turbo on stock ecu

[Fatty]

so i've read recently about people running turbos on the stock ecu. i didn't think was doable / advisable but never understood what the ecu does really so i don't know the pros and cons of either approach.

so, can someone break it down for me and explain (simply) what the ecu controls?

i guess i'm just curious why you would spend megabucks on an aftermarket ecu if you could just piggyback , for example, some of those jaycar kits onto the stock ecu (the boost controller kit and the fuel controller kit )...
also the stock airflow meter seems to be frowned upon ? why is that? do the aftermarket ecu's not require one or do they just get this reading from somewere else ?

ok clearly i need some edumacation.

[Boags]

Hi Fatty,

I can help you out with a few things, and i'll break it down to how it was explained to me when doing an EFI conversion on a Datsun 240K.

An engine needs fuel, spark and air to run. With this it will run regardless of anything else (within reason) but might run like a dog. The computer makes sure the right amounts of fuel are going in for the amount of air going in, and sparks at the right time.

Now, turbos - factory computers have certain tolerances for high or low readings from different parts, but when you put too much air through, it craps itself and doesn't know whats going on. It thinks \"this can't be right\" and goes into limp mode. That is why you need a piggyback (or a stand alone ECU) for the fuel/air mixture. This fools the computer in a few ways so it doesn't crap itself, and thinks it's not pumping in as much fuel as it is.

The stock air flow meter - i'm not sure why it is frownd upon so badly, but it is big and heavy and restricts airflow, so that might be a few reasons... I actually can't help you on how this disappears on stand alone ECUs because I don't know either... But they get the reading from somewhere else.

Why you would spend \"megabucks\" on an ECU - well, quite simply, tunability. A new ECU can display air/fuel/sometimes boost/knock sensing/timing retard/air temps/water temps/block temps/atmosphere temps/oil temps/oil pressure/blah blah blah. A lot. You can perfect every part of your setup with the right ECU.

Eg. - MX5s and those Greddy kits - with stock everything and a Greddy kit, you have very little torque below the boost kick-in at 4,000RPM because the timing needs to be retarded to 6'BTDC to stop the engine pinging on boost. With an aftermarket ECU you can set this to be as high as 16'BTDC low down, giving you more torque to get the car on boost, then it retards the timing to 6'BTDC when boost kicks in, so the engine doesn't ping.

You can buy knock sensors and timing retard devices like a piggyback, but again, it is more money, and again, if you buy lots of pieces seperately you might as well have spent the money on 1 stand alone ECU for $1000 than buying 5 different piggybacks for $200 each.

Hope that helps,

Boags

[Moggy]

Boags seems pretty much on the ball here. The stock ecu is fine until you go too far out of it's normal operating range, at which point it is still trying to operate the engine as if it is a stock n/a 1.6 when it's turboed and running positive pressure. With the aftermarket ecu it doesn't matter what you do to the engine you can program the ecu to run it. Piggybacks change the signals to the ecu to make it do something it doesn't realise it's doing, and are okay for mild tuning but are still limited by the stock ecu, this is why people change to aftermarket ecu's. You also generally cannot change the timing maps on piggybacks, which is very limiting.

About airflow meters; the airflow meter tells the ecu the volume of air going into the engine, which tells it how much fuel it needs to put in to achieve the desired fuel/air mixture.

With regard to the stock airflow meter, it runs out of resolution at high rpm. On a fairly stock 1.6 it will hit it's max reading at about 6500rpm, and tell the ecu that the airflow isn't increasing past this point. When you start increasing the power more it hits this point earlier in the rev range, making the problem worse. Many people upgrade their stock airflow meters to s4 RX-7 airflow meters, which are the same design but able to handle higher flows.

Many aftermarket ecu's run MAP (manifold air pressure) sensors, which measures intake manifold pressure and assigns fuel based on this reading, instead of airflow meters. In this case the airflow meter can be removed entirely.

[Juffa]

I went the stand-a-lone ECU replacement course. I have a Link ECU (made in NZ), with an upgraded chip from Flyin' Miata in the USA. I went with this to allow me more options with regards to upgrade paths, either staying normally aspirated or as Tweety is now, forced induction. This included being able to remove the restrictive Air Flow Meter and replace it with a MAP sensor.

Here is a link to the Greddy FAQ site. While much of the information is Greddy specific it does provide an insight into things like ECUs.

http://www.greddyturbofaqs.com/staticpa ... hp/mainfaq

There are plenty of books out there with information, such as the one by Corky Bell, Maximum Boost: Designing, Testing, and Installing Turbocharger Systems (Engineering and Performance). I hope to pick a copy up while I'm in the States later this week.

J

[Fatty]

great info guys, thanks a lot! all my questioned have been answered. thanks for taking the time to explain it, it's really not that hard to understand at all eh?