[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Boost Controllers (Effective ?)
Let me apologize in advance for the lengthy post, but it seems relevant
considering all the recent discussion on overboost.
In search of more power and at the recommendation of my mechanic and others,
I somewhat reluctantly installed a Greddy Profec B boost controller on my
4000TQ. Well, after two days of playing with the settings on the Profec,
something is definitely not right -- either with my expectations, the
Profec, the ECU, turbo, or whatever. I thought, maybe naively, that the
beauty of the Profec was that it was supposed to provide sustained,
consistent levels of boost.
This car has a dual-knock sensor, high compression MC motor with 268 degree
cam, ported/polished head, 2-piece EM, free-flow exhaust, 944T intercooler,
bypass valve, K26 , custom-programmed MAC-14, stiffer wastegate spring, etc.
Prior to the Profec, it would pull 11psig in first and second gears and 13
psig in the higher gears. The boost would fall off to 11 psig sustained in
the higher gears. Throttle response was good and there were no perceptible
timing or fuel problems.
The Profec was installed to 1)allow higher boost levels, 2)eliminate the
boost fall-off, which I thought was due to the stock WGFV. Well, I can dial
in more boost, but the boost profile is far from what I expected.
First of all, with the Profec connected (and the stock WGFV eliminated), but
with its power OFF, I now get 12psig in first and second gears, 14psig in
third and fourth gears, and 15psig in fifth gear. The boost falls off a bit
(~ 2psig) in the higher gears just as before. With the Profec ON and the low
boost knob set to minimum, boost levels are the SAME as they are with the
Profec OFF. The balance knob, which is supposed to allow you to compensate
for falling off or spiking boost, has little effect on the boost profile.
Also, I can't get less than 15psig maximum boost (in fifth gear) regardless
of how I set the Profec. I can get higher boost levels with the low boost
setting, but not lower.
With the high boost knob on the Profec, I'm now able to set the boost levels
in the HIGHER gears. If I set the high boost for say 18psig in fifth gear, I
will get about 16psig in fourth gear, and about 14 psig in third gear. The
boost level will fall off a couple of psig's if I stay on the throttle hard
in any of these gears. In first and second, 12 psig seems to be the max
regardless of where the high boost is set. Again, the balance knob setting
(mild - middle - sharp) doesn't have much effect. The boost falls off in the
higher gears regardless of how "mild" the balance is set. Conversely, if the
balance knob is turned towards sharp (eliminate overboost), I still get more
higher boost in each successive gear.
With the high boost setting at 18psig, the car definitely has more power in
the HIGHER gears (no surpise there) and there is no (audible) detonation
even when using the crappy oxygenated (ethanol-enriched) gas we get here in
the winter. Anything above 18psig and the engine will ping. (Tests were done
at 50 degrees F, altitude 6000ft. I have not yet done any tests using good
fuel with octane booster, which is what I run on the track.) I really didn't
notice any difference in boost ramp-up, throttle response, etc. Off-the-line
acceleration, first and second gears, seems the same regardless of whether
the Profec is OFF, ON low boost, ON high boost, or totally disconnected
(revert to the WGFV).
Needless to say, this is definitely NOT what I expected from a boost
controller, though I can't say for sure that it is the Profec that is at
fault. The balance and low boost controls have proven useless (why would I
want to set low boost to more than 15psig?) Only the high boost controls is
of any use to me. I was hoping for consistent boost levels in all gears with
no falling off. I'm wondering whether the problem is with the wastegate
spring or ECU or whether the boost profile is due to limitations of the
turbo, exhaust gas flow, etc.
Anyone else had a similiar experience with a boost controller or any
thoughts on what's going on?