[KingCobra]

I know we all hear the rumor that the JZZ30 ECU (Soarer) is supposedly more aggressive. I just ordered a JZX90 ECU for my Cressida, because it will fit in the glove box much better than the JZZ30 ECU will because of the plug locations on the box. (My Cressida has a JZZ30 Soarer set).

So my JZX90 A/T ECU arrived today, so I installed it and took it for a test drive. I noticed that the shift points are more aggressive with this JZX box than the JZZ box, which is understandable. The thing that suprized me was that my maxium boost was only 8psi. So I was like WTF?

So I pull off the side of the road, switch back to the JZZ30 ECU, and test again. Now I am back to building 10psi max. Now I am really wondering if I am reading the boost gauge right, so I pull off the road again, put the JZX ECU back in, test drive again, and only 8psi. (I am currently running NO boost controller BTW).

So based on just my boost readings, there is about a 20hp (2psi) difference between the JZZ30 and the JZX90 ECU (with the factory hardware, no boost controller)... but what I don't understand, and no one has been able to explain to me why my boost is being effected just by changing out ECU's? I mean aren't the wastegates vaccum controlled? Or does the ECU have some way of controlling the vaccum on these engines that hasn't been documented yet?

I mean yes I know I can (and I plan to) install a boost controller in the next week or so, but I'd like to understand WHY there is a boost difference between the 2 computers... Anyone have any ideas or wisdom they'd like to share with me?

Thanks!

 

[Jeff Lange]

Most likely different ignition maps or something. Someone else may have more info on the inner workings of the JZ ECU

 

[KingCobra]

Another thought that just occured to me...

If we stop and think about the stock configuration of each of these cars (Chaser/Supra/Soarer)... and Japan's gentlemans agreement of 280hp maximum, maybe the ECU is tuned for the configuration of the car it is going in so that it's 280hp for each car?

Case in point, the Soarer uses a clutch driven radiator fan which puts drag on the engine, so maybe the mapping of the engine ignition or something is compensating for this clutch fan where the Chaser and Supra have Hydrofans and therefore don't have that drag on the engine? This would be within the 5-10% hp drag you typically get with a clutch and explain the 20hp difference if this is the case.

This is a guess of mine of course but it would make sense to me if this is the case, but I'd prefer if someone with more knowledge than me confirmed my theory.

 

[tissimo]

did you notice any power difference even though the boost difference.. ignition and fuel maps could be different causing different boost..

I know Vj RC51 or whatever said his tranny slipped with a chaser ecu (jzx90 iirc?) ??

 

[VJ RC51]

JZX90 ecu i had. Yeah, now that i know more about how the automatic transmission works due to a big crash course in tranny electronics for the SSV4.

I honestly dunno how the chaser ECU made my tranny slip between 4-4500rpms. All the ECU does is control two selonoids and the lockup selonoid. Its a combo of the voltages depends what gear your in beween SL1 and SL2.
1st gear: SL1 12v, SL2 0v
2nd gear: SL1 12v, SL2 12v
3rd gear: SL1 0v, SL2 12v
4th gear: SL1 0v, SL2 0v.

The ECU does not control line pressure or anything! Its either in gear, out of gear, and TC lock on or off. At WOT, the TC is usually always unlocked til 4th. There is no explanation why it would cause it to slip between 4-4500rpms in any gear. Hell, you could manually control the auto with three $1 switches!!!

So throw my tranny slipping into the pot of weird things that a JZX ecu does on a JZZ car that have NO explaination to how its possible.

The boost thing, we talked about that in AIM. On the JZZ, the boost is controlled directly from the port on the turbo, to a 6in line to the wastegate. The stock CT12a's are more then capable of going past 25psi without control. Even detuned ignition and fuel, two spark plugs removed, 100% humidity, and at 3,000ft above sea level, they should easily do 10psi.

Altho, nothing a $12 grainger mbc fixes

 

[KingCobra]

did you notice any power difference even though the boost difference.. ignition and fuel maps could be different causing different boost..

I know Vj RC51 or whatever said his tranny slipped with a chaser ecu (jzx90 iirc?) ??

It's hard to tell with the different shifting patterns whether one is actually putting down more power than the other. Boost is one thing that was different (because I have a boost gauge). Other factors like hp, a/f ratio, ig timing, etc I have no way to measure while in the car.

Perhaps letting a passenger ride along for the test session might feel/sense more, or perhaps this is a good reason to put the car on a dyno... 2lbls of boost in theory means about 20hp difference, but that doesn't mean that's what's actually happening (in regards to igt timing, other data, etc).