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Waltherone
Dodge Dakota
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7/12/2002
14:06:37
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 Subject: Kinda Basic Turbo Question
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I don't fully understand a lot of the things dealing with turbos yet, I'm tryin, there's one think that is still stumping me though and I don't wanna assume the answer and assume the WRONG answer.
I've come to understand that a blow off valve's job is to release the pressure when the gas is let off for shifting and the throttle plate slaps shut/almost shut, to ensure there isnt a lot of pressure on the throttle plate. If that's wrong then its no wonder I can't understand the rest of what I'm about to type.
Now, on an automatic tranny, where you don't let off the gas to shift, I'm not seeinwhere the boost goes. It seems to me that in the small increment of time between shifts on an auto tranny, the bost/high explosive force inside the engine would cause the rpms to spike a bit. That probably isn't right, but if it isn't I don't know WHY it isn't.
And also, lets say you are runnin and are in boost, and the tranny shifts, since you would obviously be at lower RPM's right after the shift, does the turbo just spool down accordingly and the boost gradually disappear as it is ignited? Or what..
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Duner
Dodge Dakota
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7/12/2002
20:21:43
| Two different controls on the turbo
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There are two different controls on the turbo to
keep the boost pressure and turbo speeds in check.
One is the blowoff valve which is located on the
boost side, and the other is a wastegate which is
on the exhaust side.
The blowoff valve releases the pressure when you
no longer want boost. It senses a vacuum signal
and opens to allow the boost to leave the
intake... so you have that part right. The reason
for this is to keep the throttle blades from
bending and also to keep from stalling the turbo
by backing up all that boost pressure back into
the turbo.
When you are at WOT and the automatic trans
shifts, since you didn't let off the gas it
doesn't dump any of the boost out of the blowoff
valve. When the trans shifts and the engine is at
a lower rpm - all that boost helps it accelerate
thru the rpms like crazy! The rpms don't spike
but the boost could - except for the wastegate.
If the engine can't handle the extra boost at that
rpm (after the shift), the wastegate opens to
relieve the pressure from the exhaust side. This
keeps the boost pressure from stacking and
damaging par
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Waltherone
Dodge Dakota
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7/13/2002
00:05:44
| RE: Kinda Basic Turbo Question
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lol still haven't gotten that message cut off thing fixed I see..
So is the wastegate totally automated? I mean, the blow off valve really isn't going to open unless the gas is let off a good deal right? But the waste gate if I understand right senses the pressure on its own and acts accordingly, or what?
Thanks man :)
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Duner
Dodge Dakota
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7/13/2002
10:13:03
| RE: Kinda Basic Turbo Question
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Sorry about the cutoff thing.... gets kind of
aggrevating sometimes!
The wastegate bleeds off exhaust pressure to keep
the turbo from overspeeding or making more boost
than you want. It works totally separate from the
blowoff valve. The wastegate is what controls the
amount of boost pressure you get to the engine.
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Waltherone
Dodge Dakota
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7/13/2002
14:27:09
| RE: Kinda Basic Turbo Question
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Is the wastegate electronic/electronically controlled?
And also, I've heard before that its possible to adjust boost in the cab of the truck, would a boost increase/decrease from the cabin be done thru the wastegate as well?
Also, if you put a turbo setup on an auto tranny, would a blowoff valve even be NEEDED, since its much more rare that you drastically let off the gas?
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Duner
Dodge Dakota
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7/13/2002
15:06:36
| RE: Kinda Basic Turbo Question
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There are electronically controlled wastegates on
some vehicles but mine uses a Deltagate which is
purely mechanical in nature.
You can get a remote boost adjustor so that boost
can be adjusted from the cab. I've opted to not
go with one because it would be too easy to "turn
it up just this once", if you know what I mean.
The amount of boost I run is dependant upon the
quality of fuel I have in the tank. I'd really
hate to "accidently" get too much boost and not
have the fuel to back it up.
Yes, the blowoff valve would still be needed even
with an automatic. How often you back off the gas
has little to do with the damage you can cause
without one.
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Waltherone
Dodge Dakota
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7/13/2002
18:21:35
| RE: Kinda Basic Turbo Question
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With the remote boost control (something I wouldn't trust myself with anyway, but I wanna know) does the boost control do something to the computer, or to the wastegate? I.E. can you have a purely mechanical operatated wastegate, like yours, and a remote boost control as well?
And about the blowoff valves, I was under the apparent misunderstanding that cars with stock turbos had no blow-off valve. Oh well, I know now!! :D
Thanks for the info man, you da man!
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Turboguy
Dodge Dakota
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7/13/2002
18:48:34
| RE: Kinda Basic Turbo Question
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Remote boost control is nothing more than a regulator that bleeds pressure from the wastegate. A good example of this is an aircompressors little black knob. Like Duner says, you better have the fueling to support it.
Factory turbo cars started gettting *blow off* valves to increase turbo life span. I believe Mitsubishi and Toyota were some of the first to have them. THey are nothing more than a bleeder valve too.
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