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Possible Or Pointless? Rb25/26 Hybrid With Vct

Gerg_R31

By Gerg_R31,
in Engines & Forced Induction

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Gerg_R31 Mentor

Gerg_R31

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I have been building an RB30DE using an R33 RB25DE VCT head

The head has been ported, grub screwed the VCT oil gallery, I'm using RB26 valves, retainers, buckets, extra thick lash pads, RB26 cams (10.8mm lift 280° duration), organised taller springs

anyways life story a side i was thinking of maybe trying to use the VCT with the RB26 cams for a bit more low rev assistance

anyone think its possible?

or would it be pointless?

Nigel Nichols Explorer

Nigel Nichols

Posted
Posted
I have been building an RB30DE using an R33 RB25DE VCT head

The head has been ported, grub screwed the VCT oil gallery, I'm using RB26 valves, retainers, buckets, extra thick lash pads, RB26 cams (10.8mm lift 280° duration), organised taller springs

anyways life story a side i was thinking of maybe trying to use the VCT with the RB26 cams for a bit more low rev assistance

anyone think its possible?

or would it be pointless?

I could be wrong but I would be surprised if the VCT hub/timing gear would fit the RB26 cam shaft. Also the oil galleries are not in the RB26 cam for the front most bearing. (where the RB25 VCT is feed) Not sure you will get much from it with your setup.

I kept the VCT active with my RB30DE but then it was easy.

Nigel

Gerg_R31 Mentor

Gerg_R31

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I could be wrong but I would be surprised if the VCT hub/timing gear would fit the RB26 cam shaft. Also the oil galleries are not in the RB26 cam for the front most bearing. (where the RB25 VCT is feed) Not sure you will get much from it with your setup.

I kept the VCT active with my RB30DE but then it was easy.

Nigel

though if i measure the distance and location on the rb25 cam and drill an oil hole at work to meet up with the already exsisting oil hole it might work (im an engine reconditioner)

i have noticed the VCT hub sits on the cam gear

was thinking as we've done the rb25 solid shim conversion (with the little stem inside the bucket) and they kept the vct which was connected to a vernie cam gear, so i was thinking since my cam is just a tad bigger with a few little modifications i might be able to make it work

rob82 Mentor

rob82

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Definately worthwhile if you can get it to work. It will allow you to retard both cams to breath up top while allowing lowend overlap for more power and response down low. What compression ratio are you aiming for? That size cam on the rb30 twin cam will easily accept 11:1 on pump and probably more. What intake manifold are you using?

Gerg_R31 Mentor

Gerg_R31

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Definately worthwhile if you can get it to work. It will allow you to retard both cams to breath up top while allowing lowend overlap for more power and response down low. What compression ratio are you aiming for? That size cam on the rb30 twin cam will easily accept 11:1 on pump and probably more. What intake manifold are you using?

the VCT only moves the intake cam, though that the same theroy i had

my aim is 10.5:1 to 11:1

will be using the RB26 6 throttle bodies with a moddified rb25 manifold/adapter plate not sure about the rest of it but will get to that later

rob82 Mentor

rob82

Posted
Posted
the VCT only moves the intake cam, though that the same theroy i had

my aim is 10.5:1 to 11:1

will be using the RB26 6 throttle bodies with a moddified rb25 manifold/adapter plate not sure about the rest of it but will get to that later

I know it only moves the intake cam - what I mean is that if you have an adj Exh cam gear you can retard that side and then let the intake VCT advance to get you low end overlap. The wider the cam lobe seperation the more affect the VCT will have.

Gerg_R31 Mentor

Gerg_R31

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I know it only moves the intake cam - what I mean is that if you have an adj Exh cam gear you can retard that side and then let the intake VCT advance to get you low end overlap. The wider the cam lobe seperation the more affect the VCT will have.

i think a good way to work this out is maybe get a N/A RB26 with the same or similar cams,

chuck it on a dyno, advance/spastify the intake cam X degrees at certain revs, to see just where and when advancing and retarding would peak and then could work out if it be worth it or not

or i could just do it later on after i finish my motor, then pull the cam back out and drill the oil hole in the cam in X amount of degrees

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