Does anybody find it strange that Subaru is one of the only manufacturers not offering variable valve timing in the United States? Even domestic manufacturers are beginning to offer VVT in their engines. Subaru could easily push some more power out of their current engines if they incorporated something similar to VTEC. It kind of makes our engines seem "dated" compared to other cars out there. Does anybody have insight on why we don't get Subaru's AVCS system like the JDM models do?

PS - I'm not sure exactly where to post something like this on the new board??? So I put it in General

won't the STi come with AVCS when it comes out here? but then i heard that it may/may not come on the car because it would make the car too strong and fast :rolleyes: i think it would help reduce emmisions

Daios (Day-ohhss)

From what I have heard, it is very good for drivabilty but not so good for high performance modded WRX's.

- Alex

Cam phasing is very overated. Especially on FI cars.

personally i believe that the factory turbo cams are the best to use. ( well so does corkey bell).

I must be slipping in my old age, what domestic cars are offering VVT? Anyways, I'll take a nice and simple cam, less parts to break.

/\rcanum

I might be wrong, but doesn't a nice turbo pretty much negate the need for variable valve timing? I remember Honda first developed VTEC as some kinda turbo alternative or something, right? I'm not too sure on either count though, hehe, so someone please enlighten me.

...though I wouldn't hunt one down, I see more benefit in valve control than simply emission control. In lieu of a crank independent implementation ( electric solenoid actuators or some such ), it accurse to me controlling the intake and exhaust allows for better/finner control, i.e. manipulating lobe separation by controlling the centerline of both the intake and exhaust lobe centerlines with less retardation/advance. Because the amount of lift you have and the speed at which the valve moves dictates the torque your engine will produce, I see no detriment to being able to chase profiles, whether intake and exhaust or intake alone . Duration is pinnacle to what the engines basic RPM range will be. Short cams produce power in the lower RPM range, and larger duration cams pull at higher RPM, usually you sacrifice bottom end power to gain top end power as you extend the duration. Supposedly, for each ten degree change in the duration at .050”, the power band moves up or down in RPM range by approximately 500 RPM’s. This being the case ( my numbers with a grain of ~salt ), it seems a Motec and vvt is a great way to tune, particularly if your environment profile changes often; this isn't even getting into how much more beneficial this should be on a car with the high variable cylinder pressure of a turbo engine, as you could basically manipulate profiles to accommodate cranking pressure, or future displacement changes.



SLR-

Cam phasing is there simply to reduce the compromises made in cam selection. But a wild cam for a phased system will have idle problems the same as it would on a standard type system. Cam phasing is all about being able to use wilder cams maximizing the power band and still idling well. On FI cars though, the difference is small because FI cars require less aggressive cams. On FI cars too much overlap equals boost lost out the exhaust valve. So the difference in the actual cam grind standard vs phased will not be much on an FI car. Pick your grind properly, and your set either way.

The Porsche system though, oohhha. Modifys lift and timing. That you could really justify.

k2

the sti wrx has that feature. We will see more of this on most of the Subaru lines to meet EPA's ever rising standard.

I agree. With that said, over the next couple years, I'll prolly do a build up and a jdm gda power plant, 2.2.

k2

The JDM WRX (non-STi) already has AVCS so look for it on the '04 redesigned model.

Let's remember that variable valve timing like VTEC , VVT-i, AVCS doesn't get more power out of a motor.

Rather it keeps a more conservative cam profile in the lower rpm range for driveability and in the process gives less power at lower RPM. This also gives it better fuel efficiency and tends to pollute less.

Before those technology, cam profiles have always been a design compromise between two settings. The STi v4-5-6 cam profile are very aggressive and AVCS doesn't give it anything more.

A WRX AVCS cam profile at its most aggressive is almost identical to a STi v4/5 cam profile. The only thing the AVCS brings to the WRX STi JDM is a smoother idle and cruising, which I don't get on my STi motor, but then again I don't mind as much.

Very helpful, scooby5! Makes good sense; variable valve timing is like frosting on the cake kinda. Thanks.

Good info !!!

That is a very limited impression of how controlling the cam centerline works. It may be true that auto manufacturers vary profile to those ends, however, controlling the profile of the cams is not indicative of "...a more conservative cam profile in the lower rpm range for drivability and in the process gives less power at lower RPM.". It is true that varying valve timing ( outside of new concepts in constant pneumatic and solenoid actuation ) does not bring more power, however, regardless of how the manufacturer implements VVT, the nature of it allows you to tune power any where in the RPM range. It is very limited 'Hondacentric' thinking to assume that it is a low-end trade for top-end HP. Bear in mind that strong ECU replacements like the motec 4/48/800 and pectel offerings allow you to tune control of VVT systems to your own needs, i.e. you could pull all the power down into the low end.



SLR-

SuicidalLabRat, you make a great point. Variable Valve timing CAN be used to get top power out of a motor throughout the RPM range and.

However, variable valve timing as used by the Automotive Industry isn't tuned that way; we all wish it were. I long for the day someone in a design centre sees it your way.

Like you said, there's nothing stopping you from using a Motec or a Pectel or a piggy back system to control the valve timing, in fact, many people in the non-Subaru world do this.

However, if you go to a Toyota/Honda/etc. dealer and ask a rep what Variable Timing does and he answers "Gives you more power" then you know he's lying to you!

Two points

1 - The AVCS helps with mid rpm spoll u in a major way - you would not believe how much

2- I think it would be very hard to rig an aftermarket ecu to run the AVCS because it uses a starnge system to work with a dual sensor set up - one on each cam - and a two way solinoid on each bank

I am waiting for the LINK to come out for the new age sti - but I have been waiting for a long time

if link comes out with it within the next three months i will have to put some sti heads on my car.

scooby5,
You are absolutely right; I guess you are talking real world application, and I, the less finite "what valve timing can do for you" philosophy. Sure am with you on the fantasy of a manufacturer building a more dynamic performance minded control system for these rigs...

Al,
Hmmm, I dont know anything about how Subaru tunes their AVCS system, however, as I said before, the potential gains are far greater for the high variable cylinder pressure systems of a turbo engine than that of a NA car, I assume they are taking advantage of this.



SLR-

Theres no reason why an after market system could not run avcs. Just because no ones done it yet. Many ECUs have the required hardware.

k2

DOes AVCS also change the length of the intake runners like VTEC?

The only vtec plant with variable intake runners is the GSR. And that manifold transition is seperate of the vtec funtion. Plus that's a crappy manifold. I becomes a big compromise when trying to make big hp na.

k2

In Australia they make an EJ25 that has variable valve timing. Does anyone know what system that uses, or anything more about it?

-Wes

I have a Ver. 7 motor and I am waiting for the new Autronic ECU that Shiv is soon to be releasing, which he had told me will have the ability to control AVCS function. But unfortunately the word soon + Shiv = long long wait.... He said previously the release date would be in the fall but I'm hoping for at least around January..
Tom

SLR - The AVCS was so effective that I was unable to use a stock VF series turbo with an internal wastgate becuase the flapper is too small on the VF series turbos to stop the car from having major boost spikes in 4th 5th or 6th gear at about 3,200 rpm - - - this propblem did not happen on the stock WRX set up with evertything else the same

That AVCS gives you a major hit of power about 500 - 700 rpm earlier than with teh stock WRX cams/heads

I can NOT wait to get it back and working

Originally posted by Sloppy Joe
I have a Ver. 7 motor and I am waiting for the new Autronic ECU that Shiv is soon to be releasing, which he had told me will have the ability to control AVCS function. But unfortunately the word soon + Shiv = long long wait.... He said previously the release date would be in the fall but I'm hoping for at least around January..
Tom PS - those autronic guys are soo damm rude they did not even retur my emails asking when its comming out - I give them two thumbs DOWN

I can imagine this variable timing was not included on our motor for a couple of reasons. Cost is certainly one of them, but there are other factors. I would have hoped Subaru would have used variable valve timing to help achieve emissions and mileage goals, but motors tend generally to detonate in the 3000-4000 rpm region where the cylinder pressures are highest and variable valve timing does no really help this problem. It is very tricky to produce highest possible torque at low rpm with our 91/93 octane. This fact is perhaps overshadowed by the EPA nitrous oxide output limits at full throttle and the need to keep the car out of low rpm boost so that it can run the EPA mileage cycle with minimum fuel consumption. These regulations are an ugly fact of life for US specification engine designers these days. Subaru engineers reasoned, and In all honesty, what was there to gain by adding expensive technical wizardry if it cannot be exploited on 91/93 octane gas available world wide? (For the record, the European 95 RON standard is roughly 92-93 US octane these days, although they also have a "97" octane super)

Flagrantly plagiarized from SPD Tuning.
There is a wealth of information at that site. Whether or not you subscribe to Mike's tuning (commonly known as tunning or even tonning) philosophy is another story. Not many people do.

that's some badass info. like most of you are saying, not a whole lot of difference. If you look at SPT's website ( I know nobody likes them I'm, w/ you), they factor in lack of octane in american gas not justifying vvt. doesn't sound to me like that makes a whole hell of a lot of difference, but that's what they say.

I'm sure you can get more power with VVT.

The Subaru STi literature states that the valve timing is set to allow a "scavenging effect" at higher rpms. That means that both the intake and exhaust valves are open at the same time.

I doubt that you could idle with the same overlap. So you can't get this overlap without VVT. So VVT gives you more power.

100

OUT

Of course you can get that kind of overlap without VVT. Profile your cams for it; You can tune the exhaust ( read back preasure and sonics ) and timing/AF to distribute power under the curve. I think the points being made regarding the fallacy in the magic world of "VVT adds power", is that, at this point, it is a miss conception, fundamentally. The addition of power linearly and the ability to migrate the band are semi overlaping, I believe this to be the reason this subject is always a source of debate.



SLR-

I have dyno verified with an A / B test that the AVCS does not add any power what so ever after 6,000 rpm

Your stock WRX cams will yield the same HP on the top end

Somehow - it does add a significant amount of spool up in the mid range which makes it a very useful addition

The idel seems uneffected with AVCS on or off

Originally posted by Alfriedesq
PS - those autronic guys are soo damm rude they did not even retur my emails asking when its comming out - I give them two thumbs DOWN

They may not answer emails but they make a helluva computer ;) However, we've been actively involved with their efforst. In fact, we finally received the first pre-production WRX Plug-in unit for in-house evaluation late last week. It came with the new Windows software too. I believe it is the only unit in the US right now. We're going to be giving it a thorough shake down for the next few weeks. If all goes good, the producting unit shouldn't be very far behind. No dates yet though so don't shoot the messenger.

Cheers,
shiv

Originally posted by Vishnu
They may not answer emails but they make a helluva computer ;) However, we've been actively involved with their efforst. In fact, we finally received the first pre-production WRX Plug-in unit for in-house evaluation late last week. It came with the new Windows software too. I believe it is the only unit in the US right now. We're going to be giving it a thorough shake down for the next few weeks. If all goes good, the producting unit shouldn't be very far behind. No dates yet though so don't shoot the messenger.

Cheers,
shiv
Good to hear. This update of sorts gives the people who are awaiting the release of the ECU something to chew on. What about AVCS testing ? I'm sure you could find someone who has a ver. 7 motor willing to help out... Anyways good luck and hurry up !!!!!
Thanks Shiv.
Tom..

Heh,

I guess the STi will have variable valve timing, eh? :)

Is the cam timing changed through an ECU controlled solenoid? If so, anyone know from the existing Japanese versions, what affects cam timing? Is it solely RPM related, or is it also load or boost or something else related too?

Joel

Originally posted by Joel Gat
Heh,

I guess the STi will have variable valve timing, eh? :)

Joel

Yup. As well as the DCCD, 6MT, and 300HP, 300 ft/lb 2.5 turbo. This comes with EVO-slaying standard. :D

Originally posted by Joel Gat
Heh,

I guess the STi will have variable valve timing, eh? :)

Is the cam timing changed through an ECU controlled solenoid? If so, anyone know from the existing Japanese versions, what affects cam timing? Is it solely RPM related, or is it also load or boost or something else related too?

Joel
well, unfortunately I don't know about Subaru's way of doing it, .... bfwiw, Honda's VTEC also takes oil pressure into play.
Ever try to set the VTEC crossover point at say, 3500rpm?? hehe It's doesn't like that too much! :eek: :p :D

Sean