R33 Rb25det Vct Switch Points .

[discopotato03]

Hi all , someone mentioned recently that the std R33 RB25 does its cam timing change at something like 2000 and 4700 rpm . I suppose it has the cams open situation (minimum overlap phasing) for cranking and low speeds . The poster mentioned that the cam phasing then closed at 2-4700 for performance reasons and then opened again to get around high "backpressure" at higher revs .

I have to wonder how much of this has to to with Nissan playing games with internal exhaust gas recirculation for emissions reasons . I'm no automotive engineer but I would have thought that keeping the cam timing "open" at lowish revs and part throttle ie 2-3000 revs would pay off drivability wise . I can't see how you would not have a little reversion in these cases because the inlet side is below atmospheric pressure and lets face it the RB25's exhaust manifold and turbo are not the free est flowing items around . Also with better (less restrictive) turbos/manifolds/exhausts there could be some benefit from keeping the cams "closed" at full throttle a bit further up the engines rev range .

For those using an Apexi PFC and tuning with Datalogit , can you tell me if its possible to control the cam change points based on airflow signals or are we stuck with just rpm setpoints ?

For those using a PFC and Datalogit and the R34 RB25 it would be interesting to know what the factory did with its variable cam timing . Also of late Paul33 has been looking into loom adapting RB26 PFC's for RB20's and 25's and mentioned losing the ability for the computer to control VCT .

My sinister mind is wondering if R34 25 VCT could be grafted to the R33's head and some third party controller used to call the shots . Its probably possible but I don't know what would work CAS wise having never seen either VCT system in bits .

Anyhow just having control over the non variable R33 (powerglide VCT if you like) may prove interesting .

Cheers Adrian .

[BHDave]

It's more like 1100 and 5500 from factory.

I've messed about with the cutout point and found a few rwkw in the midrange by dropping it to 4500. Tried 4, no change. This is with a 256/264 cam combo, hks exhaust manifold blah blah. It was only rev based. And this is also only WOT peak power runs.

[paulr33]

the apexi default, well in the powerfc anyway is 4700rpm kick off.

its not accessible via the hand controller but you can see it via datalogit / power excel etc

i set mine to kick off at 1800rpm instead as a joke/test and the car was a pig to drive

[paulr33]

For those using an Apexi PFC and tuning with Datalogit , can you tell me if its possible to control the cam change points based on airflow signals or are we stuck with just rpm setpoints ?

you can only set the kick off or disable if you call it RPM, ie: only 4700 is the only value you can change

there is no way that i can see to change when it turns on