Camshaft Changes

[Sil8ty]

You see in modified engines, some people utilise the N/Asp inlet camshaft in the RB-25DET's. Is this so they can still utilise the variable cam timing?? Is there any advantage in doing this with a slightly modified engine, with your normal mods (exhaust, filter, cooler etc) ???

[A31_Cefiro]

I don't think it's for variable cam timing I think the NA engine has more lift and duration than the turbo one.

[Warpspeed]

The variable timing on the inlet cam is put there so that the engine can meet emmissions and still make reasonably good all around power. The actual valve timing is quite restrictive, but am unable to give the exact cam duration figure (actually I would love to know) of the VVT inlet cam.

If you remove the VVT and fit a suitable fixed inlet cam the engine will run better everywhere if emmissions are of no concern.

What cam is best for you depends on what you have, and what you wish to achieve. The n/a inlet cam is I believe 240 degrees duration. I know for sure that the GTR inlet cam is 240 degrees duration, so this is probably a good choice for a mild street engine with stock turbo.

If you overcam the engine you will lose power, particularly on the inlet cam. You can run a larger exhaust cam than inlet cam, and this will actually give you a better power gain. The standard GTR exhaust cam is 250 degrees.

[ph1]

the standard gtr exhaust cam is actually 236 deg

[Warpspeed]

I have a GTR cam right here, and I measured 250 degrees duration at .012" lift. This is about where the end of the ramps would be. I have also seen this figure published. I believe this is an R33 GTR cam (not absolutely sure though).

What exactly do you have there, because I am extremely interested.

[Sil8ty]

SO basically if i can get my hands on a set of GTR cams it will work well?? Will it be worth while, in the terms of power produced, and is there musch work involved to fit them?? ie valve springs etc. need to be changed??

You all have been a great help.

[ph1]

nismo parts catalogue also states it as 236.

which publications have you seen this figure stated?

if it was 250, the 252 deg ex cams made by tomei, nismo, mines, reimax etc dont seem like a very worthwhile upgrade.

i have a set of std camshafts from my 33 gtr, travelled about 40k,

will take $300 for the pair.

[Warpspeed]

Thanks for the info ph1.

I notice that the data you have is for R32GTR, and is undoubtedly correct. The cams I have measured are probably R33GTR, and from what I hear R34GTR are different again.

My information comes from firstly my own measurement on a cylinder head with degree wheel and dial indicator, Julian Edgars book, and also an article that I cannot now find, in one of the car magazines. While the published info can always be suspect, it all agrees exactly , with what I have measured myself.

I have seen aftermarket 254 cams advertised, but am not aware that 250 or 252 cams were also available. The aftermarket cams also usually have higher lift and more agressive profiles, even though the seat to seat timing may be the same or only slightly different.

Sil8ty.

A lot of people are replacing the stock cams in their GTRs with aftermarket cams, and so there are plenty of stock GTR cams available at bargain prices.

It is extremely difficult to predict how much if any improvement you will get, without knowing what cams you already have in the engine. Maybe you could borrow a set to try ?

Also GTR cams are mechanical lifter cams, RB20 and RB25 have hydraulic lifters. You can put a GTR cam in the other RB engines, but you cannot put a hydraulic cam into a GTR. But then why would you want to !

The GTR cams are actually quite mild as far as lift and valve action go. Looking at what some of the Japanese camgrinders are offering as replacement cams for RB20 and RB25, apparantly standard valve springs are o/k up to about 9.2mm lift. The GTR cams are less than this so should go in without any spring related problems.

[Jay95R33]

This might be a stupid question, but I'm new to the topic of cams.

Do the GTR's (RB26) engine have VCT?

If they don't, is it easy to put the GTR cam's into a RB25, would you need to disable/remove the VCT system for the GTR cams to work in the RB25???

Thanks

J

[Warpspeed]

I am new to this myself, but am trying to learn all I can.

From what I have been able to find out the cams in RB20 RB25 and RB26 all fit, there is no problem there.

Some versions of the RB25 (only) come with VVT which is an oil pressure activated helical spline arrangement on the inlet cam only. The VVT cams themselves are different on the drive end, as is the special drive pulley that incorporates the VVT mechanism.

I have been told that a non VT cam with its standard drive pulley will drop straight into the head with no other changes.

Also an exhaust cam which has the drive tang that engages with the cam position sensor will fit into either the exhaust side or inlet side. An inlet cam can only be used as an inlet cam because it has no drive tang.

I have not actually tried any of this myself yet, so cannot absolutely guarantee this is correct. But I have been interested in it for a while, and nothing I have been able to find out contradicts.

[Sil8ty]

Bottom line is, with putting the GTR cams in the RB-25DET, make any additional power than opposed to leaving std camshafts in it??

[Warpspeed]

Probably.

As you said at the start, people have put n/a cams into turbo engines and said it went better, but who knows ?

Someone somewhere must have tried GTR cams in an RB25DET by now. There are so many GTSTs and so many spare GTR cams around.

[Jay95R33]

Originally posted by Warpspeed

Some versions of the RB25 (only) come with VVT which is an oil pressure activated helical spline arrangement on the inlet cam only.

The VCT is electronically controled by the ECU, or, it could be a combination of oil preasure and ECU signal.

I'm getting a R32 computer remapped to suit my R33, and in the process they have to put a seperate board into the R32 computer so it can control the VCT in my R33.

But like I said, it could be a combination of oil preasure and electronic???? So when the ECU senses oil preasure go over a certian point it kicks the VCT in.....

On the remapped one I'm getting, the VCT will have 3 (??) different RPM points you can adjust it to.

It will be interesting when I run it up on a dyno and see what the differences will be.

J

[Warpspeed]

I believe the ECU turns a solenoid valve on or off, which in turn diverts engine oil pressure to the VVT mechanism through drilled passages in the head and cam.

I am not familiar with exactly how Nissan do it exactly, but all the other systems that I know of, retard the cam at Idle to reduce valve overlap, for lower emmissions at high manifold vacuum.

At some low RPM above idle say 1,500RPM? the inlet cam is advanced. This increases overlap, and gives earlier inlet valve closing, good for mid range torque.

At some higher RPM the inlet cam is again retarded, this gives later inlet valve closing, and better high RPM torque. On a lot of engines this might be around 4000RPM for example.

What you do is run the car on the dyno in both positions, and arrange for the VVT to switch over where the power curves cross over. This will give you the best everywhere.

If you fit a slightly longer duration cam that has both the overlap and the late inlet closing features together with a bit more lift, and no VVT, then you will get more torque everywhere, but it will probably not then pass a full formal emmissions test. Hehe.

[Jay95R33]

That's a great explaination. Thanks

Just one further question.

At idle (and upto ~1500rpm) when the cam is retarded, is this soley to help emmisions or does it increase power/torque down low as well???

The reason why I ask is that from what I know, the remapped ECU I'm getting only switches at the higher RPM (switchable at 3500, 4500, and 5500) to the retarded state.

So the stock setup goes retarded>advanced>retarded

And my setup will go advanced>advanced>retarded

as the RPM goes up.

Any idea???

Jayson

[Warpspeed]

I believe that the low RPM switching point is purely emmission related, they also do some shifty things with the ignition timing as well sometimes.

Remember the original designers get all worried about things like catalytic converter temperatures and so on. None of this is performance related, at least not in the sense we mean performance.

The upper switching point is the one you should be most interested in, the amount you gain will not be huge. In fact if it switches right at the crossover point you will never be able to pick where it has changed, because the power should be identical at that point.

[Jay95R33]

That's great.

Thanks for the info, I was a little worried there for a while, but I think it'll be fine. I'm intending to run the car up on the dyno when I get the remapped one in, to do a good check on the car (A/F, boost, fuel preasure etc), and also do a before/ after comparison with a stock one.

Aiming for 180-190rwkw.... Fingers crossed

[Sil8ty]

Jay95r33: Let me know how you go with the R-32 ECU on the R-33 as the R-32 ECU's are worth next to nothing opposed to Power FC. And i have friends that are able to re-map R-32 computers too.

[Jay95R33]

Originally posted by Sil8ty

Jay95r33: Let me know how you go with the R-32 ECU on the R-33 as the R-32 ECU's are worth next to nothing opposed to Power FC. And i have friends that are able to re-map R-32 computers too.

Yepp, no problems.

But I'd say it's like any other modded ECU - it comes down to the tuning.

J

[Sil8ty]

Out of curiosity, the other day i spoke to a few reputable importers. They seem to think that doing the GTR cam replacement in the RB-25 is not the best way to go unless to are spinning the engine to 8,500 - 9,000rpm to gain max benefits out of the cams. :eek: (According to HKS JAPAN)

Have been advised to use a set of verniered cam gears on the std cam shafts will see, set up correctly around a 10-15 kW gain.. Guaranteed!!!! Opposed to a possible 5-10kws maybe sort of power with the GTR cams with no assurances that they will fit with no hassles.

I understand with the GTR cams you need to machine the head to get clearance for the extra lift of the GTR cams. But no one can tell me the the GTR Solid camshaft setup will be okay with the Hydrolic cam setup of the std GTS-t ????

I may be proven wrong, but i have no proven evidence!!! :lol: