My RB26 Cams Experience in RB25

[Memph]

Hey guys,

thought i would whack some RB26 Cams and adjustable cam gears into my RB25...

I originally had the gears on +2/-4 as recommended by SK, but this didnt really work at all...

would run up to 3k RPM, then stop and studder and not know what to do all the way to 6....

Put the cams back to 0/0 for now untill i can get it down to the dyno for a retune.

Car seems a little nicer, seems to have lost a little down low but also wants to go a little more above about 4k RPM

The car will know not start unless i give it a little throttle..

Seems not not want to idle at any less than about 1100rpm, but im not posative thats cam related yet...

Dont have before or after dyno sheets so cant give an exact gain.

But i do have ears and it definately sounds the part now. when i first started it and stood behind the car almost sounded like i was standing behind a big block V8 ...

up high it sounds a little harsher, a little tougher i reckon

Thats about it for now

Any questions welcome

[Sydneykid]

Adj cam gears on both inlet and exhaust, so no VVT. I will be watching for the results.

[Memph]

yeah. no VVT. also using the RB20 computer which doesnt seem to be liking it much..

ABout to buy a Microtech LT-12s to see how that goes.

Had trouble with the TPS working on the RB25 computer...

currently using RB25 throttle body with RB20 pin, rb25 rocker and rb20 tps. lol

using RB25 injectors. RB20 ECU with modified RB20 loom. no igniter with RB25 coilpacks.

all seems to be ok but ECU seems to be struggling.. hopefully microtech can help that

Please provide comments and suggestions

[mabru]

This sounds eerily similar to my RB20 with 26 cams experience. The car would not idle without having your foot hovering over the gas pedal. Sounded mean as hell but in the end was not good for a daily driver, since I didn't have aftermarket management I canned the idea and put the cams on the shelf for a while.

-Matt

[lukevl]

Bad idling is caused by large valve overlap. With the GTR cams your valve overlap would be at least 30 degrees more at .25mm lift meaning BAD IDLE. Makes virtually no difference up top when the car is going but its going to sound like GTR with PMS on and low rpm and load.

[Memph]

well i ordered a Microtech LT-8s today, along with hi flow cat and 3inch pipe from turbo to cat.

also getting my cooler piping made up tomorrow... want to get everything done on the car before taking it in to get a tune so save on dyno time... as in dont want to get it tuned., then change something on the car and need to go in for another tune

would rather spend the money on something good.. either way that means i wont realy get before and after dynos... but when i get them i will post them up here for people to geeze at anyhow..

who knows. there might be some rb25 owners that would like to throw some rb26 cams in theres

btw, the cams i have are out of a 97 R33 GTR V-Spec II

Cheers

[Sydneykid]

Bad idling is caused by large valve overlap. With the GTR cams your valve overlap would be at least 30 degrees more at .25mm lift meaning BAD IDLE. Makes virtually no difference up top when the car is going but its going to sound like  GTR with PMS on and low rpm and load.

Hi Luke, 30 degrees, that's a lot! So why don't GTR's idle low and rough? I know it's not valve clearance (solid versus hydraulic) as I have run a GTR with virtually zero clearance to try and get as much lift as possible. It still idled fine.

My guess is ignition timing and fuel tuning, the low rpm maps on a GTR are quite different to the maps on an RB20/25. So with adjustments via the ECU you should be able to get it to idle and run fine.

This is a quite interesting subject as some people have got it to work and others have had no luck, despite lots of effort.

[sproosy]

This is just what i wanted to hear, thanks Sydneykid!

[lukevl]

Oh man SK this is getting painful. You do everything else right by the sounds of it but why recommend putting mechanical cams in a hydraulic motor? There is a reason why the cams are different and you know it. You wouldn't put an oil tank below the height of a dry sump pump would you? So why do this?

At 0.25mm lift the RB20/25 hydraulic cams have about 230 degrees on the seat. (0.25mm is just for a comparison)

At 0.25mm lift the RB26 solid cams have 310 degrees on the seat.

Thats 40 degrees a side per lobe!

Consider that SAE quote 0.15mm running clearance for a hydraulic lifter the problem only gets worse (because at these heights the mechanical ramps have a much smaller gradient) While these sorts of lifts don't create much airflow they do lose the vital seal needed to give the motor some dynamic compression down low which it needs for a stable and smooth idle.

In some cases I would agree you could get away with running a mechanical profile hydraulic but the mechanical Nissan profiles have such large and aggressive ramps. It is a known fact that to get the GTR past emissions the clearances would be at their correct point (about 0.50mm) and then closed up to make them sound fat on idle while not losing top end performance. My understanding is that the factory clearances are about 0.30mm or so with about 0.05mm expansion from cold to hot - is this right?

[nv033]

i tried and it failed....after giving it a big rev no matter what comp...mind u 3 different sorts were used and 2 different tuners...could not get it to idle after a big rev!!!!!

then SK mention the whole rb26 vavle train would fit into a rb25 head (solid lifter conversion) because his done it himself......once again the buck stopped when the head specialist said no can do.......

i had alot of faith in SK but after alot of $$$ was spent i dont know whether the exercise is worth pursuing

[sproosy]

Soldier on nv033! Ill be doin this in the RB20 in a month or when i can get my hands on some RB26 CAMS. Its a weekend project! Ill try it with the stock ECU first, see how pathetic my idle is then when i upgrade to the Power FC we should see some improvements indeed!

[jnr32r]

Ive tried this about 9 months ago too with no luck, same as Benny and others.

I have a PFC and played around with ignition and fuel without luck.

Idle (if you could call it that) was shocking.

I still have the cams and i wanna try it once again and getting it tune as well. when i get a free w.end sometime next month.

will keep u posted

[nv033]

Soldier on nv033! Ill be doin this in the RB20 in a month or when i can get my hands on some RB26 CAMS. Its a weekend project! Ill try it with the stock ECU first, see how pathetic my idle is then when i upgrade to the Power FC we should see some improvements indeed!

ive got a set mate if interested of rb26 camshatfs

[Sydneykid]

then SK mention the whole rb26 vavle train would fit into a rb25 head (solid lifter conversion) because his done it himself......once again the buck stopped when the head specialist said no can do.......(

This worries me, because I am far from the only one who has done this. It is not a simply throw them in, it'll be right job. You need to do a LITTLE machining, but nothing a "head specialist" couldn't do in his sleep. Did he tell you why he thought it couldn't be done?

[nv033]

This worries me, because I am far from the only one who has done this.  It is not a simply throw them in, it'll be right job.  You need to do a LITTLE machining, but nothing a "head specialist" couldn't do in his sleep.  Did he tell you why he thought it couldn't be done?

something about a gap that is left over because one is solid and one is hydraulic due to the solid lifter.....it equated to about 12mm which he said shims dont exist in this size. And the rb26 head is machined to compensate for the gap but the rb25 head is not... He was keen on this particular conversion and he said if it could be done it would be an excellent cheap conversion. hope u can puzzle it together otherwise i can ask him again

[GTRgeoff]

I tried this late last year, just for the hell of it and found a huge loss of power under 5K, but I hadn't bothered with retuning due to no hand controller. Over 5K it felt better but that may be an illusion after the low power.

I haven't given up though as I will be getting the GTR cams reground with a little less flank angle. Cost is about $350 so with the minimal cost of the cams is still worth doing.

I priced the GTR shims and followers and it was going to cost a squillion from Nissan.

Had a discussion with Ben from Racepace who had cam doctored to determine the difference and he felt it would react the way it did. Whether it is tuning or the lost seal at idle it won't matter after a cam grind.

[grepin]

RB25 head with GTR HKS 265/9.5 cams. Solid lifters fitted VVT disconnected. The valves were binding so had to go to GTR inlet valves and SR20 exhaust valves. HKS cam gears. Made 300rwkw with 2835 ProS. Wouldnt say worth it above Pon Cams however when I do a bottom end will come into its own. Did a track day and an O-Ring chewed out my compressor wheel. Thought I had a leak somewhere kept going. Could never find the leak funnily anyway went on a dyno to play with the cam gears which wasnt calibrated so took the power drop due this initially with +4/-2 279rwkw, +6/-6 gained 12kw mid range and lost 7kw up top with torque coming on earlier. 0/+2 shit. Settled on +3/-4 with 289rwkw up top with a little loss of mid range KW however kept same torque. All this with a chewed up compressor wheel. Embarassing really. Turbo comes back next week after a month at Garretts sourcing a new wheel.

[Kaido_RR]

Awsome always love the rb26 head/cams idea in the rb25.

So your running stock gtr cams with aftermarket cam gears correct?

[Sydneykid]

something about a gap that is left over because one is solid and one is hydraulic due to the solid lifter.....it equated to about 12mm which he said shims dont exist in this size. And the rb26 head is machined to compensate for the gap but the rb25 head is not... He was keen on this particular conversion and he said if it could be done it would be an excellent cheap conversion. hope u can puzzle it together otherwise i can ask him again  

OK, I think I understand what he is saying. The RB25 valves are shorter to allow for the extra thickness of the hydraulic follower. But this isn't a problem as you use the RB26 valves. The valve seats in the combustion chamber are in exactly ythe same piston, as you would expect. The camshafts are also in exactly the same position, again as you would expect. So if you change everything in between (followers, retainers, collets, valve springs, valves, and guides) then it fits up perfectly. The only issue is the valve spring seat in the head which needs machining very slightly. As per usual practise, the valve spring seat tension is adjusted by the use of spacers under the vlave springs (between the vlave spring and the cylinder head).

I have had a couple of people get confused and try to use RB26 followers (solid) with the rest being RB25 parts. You can't do that, for the reason you described, they are not thick enough and you would need HUGE shims. You have to change the lot as described above.

[RB30-POWER]

All this sounds like a big head ****, just bolt the RB26 head on in the first place.