VVT-i's questions answered [Archive] - Supraforums.com

: VVT-i's questions answered



carchitect
05-02-2004, 09:54 PM
After seeing how much interest was generated from this (http://www.supraforums.com/forum/showthread.php?s=&threadid=180785) thread I did some research about it.

carchitect
05-02-2004, 09:56 PM
First off there is a significant difference between Honda VTEC and Toyota VVT-i.

VTEC works by having an additional rocker arm per pair of valves. Take your intake valves for instance. On a four valve per cylinder combustion chamber the intake valves and exhaust valves are side by side respectively but not collectively. On most engines the cam journal also resides between the pair of valves for support for the cam and is the bearing surface for it. Honda relocated the cam journal to reside between the cylinders. They also made the rocker arms mounted on a shaft. That ways the three rocker arms will function as designed. On normal operation the left and right valves follow their own cam lobe. The cams are also designed so that one of the intake lobes opens more than the other and the same goes for the exhaust lobe diagonally across from that intake valve. This helps promote efficient combustion, generating improved low end torque and enhanced fuel economy. When VTEC engages the three rocker arms lock into the high lift cam and instantly engage a large duration, high lift and large overlap cam profile that helps generate significantly greater volume of air flow thru the engine. The operation is simply a single trigger wire from the ECM that under the right conditions gives the signal to an oil solenoid which diverts oil to the rocker arms. Hondas also work on speed density instead of mass air. So they depend on a MAP sensor for the fuel and ignition control instead. During low speed mode there is a fuel and ignition table specifically for that mode. When VTEC engages the high lift cam's fuel and ignition tables are selected. The tables switch back and forth as the ECM switches to and from VTEC operation.

carchitect
05-02-2004, 09:57 PM
Now with that out of the way letís explain how VVT-i works. The principle is simple. It changes the intake camís timing to help enhance low end torque, smooth engine operation and increase fuel economy. The control is done from the ECM by controlling the VVT-i solenoid at the top of the intake cam gearís journal. The solenoid has a valve within it that can send oil to and from one side of the gear to the other. The control is simply done by duty cycle and reversing polarity. With the control of the intake cam via the ECM, there is control of the intake cam for 60 deg of the crankís (30 deg of the cam) revolution on the fly. To help better understand how it works lets see how the simple supraís pulsed trigger sensor inputs work.

The GTE uses a crank mounted trigger with 12 teeth. Divide that with the 360 deg. of rotation and that gives you accurate timing of the crank for every 30 deg. of crank revolution. The GE also uses a crank trigger in the distributor which has 24 teeth but since the cam moves at half the speed of the crank, it also generates the same trigger signal. The GTE uses a single tooth sensor to start the #1 cylinder TDC timing sequence for the ECU to time the fuel and spark delivery. The GE does the same with the one tooth sensor in the distributor. Both engines have crankshaft accuracy for the crank and cam rotation every 30 deg and 15 deg respectively.

The VVT-i uses a 36 minus 2 teeth trigger wheel on the crank. The trigger has its teeth positioned every 10 deg with two teeth missing after the number one cylinderís TDC mark. This gives the ECM signal of revolutions every 10 deg instead of the 30 degs (better control and orchestration). You still need a trigger at the cam to determine proper cam phasing. The cam uses 3 teeth on the intake cam positioned 120 deg around. The timing sequence for the supra starts when the cam trigger sends a pulse. The timing sequence for the VVT-i begins when the cam triggers simultaneously with the two missing teeth on the crank trigger. Since the other two teeth on the cam are positioned 120 deg apart they never pass when the missing teeth on the crank are lined up. Only that one tooth of the three on the cam will pass with the missing teeth on the crank. Once started the ECM always receives signals from the cam and crank. It controls the phasing of the intake cam gear based on a preset map and table in the ECM that the factory engineering has programmed into it. Iíll find out more about when and where the timing is performed sometime in the near future. Not only is this system beneficial in performance by enhancing low end torque and top end power but it helps smooth out idle and enhance drivability for cars with crazy cams. Since the cams use overlap on demand the EGR system can be completely deleted (thatís exactly what Toyota did). In fact the cam control could be set to advance the timing during presence of engine knock to cause EGR effect and reduce knock while still maintaining ignition advance without loss of power!

With VVT-i there is a possibility for us to use the same cam for street driving while advancing it enough delivering power all the way to 10K RPMs or higher

carchitect
05-02-2004, 09:58 PM
So why did they only use it on the intake cam?

The principle of most variable cam control is an 80/20 principle. 80% of the increase or benefit is from the intake side and only about 20 percent from the exhaust side. This also means that the extra effort to make dual VVT-i may not be worth it.

So can I control the VVT-i on my supra GTE engine with VVT-i head and HKS Valcon and Vcam controller set?

No not really. The engine on the ECU uses the signals that it is accustomed to. That is the 1 tooth cam and 12 teeth crank triggers. Having the right triggers for the VVT-i Valcon controller to function would simply cause havoc for the ECU to function.

What about the AEM EMS with the Valcon controller for the VVT-i?

The only way I can think that it may be possible would be for someone to take a HKS or any other aluminum adjustable cam gear and install magnets on the cam gear. Install one on the ft of the gear for the camís single tooth trigger. And install 24 magnets on the back side for the crank trigger. Install the VVT-i crank gear for the 36 minus 2 teeth trigger and run that signal and one for the cam to the Valcon controller. That ways you can control the VVT-i independently from the driverís seat.

How are you supposed to tune it? I mean getting the VVT-i dialed in?

Well you are going to have to lock in the cam gear at full retarded and then make your fuel and ignition adjustment. Save that data. Now advance the cam 5 deg from there, make your ignition and fuel adjustments and save that data. Now advance it another 5 deg and readjust. Keep going until you have all your cam angleís fuel and ignition covered. That mean you need to go from -15,-10, 5, 0, +5, +10, +15 deg of the cam angles and get every one of those dialed in. All of this will require a chassis dyno to accurately pin point where your power curve is. Once all the data of torque and power curves is gathered the tuner can then decide which would be the best angles or the VVT-i cam to function and the final fuel and ignition curve can then be set. Since the AEM EMS doesnít have multiple fuel and ignition tables for each cam advance and retard angles this maybe the only way out.

Can the AEM EMS control VVT-i?

There is a possibility that it can however, can it control it like a Motec M600/800 with variable cam control. Probably not. Motec uses a compensation table to not only controls the cam but also to simultaneously control enrichment or removal of fuel and ignition as programmed. A control that requires such accuracy probably shouldnít be left in the hands of an ECU that runs on waste spark . AEM may want to hurry up and release a multiplex ignition expander or make adjustement to the current software/hardware to allow for compatibility of the Motec ignition expander.

The Motec ecus with cam control options are expensive. How else could I control it?

The Motec ecus are cheap ($5000) in comparisons to other ecus that cam also do the same. There are only two other ecus that can control variable cams are Pectel 10S ($25k+) or the Bosch ($40k+).

carchitect
05-02-2004, 10:08 PM
If tuning a VVT-i is so difficult why would you want to?

Better efficiency. Tuning any car is by no means easy. Cars just donít give you the desired results. They give you frustration and aggravation in immeasurable amounts until the payoff begins to show thru. If you could get more power having better control of what you already have rather than increasing the boost and wasting more. Wouldnít you want to?

Joe.

Ishii
05-03-2004, 01:39 AM
Vehicle manufacturers use variable timing and/or duration/lift changes to make the vehicles pass emissions but give more power when they are operating outside the legal parameters.
The only advantages I personally see from a VVT-i engine is that it will be a more streetable engine. For a race car it's just extra weight to me.

Ishii

supra650
05-03-2004, 02:13 AM
good stuff. very well written about the vvti.

Syed Shah
05-03-2004, 02:43 AM
Brilliant Carchitect! Thanks for that, very informative. :)

BLKMGK
05-03-2004, 06:33 AM
VERY informative however the snide remark about AEM's wasted spark technology isn't called for. There's nothing wrong with wasted spark and while I'd love to have additional ignition outputs I think some of the high powered AEM cars have already proven it's not a problem. That they chose this strategy doesn't make the EMS a "lesser" box as you attempted to indicate.

You seem to feel that the VVT-i would need to be infinately variable to be tuned unless I'm reading this wrong. Why not just come up with a profile for the cam, say retarded down low and advanced up top, and stick with it? You could then tune for that using a single mapping pretty easily I'd think. I think you may have been thinking that in there upon reread, it would certainly make life easier.

The catch here is that if you do this I'd have to wonder if perhaps a single profile cam might be able to do the same job? I'm not sure that would be the case but at some point you would have to ask if perhaps a single cam without all the monkey motion might give you 90% of the potential performance with about 95% less trouble.

I wonder if maybe something simpler ala VTEC with a single switched advance position to allow for better breathing past a specific RPM\load\TPS etc. might suit us for instance. Something like that is MUCH easier to tune for, lots of Honda guys have done this with the AEM. I'm not sure how easily that could be setup with our head.

Perhaps an external controller for this head with three positions - retarded, zeroed, and advanced could be used with specific outputs from something like an AEM would simplify things. The main fuel map, the VTEC mapping, and perhaps the nitrous maps could be used together however I'm not sure if the nitrous and VTEC maps interact together not having ever had to use them.

At the rate AEM is going I'd actually expect their box to have controls for variable cams at some point in the future, they're already looking at drive by wire so this has surely also hit their plate somewhere along the line.

Thoughts?

TurboAndrew
05-03-2004, 02:20 PM
All good info. However I would not be so quick to discount the AEM. IMO the 80/20 rule can be applied to control and tuning just as it was in the decision to put vvti on the intake cam. You should not need a seperate compensation trim for fuel/ignition adjustment. First, controlling the timing of the cam by a load/rpm map should be enough -so that for a particular load/rpm, the cam is at a certain fixed phase, the oil solenoid at a specific duty cycle. Based on that, for each load/rpm point, VE would be fixed, negating the need for a compensation map.

Hopefully I'll be diving into this on of Toyota's V8's this summer (AEM included).

BLKMGK
05-03-2004, 03:18 PM
Originally posted by TurboAndrew
All good info. However I would not be so quick to discount the AEM. IMO the 80/20 rule can be applied to control and tuning just as it was in the decision to put vvti on the intake cam. You should not need a seperate compensation trim for fuel/ignition adjustment. First, controlling the timing of the cam by a load/rpm map should be enough -so that for a particular load/rpm, the cam is at a certain fixed phase, the oil solenoid at a specific duty cycle. Based on that, for each load/rpm point, VE would be fixed, negating the need for a compensation map.

Hopefully I'll be diving into this on of Toyota's V8's this summer (AEM included).

Heh, better said than I did - I FULLY agree!

Ishii
05-03-2004, 05:08 PM
I might of missed something in all the long write ups, but there seems to be a missconception between Vtec and VVT-i.

Let me re itterate.

Vtec- (Honda)
is a camshaft that has two normal cam lobes and a third larger cam lobe in the middle that has more lift and duration. Which is operated by locking the rocker arms together.

VVT-i-(Toyota)
Is a on the fly computer controlled adjustable cam gear. Operated by the Controller (gear) and controller valve (the oil control mechanism) VVT-i has a normal camshaft, there is no two seperate lobes.

The third system which is not available on a 2JZ series engine is the VVTL-I system. Which is the best system.

VVTL-i (Toyota)
Is VVT-i with lift and duration control.
How the lift and duration is controlled is much like the Honda Vtec
system, except on the toyota each pair of valves only has two lobes instead of three. The rocker arm (if you want to call it that) uses one cam lobe for the gentle bump on both valves, then when it is time to shake it up the arm locks into its other half and uses the long duration/high lift lobe. It is very similar to Honda's vtec but less weight.

Ishii

carchitect
05-03-2004, 06:24 PM
Originally posted by BLKMGK
VERY informative however the snide remark about AEM's wasted spark technology isn't called for. There's nothing wrong with wasted spark and while I'd love to have additional ignition outputs I think some of the high powered AEM cars have already proven it's not a problem. That they chose this strategy doesn't make the EMS a "lesser" box as you attempted to indicate.

My appologies for my rudeness. Post has been edited.

BLKMGK
05-03-2004, 07:18 PM
Originally posted by carchitect
My appologies for my rudeness. Post has been edited.

Thank you. BTW, I took a look at a doc detailing features for the next beta release. I am not 100% sure I understand some of the new functions since the doc wasn't long on explanations but it appears that some sort of variable cam control is in the firmware. VVC is what the label is and there are multiple parameters controlling it. Obviously I cannot test it and I don't yet have the software in my hands that controls it but this looks hopeful. It appears it may be able to control a solenoid or possibly a set of motors to move a cam. I've asked one of the AEM engineers to comment if they can here so hopefully someone will have some time to comment and can share additional details. This stuff doesn't look specific to the Toyota system so hopefully it could be worked out. If they can nail drive by wire then perhaps the IS300 and whatnot will get tackled along with VVT-i ;)

P.S. I do appreciate the in-depth explanation on how this system works. A few people have been clamoring for information on it and solid info has been pretty sparse.

Ryan23
05-03-2004, 07:45 PM
Just to make it a little clearer for those not too familiar with Toyota's take on Variable timing with the 2JZ.....

VVTI is controlled by one PWM (Pulse Width Modulated) solenoid. Nothing special with the camshaft, it's all done with the intake cam gear, the ECU and two wires.

Ryan

turbo97se
05-04-2004, 12:02 AM
Originally posted by carchitect

What about the AEM EMS with the Valcon controller for the VVT-i?

The only way I can think that it may be possible would be for someone to take a HKS or any other aluminum adjustable cam gear and install magnets on the cam gear. Install one on the ft of the gear for the camís single tooth trigger. And install 24 magnets on the back side for the crank trigger. Install the VVT-i crank gear for the 36 minus 2 teeth trigger and run that signal and one for the cam to the Valcon controller. That ways you can control the VVT-i independently from the driverís seat.



Sounds very complex to me! You don't really need to do this. "Just" set up the triggering in the AEM software for the new triggering schemes for 36-2 and 3 tooth cam. You don't have to stick to old trigger schemes. The beauty of the AEM ems is that it was designed for almost any triggering scheme! The closed loop feedback needed will be an interesting thing to setup from scratch.

This information provided here is also in the service manuals in the DI sections (of all places!) It is nice that someone actually took the trouble of really putting this own on "paper" and with a very nice writeup at that! However, one thing to be careful and check on (maybe carchitect can verify) is that according to the 1998 Supra service manual (DI-224), the Supra 2JZ-GTE (according to the manual) actually has two cam sensors each with a single tooth cam for each (same concept as for the non-VVTi ... which is weird to me). The 2JZ-GE has 1 cam sensor with a 3 tooth cam. I have seen a few errors in the manuals so I have not dared to post things I am not sure of. I can only verify 100% that the description given here holds true for a 2JZ-GE with VVTi but cannot verify this for 2JZ-GTE with VVTi since I don't have the GTE VVTi head... why would they be different ... geez I don't know! The only real way to be sure is to grab the scope!

The drive by wire issue on the IS300? Hmmm, I honestly don't understand this issue at ALL! Mine drives very well without worrying about this too much. The idle is erratic (when warm) since there is no more IAC but the car drives just fine!

Ryan23
05-04-2004, 05:38 AM
Originally posted by turbo97se
Sounds very complex to me! You don't really need to do this. "Just" set up the triggering in the AEM software for the new triggering schemes for 36-2 and 3 tooth cam. You don't have to stick to old trigger schemes. The beauty of the AEM ems is that it was designed for almost any triggering scheme! The closed loop feedback needed will be an interesting thing to setup from scratch.

This information provided here is also in the service manuals in the DI sections (of all places!) It is nice that someone actually took the trouble of really putting this own on "paper" and with a very nice writeup at that! However, one thing to be careful and check on (maybe carchitect can verify) is that according to the 1998 Supra service manual (DI-224), the Supra 2JZ-GTE (according to the manual) actually has two cam sensors each with a single tooth cam for each (same concept as for the non-VVTi ... which is weird to me). The 2JZ-GE has 1 cam sensor with a 3 tooth cam. I have seen a few errors in the manuals so I have not dared to post things I am not sure of. I can only verify 100% that the description given here holds true for a 2JZ-GE with VVTi but cannot verify this for 2JZ-GTE with VVTi since I don't have the GTE VVTi head... why would they be different ... geez I don't know! The only real way to be sure is to grab the scope!

The drive by wire issue on the IS300? Hmmm, I honestly don't understand this issue at ALL! Mine drives very well without worrying about this too much. The idle is erratic (when warm) since there is no more IAC but the car drives just fine!

I guess the real question boils down to how many cam sensors the GTE VVTI motor has? Depending on what EMS you want to operate with, the AEM only uses one cam sensor input anyways. As a side note, the cams are different enough that machining needs to be done to fit the usual HKS GTE intake cam in a VVTI head.

As far as the DBW throttle body goes, I can personally attest that the pre-VVTI throttlebody (with an IAC) fits. You need the "Y" intake pipe from the older motor to make it work. You would need to add a couple small vaccum fittings to the "Y" but it bolts up and is the exact same length as the DBW/Phenolic Spacer/Y-pipe (~25 1/4"). The biggest difference is that the DBW throttle body is around ~55-56mm ID vs. the standard NA throttle body of ~71mm ID. This becomes a limiting factor in Turbo apps. I've seen the dyno of a before and after pull and 90rwhp was realized by swapping out the TB from the diminutive factory one.

Ryan

sw20T
05-04-2004, 06:31 AM
I've seen the dyno of a before and after pull and 90rwhp was realized by swapping out the TB from the diminutive factory one.

off topic but i would really like to see proof of this.

Ryan23
05-04-2004, 06:44 AM
Originally posted by sw20T
off topic but i would really like to see proof of this.


Well, you're in Baltimore, it was Bob's (AKA Parcelpimp) IS300 dyno'd at SRT. I saw the two dyno plots on their dynojet computer. 660 RWHP with a stock T/B, 750rwhp with the larger TB. Haltech and a T76...That's about all the proof I can give you. Don't expect me to make a special trip to Beltsville to print them out, come home, scan them and post them up for some MR2 owner in Baltimore. I could really care less whether you doubt it or not. I have seen dyno plots and talked with the shop owner personally, what concrete proof do YOU have otherwise?

/Back on topic

Ryan

sw20T
05-04-2004, 06:52 AM
Take it easy, whats wrong with asking for proof?
I am incline to belive YOUR story since the car in question had a 76 on it. I just hate to see some kid with a o4e50 think he is getting 90whp out of a TB swap....

Oh, for the record I own a IS300.

aaronyoung

Ryan23
05-04-2004, 06:58 AM
Originally posted by sw20T
Take it easy, whats wrong with asking for proof?
I am incline to belive YOUR story since the car in question had a 76 on it. I just hate to see some kid with a o4e50 think he is getting 90whp out of a TB swap....

Oh, for the record I own a IS300.

aaronyoung

Sorry, didn't mean to come off harsh and for the record, I didn't know it was you Aaron. We're all "Big power ballers" over here on SF...if you are making less than 450rwhp you're a "basic power" kinda guy :p :D

Ryan

BLKMGK
05-04-2004, 07:05 AM
Looked over the AEm document I have again - it's called VVC not VCC. It's possible this function is designed for the tumble valves (?!) in the WRX but could be used for the VVT-i. IT has some interesting things in it like default failure positions and things like that so that if the computer sees something it doesn't like it will default to some static values. <shrug> We'll see.

As to the DBW - the IS300 may have a perfectly working backup cable but that may not always be the case and the AEM is designed to work for more than one platform - they want DBW to WORK. Honestly I don't understand the point of having a working cable AND an electronic throttle. Do the C5 Corvette's, STi, and other DBW vehicles have cables too?

turbo97se
05-04-2004, 07:34 AM
Originally posted by BLKMGK
Looked over the AEm document I have again - it's called VVC not VCC.

Honestly I don't understand the point of having a working cable AND an electronic throttle. Do the C5 Corvette's, STi, and other DBW vehicles have cables too?

Haha! We knew what you meant on VVC! The additional cable is probably for limping home in case there really is an issue. The throttle plate with the cable does not close all the way when you let off the throttle and when you press the pedal, there is no reaction until you push it about 1/2 to 3/4 of the way down if there is a problem ... like power not reaching one part of the ECU. I have seen this before!

carchitect
05-06-2004, 09:24 PM
Originally posted by turbo97se
Haha! We knew what you meant on VVC! The additional cable is probably for limping home in case there really is an issue. The throttle plate with the cable does not close all the way when you let off the throttle and when you press the pedal, there is no reaction until you push it about 1/2 to 3/4 of the way down if there is a problem ... like power not reaching one part of the ECU. I have seen this before!

Its a fail safe system incorporated in the early DBW systems. We call these vehicles Transition DBW. Today all the vehicles aside from the 2JZ engines use full DBW incorporating floor mounted accel. position sensors, deleted IAC, and incorporated cruise and Traction control within the throttle body. The GX 470 uses an 83mm throttle body with a single connector for TPS and motor drive circuit. This can easily be incorporated into the 2JZ with a Motec with DBW option activated.

Ishii, VVTL-i is far from perfect. I'm sorry to inform you that. The way it functions involves taking away lift from the valve and since it always follows the same cam lobe, cam changes would change it down low unless you create new rocker arms to match the cam profile. As far as weight goes, it doesn't incorporate loss motoin assemblies like Honda did with VTEC. The loss motion assemblies use the rise in oil pressure during high RPMs to act like an additional valve spring. They pushed away the VTEC rocker just like another valve spring. This way you wouldn't require having a very stiff valve spring that hammers and prematurely wears away the valve into the seat from excessive spring force. Honda also incorporated something very similar to VVT-i into their engines lately. They call it VTEC-i (intelligent). It incorporates VTEC (cam lift control) with VTC (variable timing control). Since their engines are speed density they use multiple fuel and ignition maps. Standard VTEC engines use 2 fuel and 2 ingnition maps. VTEC engines use 2 fuel and 2 ignition maps every 10 deg of cam advance angle (-25,-15,-5,+5,+15,+25) which makes 24 fuel and ignition maps followed by a final map to control the Cam phasing based on RPM and load (MAP) points for a total of 25 timing maps!!

BMW has a wonderful system (VANOS) which varies the ratio of the rockers. Using the variance of the rockers the lift is controlled independantly and elliminates the usage of throttle bodies (major restriction according to BMW). This technology far surpasses anything else out there.

The whole point of getting a standalone system which incorporates variable cam control system is to be able to tune it better. Running a piggy back controller for the cam and tuning would work until you were to make any changes. Once any change is made the fuel and ignition maps would require readjustment. With a standalone that uses variable cam control, the tuner can adjust the ECU to add or remove fuel and or ignition timing and how much as the cam gets advanced and retarded all from the same box. Once the fuel is nailed down for the base and cam control compensation the vehicle can then be adjusted for ignition and cam phasing to get the power where it is desired. In our case a gain may be found everywhere.

Joe.

carchitect
05-06-2004, 09:42 PM
Toyota has designed the cam phasing based on certain driving conditions:

1: Idle operation

The valve timing is set to the advanced angle 0 (most retarded) and because of the lack of overlap, the idle is stabilized.

2: Medium load range

The valve timing is advanced to increase the amount valve overlap. Thus the internal EGR rate is increased and the pumping loss is decreased resulting in improved fuel economy.

3: Low load range

The valve timing is retarded to decrease the amount of valve overlap, thus ensuring the engine's stability.

4: High load, low to medium speed range

The valve timing is advanced to advance the timing of the closing of the intake valves. The volumetric efficiency is thus improved resulting in improved low to medium speed range torque.

5: High load, high speed range

The valve timing is retarded to retard the timing of the closing of the intake valve resulting in improved volumetric in the high speed range. (Funny, but here is where the torque fall of the graph. I believe keeping it advanced may result in more power)

- Engine started and stopped

When the engine is started and stopped, the valve timing is at the most retarded state.

- Low- temp operation

The valve timing is at the advance angle 0 (most retarded) w/o any overlap. This prevents the fuel from flowing back and minimizes the need for transient increase of fuel. Furthermore, because the idle rpm is stabilized, the fast idle rpm can be lowered more than one with a fixed cam, thus improving fuel economy and drivability during low-temp operation.

The only way we maybe able to figure out the amount of advance and retard would be to either simulate the setup on a bench or place a lot of data sensors everywhere on the engine and gather as much data as possible using a datalogger.

Joe.

danielm
05-18-2004, 02:35 PM
This may sounds stupid, but I am curious... I drive an IS300 with VVTI and I have no idea what the duration on my cams is, what if I was to magically get a 276 degree cam with lets say 9 mm lift and swap it with the stock cam, what effect will that have on the car? Will it make power or? will it brake shit, will it even start?

Also, lets say the head was ported and it would actually have flow at 9mm lift.

carchitect
05-21-2004, 08:22 AM
The problem lies if you were to use a high lift cam on the exhaust side. The VVT-i GE doesn't use any valve reliefs in the piston tops so the increased lift and duration may very well cause valve to piston on an already interferance engine. With a higher lift wou may also get coil bind. The duration may still give you a mild amount of overlap at idle and the engine's ECM may pick misfire at idle and goto limp home mode. For this very reason you should invest into a true standalone.

If you were to run this type of cam I would the head removed and inspected for valve lift from the surface of the cylinder head and compare it to the depth on the valve reliefs to determine if you have contact or not. The valves on these vvt-i GE enignes dont just bend. They snap off and destroy everything from the block to the head.

Joe.

Lex Luthor
05-21-2004, 09:09 AM
Great thread, solid info...but I have to address that last post Joe.
1. There are valve reliefs in the GE pistons.
2. The 2JZ is a non-interference engine.
3. The valves on the vvt-i GE certainly do bend.

- Jon

carchitect
05-21-2004, 03:27 PM
Sorry to argue about this, Jon, but I have seen this in person and have proof of this:

VVT-i GE engines only have valve reliefs in the pistons for the intake valves. Even have a toyota document to prove it.

2JZ non-vvt-i engines are non interferance. All VVT-i engines and the tundra engines except for the FWD V6 vvt-i are interferance.

Due to the nature of the lift on the 2JZ vvt-i GE engines in conjunction to the hardness of the material used for the valves. The exhaust valves will snap off and will lock up the engine on the next revolution and cause significant damage.

Joe.

Lex Luthor
05-25-2004, 12:14 PM
Originally posted by carchitect
VVT-i GE engines only have valve reliefs in the pistons for the intake valves.

Agreed, you said there were no valve reliefs, but we're splitting hairs, we're both right, I was holding one in my hand when I typed that so I knew I was on solid ground.



[i]
Due to the nature of the lift on the 2JZ vvt-i GE engines in conjunction to the hardness of the material used for the valves. The exhaust valves will snap off and will lock up the engine on the next revolution and cause significant damage. [/B]

Got to disagree with you Joe, i've bent enough valves on the vvt-i motor to know....never snapped one, they bend just fine bro, i'll post a pic if you'd like. ;)

- Jon

blue.label
05-16-2006, 05:56 PM
Is there any ways of getting rid of DBW, or is it necessary for VVT-i to function.

mugg
03-17-2009, 09:03 PM
Holy cow ...I feel so dumb !!!!! Awsum Info

87supramario
08-06-2009, 07:28 PM
Very informative, and well thought out aswell. Thx.
Is it possible to transplant a VVT-i system from any JZ to a 7M?