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Posted for <13brv3@mchsi.com>:
[It has been my plan all along to incorporate a manually-actuated turbo on
my
13B installation, and redlining the MAP at 34"hg... this equates to (about)
2psi boost on a standard day, so I think we're singing the same tune.
Indeed we are. I've also considered using a manual control, but dismissed
it. Now, you've got me re-thinking again. I understand you can find a pop-off valve that installs in the intake
manifold
that vents excess pressure to the atmosphere. I had intended to install one
on my intake manifold to prevent me from inadvertently overboosting. In a classic turbo installation, the popoff valve is supposed to be a safety
device only. In other words, it's not supposed to be used to control boost.
That's the reason I dismissed the manual wastegate control in favor of a
wastegate actuator. I just re-read the control section in the Maximum
Boost book, and they state that the popoff valve is an effective way to
limit boost, but should not be used as the "primary" boost control. Hmmm,
as the human wastegate actuator, I guess I would be the primary boost
control, and the popoff valve would be there to save me if I screw up. I had planned to have a popoff valve all along, but was also planning to
have a blow off valve, and wastegate actuator. Now I'm starting to see that
I can manually control the wastegate for my intended usage, and the popoff
valve will keep me honest. I've also realized that for our purposes, the
popoff valve will perform the duties of the blow off valve too. This all
just got a whole lot simpler :-)
FWIW, my plan is now (again) to use a vernier cable to control the
wastegate. For normal operations, it would be set to fully open, though it
will probably be quieter to taxi with it closed since I have no muffler.
The only time I would adjust the wastegate closed, would be during steady
cruise, or perhaps an extended climb. The popoff valve will make it safe to
test the turbo system, since it will catch my mistakes. There's also the
concern that I'll get more boost than I want (boost creep), even with the
wastegate wide open. The popoff valve will let me find that out the "easy"
way. I just ordered the best popoff (relief) valve that I have found. I looked
at this before, but could never figure out the pressure rating. According
to the manufacturers page (
http://www.greddy.com/products/blowoffvalves.htm ) it's adjustable from
.08 kg/mm2 to 2.0 kg/mm2. Converting that to psi, gives a minimum setting
of about 114 psi. Some safety device :-) I noticed that some of their
other devices are listed with ratings in the kg/cm2 range. Assuming that's
what they meant, the relief valve should have an adjustment range of 1.1 to
28 psi. Now we're talkin'. I'll probably set it for about 2 psi normally,
and maybe 10 psi during any rotary race :-) I'll let you know how it
looks when I get it.
Thank you very much for making me re-think this Marvin! Rusty
Turbo 13B powered RV-3 (experimental aircraft)...Be Afraid :-)
1993 RX-7 R1... Not stock, carry bail money :-)
[I have thought all along about using the pop-off as my safety net, as you described in your second paragraph. Many moons ago I had the good fortune to log lots of hours in an older turbo Arrow... the wastegate was controlled manually and that system always worked very well for me. My intention is to hook the wastegate to the throttle control... movement of the throttle to about the midway point will yield WOT. Movement past that midpoint starts closing the wastegate and brings the boost online. The turbo Arrow had a big red light on the panel that came on if you tried to overboost, and it worked very well. Between the red light (actuated by a MAP sensor switch that closes at 32") and a pop-off that vents at 34" you have a pretty bullet-proof and simple system. I never intended the pop-off to be the primary boost control... as you moentioned, _I_ am the primary boost controller. Works for me. <Marv> ]
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