APEXi and other boost controllers

Ameer Antar ameer at snet.net
Sun Nov 26 23:36:04 EST 2000

the mileage shouldn't be too bad...it's only 2.2 liters. I got 21 mpg from 
a tired '84 5kT. You might want to check your fuel system. Under 
acceleration, engine lights come on...usually means engine knocking w/ 
fully retarded timing. If it is that code, try changing look for any lean 
running [vac. leaks!], if not try changing fuel brands. I usually used 89 
octane, sometimes 93, never 87. But I noticed I would get the engine light 
only using Citgo or Merit gas, not Mobil, definitely not Shell. It turns 
out my problem was 2 things...a vac. leak as well as my mechanic left his 
3mm allen wrench in the fuel distributor, so the air flow plate didn't move 
all the way.

About Apexi aand all them, they're more designed for modern cars like a4's 
and such. You could prolly use one though. The Apexi AVC-R [espensive!] 
diverts excess boost to whatever boost sensor or wastegate valve your car 
may have. The only way to fool a 5k ECU is to use this on the ECU manifold 
pressure hose. This would fool the ECU into thinking the boost is only 1.4 
bar when it really was 1.8 or something by diverting excess boost into the 
atmosphere. It will defeat the fuel pump cutoff and ignition retard of the 
stock ECU above 1.6 bar. The only thing is that will only help you during 
WideOpenThrottle, b/c the ECU only controls boost at WOT. The wastegate 
actually controls boost at all other times...no matter what you have to 
upgrade the wastegate spring or do the wg cap mod people have been talking 
about. You can't use the Apexi or other units, b/c they are a different 
type of wastegate. 5k wastegates are controlled by the exhaust pressure on 
the wg spring. The Apexi units are designed to work on a wg that is 
controlled by intake pressure. The controller just diverts excess boost to 
the valve which allows the wastegate to stay closed more.

Stock boost is 1.4 bar. You can get maybe 1.6 bar just from a wg cap mod, 
but you have to be careful of fuel cutoff point [1.6-1.7 bar]. This is 
really a hack and may not be the best for long term use. The best would be 
a good chip mod w/ a wg spring. The ? is who makes the best chip. That's up 
for debate, b/c I've heard all 3 sources [I know of] bad mouthed...2Bennet, 
TAP, and Intended Accel. I've never tried it so I can't say....


At 01:00 PM 11/26/2000 , you wrote:
>I've been driving my '88 5kcstq fairly regularly now.  I'm enjoying the
>car.  Since nothing has broken yet, I was thinking of chipping it
>soon.  Fuel consumption really seems to suck tho'.  Between the
>full mark and the first part of the red on the gauge, I'm getting like
>250 miles.  I haven't done the math with the receipts I have to see
>what actual mileage is.
>By the way, yesterday the check engine light flashed momentarily
>while accelerating around 4 separate times.  No other symptoms
>were apparent, and I haven't pulled the codes yet.
>But, the purpose of this post is to ask about those aftermarket
>boost controllers that companies like HKS, APEXi, and Blitz sell.  I
>have a friend with a 2001 A4 1.8tq, and he's got one of those
>APEXi ones.
>What exactly do those controllers do, and do they help on a
>chipped/WG springed car?
>I thought the digital rendering of an analog tach was pretty cool, as
>well as apparently being able to select the boost at specific rpms.
>It may have had a turbo timer as well.
>Ken Keith
>'88 5kcstq
>'85 4ksq
>'94 SL2

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