Variable Valve Timing in US
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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-
SLR-
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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!
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!
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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
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
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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-
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-
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
k2
Registered User
Joined: Nov 2002
Posts: 75
From: New England
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
Tom
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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
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
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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
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
@Stoptech
iTrader: (5)
Joined: Nov 2002
Posts: 2,416
From: San Francisco, CA
Car Info: 2002 WRX Wagon
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.
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.
Last edited by Steppin Razor; Nov 26, 2002 at 11:52 PM.
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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.
Registered User
Joined: Nov 2002
Posts: 38
From: Oakland
Car Info: Blue WRX Wagon, Stage II ish, 260 whp
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.
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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.
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