This is something I've always wondered..

i've worked on my share of JDM cars.. (supra, evo, 180sx, GT-R's,etc etc) even DSM's and such

The FD is the only Car I know which has an ecu that doesn't compensate for boost increases

does the map just not scale that far? or what?

IMO opinion the map should be tuned to the point of boost/fuel cut... where the ecu will stop the motor from grenading at that point

I have friends who will more than double their stock boost pressure and still be ok on the stock ecu..

hell even my FC is ok with raised boost..

why isn't the FD?

the map sensor is good for ~1.15bar so it should be able to compensate.

don't tell me it's a MAF vs MAP thing either

i've seen many 1JZ and 2JZ's with the oem map sensor running just under boost cut all the time...


why couldn't our ECU be like that?

 

If you increase air flow with mods such as exhaust, intake, and intercooler you will get much more oxygen through the engine and yet still maintain the same pressure. i.e. the MAP sensor gives the same reading but now you are running lean as there is no extra fuel to compensate. Thats the advantage to running a MAF (mass air flow) as it will monitor the actual amount of air going in the engine so whatever you do for mods the ECU knows how much fuel to compensate.

The disadvantage to MAF is that its generally an airflow restriction. Either its a flapper door in older systems or its a circular passage with a couple diodes or a wire through it that senses air flow.

Like it or not, it really is a MAP vs. MAF thing

 

the engine usually grenades due to boost creep from free flow mods.. not the mods themselves..

if u were to port the wastegate.. so it didn't creep.. ur motor would most likely be fine

and we're talking about 2-3psi here..

1JZ and 2JZ's are doubling their boost pressure.. and the car isn't detonating..

besides the IAT is there to compensate for colder and denser air from mods like the SMIC

so obviously the map can't be that off..

 

The stock ecu will compensate for some mods. However, it will only go so far. The factory has to set the ecu to have fuel cut at a certain point. They do this so that people don't blow up their engines. If they didn't do this, many owners would destroy their engines and want them replaced under warranty.

The life of an unmodified FD engine probably averages 80-100k. An engine running high boost probably averages less than 30K. There are many FD's running higher boost that blow up with less than 5K on them, so that's why I estimate the average to be this low.

 

I always wondered too but never tried to find a real answer.

Like someone said, i think its because the fact we dont have MAF's.

 

Unlike the Terminator's CPU, the FD ECU is not a neural-net processor or a learning computer.

 

lol u mean sky net CPU :p

heheh


I know the ECU has fuel cut

but many engines blow without ever hitting fuel cut..

 

the issue is basically heat. around here in CA we're kind of gun shy about running more than 12psi NO MATTER WHAT ECU is in the car.

and hey we did run more boost in the 90's before there were a lot of ecus, and when we had better gas. it can be done.

 

My 32 has a MAP sensor too if i am correct, and i don't have any problems. But, then again..i only have a downpipe, exhaust and Blitz SBC.

I peak boost at around 15-16 Psi on a good cold night. This is about the limit for the ceramic wheel turbos. The engine can take a bit more.

 

Think of it this way, when you change a turbo you have to have it retuned because it flows different. So if you change the flow with bolt on mods, you also need to have it retuned because of the same reason. Adding more flow and keeping the same tune is going to make it run leaner, which rotaries do not like because it generates more heat and can/will lead to detonation.

thewird

 

all RB's stock had twin MAF's

 

The reason is that the manufacturer didn't map the standard ECU much higher than stock boost levels... therefore you start running lean the further up you go....

Certain cars, manufacturers map higher as a safety precaution.

MAP sensors and MAF sensors are not the issue here.

 

Actually, thinking about it, this is a really good point. Mazda could have saved a LOT of woes if they would have simply made the ECU go REALLY damn rich if you start going up in boost. Still have fuel cut in there, but add in a bunch of fuel to keep things safe.

Just one of many engineering decisions that are WTF. Add that in with the crazy fuel filter location and the world's cheapest plastics for the interior.

Dale

 

You are incorrect. If you increase flow the stock MAP based system cannot compensate for that because the ECU does not know there is additional flow. MAF systems can compensate because they know exactly the amount of air and adjust fuel accordingly.

In a MAF system air goes in and is measured by air flow meter, the ECU looks on a table and says for X amount of air I need Y amount of fuel. It puts in Y amount of fuel and all is right with the world. You increase X the amount of air and it looks up the new value of Y and fixes it.

In a MAP system you have tables written based on RPM, and boost pressure. These tables were written to assume at a certain RPM and Manifold Air Pressure you should have X amount of air. Looks it up and finds Y is the needed fuel and sprays that in. If you increase air flow by upgrading intercooler, exhaust, etc, you still have a map based entirely on RPM and Manifold Air Pressure. You now can have lots of extra air but the RPM and manifold pressure values are the same. The ECU does't even know there is more air so it doesn't even have the chance to compensate for it. That is why you need to re-tune a MAP based system every time you change anything. Granted there is some fudge factor, like the stock ECU is tuned rich. Adding a down pipe and high flow cat will be ok but add much more and you will be lean and go boom. The FD could have a stock map that goes to 10000psi and it wouldn't matter, a full exhaust could still pop the motor on a stock ECU.

 

^I understood the differences before, but that's still a nice explanation.

Yes they are.

 

I agree that a MAF-equipped system can do a much better job of detecting (and potentially compensating for) additional airflow due to modifications, assuming that the MAF sensor is sized appropriately.

With regards to blown motors, this might be less likely if the stock lower intake manifold did a better job of equalizing air flow between the front and rear rotors (USDM intake runners are dodging EGT and ACV passages). Also, the OEM fuel system isn't the best either: fuel pump isn't wired well, rear secondary injector is plumbed last in the system (will see the least pressure). The rear rotor housing never sees fresh (cold) coolant from the water pump, so it's more likely to run hot.

Quite a few factors stacked up against our rear apex seals, aren't there?

 

So by your logic, the tried and true method of "Keeping your boost at 10PSI on the standard ECU and you'll be fine" doesn't work?

 

Its only tried and true up to the 3 mod rule and then things get risky. Tom93R1 is correct. You increase the flow, you need a new tune.

thewird

 

Like I said earlier, the stock ECU will support some mods. At 10 psi, it still will support just about any mods on a stock motor.

 

The problem is too much flow and the car starts boost creeping and spiking which equals pop on an untuned ECU.

thewird

 

Nothing is absolute...at least I never regarded that as an absolute when I was on the stock ECU.
Keeping it at 10 psi is important, but he also said that there is a "fudge factor" in that the stock ECU is tuned a little rich. There is also the long standing notion of the "3 mod rule". A little outdated maybe, but the logic was there. Don't over reach on the mods, keep it at 10 psi and your fine.

 

Seems like you are missing the point. 10 psi maximum means no more than 10 psi. If you can't control it, then it isn't 10 psi maximum .............. is it????

 

its an old ecu, 8 bit

it simply does not have the power to do it.

 

Another issue is the stock fuel system. It just doesn't hack it for the amount of fuel you want to run in an FD at higher than stock boost levels... especially with all the flow mods too.

And to be blunt... the FD ECU was not designed to run over 10psi consistently.

Its not MAP vs MAF, its not supra vs skyline, its not Obama vs McCain. It just simply was not designed to do the things you wish it did. Call the Engineers that were in charge of the ECU. Otherwise, it's all speculation.

It just wasn't made to do what you desire.

 

it IS rich, they peg the wideband stock, you have to run a little more boost and a DP to get the afr into the 10's....