Re: Boost control
Sy#26 said:
I'm really gettin' frustrated in obtaining the "rock solid" boost control that some folks calim to have. Built motor, all the goodies except headers; turbo is hybrid, stock center section, Mitsu 14cm turbine, Garrett TE60 compressor; cam, heads, etc. Tried Deltagate, HKS, both in crossover, still get about 5psi variation over a WOY 1-2-3-4 run. MAP peaks just after shifts (20psi), gradual fall of about 5psi as the gear winds out (to 15psi), peak again @ shift, etc.
My question(s) to you datalogging guys is:
What engine build?
What is the max/min MAP during a WOT run?
I've fabbed up several butterfly style WGs out of SS bits - need to make these a bit larger diameter to flow enough gas; present ones using 1 1/2" OD tube - next one gonna be 1 3/4", should be enough flow there. Reason for the BF style is backpressure immunity - should work better (in theory).
Really appreciate any replies, guys - thanks.
I had similar problems with a Hybred Garrett/Mitsi setup... I was able to
get it down to a 2-3 psi swing or less.
Build:
Similar turbo as you listed
2800 converter
50# injector
Mild (cleanup) L35s
Lunati cam
The thing that made the biggest difference? Fuel. It would go a bit leaner
on the shift point than it was elsewhere, which would send the boost
ballistic. Richening it up at the RPM pulldown of the shifts helped a bunch.
What you're describing with your HKS, though, is somewhat symptomatic
of not having the WG DC reset to the right places... that also helps a
bunch.
Basically, what you're looking for is something like this (the actual numbers
might be different)
Note: the dotted lines are the right ones, the solid is just there to keep
the non-proportional fonts from not representing spaces as it should.
WGDC|
80 | -----------
50 | ________ |-----------
30 | __________________ |--------------
______________________________________
MPH 10 40 70
To make this work, you have to have your init DC boost table set up
to index off of scaled (0-70) MPH, instead of TPS like it does for stock.
(Maybe you already do, dunno) It's a 1 byte code change.
One thing to note, you have to have the Delta RPM thresholds for WGDC
reset set fairly low to make this work right, like 200-300 RPM. Generally,
I set this such that a non locked 9/11 that doesn't drop RPM much won't
cause a reset until the TCC locks. (High load areas)
Once you have that, you'll set the closed loop update rate to 0 (so it never
changes, except for the inits), and set your init levels according to what
your WG likes. The stepped pattern above is what it usually ends up
looking like.
The large-step resets will "lead" the boost spikes on the shifts (if the reset
happens too late, you need to lower the reset RPM threshold), and tends
to smooth things out.
You'll still see boost overshoot .5 - 1 psi or so, and it'll likely droop below,
right after the reset. (Even with closed loop turned off!). There's some
really odd dynamics in the mitsi exhaust housing, I think mostly due to
the 90 degree turn the WG air takes.
Anyway, once you get things close to where you want 'em with the above
process, turn the update rate back on (I'd suggest a low number, like
02h-03h), and slow down the closed loop update timer (make the number
bigger). I set the update timer to 3-4, but there's a lot of tweaking to be
done there. It likes what it likes, every turbo/exhaust combo is different.
This really applies to any turbo, although the Garretts don't need a lot
of step (ie, none). Mitsi housings (stock-14cm2) seem to like the steps.
I haven't played with 3-bolt (Buick-style) housings much, but I'd suspect
they're like the other Garretts. ATR externals act really weird on solenoid
control.
One thing that kinda needs to happen, is that the frequency of the WG
pulse stream needs to be lowered... it's too fast. My ANS controller at
20% DC makes less boost than the stock ECM at 20%, using the same
solenoid, wiring, etc. The ANS has a considerably lower frequency, which
leads me to believe the frequency response of the solenoid is really,
really low. Which stands to reason, since it's essentially a really big
inductor.
Also, regarding the butterfly WG, I'm betting you have reliability problems
with it. The flapper has to seal quite tight, and that tight of a tolerance in
a hot exhaust environment will be really susceptible to binding due to
thermal expansion. Just my thoughts... interested in hearing how it
works. I had considered, at one time, having a screw pintle sorta like
an IAC, with the moving parts outside the hot parts of the turbo.
No spring at all, and the amount of open/close could be varied based
on what the boost error was.
Hope that helps...
Dig
k::