Chip Options

[sawood12]

Me again with yet questions on chips and ECU's. Alot of you already know I effectively have 1/4 of a Promax level 2 kit fitted i.e. a DPW and Piston style recirc valve with standard ECU chips and FPR. I fitted it with the intention of going the whole hog to a Promax L2 kit, however I've since discovered that the Promax chips are designed for use above 1 bar boost working in conjunction with the Bosch 3bar FPR which is a bit more than I originally intended to take the car to. I would probably want to take it to 0.85 to 0.9 bar boost as I want to squeeze a bit more life out of my cylinder head gasket. So what are my options regarding ECU chips that I can run upto 0.9 bar boost with assuming and can I run upto 0.9 bar boost with a std FPR? Are there any options?

 

[944turboS]

Check out the FPR pressures for the other models as they are not all the same. I can't remember which are the higher ones right now.

 

[sawood12]

Ok, so the std Promax chip has two maps does it? That sounds better. I think the chances of my car running too lean at the top end is reduced with it being a 220bhp car with the smaller turbo, but i'm sure it can still be a risk at higher boost levels. My short term aim is to minimise the cylinder head gasket going as it's a cost I would struggle to cover at the moment with other 'projects' on the go but i'm starting to get a bit peed off with the std chip overboost cutting in during these cooler days and I don't really want to be turning the boost down! I'd be happy to break 250 bhp mark for now, so only 13 more horses to find which I should get with 0.1 bar more boost and the better chip.

I assume with the aftermarket chip I can also start running higher octain fuels as well?

As soon as my head gasket is replaced at some stage in the future then I'm sure the boost levels will start to creep up again.

 

[944Turbo]

You can run higher octane on standard chips and it should improve the situation.
Tony

 

[Fen]

Yeah, try Optimax. It might make your overboost cutout problems go away wuth no more work or expense at all.

 

[Fen]

Sorry Andrew, but I have to disagree. Back in the day when my car was standard save a boost enhancer I fiddled with it to the point where it would trip overboost all the time on 95RON, but rarely at all on Optimax. That situation carried on for several months and a five-figure mileage so the testing is comprehensive (maybe if I hadn't tested it so comprehensively I wouldn't have blown the head gasket, but my job at the time took me to places I was unfamiliar with and Optimax was not available at all Shell stations back then so sometimes it was 95RON or run out). Since the grade of fuel can have no bearing on the boost pressure that tells me is that either the KLR drops boost purely on knock or that there is at least a window Scott could utilise where the boost is not too high but there is knock with 95RON fuel. My money is on knock only as there will always be knock whether the dangerous situation is due to poor fuel or too much boost, so no need to engineer a circuit dealing with boost explicitly. edited for typos

 

[Fen]

I agree it retards timing as well as restrict boost. On my car it would stay in a failsafe mode for about 30 seconds during which time anything more than very light throttle would trigger it again. After 30 seconds or so of taking it easy it would reset and be back to normal. I know some people say that the ignition has to go off and on to reset their's, so maybe it behaves differently on different cars, but with mine being a relatively late (1990) Turbo I doubt the basic concept of the KLR protection triggers would have changed after mine was made, and equally I doubt they would have removed a boost-pressure related trigger if it had already been designed and implemented pre-90, unless it caused problems.

I think also that Paul can confirm Phil Rowley's Turbo boosted to way more than 1bar when the Reliaboost was fitted incorrectly, but did not trigger the KLR to step in.

 

[sawood12]

Don't get me wrong I will upgrade my chips as I soon as I can - I realise that once you upgrade one part of the car it's like throwing a pebble into a pond and the ripple effect meaning that other components need to be upgraded to cope. I am not in the premiership league of Boostie boys like Fen is but I do want to improve or update my car moderately hence my initial target of 0.9 bar boost and over 250bhp and I realise I need to upgrade my chips to do proper job of it.

I sort of understand all the technical talk above but one thing doesn't seem to ring true. The situation I have experienced which I am interpreting as over boost does not require the car to be restarted to reset the ECU's as Andrew suggests above. The situation resets iself afer a few minutes of much more sedate driving off boost - so is this still the KLR kicking reigning in knock or something else?

 

[Diver944]

ORIGINAL: Fen

I think also that Paul can confirm Phil Rowley's Turbo boosted to way more than 1bar when the Reliaboost was fitted incorrectly, but did not trigger the KLR to step in.

Yes. I can't remember the exact peak boost but it was getting towards the top end of my gauge (30 psi) so was probably around 25psi (1.7 bar) []

It was only hitting that for a second or so when full boost arrived at circa 3500rpm and tailed off very quickly to be back down to standard levels by the red line. You could easily hear the tell tale 'gravel in a can' sound of pinking/ knocking from the engine.

The car was very rapid [8D] I think Phil had his eyes shut.

 

[berg944]

Whats the verdict?

Knock sensor, Overboost protection or do we have both?

Mike[:'(]

 

[Fen]

We have a knock sensor for sure - just the one whereas S2s got 2. Jury maybe still out on excess boost alone, though I am convinced the pressure plays no part. "Overboost protection" is just what it has become known as because turning up the boost is what usually trips it (by causing pinking).

 

[sawood12]

I can't see it being actual overboost in my case as it doesn't kick in immediately when the boost is at it's highest pressure. It probably kicks in at around 4500 to 5000 rpm (maybe a bit more) after a good few seconds of full accellaration, certainly after i've overtaken the car and long after my car has hit max boost pressure and started to bleed off as the revs rise. Wouldn't genuine overboost more likely happen as soon as the boost builds up to its max level at around 3500 rpm?

 

[Fen]

What you are describing is exactly what my car used to do.

 

[944Turbo]

yep mine used to trigger around 4500 as well, its when the turbo is really doing the goods it was worse in 4th and 5th as the engine is prodiucing more energy (heat) to work the turbo better. This is probably also the point a good standard wastegate has started to open itself. the protection resets itself after 30 secs or so, but a switch on/off will reset it instantly. (stops that M3 getting too far ahead..............erm possibly [])
Tony

 

[sawood12]

I've just filled up with Sainsbury's 97 RON as there is no Optimax round me in a 20 mile radius and i'm not prepared to be ripped off by BP (it's 10p per litre more than Sainsbury's 97 RON) so I'll see if that makes things better.

I'm still struggling with the concept of why it happens so high up in the rev range. If it's knock that's causing it is it due to the accellaration wanting to advance the timing as much as possible, does the higher revs affect the onset of knock? If knock can happen at any RPM then why isn't it just as likely to kick in lower in the rev range?

 

[Fen]

As Tony said it'sto do with the turbo and its characteristics. The turbo spins due to the heat energy of the exhaust gas and to a degree it's self-fuelling (without a means of venting pressure, the wastegate, the turbo would destroy itself first time it runs), so it takes a while to get going at all as heat builds in the exhaust gas off-boost, then when the boost starts to kick in it causes more heat in the exhaust and the turbo spins harder. An undersirable by-product of that is the heating of the compressed intake air. That all takes so long that even in third a 944T doesn't really hit maximum boost as the throttle has to be closed due to reaching maximum engine revs before it has. In 4th and 5th the whole boost system gets to its maximum output and the wastegate controls it to maintain a steady state, including heating the intake air. During that steady state of maximum turbo efficiency the demand for fuel is at its highest and the hotter intake charge promotes detonation. A turbo on WOT runs AFRs into low 11s or even high 10s, which has been described to me as using fuel to cool the cylinders.

 

[944Turbo]

Yes all to do with efficiencies, compression and therefore heating of the intake charge, air fuel ratios, the amount of time the mixture is in the cylinder, the density of the mixture in the cylinder, denser air has more oxygen which is why the overboost is more likely to trigger in the winter months, the ignition timing the cam timing, the overlap etc. I would guess its near the point of peak torque which is where the engine will be at its maximum efficiency. Everything working in harmony to create the sweetspot, so any thing that goes outside the preset parameters will show at that point first. At other points in the rev range the engine parts are not in the same perfect harmony so there is more tolerance.
I think that is why F1 engines now run camless designs you can vary the valve timing to suit more points through the rev range. However other factors have an effect and are harder to change, intake & exhaust design, compression ratios, injector size and pulse length, turbo and intercooler etc etc.
Tony

 

[sawood12]

OK, so it sounds like it's all about pre-detination due to heat build up? If that is the case then why does higher octane fuel improve things as I thought the higher the octane the hotter the fuel burns?

 

[Fen]

The higher the octane of the fuel the more resistant to knock it is, or alternatively the more stable it is under heat/pressure.