Ver4STI

Hi,

The car is a Version 4 Wrx Sti 1998 - with 60,000 miles on the clock roughly.

Its running a 3" turbo back exhaust system including sports cat, and a K&N cone filter along with a baileys dump valve.. and ARP head studs for some reason....

the car also has an A'pexi Power FC which was fitted by andy forrest originally.

this has since been tuned and tweaked by Clive Atthowe (as he is very local to me in norfolk)

the car made a healthy 297 BHP at 1.2 bar boost..

there is also 2 other tunes on there 1.0 bar which gave 282 and 1.1 bar which gave 289

It drives fine and boosts perfectly. HOWEVER .

If i build up revs from say 2000RPM in 4th or 5th it hits boost cut at about 3200 - 4500 Rpm..

If i rev out 1st 2nd and 3rd gear its fine going into 4th..

it also does this at motorway speeds so 70Mph in 5th if i put my foot to the floor it hits boost cut pretty quick.

CLive said the only thing he can think of is the A'pexi has an over boost detection which is only about 2 - 3 % of max boost so if it goes over by the set boost by this much it will cut boost ?? I think i've remembered that right lol. he also checked the solenoid and said all is clean..

does anybody have any experience of this with the Apexi Fc.. having had it fitted and tuned by Andy forrest originally and then looked at again by Clive Atthowe, thats 2 well known subaru speciailists looking at it ?

it actually drives better on the 1.2 bar setting..

would i benefit from adding a AVC-R ...

literally any advise would be beneficial. thanks.

Ver4STI

Does anybody have experience with A'pexi Power FC and this issue ?

I have the hand held commander unit if anyone needs to know settings etc ?

53

iTrader: (41)

Put simply you need the AVCR You can't run 1.2 and not hit boost cut.

53

iTrader: (41)

Besides 1.4 is better I run the AVCR on 1.4/5 bar and 320 is a nice place to be in a classic

Ver4STI

thanks for the reply

I Don't have fueling mods to run 320Hp surely ? i have turbo back exhaust and an air filter lol. would i not require an upgraded fuel pump and FPR for that boost.

Clive was saying the Apexi Power Fc can control boost hence it has 4 levels of boost, andy forrest's site also says the same and he fitted the ECU.

would i need anything further with the AVC-R to fit ? or does it work with the standard solenoid.

Yep i'm new to impreza's if you haven't guessed haha, thanks for the help

53

iTrader: (41)

It comes with a new map sensor boost sensor etc It needs splicing in the loom but there are guides

320 you would need to upgrade the pump, but you have 440's, decent intercooler and a VF24/28/29 ?

Ver4STI

I wouldn't be fitting it myself so that would be fine.

It's a VF24, I didn't realise i had 440's sweet.

I'll see about an AVC-R first and a tune to suit and then upgrade the fuel pump and see what happens.

Appreciate the advice thanks again.

53

iTrader: (41)

No probs yes you have 440 phase 2 injectors which are multijet and way better than phase1.5 injectors. You also have the later 1.7 bar map sensor but the AVCR supercedes this. Your intercooler is more than man enough for 320.

sean turbo2000

iTrader: (1)

you dont need an avcr, yes you will have better control but the power fc will control boost using the stock solenoid, plus your stock map sensor is ok to around 1.6bar.
if your hitting boost cut then drop the boost duty down a % or 2

53

iTrader: (41)

That is true but the stock map sensor didn't cope particularly well when I had just the Apexi and 1.7 bar OEM sensor. The boost was very irregular over 1.1/2. As soon as the AVCR was fitted it held boost amazingly and blew the water out of the OEM/APexi setup.

Ver4STI

Thanks Guys,

Sean this is what Clive was saying that the Apexi FC should be fine and can handle it..
when you say drop the boost duty down ? what do you mean by this ?

clive said he had dropped this down but was still cutting.. is this the waste gate duty cycle ?

53 you are right it is a little irregular, i can spoike to 1.35 at times under hard load. and as clive mentioned to me, if the Apexi detects it going a certain percentage over set boost it will cut boost for safety.

i can accelerate in 5th at motorway speeds by feathering throttle but i want to be able to put my foot to the floor so i don't have to drive watching a boost gauge haha.

i have the commander unit so can always drop it a few % and see if this helps.. but i think an AVC-R will as you say control it better and then i'm safer. plus its another toy

appreciate the input greatly

sean turbo2000

iTrader: (1)

yeah the wastegate duty cycle, just reduce it a little, the boost cut works off the target boost, if it exeeds the set target boost by around 0.2bar it enables boost cut

Ver4STI

I knew there was some sort of cut. Makes sense it's .2

Currently it's set to 1.20 kg/cm -- 60 -- 255

Checked a moment ago and I can reduce it by increments of 2 all the way down to 20

Shall I try 58 to start with ? What is happening when I lower the duty cycle does this mean the wastegate opens earlier ?

Do I try 58 build up power in 4th say and keep lowering it till it doesn't cut ?
I don't want to keep hitting boost cut though through fear of doing damage

What I'm puzzled at is the next boost setting down is

1.10kg/cm --- 55 --- 255
And the one down from that is
1.00kg/cm --- 50 --- 255

Yet it seems the 1.2 setting works best. It's cuts earlier on the lower boost settings

Appreciate your help

sean turbo2000

iTrader: (1)

yeah id drop to 58 and give it a try, do all tests in 4th gear, and just make small changes untill its where you want it, the lower the duty, the lower the boost, as you can see theres only 10% between your low boost and high boost, so likely only a % or 2 change will be needed

Ver4STI

Ok great thanks it only seems to be high load at low speed in 4th it's cutting so I will try this.
Thanks for the advice. I'll be looking into the AVC-R also to help control it.

Will update once changed the duty cycle

bludgod

iTrader: (3)

it's the same process as setting up a standalone boost controller - it's possible that it was setup for max power/max boost in 3rd gear so the higher load in higher gears gives you the overboost/fuel cut experience.

As above if you set the boost/wastegate setting in 4th gear then you should only be a little over in 5th and a little under in 3rd but it shouldn't be far enough out to cause an error/fuel cut unless there's a big change in the weather that it can't cope with.

The AVCR has a bunch more settings you can adjust so that you'll reach your boost target in 3rd/4th/5th without overboosting so it's a better setup if you really need the target boost in every gear, for most cars you can make do with the apexi's own boost control and live with the fact that you get slightly different results in each gear.

Ver4STI

thanks for the information bludgod

i will try to set this up later and see how i get on,

In the long run i think i'll go for an AVCR just for piece of mind

at least then i can upgrade the fuel pump and fuel pressure regulator so i know i am safe for more power and can hold it safely.

thanks again.

Ver4STI

Went the long way home.
Dropped the duty cycle to 58.

Hey presto full throttle from 1500rpm in 4th pulled smoothly all the way to 5500rpm when I came off the throttle tried it a few times also even pulled from 2000rpm in 5th through the Rev range and no boost cut.

As if all it took was dropped the duty cycle to 58 from 60

Seems to spike to 1.3ish still but no boost cut.

Drives like a different car as I don't have to ease on the throttle to now hit boost cut

Thanks so much for the help

Will be driving it over the weekend properly and hopefully all is well

Ver4STI

so i built up speed from 2000RPM in 5th the other day and it hit boost cut at about 3600RPM.

i lowered the duty cycle to 56 and this cured it

so basically i have lowered the duty cycle from 60 to 56 how much power do you expect i have lost from doing this.

bare in mind its still running 1.20 - 1.25 Bar and it made 297 Bhp.

have i lost only a few bhp or more ? i'm genuinely un aware and tbh it still feels fast.

little'un

iTrader: (9)

Because the PFC's internal boost control is fairly basic and has no duty cycle or feedback speed compensations per gear, you'll always find for a given duty cycle you'll hit more boost in higher gears - this will become more apparent and you'll be more prone to hitting boost cut in higher gears if you run a duty cycle that allows a slight initial overboost on spoolup in the lower gears.

The trick to making it work correctly is to get the duty close enough to hit the target set point without overshooting. - set your duty and make one or two full throttle pulls in 3rd or 4th from around 2000rpm to the top of the Rev range - now go back to the boost setting screen and look at the 3rd setting next to your selected boost level and base duty cycle - if you've set the duty close enough to hit target you should see this value drop from 255 to 200 or lower, indicating that it's close enough for the Ecu to 'home in' and make minor corrections to hit target.

The issue you'll have trying to set boost control up accurately on the commander is that you can't see the live value of solenoid duty cycle in order to dial it in close to start with. You really need an FC Datalogit interface to see and modify all Ecu parameters and record data in log files. - Also, some form of det detection in addition to the knock level recorded on the commander and a Wideband lambda to measure fuelling would be a wise move whilst trying to set boost!

Ver4STI

Thanks for the feedback.

I have lowered the duty cycle to 56 and it seems to boost fine now.

I did 3 or 4 pulls in 4th and 5th from 1800 rpm through to about 6500rpm in 4th.

The 3rd reading hasn't changed though still reading 255

I've lowered the duty cycle accordingly so when running 1.10 bar boost the duty is 51 and when running 1.00 bar it's now at 46..

All of these setting from 1.00 to 1.20 bar seem to hold boost well and no boost cut when pulling from 1800 to redline in 2nd 3rd and 4th and even 5th. But this 3rd reading of 255 doesn't change ?!

The ECU was set up by Andy Forrest and Clive atthowe I have simply lowered the duty to stop it boost cutting in 4th and 5th.

I will be going back to Clive atthowe soon anyway for other works so will get to put on the dyno and see whats going.

As advised earlier I didn't think lowering the duty cycle by 2 or 3% would have much affect on fuelling. I would have thought it's better running slightly less.

I'll be saving for an ACV-R also it has more control.

Thanks for your help