R35 GTR v My 944 Turbo
- Thread starter bennyboy
- Start date
DivineE
New member
ORIGINAL: barks944
Awesome! That car is really flying. Well done Vitesse!
The vid : http://www.youtube.com/watch?v=FCVodImUOrg
Thats one funny looking 994 or even 944. I assume it has had a headlight conversion?
ORIGINAL: TTM
I wonder how many people on here who run a Vitesse MAF with the V-flex actually control fueling with boost, as it's not mentioned anwyhere in the Vitesse instruction sheets [
Do you mean that the AFR doesnt really need to change with boost and that its really only ignition advance that changes?
sawood12
New member
The 944 ECU will only adjust ignition if it detects knock or overboost. Other than that the ignition is mapped against assumed boost pressures and therefore is very safe and conservative. What V-Flex does is introduce a MAP sensor to read manifold pressure and the piggy back computer will determine optimised ignition all the time - when on boost and not on boost. This unlocks more HP, especially on boost. It is myunderstanding that the Vitesse system does fuel according to boost apart from when on WOT - on WOT, as the stock motronic - it just opens the taps and gives it at much fuel as possible to ensure you don't get into knock. At WOT things happen very quickly and the knock protection system can't react quickly enough if you get into a knock situation and the engine will blow itself up.
Above 4krpm and 75% throttle the 944 turbo ECU doesn't use the AFM signal at all (it is fully open at that point anyway and giving a constant +5v signal) and fuels according to RPM and throttle position only. So yes, the car does fuel according to boost pressure but it is very crude and you'll notice that they run very rich on boost. A mate of mine was following me once and when I floored the throttle he said he got a nice wiff of rich exhaust smell.
Just because it is possible given the sensors to calculate mass the motronic doesnt. The temp sensor in the AFM is only switched on momentarily on startup and is not used at any other point so the motronic doesn't know air temp in real time. The AFM barn door is a very crude sensor and is not precise enough to use as a sensor for air mass calculation - I wouldn't want to anyway.
Nice to see a 944 hanging onto the coat tails of some tasty kit! We all now in our heart of hearts it is possible given enough £££
Yes the air temp is only sampled at startup but the value is used continually through running. As such it becomes less accurate if the air temp changes while you are traveling. I still stand to the fact it is essentially air mass . Every time the DME works out how much fuel to inject it compensates for the air temp using the air temp fuel compensation table (Maybe not at WOT). Not sure why they only sample it once though, seems like a strange decision.
My m8 was saying the car spits flames on the overrun. Certainly would explain why the area around the exhaust looks a little blackened. Always wanted a car that spits flames . I guess if you back right off the accelerator so the idle throttle switch is made then it will cut the fuel but that would certainly give a good shock load. A TPS would probably be a very good way round this.
I'm chatting to a guy in the states who is tuning with the Ostrich device I mentioned, he has managed to hook up a MAP sensor using a spare analogue input on the Motronic. I think that the current TPS on the 951, open/closed is also using an analogue input. So you might be able to plug a 0-5v TPS onto it instead and adapt the software.
. Every time the DME works out how much fuel to inject it compensates for the air temp using the air temp fuel compensation table (Maybe not at WOT). Not sure why they only sample it once though, seems like a strange decision. My m8 was saying the car spits flames on the overrun
. Certainly would explain why the area around the exhaust looks a little blackened. Always wanted a car that spits flames . I guess if you back right off the accelerator so the idle throttle switch is made then it will cut the fuel but that would certainly give a good shock load. A TPS would probably be a very good way round this. I'm chatting to a guy in the states who is tuning with the Ostrich device I mentioned, he has managed to hook up a MAP sensor using a spare analogue input on the Motronic. I think that the current TPS on the 951, open/closed is also using an analogue input. So you might be able to plug a 0-5v TPS onto it instead and adapt the software.
I believe the vittesse MAF with the chipboard monitors airflow throughout the rev range, however this will still have to be combined with throttle position / engine revs / to come up with a preset ignition and fuel amount from the map in the ecu, This will be conservative (retarded boost / more fuel) compared to what you can do with V-flex.
Does a MAF not take into account air temp anyway - its a hot wire which changes resistance as air flows over it more air or colder air cools it more than hot air.
Obviously intercooler and turbo efficiency also have to be taken into account in the mapping.
Tony
sawood12
New member
Hot wire MAFs are old technology - not sure what Vitesse uses, but yes, in essence that is how MAFs work.
The flame spitting is a nice feature and just goes to show how rich these cars run on full throttle - i.e. it is basically dumping unburned fuel into the exhaust system so as soon as you come off the throttle and start braking allowing air to get up the exhaust it ignites.
There is no need for the motronic to calculate air mass - that is the whole point about having maps encoded into he ECU's. The values are read off the maps based upon what the various sensors around the engine are reading, therfore no need to calculate anyhting - it simply looks up the answers from the maps. All the mass air calcs would have been done during the creation of the maps and then tweaked during pre-production test running.
The flame spitting is a nice feature and just goes to show how rich these cars run on full throttle - i.e. it is basically dumping unburned fuel into the exhaust system so as soon as you come off the throttle and start braking allowing air to get up the exhaust it ignites.
There is no need for the motronic to calculate air mass - that is the whole point about having maps encoded into he ECU's. The values are read off the maps based upon what the various sensors around the engine are reading, therfore no need to calculate anyhting - it simply looks up the answers from the maps. All the mass air calcs would have been done during the creation of the maps and then tweaked during pre-production test running.
I think MAF setups still look at air temp, the motronic retards ignition based upon air temp, a function I expect MAF based setups also do. Above a certain temp it starts retarding ignition, a knock related safety feature I expect.
Sorry Scott, I keep saying calculating when I don't mean it. Its just using maps to look up how much more/less fuel it should inject based on the air temp.
Sorry Scott, I keep saying calculating when I don't mean it. Its just using maps to look up how much more/less fuel it should inject based on the air temp.
Neil Haughey
New member
AFAIK perhaps the biggest difference between these old ECU's and modern systems is they are not strictly speaking adaptive. I have read backwards and forwards through the DME section in the 968 manual many times now as I have been testing everything I can. In pretty much all circumstances it says the same thing, if something isn't right it retards the ignition 6 degrees. In any other case you can assume on these old systems values are just read off a predefined map, or at least that is what it looked like when I studied the motronic cracking software several years ago. Its not a bad thing though as modern systems can suffer from the maps getting corrupted due to a bad oxygen sensor for example.
TTM
Well-known member
As I said earlier the MAP sensor isn't used to control fueling at all, and I haven't noticed much difference between with and without controlling the ignition with the MAP sensor. What I have observed so far with my car suggests it doesn't work any "better" than the Motronic and that it's a bit overestimated with regards to what it costs.
Nothing unusual about that car Ben except that it has some GTS lights instead of stock. Apart from that it's actually pretty stock looking from other pics I've seen.
Also, I've hit over 2 bar boost a few times and never felt any perceived ign pull. You would think 6 degrees would be very noticeable. Perhaps I'm just an insensitive soul. []
Also, I've hit over 2 bar boost a few times and never felt any perceived ign pull. You would think 6 degrees would be very noticeable. Perhaps I'm just an insensitive soul. [
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sawood12
New member
You're right Thom, at partial throttle the AFM controls fueling. The MAP sensor on the stock motronic is only there to protect against overboost. The MAP sensor that comes with the Vitesse v-flex does control ignition against a map.
I don't think you would would you Pat? You're not running stock ECU chips so your overboost protection would either be set to a higher boost value or disabled altogether (I think you're running Link G4 aren't you?). I think the only thing that would kick in any kind of safety protection in your car would be knock protection - unless there is an overboost protection feature with the Link ECU.
Not on the link yet Scott. Lots of changes and additions to project. However when I hit 2.1 bar boost it was firstly only with Vitesse AFM chips, and then with the Vitesse Stage 5 kit (Maf, turbo etc). The first occasion was on the track when the Tial DPWG failed and with the helmet on, I was wondering what the 'hail' sound was on a bright sunny day. Turned out to be the engine pinging it's head off. Amazing that the engine didn't blow up and testimony to all the stock components. The more recent occasions were when a vacuum line came loose from the Manual boost controller (from memory). I can tell you it didn't ping or feel like boost or ign was pulled at all. This was on E85 which is a 'magic potion' when boost comes into question. 2 bar feels very nice let me tell you. []
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