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rb26 cams into rb25

rb25

By rb25,
in Engines & Forced Induction

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Mesmer Enthusiast

Mesmer

Posted
Posted

The rb20/26 inlet cam gears bolt on the same a the exhaust ones (4 bolts) but the rb25 has one large hollow banjo style bolt that holds the vct gear on.

So without modding the center of the cam aswell as the front bearing surface the stock vct gear wont fit so you need the rb20/26 pully.

John

Sydneykid Grand Master

Sydneykid

Posted
Posted
surely if you put gtr cams onto hydrolic buckets your seat to seat timing would be increased to the point that idle quality will suffer, unless you plan on letting the buckets pump up and running a lash setting that match the gtr cams,  18 thou or something like that.

Not actually correct as the hydraulic follower allows clearance, due to the timing of the oil inlet, but let's just say it doesn't....

Then you end up with 18/1000 extra lift, this is not a bad thing :rofl:

And you end up with longer duration, again this is not a bad thing :D

I really can't see a problem, an RB is not a an old style engine with the hydraulic lifter at the opposite end of a push rod. :D

GTRgeoff Grand Master

GTRgeoff

Posted
Posted

Just interested in discussing a recent incident with an RB20 that fitted GTR cams. The owner believes some of the inlet valves were staying open off lobe. So would the problem be:

1. The hydraulic follower is pumping too far open

2. the extra lift is pushing the follower too far into the guide and making it stick(the engine is 180K old), I think unlikely. it would stay well open.

3. the off lobe diameter of the cam is a larger diameter than the stocker and the hydraulic follower is jammed at one clearance and won't close to accomodate.

4. bent valves due to timing belt slipping a few teeth as the inlet cam was apperently very tight in the journal.

There were signs of at least one set of valves touched the piston so the timing would have been out slightly, but at least 3 sets stay slightly open. I'm yet to see the head but very keen to follow up and see if they ar all bent valves or one of the other problem I mentioned.

  • 3 weeks later...
  • 3 months later...
darrinspencer Grand Master

darrinspencer

Posted
Posted
We are doing this conversion but modifying the inlet cam to run the VVT. May be crap but costing nothing to find out so will let you know.

This is on GTSt VSPECs GTS that has 450rwhp on the Stock cams so should be an interesting test.

Has these been done yet??

Any results available?

I have 3 sets of GTR cams and would like to put 1 set in my RB25det if it is worth while.

RPMGTR Community Regular

RPMGTR

Posted
Posted

Save your energy guys, this swap does NOT work.......GTR cams are designed with ramps suitable for .015"-.018" clearance with solid lifters. Put them in a hydraulic lifter engine (RB20-25) with .000" clearance, and you now have longer duration, but ultra-low lift for a fair portion of that duration! Result = bad idle vacumn, crap power, etc, etc.

With that said, I do have 2 sets of GTR cams for sale...$200 per pair, so if you still want to try this swap, knock yourself out. :kick:

B.

GTRgeoff Grand Master

GTRgeoff

Posted
Posted

Which is why it works for Sydneykid, and the suggestion that it wouldn't work due to ramp angles was laughed at by one of the Northsides' (Melb) better engine machining and building shops.

So you will of course provide dyno charts to support this advice? Make it quick as I'll be limited to occasional whoring from Thailand from 12 tomorrow.

I'm more than happy to concede to concrete evidence that it won't work, but there is evidence to the contrary.

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