Jump to content
SAU Community

Rb25de Vct Not Active - How Much Power Am I Losing?

clip14

By clip14,
in Engines & Forced Induction

 Share

Recommended Posts

Sandeep Community Regular

Sandeep

Posted
Posted

vct affects your midrange torque and power more than peak (high rpm) power. not 100% sure on the rb series, but on the vg and vh engines it is only on until around 5000-6000rpm, then it switches off.

from what i understand, the idea is to increase valve overlap at low/medium rpm (not at idle though) to help suck in the in intake air/fuel mix and blow out the remaining exhaust gases. however at high rpm the pressure in the exhaust manifold may be high enough that some of the exhaust gas will actually be pushed back into the intake due to the bottleneck in the exhaust manifold... this would cause a decrease in power and increases your cylinder temps. so to avoid this they switch off vct at higher rpm's.

basically with vct disabled, there will be very little (if any) difference in your peak power compared to if you had working vct. your torque curve however will drop away after the peak torque, whereas with vct it will be abit flatter towards high rpm and your midrange power would be reduced.

Link to comment
Share on other sites
clip14 Rising Star

clip14

Posted
  • Author
Posted

my vct isnt working because I'm running a r32 loom and ecu.

I know the peak power is the same as vct is turned off in the higher rev range. was just wondering if anyone had some dyno plots so i could see the midrange difference.

Link to comment
Share on other sites
Eug Grand Master

Eug

Posted
Posted

i know the RB30 guys had a couple of dyno graphs in the forced induction thread with and without VCT. not a 100% sure exactly, but the difference was something like 10-15kw over a 1000-2000rpm range.

i don't know how applicable that would be over to an NA RB25, but i would say probably about the same taking compression into consideration????

Link to comment
Share on other sites
MissR34 Grand Master

MissR34

Posted
Posted
my vct isnt working because I'm running a r32 loom and ecu.

I know the peak power is the same as vct is turned off in the higher rev range. was just wondering if anyone had some dyno plots so i could see the midrange difference.

why are you running a 32 loom and ecu? did u do a engine swap?

Link to comment
Share on other sites
LUME Enthusiast

LUME

Posted
Posted (edited)

when did the vct's start getting used? what model onwards with the skylines?im not trying to hack the thread but my 33 is extremly gutless low and mid nothing starts happening until 5500 rpm?

its a s1 1993 r33 btw

Edited by LUME
Link to comment
Share on other sites
LUME Enthusiast

LUME

Posted
Posted (edited)

or better yet a picture of vct?, and my car isnt running on tps its running on map does it make any difference?

Edited by LUME
Link to comment
Share on other sites
G0DZLR Mentor

G0DZLR

Posted
Posted

VCT got bought in with the S1 R33s and from thereonwards was standard. easy way to tell whether or not it has VCT is whether it has a buldge on the lefthand side of your timing belt cover.

the only RB25DEs without VCT were the ones from the R32s, VL owners usually use them on RB30DE builds as they dont have to modify the block as much.

Luke, i had the same problem that your having. just launch it at about 4-5k RPM and you should be alright if youv got grippy tires, cos thats where the torque band is. i gained heaps of bottom end go when i turboed mine, cos of the high-comp motor.

Link to comment
Share on other sites
LUME Enthusiast

LUME

Posted
Posted

LOL yeah thts what i normally do(or limiter love) well what can you expect for something flat out pushing over 100kw out of a 2.5 so lack of torque much??

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • TurboTapin
      R32 GTST - 600KW+ RB28/CD009 Build

      By TurboTapin · Posted

      So I've been working on the car a fair bit, doing a lot of little things. Preparing some projects for this winter, as I'm taking 13 weeks off very soon for parental leave. Have my second kid on the way and he's due any week now. I'll need something to do while he's sleeping. I also usually take the car off the road in about a month and a half, until sometime around the end of March.  Still making slight adjustments to my tune, as the cold weather settles in. I've also had to start dropping boost and tire pressure as the weather gets cooler. It's getting very swirly at highway speeds. I drop to 20psi at 20C and 18psi spring pressure at 10C IAT's. I'm currently on 255 Falcon RT660's, but may look into running 275's next summer. They will fit, but barely. Might have to raise the rear a tad.  I'll start redoing my exhaust Monday, as I have the week off. I currently have an oval center muffler and cannon rear muffler. I've been told more then once from people behind me that my rear bumper is going to catch on fire one day. Seems I blow 5-10 second flames after doing a pull. No clue if that's the WMI, as I've never been able to do that before with other cars. I wanted to angle my tip down a tad so flames are pointed down and away from bumper. I also wanted to take the opportunity to reconfigure my exhaust line. I'm going to move my oval muffler to the rear with a pie cut angled tip and put in a new smaller round muffler in the center. I've rocked cannon mufflers on this car for the last few years and want to transition back the oval muffler look. I've also been looking for a stainless project to try out the new solar flux I bought. I'll post pictures on Monday, should be able to wrap that up in a day.  I'm also picking up another rear subframe this week. I wanted a second so that I could modify one with a gk tech anti squat reduction kit during the winter, and still be able to keep the car a roller so I can back it out of the garage if needed. I will also be caging it this winter. More on that later. Lastly, Speedtek still hasn't given me diddly squat. Every week for the last 4 weeks, they have been saying next week. They told me Friday to expect a shipping label that day to ship my two bad sets of ring and pinions back and nothing. There's definitely been more contact since I started destroying their company any chance I get on Facebook, but it's still just words without action.   
    • TurboTapin
      Idle issue rb20det

      By TurboTapin · Posted

      Have you done a pressure test on your intake/piping? Cleaned your IACV and Cold start valve?
    • r32-25t
      Spotted on the street....

      By r32-25t · Posted

      Bit of a dump of ones I saw on my trip. I also have a heap from daikoko but that’s technically not  on the street 
    • HYBRID VL
      KISLOC2 line output convertor for subwoofer in Q50/V37

      By HYBRID VL · Posted

      i was thinking that the 2 wires that go to the sub from factory has some sort of preamp like you mentioned and also a lo Pass filter to get just bass. now that will only use 1 channel and that really should be all i need for a sub? if i was trying to put a set of speakers in the back i can understand cutting into the left and right speaker wires. i will try how im talking about doing it and if that is crap i will do it the way of all wires. thanks for the input guys.  
    • Equilibrise
      M35 Stagea intake suction pipe

      By Equilibrise · Posted

      Challenging mig welding thin Aluminium pipe and trying to fit it in, having to bend and twist, but got there in the end. Fits really well and can easily get a socket wrench in there now to put it on/off. I'm in the middle of another project, so haven't installed the suction pipe yet. I'll post some pictures and results when i do.
×
×
  • Create New...