a friend of mine has a gsr and he was explaining to me that the vtec on his b18 has two engagment points, one at a lower rpm, and another at like 4400. and my si only has one at 5500. i just wanted to know the difference in these set ups, and the performance dfferences. i know his gsr is faster, and im not trying to research his car to make mine faster. i would just like to better understand this theory..

 

GSR VTEC engagement is 4400, secondary butterflies for GSR Intake Manifold open at 5700.

 

Well his VTEC really engages once, but hits harder at the higher RPM. The intake manifold has these butterfly things which open up halfway at like 4400 RPM or so, then at 5700 RPM(I think) it opens up completely getting the most air flow.

Honda did this for midrange power. H22 motors have this as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lazy bum shaughn &raquo;</TD></TR><TR><TD CLASS="quote">Well his VTEC really engages once, but hits harder at the higher RPM. The intake manifold has these butterfly things which open up halfway at like 4400 RPM or so, then at 5700 RPM(I think) it opens up completely getting the most air flow.

Honda did this for midrange power. H22 motors have this as well.</TD></TR></TABLE>
ehh your close
vtec engages at 4400 and the butterflies open at 5700
there is no half open.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Kamin &raquo;</TD></TR><TR><TD CLASS="quote">
ehh your close
vtec engages at 4400 and the butterflies open at 5700
there is no half open.</TD></TR></TABLE>

Can you explain about the butterflies then, I'm not too sure about the process.

 

sure, there are 2 sets of runners on the intake manifold, one is open all the time and they are the primary runners the secondary ones are closed off by the butterflies. at a certan RPM (5700~) the ecu sends a signal telling them to open and they do. its eithre on or off, no halfway.
think of them like a light switch.

 

I'm still confused. So there is a total of eight runners, four are open at a time untill a certain RPM? Sorry, I'm dumb.

 

well if you have looked at the ugly *** GSR intake manifold, there ARE 8 runners after the main collector (where the throttle body is) then another small collector where all 8 runners go into 1 then into the head.

yes 4 are always open (because they cant be closed. like any other engine) and the secondaries have the butterflies (4 metal plates that open and close by rotating. take your intake off and look at the throttle body. when you open it the butterfly opens, its the same principal as in the intake manifold. just 4 of them and smaller)

 

There are still only 4 runners but they are divided into 2 sections in the plenum itself... at low rpm (below ~5700) the entire second rack remain closed not allowing a dense charge of air to flood the cylinders... This produces good low/midrange power which is similar to how VTEC makes power... It is a very simplified version which is done simply with the manifold... I actually hate the stock P72 ECU and IABs... Anyways when the car is started vacuum over the manifold causes them to close down... At their preset point ~5700rpm the ECU outputs a 12vdc signal which then causes the IAB solenoid to open up dumping the vacuum to the butterflies vac activated diaphram... Since they are spring loaded they open right up, just as they are when the motor isn't running... I prefer the stock P72 manifold over say a SK2 but the two downsides to it are the IAB's which you can remove... To me (especially when running R cams) they cause the motor to bog, not to mention that you have to bump up the VTEC ~1000rpm from the stock P72's point of 4400.... The second is it's runner design which is a little on the long side... It is still a good manifold with a lot of potential and is why I like it... Just my $0.02... Hope this helps... Peace
EDIT: Kamin, you just it just right and beat me by a few seconds... hehe, oh well!!!!

 

hey thanks lot for all the feedback, i understand now the GSR vtec system . thanks a lot everyone.