ACEparts_com

My UMW stage 2 car has been somewhat temperamental since conversion - having days where it would go like a bomb, others where it wasn't so good.

It's in a tuner's now and after data logging have deduced that they can have 3-4 good runs where the car pulls like a train and develops 16psi of boost but after 5+ runs boost has tailed off to 13-14psi and performance suffers.

I appreciate the boost going off maybe a symptom rather than the cause.

The Turbo's are apparently fitted with 1bar actuators that crack open at 6psi. Could they be opening too early and then cause overboosting or do I need to look at programming?

TIA

Alan

Quadcammer

I'm confused. You say overboosting but then you mention boost dropping.

The boost dropping as the motronic will pull boost as the intake air temps rise, which would happen in such a setting.

Where are your "overboost" allegations coming from?

ACEparts_com

It's perhaps producing too much boost on the first few runs, increasing temps. Surely the boost being reduced is a symptom of timing etc being pulled? Would like to know about reducing the boost to begin with for more consistent performance.

JBL930

You need to do some data logging Alan, so you can see what's happening with ignition and intake temps. If you had a bad sensor, like one of the oxygen sensors was shot, then you should only see 0.5bar, but with your 1.0bar actuators it may be masking it. Do you get the engine check light coming on?
Have you tried changing the N75 boost solenoid valve? These can act up and not throw an engine check light.
You can expect 16psi (1.1bar) as normal on a mapped car, maybe less when it's really cold out, but on a normal day i would think 1.1bar is right. What has Kevin said?

Kevin

Alan, what you have mentioned is actually how the Motronic will work. As laps progress power will be reduced as the engine heats up and as the intake air temps rise. Leave the wastegates alone. The ECU controls them as needed to adjust the boost. There are temperature corrections and timing retard maps in the ECU. The easiest way to keep your boost levels is to run RACE GAS.

JBL930

Hi Kevin
So your maps are done knowing the power will be lost due to high temps, shouldn't it be mapped so that it keeps the same power at all times? Isn't it stressing the engine taking it to such high temps that the ECU has to pull ignition timing and boost all the time?

Kevin

The factory maps has the temperature corrections in place to allow for this to occur.

Believe it or not, a factory GT2 has even more sensitivity correction.

You state it as high temps. But it is a gradual curve. There are other factors such as engine oil cooling. Speed in each gear, and detonation and intake air temperatures.

bb993tt

Alan, have you had any discussions with Felix about this? I know he data logged his car at vmax events with the same kit on it.

JBL930

I understand that the ECU has these safety factors so that it can reduce timing and boost etc if something is wrong, but in normal running conditions, whether it's in freezing or sweltering desert temps, the power output will always stay the same, as the ECU is programmed with headroom to compensate.
You won't be able to take a stock car out along side Alan's car, and after 5 or 6 runs it will start to loose power, if everything is working as it should a stock car will 'always' put out at least its quoted figures.
If i understand it correctly, you are saying that Alan's car has XXXBHP for for a few runs, but it's perfectly normal for that power to drastically reduce once it gets hot?

Kevin

The stock car is putting out .7 and .8 bar.. The stock car will not be along side of the Alan's car.

The stock car will pull the same amount of timing if ambient temps are high or if you start to get detonation due to lower octane.

As you increase the HP output in the engine, the ECU's safegaurds will kick in. To prolong this effect, race gas, or a more efficient IC need to be fitted.

JBL930

I realize a stock car wouldn't be as quick as Alan's, what i meant was if they were run on the same day, let's say around the same circuit, the stock car will give the same power lap after lap after lap regardless of outside temps, because it has been mapped with headroom, and as long as everything is working as it should, and it has decent pump fuel in it, it will perform the same..... The safeguards are there to protect the engine if something goes wrong, dodgy sensor, bad fuel etc etc. Am i right there or badly informed? Or will all stock cars pull timing in hot weather?

ACEparts_com

The most frustrating part is that under load in higher gears (4th+) sometimes I get the boost and the associated torque, others I get the boost but can feel it holding back. NineExcellence are looking at it at the moment.
They data log for their analysis, they recorded a 60-130 time of 10.4 seconds vs a standard car 13.0. 60-100 is .5 quicker than a car they recently converted using one of their own kits, but 100-130 is the same. A few runs on and that seems to change.

Maybe I have another fault elsewhere, all I know is it's a real PITA as I only get to drive the car every 3 months and I'm spending more time under the deck lid than behind the wheel

Kevin

JBL, the stock 993TT has the same temperature corrections to retard the timing and boost. The stock ECU will retard the timing and boost.

Alan, have you had your engine leak down checked recently? Tune up was when, plugs, plug wires, cyclinder head temp sensor? Like I said in my previous post, to prolong the HP effects, run race gas.. 104 ELF, or greater.

FYI you do NOT have 1 bar actuators unless someone fitted them other than myself. Your actuators are running correctly.

JBL930

Kevin, i think you're missing my point, or maybe i'm not explaining myself? I fully understand that the Bosch motronic ECU will pull timing and boost, but in a stock car it will only 'need' to do so if there is a problem.

Quadcammer

thats not correct at all.

The stock car, when running hard on the track, may also see levels of IAT that cause boost/timing reduction.

Obviously more power creates more heat, so a higher powered set up will reach this sooner.

The only ways to avoid that are better intercooling, more freeflowing components to reduce the level of boost needed to reach power goals, or even more efficient turbos (which the hybrids should already be).

There will always be trade offs.

Then again, would you prefer a car that starts at 470bhp and after many hot laps drops to 440bhp, or would you prefer the car that is always at 440bhp?