VVTi Heads Question

[rarson]

I am curious to know whether or not you can modify the VVTi heads to take regular 1UZ cams. Since there isn't anyone making VVTi cams, and it would be somewhat more trouble controlling VVTi with a standalone, I figure the easiest thing to do is to get rid of it. Is this possible?

 

[turboandrew]

The scissor gears are in a different part of the cam, so I don't think you could swap them out. You probably can't get new cast cams, but I am sure you can get the originals welded/regrinnds. That's what I plan on doing eventually. You can also simply not use the vvti function if you want, but I hope to make use of it with the AEM EMS.

 

[rarson]

Good call, I didn't even think about that. Thanks.

 

[rarson]

Do'oh! I was thinking VVTi was like V-TEC with separate lobes. It's obviously not. So all VVTi does is change the cam timing on the fly? On the 3UZ, the system is a sudden switch, right? Not a gradual advance in timing. Is this only on the intake cam or the exhaust cam too?

I really like the idea of being able to retard the intake cam at low rpms.

EDIT: Grrr... I need to keep reading more before I post. I see now that the "i" part annotates the ability to vary cam timing anywhere between the two extremes. And it seems to me that this is only for the intake cam, thus basically just controlling the amount of overlap.

 

[rarson]

Okay, I've been looking at a few pictures, and the only difference I can find with the VVTi cam is the oil gallery in the #1 cam journal. Call me stupid but this looks pretty damn easy to replicate, as long as care is taken. On the 2g Eclipse, the cam angle sensor was on the end of the intake cam, which required aftermarket cams to be drilled and tapped. This was very precise, but very common thing. This looks like the same process with an extra step.

Are the exhaust cams even different at all? It looks to me like we can use 1UZ performance cams with a little modification of the intake cam.

 

[turboandrew]

Assuming that scissor gear can be move to the right place, possibly. I have not looked at both cam types close enough to compare them.

 

[rarson]

Ah. I'm not thinking again. I forgot about the scissor gear. Okay, so the best option is definitely to regrind the stock cams and keep the VVTi. Can we use a stepper motor and use a PWM output to control it? The AEM has a PWM output, right?

I won't be using the AEM, but hopefully I can create something similar to the stepper motor idea... probably voltage based off rpms.

 

[turboandrew]

Stepper motor, sort of. You just need to pwm the actuator already on there. There are two of them, one per bank. The problem is x pwm != y cam advance. The variable phase cams gears are adjusted by oil pressure. The actuator controls the oil flow. The amount of oil pressure needed to get Y cam advance will probably vary by engine rpm/accerlation and oil viscosity, so there is no simple table lookup to give you actuator PWM signal for a given cam advance and rpm. This is why there is another cam sensor for each intake cam, and when compared to the cam sensor which does not advance/retard, the ECU can figure what the current cam advance is and adjust the PWM signal to reach the desired cam advance. So, in a nutshell, this is not so easy, but with the right hardware (closed loop control) it is doable. The AEM EMS does have the hardware to do this (extra 2 cam sensors and two spare PWM drivers), but to my knowlege noone has done it yet on the 1UZ. They have done it on other motors like the Hondas which have vtec -and- variable cam timing. I do intend to do this on the 1UZ eventually.

 

[rarson]

So we need two PWM signals (thanks again for filling in the voids that I completely forgot about). We need 4 cam sensor inputs. And we need to take that data and use it to create a table that will control the PWM signal. Is it possible that we can split the same PWM signal to both actuators?

Wait, I don't understand why we need sensors on each bank. Why can't we just use two cam sensor signals? The cams are going to both be advanced the same and should be at the same position on both banks, barring a failure of the timing belt (but if that happens, you've got a lot more problems than that). Is this part of a redundancy system that Toyota used to ensure the engine stays running? I know in the V12 thread, it was mentioned how Toyota designed the engine to be able to run on one bank. That is the only reason I can see for having 4 cam sensors.

If we can use one signal for both banks, then we cut our requirements in half.

Edit: Just to clarify, what I meant was that the cam timing of both banks should be the same, since they're identical. Right?

 

[turboandrew]

I would think just one bank might be ok, but I suppose there could be small variances in PWM needed to have both cams with the exact same advance. So, at a minimum, 2 cam sensors (one static, one measuring advance), and one PWM driver. Best case would be 3 cam sensors (one static, two measureing advance) and two PWM drivers.

I have seen redundant (static) cam sensors, in my case the 2JZ. I don't think the 1/2/3UZ has them. Having two alows the ECU to sync up the timing pattern faster, which means fatser starts, and also obviously you have some redundancy.

Also, you might want to search for HKS valcon, which apparantly can control some vvti cams, but I am not sure they have it for the 1UZ.