Gez

Pavlo you must be a university of hertfordshire student. This MAY be the explenation of the boost problem. At the moment we do have v-high atmospheric pressure which could be the answer to my problem.
Any comments on this anyone??

Pavlo, noticed you are a Mech Engineer! Where did you graduate??

[Edited by Gez - 8/5/2002 10:08:47 AM]

john banks

Difficult to say - you need to log the car to see the wastegate solenoid duty cycle. More likely it is just the boost control being its usual difficult customer (!) since if it was detting the response is to drop the duty cycle to zero which is quite noticeable - you would go down to wastegate controlled boost - say 8 PSI.

Well, I should say, that if the ECU thinks it is detting, since they are not always the same thing.

I find the scariest thing about all this is that midrange boost spikes sometimes result in transient detonation on both modified big turbo UK cars and STis that the ECU does not seem to do anything about. I just wonder if the spikiness of some STi's with decats and the low grade detonation that occurs over time (because of the 100-102 RON map) may be the reason for some of the failures on STis? Not saying it is, but can't be good.

[Edited by john banks - 8/5/2002 10:32:22 AM]

Gez

I have been driving my STI 6 Type R V-LTD for the past month during warm weather achieving 1.27bar maximum boost read on my Blitz turbo timer. Yesterday i thought it would be ideal to give the car some welly being cool and damp therefore keeping charge temperatures down etc etc. I was driving around less than 3k rpm for 1/2 hour ensuring the car was at optimum temperature.
I gave it some welly on a wide stretch of road up to 6k rpm and gave me no more than 1.14Bar.
Anyone have any idea why its doing this? I was under the impression that the denser/cooler the air is the better the performance.
It seems the warmmer the the air the more boost i get. Weird ehh?

chuckster

Could be as simple as a bad tank of petrol, car's retarded the ignition due to onset of det? I've seen boost loss after bad tanks in the past. End up taking it easy until I can get a refill.
C

Gez

I thought that the check engine light comes on when ecu detects det. Also thought that boost is cut by more than 0.1Bar in these cases. Am i right?

mutant_matt

Gez,

It varies. Also the CEL will not come on when you experience DET. What fuel/booster were you running on at the time of the 1.27 and 1.1 readings? Bear in mind that the Turbo Timer is probably not very accurate when it comes to reading boost either. Are you using a Boost controller or the OE Boost Control (Max Boost on your car as standard is IIRC, 1bar)

Matt

Gez

The car is an STI 6 TYpe R V-LTD with a Fujitsubo exhaust system.
Im using standard boost controler with a Blitz Turbo timer. I have been running the car on Optimax and NF(200ml/tank) since i bought it and has never had anything since. Berfore that it was always running on 100Ron back in Japan.
Would i be able to notice a difference while the car is detting or be able to hear something???
I have also got a small boost guage which under full boost does hit just over 1.1bar. Im wonder whether its just been spiking higher in warm weather.

Pavlo

Pressure sensor is measuring absolute pressure, boost gauge relative (to atmospheric) pressure. Therefore is the atmospheric pressure is high, the relative pressure of the boost will be less, as it's controlled according to absolute pressure.

Eg, (mb = millibars)

If atmospehric pressure = 1013mb (1 standard atmosphere) and boost is 2250mb absolute, gauge pressure = 2250-1013 = 1237mb or 1.24bar

But if atmospheric pressure = 1100mb (high air pressure) and boost is still 2250mb absolute, gauge pressure = 2250-1100 = 1150mb or 1.15bar boost.

I think that 1100mb is an acheivable high pressure? If so, you can see how boost, measured by gauge pressure might vary with the weather. Also damp air is not great, as it reduces the density of dry air, which is what th engine really wants, as it can't burn water vapour.

Paul

Pavlo

I've never been to Hertford uni, but sometimes I wish I had...

Went to loughborough for Automotive engineering, which was pants, then went to Kings in london (which was great) before having to get a job.

But i'm ancient compared to many round here.

Paul

Gez

We will have to meet up sometime for a drink! Are you going to the Herts Meet next Sat

john banks

Although the boost is controlled with absolute pressure targets, these are compensated by atmospheric pressure leading to effectively relative targets being used, so the ECU will always shoot for the same point on your relative boost gauge.

However, the closed loop control is a table of offsets for various boost errors for various times which contains a duty cycle that is used to compensate to try to get the correct boost. On the STi5/6 the corrections are quite soft, and the targets are quite low (15.7 PSI = 1.08 bar), so when people are getting higher than this they are seeing overboost, the size of which are very dependent on environmental conditions.

There is a big compromise with JECS to get the right boost and response in all gears and conditions - it won't happen is the long and the short of it.

Gez

So John, im i seeing a case of over boost or a reduction in advance due to det? The car is still running ok, infact its running better then ever. Didnt realise the cold air would make such a difference.

Gez

Exactly the reason why im investing in a new ecu. I think that the change in Atmospheric pressure and ambient temp is effecting boost. I pressume the hot temps we have been experiencing has caused the boost to spike hence max boost pressure on my turbo timer being 1.27bar. Nevertheless i will be taking it easy just incase it is a bad batch of Optimax.

Cheers

Gez

john banks

I run a 20 PSI boost target, and can see anywhere from 19 to 21 PSI depending on the conditions and gear despite a 1 bar actuator. There seems little rhyme or reason for the differences - yesterday it went to 21 PSI in the really hot midday - probably the hottest day this year. This morning when much cooler only 19 PSI!

I have tried progressive boost control like the AE802 rather than the same duty cycle and target across all load zones like the AE800/801. I have tried adjusting the table that controls the closed loop control. In the end the only way to control it is to do so with the maximum duty cycle. The closed loop control is just not good enough to get perfect boost control in all conditions, so you end up with a compromise and live with it.

Gez

With the drop in max boost pressure, would a loss in performance be of consequence?

Pavlo

Have you tried running high duty cycles and low target?

I am playing around at the moment with very high targets, just letting the duty cycle control the boost in a open loop fashion. My plan is to get the futy cycles pretty good then introduce the boost targets to finallise it.

Paul

Gez

CAnt do much with the ecu at the moment as its the standard unit. Will soon be getting a Gems ecu so ile be able to fiddle around with it.

Cheers

Gez

mutant_matt

Gez,

If you are coming to the meet on Saturday, AND I can get my DeltaDash connector back this week, I can plug you car in and we can log some runs if you like.....then you should have a better idea.

Matt

Gez

Most definatley will be coming to the meet on Saturday.

john banks

High duty cycles result in a bigger peak. It takes only a small change in environmental conditions to make it a really big peak and then it fluctuates, unless you use low offsets, but then the boost is really high. The only stable way I have found when mapping in the summer is to use a high target and accept that the boost will undershoot it until winter. One car has overboosted and I sent him a restrictor, despite being 1 PSI below target in the Scottish summer it then over shot by about 3 PSI when it rained. Can't win sometimes

Pavlo

I was trying to aim about 1psi above target boost with duty cycle. On 96 ecu boost control is stacked around the 3krpm point, where the boost comes in. goes something like:

0, 2700, 2900, 3100, 3300, 3800, 5600, 6600

So very fine control around where the boost really comes in.

Paul

john banks

Problem is though ideally there should be different duty cycles for different gears - since in 3rd gear you can and should hold the duty cycle high until higher revs than in 5th gear. All a compromise.