/heat it needs, lol or something like that.

[badandy]

You don't build boost at idle because the exhaust turbine is not spinning the compressor fast enough.

For example:

I'm sure at some point you have seen a window fan before right? When you turn it on it blows air right?...okay, now if you turn it off and a slight breeze goes past the fan blades it will spin like a pinwheel...but it is not blowing air correct?...simply because it isn't spinning fast enough.

[minigts]

Ok, that is a bad example, but only because YOU WEREN'T AT SDAC! What the heck man?! You and Ken should have been there; we did ask about both of you.

No, I think I'm good with why, just thought for sure there would be SOME pressure in there.

[turbovanman²]

Ok, that is a bad example, but only because YOU WEREN'T AT SDAC! What the heck man?! You and Ken should have been there; we did ask about both of you.

No, I think I'm good with why, just thought for sure there would be SOME pressure in there.

There is, but it doesn't spin the turbine wheel fast enough to create boost, unless it was designed too, IE big rigs like I said earlier,

[minigts]

Well I heard about somehow building boost by allowing fuel to leave the chamber and then blowing it up in the housing or something, but I don't remember the whole conversation. I think it was a race application to build boost at the line. Interesting theories in my book.

[badandy]

Ok, that is a bad example, but only because YOU WEREN'T AT SDAC! What the heck man?! You and Ken should have been there; we did ask about both of you.

No, I think I'm good with why, just thought for sure there would be SOME pressure in there.

Yeah I know, I know! I had my heart set on it too I REALLY did! I'm afraid my car projects depleted my funds a bit more than I anticipated

On the other hand I am enjoying seeing all the pictures...it's pretty cool when I look at them and know 90% of the owners

I'll catch up with you again...and everyone else too

[turbovanman²]

Well I heard about somehow building boost by allowing fuel to leave the chamber and then blowing it up in the housing or something, but I don't remember the whole conversation. I think it was a race application to build boost at the line. Interesting theories in my book.

Retarding, advancing timing, rev 2 steps where they cut cylinders can also create boost. Whorse has one built into his stock VNT cal, he can pin the gas and it drops cylinders, keeping the rpm capped at 3000 rpm I think and you can hear the turbo spool, its neat,

[minigts]

Maybe I'll drive by your place one day and compare notes. That is, when I have about 3 days to kill and feel like driving 2500 miles.

[GLHNSLHT2]

Just think of it this way, when free-revving the car the motor uses more air than the turbo can push. So no pressure is built in the intake (boost) because for every molecule the turbo puts out the motor uses and throws it out the exhaust.

Anti-lag is what you're thinking off. Rally cars use it. Basically they have a bypass around the throttle body, retard the timing huge amounts and dump loads of fuel to burn in the exhaust manifold and spool the turbo.

A two step rev limiter basically does the same thing but you're on the gas when it cuts spark (fuel in our systems) and keeps the motor from revving past a certain point. Since you're at WOT you have tons of air going in which helps to spool the turbo.

[Mopar318]

Just think of it this way, when free-revving the car the motor uses more air than the turbo can push. So no pressure is built in the intake (boost) because for every molecule the turbo puts out the motor uses and throws it out the exhaust.

Anti-lag is what you're thinking off. Rally cars use it. Basically they have a bypass around the throttle body, retard the timing huge amounts and dump loads of fuel to burn in the exhaust manifold and spool the turbo.

A two step rev limiter basically does the same thing but you're on the gas when it cuts spark (fuel in our systems) and keeps the motor from revving past a certain point. Since you're at WOT you have tons of air going in which helps to spool the turbo.

Yep rally cars are able to stay in boost even on Decel. Anti lag is very nice, when set up properly.

[roachjuice]

^^ seriously?!?! i have to see this!!

[GLHNSLHT2]

search youtube for rally car vids, the flames shooting out the exhaust on Decel (i.e. throttle closed but the huge bypass around the TB is open) is the Anti-lag being engaged.

[WickedShelby88]

funny you mention the rigs simon as the detroit 60 series used 2 different turbos in the trucks I used to service. One was more prone to spin at idle, but didn't make the power as the one that hardly spun at idle but really wound up at higher RPM's. The detroits are pretty high strung in the diesel community though.