I'd like to know why everybody seems to think that MIVEC and AVCS need to be compared to VTEC. The technologies are completely different and attain different results through different means. MIVEC is MIVEC, it isn't a poor anybody's anything.

I will admit, I haven't fully investigated MIVEC yet, so I'll go over this conceptually. Performance-wise, it is all positive. Varying the timing on the intake, exhaust, or both cams has the affect of shifting, widening, or narrowing the powerband. It is similar to having adjustable timing gears on the car, except now they aren't statically set in any one position. The difference could be in implementation. Some Subarus have AVCS on just the intake cams, some have it on both the intake and exhaust cams. Some motors benefit from adjusting (either advancing or retarding) the intake cam, some motors benefit from adjusting the exhaust cam, some motors benefit from both being adjusted; sometimes in the same way and sometimes in opposite ways. What I am getting at is that adding in electronically variable cam advance/retard has only given even more control to the ECU for optimum performance in economy or power or anything in between. If somebody has acquired access to tuning the maps used by the ECU, then that control is transfered to the tuner and, later, the end-user.

As for actual gains? I'm not privvy to much MIVEC tuning, but Subarus saw ~500rpm decrease in spoolup when enabling AVCS and advancing the intake cam ~20 degrees in the lower rpm. Some of the Subarus have seen increases through advance of the intake cam as far as 50 degrees. Specific cams in specific motors benefit more than others simply due to how far off from the ideal degreeing the cam gears sit normally. Fuel mileage can be attained by advancing the intake cam and providing additional time to burn the fuel provided; this can also be used to increase torque for the same reasons. The gains often diminish as rpms rise so, typically, what is seen is an earlier onset, and sometimes an increase, of torque in the lower rpms. This can have a byproduct of increasing power simply because the engine is able to be tuned for a greater range of efficiency. More torque provides more exhaust gases which, in turn, can provide quicker spoolup and more boost.

Now, why wouldn't you want MIVEC or AVCS? Wieght and complexity. In Subaru's case, the system actuates solenoids via oil pressure. More parts mean more things that can break in a motorsports event. Aftermarket replacement of factory parts also becomes more difficult. In the Subaru market, some people opted for aftermarket, non-AVCS cams, simply because the high-rpm gains far outweight the low-rpm losses necessitated by the lack of the AVCS. As somebody said, if your powerband and transmission are working together, once you are moving you aren't going to see the benefits of any low-rpm gains of the MIVEC or AVCS. In the case of the Evo where the transmission is nice and close, each shift drops the rpms down into the meat of the powerband. As a result, once the Evo 8 is moving and on boil, the missing MIVEC is of no matter. Who are we kidding, though? How many of us bought an Evo for a dedicated track car? Chances are, most all of us could benefit from MIVEC.

This brings us to the next part of the Evo IX: everything else that changed. What may account for any power differences? Could be nothing, as some have reported the exact same results from an Evo 8 compared back to back with an Evo IX. The engines vary and some cars are stronger than others where different tolerances can often have a profound effect. Other possibilities are that of the revised combustion chamber design, revised quench on the pistons, revised cam profile on the new cams, revised turbo (TD05HR-16G6C-10.5T vs TD05HR-16G6-10.5T), or just plan and simple ECU tuning. I'm obviously speculating here since I haven't personally had the new motor apart, but I do know how big of an affect little things cans have. It could be something as insignificant as the revised coolant passages require less fuel to cool the combustion chamber which, then, allows for a leaner, more powerful burn.

-Jon
(apologies for all the Subaru references; I'm a long-time Subaru guy)

 

but if you have infinitely variable or at least very incrementally variable valve timing then you can also shorten duration... in a direct way too. a vtec second lobe profile is something like cracking an egg with a sledgehammer... you can do it but why? it's an excuse to NOT have a base high lift cam (which is fine for cute emossions, but once again, why?). there's nothing wrong wtih a nice strong high lift set of cams on a very very variable valve timing system. the added second cam lobe profile is just.... i mean it's just there...

the other thing is... with variable lift... when are you ever gonna see a cam made for variable lift cars? they usually just take that out cuz it's too clumsy to produce. and when the options do come around... do you keep the low end part of the cam stockish... more aggressive... might as well just throw in a race cam. be done wtih it. until they can make an infinitely variable lift cam like ferrari affordable... i will maintain that it's a sandbagging complication taht i'd rather not deal with.

 

Not with any system like MiVEC (on the IX) or VANOS; no matter how precise the control, the mechanism will not support variable duration.

All the IX's MiVEC system does is move the IVO and IVC times relative to the crankshaft. It cannot in any way alter the duration of the camshaft because it cannot alter the time between IVO and IVC. Not by a long shot.

The big advantage of variable lift has more to do with fuel economy than power. You can get best torque/horsepower for all RPM/load conditions with a variable duration/timing cam system which uses only one lift- high lift. But high lift places a minimum duration which is based on valve-train inertia- the valves can only open and shut so quickly without floating, so you have a minimum duration to reach full lift and close again. Variable lift solves that problem and allows you to reduce manifold vacuum under cruising by reducing VE, which reduces pumping losses dramatically. (Lower BSFC)

-Adrian

 

So does this mean the turbo is responsible for 95% of the power increase?

 

Doesn't the IX have a revised head design also? Something significant changed about it.

Also, I can't remember where I saw it, but a little blurb about the IX mentioned that MIVEC was added mainly to help emissions, as 2006 was a milestone in Japan for requirements.

 

yes the head has revised cooling passages and revised pistons

 

From what i have seen from BR 20g-9 upgrades on VIII's it's the turbo..

 

It was revised to fit the oil passages for the MIVEC cam. The IX also has 10% reduction in oil usage, my Evo uses less then 1/2 a quart per 5,000 miles with 63,000 miles so I am good.

 

oops!

 

I'm still curious to see whether at some point Mivec will become a handicap for the Evo 9. I was so gunho about trading in my 8 for the 9 but threads like this make me hesitant.

 

handicap? why would it ever become a handicap?

 

Reliability, it may not work well with time. But this is purely speculation.

 

One thing I'm concerned about with Mivec is... how well will it or not work when coupled with standalones, drag turbo's, stroker kits, and high duration cams. Basically what kind of nightmare or blessing will it be once people start building all out race cars out of Evo 9's.

 

MIVEC simply adjusts the intake cam the same as an adjustable cam gears would only on the fly and infinitely variable? If that is the case then all it does is shift the power band around by changing how long the intake side is open compared to the exhaust side. KINDA like how the early 1G DSM's did with those awful Cyclone intakes with variable intake length runners. I know that cams and intake manifolds are apples and bowling ***** but the end results were the same, better lowend and increased spool up. The Cyclone intake really didn’t work although the MIVEC certainly did.





AS far as a POWER gain, I believe it is 90% the turbo, it has to be. Increased efficiency cooler air. More low end power is caused by the MIVEC for sure so there is your 10%.

 

So basically the Mivec will not become an issue and mod for mod a Mivec motor should be better than a non-Mivec?