1JZ AFRs

MadRPM

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Hey guys,

which 'bank' runs leaner from factory, cyl 1-3 or cyl 4-6? Let me know if your data comes from a VVT or non VVT 1JZ.

Thanks!
 

hvyman

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That would require dual wideband a which I haven't seen or egt setup on each runner which usually if that is done each cylinder has been tuned to where they wanted.

Is there a specific reason to which you are curious?
 

Radial

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Aug 20, 2011
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As a rule of thumb: All intakes with front mounted TB like the JZ-GTE engines have one common tendency:
The rearmost cylinders run leaner than the front ones.

Its a very minor difference, and especially in boost, but needs to be taken in to consideration when you have extreme power. Especially on the stock JZ intake. (You need 1x EGT on each cylinder, and full sequentual injection to be able to correct for lean conditions).

Its a logic in this ;
Even though air is pressurized,the direction of flow in to the intake is towards the rear of the plenum, the air needs to change direction almost 120 degrees to reach runner no1.

At runner no 6 on the other hand, the air meets the end of the plenum and direction of flow has almost stopped. Air only needs to change direction less than 90 degrees which is good for airflow.
Thats why the rearmost cylinders will usually receive more air, and have a tendency to run leaner.


But, as mentioned...it's easily compensated for with egt on each cylinder and full sequential injection on such applications.
 

MadRPM

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hvyman,
I'm in the market for a 1JZ and I had the idea of running a 2.5" DP going to a 3" exhaust for each turbo meaning I would need to 2 WB sensors. I wanted to know which bank is leanest so I can plumb the wideband in it. The AFR difference will be minor (as pointed out by Radial) since Toyota already balanced everything out but I wanted to confirm my hypothesis that 'bank' 4-6 will be leaner than 'bank' 1-3.

Radial,
I looked at the picture of a 1JZ IM and it seems like the flow characteristics of cyl 1 & 6, 2 & 5 and 3 & 4 will mirror each other. I'm not refuting what you said, just looking at from a different angle.

I feel like it won't make a difference whether the WB gets plumbed in bank 1-3 or 4-6.

The exhaust idea is still in the air as I don't if there will be enough space to run a pair of 2.5" DP. I also understand that the wastegate outlet of the turbos will have to be ported to regulate boost and a stronger actuator might be needed.
 

hvyman

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Im not sure if it is possible with stock twins as there might not be enough room.

But if you were to have 2 twins facing forward you could run 2 dp easily. I know there is a couple twin tubular manifolds out there and could eaily run like a gt28rs off sr20 with custom lines and such.
 

MadRPM

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I was thinking of a design similar to the aftermarket y-pipe: Instead of having the DP's merge into 1, I'd get the DP's angled so they clear each other. It will be a challenge but I hope I can physically make it happen.

The forward facing twins will happen in the future. A fat single is sexy but twins tickle my fancy more.
 

Radial

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Here is a picture of a high-flow intake, specially designed to perform well and give all runners the same angle of flow, as well as a more stable pressure through out the manifold.
7M_Intake_Flow_Images2.jpg

Here is a stock intake from the inside (though slightly modified), you can easily see the angle flow angle difference.
2rcpmyu.jpg


This does not come in to play before well up in the 700hp++ area, but then stock twins are scrapped a loooong time ago :)
 

MadRPM

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What kind of Mach Number are you trying to reach with the above intake?

I see what you're saying about the factory plenum. Wouldn't be a problem mostly for startup? Here's why I tank so: The plenum (a tank) is pressurize post startup so when the intake valve is closed on cyl 1, there will be a volume of air filling the runner, waiting to get discharged inside the cylinder. That volume will vary on RPM, cam specs, air temp, air purity (dust, oil...). When the volume gets discharged, the amount of air filling the cylinders should be fairly even.

The above is assuming the shape of the tank is uniform throughout its length.

In the above case, I think that the angle makes a difference due to the tapered plenum, thus the increased pressure at cylinder 4, 5 and 6. Try increasing the taper (relative to the plenum's baseplate) to add a bit more volume to the aforementioned cylinders, decrease the taper near cylinder 1 and lengthen the plenum's mouth to see what happens.
 

Radial

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you are asking what cylinders that run "leaner" from factory, and that's the rearmost cylinders.
In almost every JZ-failure related to lean conditions, it's the rearmost cylinders thats affected.

I've searched for a reason, and the explanation I got was the one i mentioned above. It sounded logical to me, when you are pushing a intake to its limits.
 

MadRPM

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Im not arguing with your explanation my man, it makes sense to me too. I just wanted to pick your brain a little.

Thank you for answering my question. :bigthumb: