Standalone VS Piggyback ECU's

[BDKW1]

An RC51 with a good tune on a turbo should need about 6PSI to get 50HP. You may not need to drop the compression at this level, but you will need good fuel.

[RC51 Rhino]

 Yeah, figured it wouldn't be cheap! A guy can dream, can't he?

[trojan]

Sorry for the delay, I haven't been hanging back for the snipe :P I've been busy. 

Firstly let me point out that when I say PBs I'm referring to a fuel injected motor that is already controlled by an ECU and the PB intercepts the signals from the various engine sensors and "fiddles" them to fool the ECU into doing what the PB wants it to. Further when the "map" gets out of range for the ECU the PB takes over completely and ignores the ECU. PBs for what they actually are and not what people generally perceive them as, are generally nifty and really well done.

To me, setups that are not PBs in the context I'm referring have carbies. In this context the PB is a programmable CDI and will do perfectly well in that the motor is not actually highly tuned at all (compared to a busa).

Now to the "why". To do certain things electronically eg: take a air temperature reading, can be achieved by many many different ways. The differences between these methods comes down to cost, accuracy/stability and energy usage. Generally the more accurate the more it costs. That applies to the sensor  and the circuitry to "read" the sensor.
PBs are significantly cheaper than ECUs partly because they use less accurate and less reliable circuitry.
In my opinion the issue is compounded when the PB takes over completely in that, it is when the motor is most vulnerable that it has the least precise control.

Many times, if a sensor signal is intercepted it is changed, either in value or time (frequency). The ECU is not expecting that difference to exist. The least detrimental result in the end is a slight misscalculation with respect to reality. This is then passed on to a less capable system (PB) to add even more error to the control. The worst is an engine failure due to lean moment or a timing mistake etc. The most common is in between where the ECU and PB are continually fighting each other. This makes the diagnostic systems in the ECU go mad, filling up your error tables. Sorting out any problems via the diagnostic features of the dash (eg busa) basically useless. Commonally it manifests as a flat spot or running rough at a certain point. Sometimes these problems cant be fixed because they are a result of the fighting.

ECUs are constructed to do the job at hand - reliably. I don't know of any late model ECU that is not. If the circuitry could be made as cheaply as a PB AND be as reliable as a modern ECU then the ECU manufacturers would go with the cheap construction, it's just business to them. Well all except Motec, it's a religion to them and they charge like the Scientologists

Generally the level of control the PB's tuning software provides is limited when compared with an ECU.

I don't consider this is an example of "you get what yo pay for" in that with a PB you are not getting a cheap ECU but rather a kludge.

With respect to a turbo busa, most setups involving a PB don't give enough credence to the fact the busa is highly tuned in the first place. Bottom line, the ECU is an integral part of the system, equal in importance as forged pistons... skimp and you will be sorry.
ECUs start at $1500.

[trojan]

Can you guys explain more in detail what is needed to "sync" this stuff and/or how to know if they can work together?

Mate, your sync has to be fixed!

[fabr]

Ummmm,OK, now for an answer to the question..........

[trojan]

Fab, you're like a busa, highly tuned, spinning fast...... but half the spark is wasted [on you] :p

I think he's referring to adding an encoder-daisy-degree-trigger wheel to the crank and having that initially set to the correct angle. But as  said it's a stretch to call ignition controll an ECU.

[Yummi]

Trojan - you forgot "blowing hot air...."  :P

[fabr]

So now I'm turbo'd?

[trojan]

but not intercooled

[fabr]

I gotta be,there's a bunch of hot air coming off of me and I'm so cool ya know.

[Odyknuck]

I am running a 2000 Subie 2.5 motor in my car. I am using a Greddy Ultimate PB on it and the larger 440 CC Injectors. I will tell you its easy to get the car to run however not as easy to tune it. The trick to any PB in my opinion is to get the OEM ECU long and short term fuel trims right in general crusing speeds first before you try and tune for Boost.  This way the so called learn around can be somewhat eliminated. It does require you to log the STFT, LTFTs, AFR and RPM to make it work out.  And also log the the Greddy (or similar) PBs fuel cells so they can be compared with the ECUs and the PB can be compensted in the area that are not optimum.  I am new at this and still have a ways to go and may be one of the reasons I am not getting the Boost levels I need as I have stated in another post here.  The PBs have there place however when you get into Boosts above 10 psi I would opt for a stand alone.

[RC51 Rhino]

 So would there be a possibility of running low boost numbers on the RC and maybe just bump yhe fuel pressure and get lucky enough to find some bigger injectors? I;ve seen a few guys (done it myself, too) cap off the return to bump F.P. some and the motor will make a small gain??? I was also studying a RC site that claims a 2-4 H.P. DROP(!!!) using high octane pump or race gas, I guessing the higher octane would help w/ the turbo?

[chrishallett83]

Don't cap the return, use an adustable rising rate fuel pressure regulator.

You set the base rail pressure you want, and it goes up with the boost pressure.

Some higher-octane fuels actually have a lower heat content than regular pump gas, so used in an untouched engine that is tuned to run on regular pump gas, your cylider pressures will drop a bit, resulting in less torque. The same engine retuned to run on the higher performance fuel will probably achieve the same or higher power figures, along with better throttle response.

[fabr]

Don't cap the return, use an adustable rising rate fuel pressure regulator.

You set the base rail pressure you want, and it goes up with the boost pressure.

Some higher-octane fuels actually have a lower heat content than regular pump gas, so used in an untouched engine that is tuned to run on regular pump gas, your cylider pressures will drop a bit, resulting in less torque. The same engine retuned to run on the higher performance fuel will probably achieve the same or higher power figures, along with better throttle response.

You gotta decide whether to use a 1:1 regulator or a rising rate(FMU) regulator though. Depends on the needs of the system. I have no idea which for RC's setup tho.

They have a slower burn rate and therefore will tolerate earlier ignition producing higher cylinder pressures without detonating at the higher cylinder pressures.I completely agree with the rest of that.

[RC51 Rhino]

 OK...So to turbo or not would be the question. I have a perfect spot for it, if I do it and a good place for an intercooler if needed, too.