RB26 Cam Trouble in RB25

[Memph]

Hey all

Car came off the dyno today. only made 160 rwkw with the rb26 cams. The tuner said there is definately a fair bit of room left for more but the cams are holding it back

Its struggling to idle at anything under around 1200rpm and at that its making bugger all vac.

over all he said he reckons the cams could work. but the cam timng is way off. i said i had been recommended to try +2/-4 but he said even if it is a few degrees out it wouldnt be that bad...

seemingly i shouldnt rule the cams out yet as they might still be ok.

I was told to just adjust the cam gears all the way on way. see how it goes for vac on idle. then turn them all the way the other way and see how that goes.

Does anyone know if th GTR cam gears are timed the same as RB25 gears? as in when mine are set on 0/0 would they be in the same spot as if they had stock rb26gears? cos he was thinking makybe the gear is a tooth out. though for the 25 cams they are perfect. so we thought maybe the rb26 gears are different out of the factory..

so if i have repeated my self a bit. just dont really know how to type what i want to say hehe

anyone done this before?

Any help at all would be appreciated.

also, on a side note ... would the top half of the intake plenum off an rb20 fit on an rb25?

Cheers guys

[Memph]

also.

the standard rb25 intake camshaft has that big lump on the end for the VCT which i believe is part of the camshaft itself yes?

so i got some poncams say, would that then mean i wouldnt have the vct? or do they include the lump aswell?

surely someone can clear that up for me

Cheers again

[TODA AU]

Are you still running the std RB25 hydrulic lifters?

[GTRgeoff]

Memph I tried a set in my 25 which was producing 220rwkw. Power under 5krpm was very poor and idle not so great but over 5k it really picked up. Using vernier gears I found the thing was worse whichever way I went. I'm sending them off soon to get the profiles, which are great for solid lifters as in RB26, reground to suit hydraulic lifters as in RB25. The ramps on the 26 cams are more aggressive off the base circle to take up the clearance needed for solid lifters, so with hydraulics it cracks the valves earlier leading to poor idle nd loss of power. Cost to regrind is 280 at Ivan Tighe in Brisbane. There is a current thread on here so do a search and you'll discover more.

[R31Nismoid]

Dont bother with them.

Just get the Tomei Poncams.

the go straight in without any hassle and dont really need a cam gear either.

With all the time saved and the car on the road in a day with it fine... it's worth a tad more $$$ IMO

[GTRgeoff]

Likewise a set of reground GTR cams is no hassle to fit and way cheaper for similar specs. And they all need something to drive them Ash, in an RB's case belt driven gimbal sprockets, commonly known as cam gears. The choice is whether you want VCT or not, or vernier or fixed.

Fitting takes an hour for a skilled mechanic (well me anyway) so that is no issue and you already have one.

As far as the R32 plenum goes, I took a look and they don't appear compatible as the 2 rear runners are offset to clear the master cylinder.

[RPMGTR]

When reground to suit the hydraulic lifter the RB26 cams work ok......but you will really miss the VCT.....Poncam or even std RB25 is way better.

[GTRgeoff]

Ben, stop taking the fun out of life. Shouldn't you be off fleecing some rich bugger while providing them another awesome setup?

Just clarify for me what circumstances the standard cams are better for with the VCT? I have a favourite answer for every question. It depends. In this case there are 8 direct variables and multiples of associated variables. What grind on each cam, not just a flank trim but maybe different lift and duration; what cam gear on each cam; what advance or retard on the cam to match powerband to application.

I realise you have your favourite setups that you know work, which is great when you have to offer quality product and service, but some folks like to tinker, and that is part of their learning process including the limitations and failures.

Someone as well respected as you should offer more than a one liner.

[Memph]

hmm. ok.

well i hace never done this before so i dont really know how it works...

Can i just take the cams to a head specialist and say i want these cams ground to suit hydraulic lifters?

Or is it more than that? do i have to provide specs or anything? is there more than one way to grind them?

as in can you get them ground keeping the same specs? can you get them ground then with different lift or duration?

Sorry about the many questions. just try to understand what i can do

if depending on the case could i just give them the specs of poncams and say i would like these cams ground to as close as you can get to these specs

hehe

Cheers

[RPMGTR]

I know you love to tinker Geoff as do I. ....and I've tinkered with the RB25 cam thing alot and found.... the std cams are really quite good...you get a broad power curve and power up to 300rwkw is really only limited by the turbo/ancillaries bolted on to it. Sure you can usually find another 10-30kw by upgrading cams but you need to choose carefully to get that gain and not a net total loss....The poncams are the best I've tested on many setups (Mr Tomei really seems to have done their homework on these)...they retain VCT giving superb drivability and great power.

Other jap brands work quite well to but these are the best aftermarket I've found so far. As for the much touted GTR cams,..these work reasonably when given hydraulic ramps, but the loss of vct is too much like backward engineering for me.... they make the engine really quite 'flat' off the bottom and thru the midrange with no more top end than the poncams. I've tried just about every cam timing/tuning combination possible and although you can move the power around, you cant go close to matching the 'overall ' performance of either the std or Tomei cams...Even RB30/25's Non VCT engines are quite disappointing in the low-mid when compared to the same engines with VCT...(I just wish RB26 had VCT too)......

So save yourself a stack of dyno-time and go with std or poncams!

Hope that helps...

Ben

BTW....Its great to see someone put 34GTR turbos on a RB25.....they should work really well...good luck with it.

[Memph]

hmm

the thing is although the VCT you say is better. i dont want to keep it.

as i wish to continue using the rb20 timing cover.

so what should i ask for when getting the 26 cams ground?

[TODA AU]

It's probable if you use std RB26 cams (ground to suit hydraulics).

It's unlikley you'll be happy with the results.

Appart from losing the VTC, you're only gaining lift, not duration.

240deg @ 7.80mm vs 240deg @ 8.58 - Intake

Std RB26 exhaust cam is actually shorter than the 240deg cam of the RB20/25at 236deg.

Lift is higher @ 8.28mm vs original 7.80mm

NB: Some of this lift is lost when they're ground too.

For what it's worth, regarding std cam timing of RB25 vs RB26.

A std RB25 intake cam LCA is 120deg (with NVCS at rest)

The RB20 std intake cam LCA is 115deg

The RB26 std LCA for the intake is 113deg (117deg R34)

This is where the cam will be (approximatly) by lining up the dots, using an RB aftermarket cam pulley, on zero. (Asuming no head machining, thicker, thiner head gaskets & or cylinder block machining)

Exhaust LCA's are as follows... (Std cams)

RB20 - 120deg / RB25 - 117deg / RB26 - 120~125deg (model dependant)

Regarding how many degrees on the cam gear (Using std GTR cams)

For 115deg intake LCA - Retard intake 2 deg (R32/33) / Advance intake 3 deg (R34)

For 110deg intake LCA - Advance intake 3 deg (R32/33) / Advance intake 7 deg (R34)

For 115deg exhaust LCA - Retard 5deg exhaust (BNCR33 N1) / Retard 6deg exhaust (BNR34) / Retard 10deg exhaust (R32/33)

Regarding camshaft timing,

You should always use a TDC guage, a dial indicator & a crankshaft degree wheel to set the LCA rather than simply guess by advancing or retarding the cam x many degrees on the cam pulley.

With no NVCS fitted, tighten the intake cam LCA (lobe centre angle) to 115~110deg. Depending on the rest of your combination.

115deg offers better low end & higher vacuum. 110deg more mid range & topend.

Set the exhaust to 115deg (if idle vacuum still poor, widen to 117deg)

Fow what it's worth,

I would use the Tomei Pon Cam. With 256deg @ 8.5mm lift keeping the NVCS

It offers better all round performance without the hastle of the reground 26 cams.

Plus, you get more cam.

If you must eliminate the NVCS (VTC), use a Tomei RB20 intake camshaft. (Pon cam)

This would be the zero greif method.

Hope this is of some help.

Cheers

Adrian

[Sydneykid]

Great post Adrian it filled in few gaps in my knowledge. I have a couple of suggestions;

[Sydneykid]

Great post Adrian, it filled in a few gapsin my knowledge bank. I have a few suggestions to add;

Lift is higher @ 8.28mm vs original 7.80mm

NB: Some of this lift is lost when they're ground too.

Luke has advised that they grind the heal to eliminate the solid ramps. so lift is actually gained not lost.

You should always use a TDC guage, a dial indicator & a crankshaft degree wheel to set the LCA rather than simply guess by advancing or retarding the cam x many degrees on the cam pulley.

I don't see the benefit in knowing that my cams are actually at 2.34 degrees. not the 2.00 degrees as shown by the slots on the adj pulley. As with most people, I tuned it for the power curve I wanted on the dyno. Whether I got that power curve at 2.34 degrees or 2.00 degrees, I really don't care. Personally I don't see why I should spend a lot of time getting the cam timing exactly spot on, when I am going to change it on the dyno anyway.

I am really looking forward to seeing how Geoff gets on with the RB26 cams trimmed.

[GTRgeoff]

Mmmm, so am I but as is now commonly known the first drive with the GTR34 turbs on ended in a massive loss of power. Resulting checks showed 25psi compression on 1,2,3 and 125psi on 4,5,6 with no fuel to 4. I realise I should have had the injectors checked for peace of mind but in the haste to ready the car for PI it was lowest priority since they were supposedly cleaned and flow tested 440cc toyota injectors. Might be a little while before I get off the butt and sort it out.

[Memph]

awesome post adrian

And thanks everyone for the help.

i think i should sell the GTR cams and my adjustable cam gears (as i hear poncams wont need them as they are timed perfectly out of tomei )

and buy an RB20 Intake cam and rb25 Exhaust cam.

wander how much i can get some pon cams for?

i take it nengun is the place to get them?

or what about greenline?

anywhere in vic?

thanks again everyone for all the help..

the amount of knowledge on these forums astounds me everytime...

cheers

[lukevl]

For what it's worth, regarding std cam timing of RB25 vs RB26.

A std RB25 intake cam LCA is 120deg (with NVCS at rest)

Do you know how much the NVCS moves the cam? Also is it a 2-position unit or can they open and close the solenoid to create variable movements?

Regarding camshaft timing,

You should always use a TDC guage, a dial indicator & a crankshaft degree wheel to set the LCA rather than simply guess by advancing or retarding the cam x many degrees on the cam pulley.  

Adrian

Agreed. Like on my motor where the gears have no relevant marks and you have to degree them in from scratch.

However Sydneykid makes a very good point by saying who gives a toss where they are cause he moves them on the dyno and he knows when he puts the gears on they will be within a few degrees. My cams will be moved on the dyno also.

[TODA AU]

I don't see the benefit in knowing that my cams are actually at 2.34 degrees. not the 2.00 degrees as shown by the slots on the adj pulley.  As with most people, I tuned it for the power curve I wanted on the dyno.  Whether I got that power curve at 2.34 degrees or 2.00 degrees, I really don't care.  Personally I don't see why I  should  spend a lot of time getting the cam timing exactly spot on, when I am going to change it on the dyno anyway.

I guess we're different that respect,

In my experience, it is not that common that altering the cam timing on the dyno will deliver superior results, compared to a correctly timed cam.

It will however deliver gains more commonly, when the cams are not timed in the first place...

Further, I like to know exactly where the cams are & where they are timed, so if you do play with them on the dyno resulting in a gain, you're able to record exactly what LCA they performed best at, & then use this information to your advantage in future.

But as they say, horses for courses...

Both methods have their merits.

[Sydneykid]

I guess we're different that respect,

In my experience, it is not that common that altering the cam timing on the dyno will deliver superior results, compared to a correctly timed cam.  

It will however deliver gains more commonly, when the cams are not timed in the first place...

Further, I like to know exactly where the cams are & where they are timed, so if you do play with them on the dyno resulting in a gain, you're able to record exactly what LCA they performed best at, & then use this information to your advantage in future.

But as they say, horses for courses...  

Both methods have their merits.

I see where you are coming from Adrian, but I have yet to put an engine on the dyno and not find some power (either increase in max power or average power) by adjusting the camshaft timing on line. Obviously on something with difficult to adjust cam timing (eg; Chevy or Ford pushrod V8) I spend a lot more time getting the timing spot on.

But on an RB enigne it is really waste of time as it is so quick on the dyno (engine or chassis). By all means check it after it is tuned, so that I have an aproximate starting point for the next similar RB engine. But my experience has been that every engine is different.

[pnblight]

Cam timing in my limited experience can reep hugh gains but not always, as said earlier ever motor is a little different. On tuning my rb26 we found well over a 100rwhp in the cams and didn't continued tune until we made losses more reached a level i didnt want to cross with out internal upgrade (so there likely more in them) and what amazed me the most was the very small adjustment need for large gains (2deg adv (crankshaft) exhaust timing= 30rwhp increase) which is like 1 deg move on the exhaust cam. So i tell people not to go out run xx timing but more like Sydneykid does just try tuning the cams and motor on the dyno.