VVT Retrofit Considerations

[Hurmeez]

So after doing myself a mischief on my bike a week before Christmas, I've been laid up for a few weeks unable to do any meaningful work. Instead, I've been reading old threads and day dreaming a bit. 

VVT is very alluring. When it comes to NA optimisation, it looks very valuable in terms of getting the most out of otherwise an otherwise limited platform. 

For better or worse, I decided years ago to put a Mazda V6 in my Escort. Based on Yoeddynz's Viva thread, and excellent exhaust sound videos on YouTube, it looked like a fantastic option. Of course in the seven years since then, the engines have become increasingly scarce at Zebra, and technologically even more dated. That, combined with limited aftermarket support, means if I want to get more out of it than stock, I'm going to have to do a lot of custom stuff, and ideally with low risk to the engine. I've only got one spare block and I haven't seen one at the wreckers in years. 

So far the plan is to follow the fairly standard formula of better intake (ITBs) and exhaust (custom headers), but beyond that I'm pretty limited. No one really makes cams, so if I want to keep it NA (which I do for now) that's pretty much it. I could skim the heads to try and bump compression a bit, but that would lead to timing troubles as well. 

Which after a bit of waffling brings me to the actual point. I'm wondering if it's worth looking into retro fitting VVT. As standard, the timing belt drives the intake cam, which in turn drives the exhaust via a fixed gear. So the options in order of effort would be as below:

1. Modify the intake pulley to fit a vernia cam gear. No one sells them so I'd have to make my own. 

2. Modify the intake and crank drive pulleys to fit a VVT version from a different engine. I'm thinking JZ or 4AGE or something. 

3. Modify intake and crank drive pulleys, as well as decoupling the exhaust cam and fitting a dedicated pulley for that side too. 

If I were to skim the head, I'd probably have to at least fit a vernia gear to the intake to correct for the shorter belt run. Options 1 and 2 of course would mean both cams are still tied together. I'm not sure what the performance implications of that would be. Option 3 comes with much greater effort, including but not limited to making an adapter to poke the exhaust cam drive out through the head, swapping to smaller cam pulleys to allow clearance, finding a longer drive belt, etc etc. 

Granted, this is all hypothetical and mostly a thought exercise, but I wonder how useful it actually would be. Given stock cams, would it actually make any noticeable difference? I'm probably still years away from turning the key, and for all I know it'll be plenty grunty for my driving abilities as standard without further modifications. Regardless, it'd be fun as an engineering exercise either way, but I'm interested in wider opinions. 

Of course the real answer is probably ditch the dated engine and fit a 1NZ like God intended, but I'm a firm believer in the sunk cost philosophy so let's pontificate based on the V6 for now. 

[GregT]

VVT was introduced to fill in dips in the power curve caused by longer duration/bigger lift cams. I see no gain at all with stock cams.

/My opinion.

[Hurmeez]

Fair point. It's obvious in hindsight but of course the OEM would optimise the cam profile for the drive system's abilities and visa versa

[ajg193]

@kpr and @Roman would be the guys with brains  to pick.

 

 

[kpr]

Feeding the oil to the vvt/i  pulley  from the solenoid  is probably the biggest hurdle.  adapting pulleys to a vvti pulley is a decent amount of work, depending what parts you can find that play happy with each other, but not a huge deal if you can machine stuff.    If running vvti  you will need cam position sensors and trigger wheels on the cams themselves .  if running a basic vvt system these arent required. 

Personally  i probably wouldn't attempt it on your engine configuration.  having the exhaust cam driven off the intake just adds to the above.  making an engine swap a whole lot easier  job even if you are attached to you current setup. 

Also as above.  if the stock cams are quite small  wont be a big amount to gain.   if can combine  with bigger cams it allows for gains while retaining a nice running engine

for example this is my 4age with little stock cams and vvti.   only small gains to be had

fixed timing  vs vvti

 

same  engine with  284/278  cams 

 

 

[Hurmeez]

Regarding needing cam position sensors, would it not be a good idea to do that anyway to allow sequential injection/ignition? Or is sequential more of a discrete position requirement per cycle rather than a continuous reading needed for position control? 

[kpr]

There are a couple ways to do it.      Jz engines run a missing tooth crank trigger wheel and 3 tooth wheel on the cam with vvti.   this works long as the swing of the vvti doesnt go through the missing gap on crank trigger wheel. so the  2 sensors do both the injection/igntion etc and vvti.     Oher stuff like honda k series  run a trigger wheel on crank and a one the non vvti exhaust cam.  which  does the injection/igntion.   then they have another sensor on the vvti inlet cam,  for the vvti cam position.  so is 3 sensors

i run a 3 sensor setup on mine

 

[Unclejake]

VVT is a genius response to keep low-mid RPM driveability but have a semi screaming engine at higher RPM.

The best fun n/a engines are largely either 1) smooth high tourqe groaners (think MGB C, Jensen Interceptor) or 2) barley driveable screamers (think anything period Lotus).

If you're committed to this Mazda engine consider going old school mods. Balanced rotating assembly (probably already good from factory TBH), light flywheel, high lift and duration cams (Kelford or the likes will make you a pair) and fluff around a bit with your intake and exhaust tracts.

Barely driveable can be fun.... and then you only need to add a chrome Ramflo air filter to become a legend

[Roman]

Possibly incredibly hypocritical of me to say this. 
But just stick to the main plan to get the motor running first.
Projects like this are good for a spare motor on the side, then swap the whole thing in. But need to treat it as disposable as it's risky.

If you've not even driven it yet, you might be surprised that the powerband is how you'd expect it to be if it had VVT anyway. 
Since its a V6 in a fairly light car. 
Surely there are big cams or regrinds available for these? 
Standard cams (and then possibly valve springs) are likely going to be the bottleneck that will make or break the car making power. VVT or otherwise. 
It will be heaps of fun dialling in the fixed timing engine and getting it running.

[yoeddynz]

I'd be keeping it simple too and just enjoy getting it on the road. It's pretty impressive how fast a lightweight car (like my viva which was around 1 ton iirc) can feel with circa 200bhp the KLZE engines put out. Get your itbs and exhaust sorted and you may well be looking at a bit more.

I'll just put this video here. I imagine he's running some high compression and it has itbs etc but certainly no variable valve timing or other alien magic   Just pretty oldschool tuning on a fantastic base engine design.

 

[yoeddynz]

Oh and there are other cams available. I was going to get some. I can't remember who/what brand but it was via the mx6 forums I'd found them.

 

[Hurmeez]

12 minutes ago, yoeddynz said:

I'll just put this video here. I imagine he's running some high compression and it has itbs etc but certainly no variable valve timing or other alien magic   Just pretty oldschool tuning on a fantastic base engine design.

 

I'm sure the sweet backing track played a not insignificant part in the ET as well. 

10 minutes ago, yoeddynz said:

Oh and there are other cams available. I was going to get some. I can't remember who/what brand but it was via the mx6 forums I'd found them.

 

Yeah allegedly Colt used to do regrinds, though that looks like another example of coming to the K engine party a decade or two late. I've since found a site called CatCams that offers off the shelf billet cams as well, though the way they've displayed their specs is somewhat confusing. Likely an issue in understanding on my end there but. A cousin that happened to build a K engine a year or two back reckons Kelford might have existing regrind profiles too which would be far more convenient, so I've sent them an enquiry in the meantime. 

Beyond that I suspect you're right, getting the car moving under its own steam should be the first priority and there's a good chance I'm happy with the performance as is. 

[fuel]

11 hours ago, GregT said:

VVT was introduced to fill in dips in the power curve caused by longer duration/bigger lift cams. I see no gain at all with stock cams.

/My opinion.

are you confusing VVT with variable valve lift such as early VTEC, MIVEC etc? Variable Valve Timing is very much useful even with stock cams - there's a reason why just about every engine since the 2000's uses VVT. Static timing is always going to be some kind of compromise - having VVT allows the cams to be advanced and retarded to the ideal values depending on actual conditions such as load, grade of fuel used etc. Every engine with VVT gets a better broader power band with increase in fuel efficiency and reduction of emissions over the same engine without VVT. 

[GregT]

Plenty of argument for and against. As an engine builder/tuner specialising over the years in matching cam lobe centers to the application I see your point. But I'd still argue that there's little point in grafting it onto an engine optimised for standard cams. Too much work for too little return IMO.

My personal opinion is that too much time,money and complexity has been spent trying to make the ICE drive like an electric motor.

I like some character in what I drive or ride.

[GregT]

43 minutes ago, Hurmeez said:

I'm sure the sweet backing track played a not insignificant part in the ET as well. 

Yeah allegedly Colt used to do regrinds, though that looks like another example of coming to the K engine party a decade or two late. I've since found a site called CatCams that offers off the shelf billet cams as well, though the way they've displayed their specs is somewhat confusing. Likely an issue in understanding on my end there but. A cousin that happened to build a K engine a year or two back reckons Kelford might have existing regrind profiles too which would be far more convenient, so I've sent them an enquiry in the meantime. 

Beyond that I suspect you're right, getting the car moving under its own steam should be the first priority and there's a good chance I'm happy with the performance as is. 

Kelford have an enormous profile library. i used to go into it frequently. Staff turnover has meant some knowledge has been lost.

Phil/Gumby now gone used to immediately say -yeah,we did this for so and so- and have the results too.

[RUNAMUCK]

I bought some CA18 parts of @bean.101. He kept a timing cover whuch had been modified for a VVT pulley. 

unfortunately when i collected the parts from his work, he was home with a sick kid. 

[yoeddynz]

11 hours ago, Hurmeez said:

I'm sure the sweet backing track played a not insignificant part in the ET as well. 

I play the exact same music whenever I'm out racing the gringo tourists in their Tiidas here.