Having trouble understanding 550cc injector swap into 2JZ

[ifyouaint1sturlast]

As the title states, I am a bit confused. I run an Aristo swap (stock 440cc injectors) and I know that I can drop in some USDM 550's and wire in some resistors and everything will be gravy.

Why?

Why does this not flood the engine? You can't do this with any other setup without adjusting tune.. So why can you do it here?

Sorry for the dumb questions. I just hate chalking things up to "electronic magic", I like to have an understanding of why things do the things they do. I feel it helps in the long run.

Thanks

 

[flight doc89]

My understanding (read: take this with a big damn grain of salt, cuz I'm not really experienced with this stuff): Engine fuel injector timing is based off a graph, or fuel map. Input 'x', output 'y'.

'x' = (MAP output)*(rpm)
'y' = output to injector

So, if you put in larger injectors, it should go rich, because that larger injector would spray more fuel for that same 'y' value.
This is where the resistors come in. If you resist the output from the MAP sensor (thus decreasing the voltage), the ECU interprets this as less air. So, with lower MAP output, the 'x' value is decreased, with a resulting decrease in 'y' value, or injector signal. As long as the resistance is correct, you can lower that 'y' value correctly to balance out the larger injectors and have a correct mixture.

If we have to decrease MAP signal to allow bigger injectors, then what is the purpose? This is the purpose: (I don't know the actual values, only the theory, so I am going to use theoretical values)

Suppose you have a stock setup. ECU programming limits the 'y' value (injector signal) to a maximum threshold. Remember 'y' is the product of MAP signal and RPMs. We can't alter the interpreted RPM value because the engine and ECU have to be synchronized. We can alter the MAP signal, however.
In this stock setup, let us say that at 5k rpms, the ECU is limited to a max of 1 Bar of pressure. The moment pressure hits 1 Bar, fuel cut.
Now, we modify the engine, 550cc injectors and wire in those resistors. The ECU is still limited to 1 Bar of interpreted MAP output. We are back to 5k rpms. Our new fatdaddy turbocharger has pushed intake pressure to 1.2Bar. If the ECU knew there was that much pressure, it would have hit fuel cut because that exceeds the max value allowed by the fuel map. BUT, because of those resistors, the ECU only sees 0.9Bar, so it continues to send signal to the injectors.
Now, if we were still using those 440cc injectors, we would obviously be too lean. Lucky for us, we have those 550cc injectors, so the injector signal that would have resulted in a lean mixture, actually results in a good burn, but at greater intake pressure than the stock setup.

I think I explained this correctly, but I'm not strong on this kind of stuff, so somebody smarter than me please chime in and fix my errors.

 

[ifyouaint1sturlast]

My understanding (read: take this with a big damn grain of salt, cuz I'm not really experienced with this stuff): Engine fuel injector timing is based off a graph, or fuel map. Input 'x', output 'y'.

'x' = (MAP output)*(rpm)
'y' = output to injector

So, if you put in larger injectors, it should go rich, because that larger injector would spray more fuel for that same 'y' value.
This is where the resistors come in. If you resist the output from the MAP sensor (thus decreasing the voltage), the ECU interprets this as less air. So, with lower MAP output, the 'x' value is decreased, with a resulting decrease in 'y' value, or injector signal. As long as the resistance is correct, you can lower that 'y' value correctly to balance out the larger injectors and have a correct mixture.

If we have to decrease MAP signal to allow bigger injectors, then what is the purpose? This is the purpose: (I don't know the actual values, only the theory, so I am going to use theoretical values)

Suppose you have a stock setup. ECU programming limits the 'y' value (injector signal) to a maximum threshold. Remember 'y' is the product of MAP signal and RPMs. We can't alter the interpreted RPM value because the engine and ECU have to be synchronized. We can alter the MAP signal, however.
In this stock setup, let us say that at 5k rpms, the ECU is limited to a max of 1 Bar of pressure. The moment pressure hits 1 Bar, fuel cut.
Now, we modify the engine, 550cc injectors and wire in those resistors. The ECU is still limited to 1 Bar of interpreted MAP output. We are back to 5k rpms. Our new fatdaddy turbocharger has pushed intake pressure to 1.2Bar. If the ECU knew there was that much pressure, it would have hit fuel cut because that exceeds the max value allowed by the fuel map. BUT, because of those resistors, the ECU only sees 0.9Bar, so it continues to send signal to the injectors.
Now, if we were still using those 440cc injectors, we would obviously be too lean. Lucky for us, we have those 550cc injectors, so the injector signal that would have resulted in a lean mixture, actually results in a good burn, but at greater intake pressure than the stock setup.

I think I explained this correctly, but I'm not strong on this kind of stuff, so somebody smarter than me please chime in and fix my errors.

That all sounds theoretically correct, except that I've never heard someone putting resistors on the MAP output.. From everything I've read, people put resistors onto the injector circuit to increase the impedance.

So, I'm still confused

 

[flight doc89]

That all sounds theoretically correct, except that I've never heard someone putting resistors on the MAP output.. From everything I've read, people put resistors onto the injector circuit to increase the impedance.

So, I'm still confused

That, confuses me.

With the 7M setups, they drop in the bigger injectors and then swap out the stock afm for a lexus afm, and the results are as I described above (instead of resistors, the lexus afm has a different output, which negates the need for any resistors)

The end result is that have to achieve is that you have to trick the ECU into allowing more air flow than it would normally allow. If all you are doing is swapping injectors and then modifying the signal to the injectors, the ECU still sees the same amount of airflow, so I don't know what you would gain :shrug:

 

[ifyouaint1sturlast]

That, confuses me.

With the 7M setups, they drop in the bigger injectors and then swap out the stock afm for a lexus afm, and the results are as I described above (instead of resistors, the lexus afm has a different output, which negates the need for any resistors)

The end result is that have to achieve is that you have to trick the ECU into allowing more air flow than it would normally allow. If all you are doing is swapping injectors and then modifying the signal to the injectors, the ECU still sees the same amount of airflow, so I don't know what you would gain :shrug:

Well, from talking with others about this..

My original thought, which is what I was confused about: You can drop 550s into the Aristo 2JZ without needing to tune. I've ready so many threads and how-to's and nobody has ever mentioned tuning. I was wondering HOW this is possible.

After talking with others: I've concluded that these people were simply misinformed/incorrect. You absolutely need to tune the new mixture and the reason the 550 swap is so popular is not due to "plug and play" ability but just the cheap price tag and easy upgrade ability (same rail, same everything).

Thanks!

 

[destrux]

Yes those people were misinformed.

You most definetely don't put the resistors in the map wiring.

The 440 injectors are high impedance and the 550 are low impedance. You need to add a ceramic high Watt resistor in each injector power wire so the injectors don't burn out the drivers in the ecu. The 7mgte and usdm 2jzgte have the resistors you need.

The factory Ecu can correct for up to a 20% injector size change. It uses the oxygen sensor to do this. Its not ideal. An afc or programmable ecu works better.

Sent from my Huawei-U8652 using Tapatalk

 

[hvyman]

Ya. If you got high imp side feed 550 they would be drop in with no resistor pack. But top feed flows better.

 

[destrux]

Also want to add that the 550's are outside of the 20% correction capability of the stock ECU. You'll throw "rich" codes with them in and the car will run rich.

Guys with the 1JZ have upgraded from their stock 370's to 440's without any piggyback though, since 440's are just barely within what the ECU can correct for. Still not a great idea though if you ask me.

 

[hvyman]

It's always in the tune.

 

[SupraMedical68]

I knew about the 1JZ ECU being able to adjust for the 440 injectors, but didn't know about the 20% correction. How do the AFRs look without a SAFC? Also on topic, the Aristo ECU is able to somewhat compensate for the change in fuel?