Rusty,
Of course you're right about residual boost with wastegate open.
My 30" take off would have to be done at partial throttle. Am I correct
in my inference that gradually closing the wastegate as I go higher and
higher will minimize intercooler requirements and wear and tear on the
turbo?
Additionally, I have put a 36" or so limit on MAP to safeguard the
engine. Does the turbo also have a boost limit? If the turbo
has, say, a 10" boost limit, then as ambient pressure dropped off, I would
reach my turbo normalize limit at about 20" ambient or around 10k'.
What would the boost limits be on the Mazda stock turbo? Are they
a factor in normalizing to 15k' - 18k'?
I can't see my way clear to use any turbo other than Mazda stock since
that is the only one that has demonstrated ability to hold up under the
hideous exhaust pulses of an unrestricted rotary.
--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
Russell Duffy wrote:
I am totally new to all of this, but have to
learn. I don't want much boost (maybe 35" or so MAP) for takeoff,
but want to turbo normalize to around 15k'. I know detonation is
a problem with high boost and I will have limited intercooler resources.
With that in mind, how does this sound ..... Sounds
like we're after the same thing. BTW, I have no intercooler at all,
which is another reason that I'm afraid to run too much boost for too long
at Summer sea level temps in Florida. I
can definitely tell the difference in mixture between the A and B controllers
on the EC-2. The A controller uses the temp sensor, and the B controller
does not. The temp must be elevated quite a bit, but until I get
the EM-2 to read it, I won't know how much. I
would have a manual internal waste gate. The waste gate would be
normally open (dumping all exhaust past the turbo). On takeoff, I
would run WOT (say 29"), no boost. I could close the waste gate a
little and get 33" for example for a hot day or short field. As I
climb out at WOT, I gradually close the waste gate to maintain 30" MAP.
Since I'm running essentially NA at low altitude (where the atmosphere
is warmer) I don't need much in the way of an intercooler. As I climb
and progressively close the waste gate to maintain 30", I need more intercooling,
but this need is reduced by the cooler atmospheric temps. At altitude,
say 15k' - 17k', 30" has me going like a bat out of hell, and the cooler
air going into the system requires less intercooling.
The
only problem I see with this plan is your assumption that opening the wastegate
will eliminate all the boost. In reality, stock wastegates aren't
able to do this for us. If you look at how an internal wastegate
works, you'll see that it isn't a valve that diverts exhaust from the turbine
to the open exhaust pipe. It's really just a door that opens to give
the exhaust an easier path to the tailpipe. This doesn't stop some
of the exhaust from turning the turbine and creating some boost.
In
a car, where you have catalytic converters, mufflers, and restrictive air
filters, there's enough restriction in the system to limit the amount of
air that can move through the engine. In the case of a stock engine
with these restrictions, the stock wastegate is as effective as it needs
to be. When you remove these restrictions, even in the car, boost
can't be completely controlled by the wastegate anymore. Some wastegates
are more effective than others. In RX-7's for example, the series
5, 89-91 turbo wastegate is quite a bit bigger than the one on the series
4, 87-88 turbo. My series 5 wastegate has been wide open, and
the turbo still wants to make more than 3 psi of boost. Until I set
the pop-off valve for a higher number, and go to a safe altitude to test
it, I won't know how much it will really make. Ideally, I'd like
to be able to open up the flow of the wastegate until I could only produce
3 psi of boost with the wastegate open. At that point, I would only
have to insure than the wastegate is open at low altitudes, then I couldn't
overboost the engine. I can't wait to get my temps in order, so I
can see what the turbo will really do.
Cheers,Rusty
|