Cams for RB25DET

[GTS-t VSPEC]

Hi guys,

When I was having my car dyno-tuned the other day I was speaking to the guy and he recommended getting cams for my car, as he said there is significant gains to be had.

He told me to go for 256 and 264 cams for an RB20, and do away with the variable cam timing (NVCS?) on the RB25. Is this the road you would take?

If you have had cams done to an RB25 can you let me know what you did and the results, this would be most helpful in making a decision.

See'ya

:burnout:

[meggala]

first of ~~~ I think a turbo upgrade would be a better option there are better real gains to be had there. and intercoolers ecu etc

before you go for cam or is your car already modded.

you cna also use the cams from the rb26 or you cna get special cams from apexi that work with vvt. wait a bit fo rthe cams btw what did he quote you to do them and how much power did he say you would get. and cheap cma thing wiould be to have an adjustable cam gear fitted and to have it tuned not sure which one they do in the rb25 but that would find you around 5-10 rwkw

meggala

btw on my web page I have written a few thing on mods in the modification section its not finishes but it might help.

[GTS-t VSPEC]

Hi Meggala,

I already have:

R34 GTR FMIC

Wolf 3D Ver4 ECU

Blitz SMC

OS Giken Twin Plate Clutch

Greddy Plenum

90mm Throttle Body

Over the Christmas/New Year period I will be having a set of Weiseco Forged Pistons and a GT30 turbo with exhaust manifold and 45mm wastegate added. The cams are for after that, I don't know whether to keep the VVT or not, and whether 256/264 are better than going for 264/264. The variable cam gears go without saying, I like the look of the new OS Giken ones.

The car is just for the street, so I wont to keep it relatively driveable, any more suggestions will be welcome.

Thanks

:burnout:

[meggala]

do you have a target horse power or do you just want heaps will you be drag racing the car or circuit racing.

will you be running high boost often high being 20psi +

do you want reliability. in the long term.

Cams increase engine wear quite abit they will also increase the revablility of your motor you red line could over to 8500-9000 quite easily.

person~~~y while the motor is open if its in your budget and you want power then yes cams are good they have many benifits and a few detractions. you need to set you goals as Is aid in the article I wrote and work out where you are going to and how you are going to get there for some people with the same set up as you 256 would be right for others it might be 272's you might want to convert you cam gear to solid rather than mechanical then the rb26 ones would be better. the options are wide and varied. you need to sit down with your tuner and work out you goals ie do you want to run 12's 11's 10's or what ever and then set about planning for it that s ~~~.

as an example mine have built a circut race car that uses 256 cams and it hold the lap record at a track some of the other tuners use 272's and bigger turbo's and run slower it ~~~ depends on the set up of the car.

meggala

I know it is as clear as mud

[PurpleR32]

Tomei Make cams especially for the VVT RB25.

I think since you are getting the GT30, which is big turbo, cams are a good idea, as your power will be coming at much higher revs. However make sure you have exhausted most avenues of modifications before you do cams

[Steve]

Originally posted by GTS-t VSPEC

He told me to go for 256 and 264 cams for an RB20, and do away with the variable cam timing (NVCS?) on the RB25. Is this the road you would take?

Dude, I have met some lads that were making 640hp at the wheels on an RB26 with the same duration cams. Got it built by SST and were very happy with the overall performance (once it had been detuned a bit for driveability).

[Freebaggin]

GTS-t VSPEC, that sounds like a real nice set-up already there mate. Do you have the power readings after each stage of your upgrade so far? What differrence does the 90mm throttle make and has it made it crappy for light load throttle usage?

I have done almost as much as you and want to go GT30 next and am thinking about the same thing re cams but then again I am not opening up my motor like you are and there is less incentive for me to change cams I spose.

If you were gonna go for cams, then one compatible with the VVT would surely be the best. My car sucked when we the VVT was off accidentally during ECU tuning, BIG mid-range hole.

Freebaggin.

[GTS-t VSPEC]

Thanks for all the advice guys, I don't know if I'm any clearer on what to do yet but it helps to have other viewpoints.

Meggala,

The problem with setting targets is that once you reach them you always want more, but in the essence of keeping it street drivable then 12's would be more than adequate. I was told that even with the bigger turbo that your not making use of all of the power available without having cams done. Is it worth doing the conversion from hydraulic to mechanical lifters, what's involved and approximate cost?

Steve,

It was in fact Steve at SST that told me to do the RB20 cams with the 256/264 setup, he says it is the best, and seeing as he produces some pretty cool race cars it is hard to argue with him.

Freebaggin,

The 90mm throttle bolts up to the Greddy plenum, I thought that there is no point having a large plenum inlet and then restricting it with the factory 55mm throttle. It takes a bit more to tune with the larger throttle, and idles at 1000-1100 rpm, sounds more aggressive, but other than that there is not much difficulty.

I have been working on maximising the airflow side of things with 4" and 3" intercooler piping, removal of airflow meter, R34 GTR intercooler, larger plenum and throttle body. This is in the expectation of adding the GT30.

Its just that when the forged pistons go in the block is being slightly over bored, bringing compression down to 8.5:1, conrods are being shotpeened so I thought that it would be a good oportunity to do the cams.

Thanks for the advice keep it coming.

:burnout:

[Freebaggin]

Good stuff! Sounds like the right way to go about it. What power are you getting right now and at what boost? Do you have any of the earlier power numbers from the less modified set-up?

Good luck!

[GTS-t VSPEC]

Freebaggin,

Unfortunately the only times I've had it dynoed is when it was completely factory and when everything was in it. But you could tell the difference just by driving the car. I'm currently getting about 280rwhp, which really is the limit of the factory turbo, other wise it will start pinging if you advance the timing.

I have plenty more stuff to do to this car, but I have an ordered plan to make reliable and street drivable power.

See'ya:burnout:

[Merli]

I'd save the cams for later...

Do your internals (pistons, rods, crank?) and put the GT30, high mount exhaust manifold and external wastegate and see what you get.

If you're not happy, you can always drop cams in later, as it's easy to swap cams out... Just remove the rocker covers and swap the cams, no need to remove the head to do this (if you get low lift cams that doesn't require head machining)...

[GTS-t VSPEC]

Hi Merli,

Thanks for the advice, do you think shotpeening the rods will be enough? And what about the crank, just polished and balanced?

Do the adjustable cam gears make much difference on factory cams?

Sorry for all the questions, but its good to know some people have already done some of these things and to get as much info as possible, before making a big mistake.

See'ya:burnout:

[rev210]

Originally posted by GTS-t VSPEC

Hi Merli,

Thanks for the advice, do you think shotpeening the rods will be enough? And what about the crank, just polished and balanced?

Do the adjustable cam gears make much difference on factory cams?

Sorry for all the questions, but its good to know some people have already done some of these things and to get as much info as possible, before making a big mistake.

See'ya:burnout:

The engine build depends on what power you want. I guess if you go the forgies etc. it should read kinda like this:

Rods -shotpeened /linished and crack tested ( no not the cocaine)

Pistons - forged

Rod bolts --- strong aftermarket bastards

Crank --- ballanced

Bearings --- Clearanced for extra power/revs

There are other things machining wise you can do to the bottom end but this is probably the basic start.

Up top get the head ported and flowed correctly for the anticipated power / air flow of the turbo selected. The selection of camshaft and turbo will be important to the head work. Ultimately getting the head properly CNC machined and flowed is the best bet. Adjustable cam gears are a good idea btw.

Now for the big tip:

Avoid the jap style tuners for an engine build. Get quotes from Chris mills, Kosteki (best cylider head flow bench and machining in WA) and the like for the work , ask for their 'best price' and shop around. These guys do very high horsepower engines in their sleep and charge fair prices with all the machine work done in house unlike the jap tuners we all know and love.

[GTS-t VSPEC]

That's some good advice rev210, I have already lined up some people to do the machining, they are less the half the price of going through a Jap tuner and have worked on race cars for many years.

What do you think about the swap from hydraulic to mechanical lifters? And do I get rid of the NVCS (variable cam timing) or keep it?

Thanks for your help.

See'ya

[rev210]

I'd say for street purposes avoid the solids, don't know if thats possible with the cams you end up selecting.

I'd say going for a fairly mild grind of cam would be the best bet. Keeping the power in the 'mid range' for the street. Maybe you could look at keeping the stock cams with a little bit of a play with the shaft timing?

If you haven't got that machining joint 'locked in' I'd give a few other places a call just to be sure. There is about half a dozen places I'd be perfectly happy to hand my engine over to (all of them do work on race cars day in day out. So it comes down to the best prices for the same work. That way you might save a few $$$ for another mod.

[GTS-t VSPEC]

Thanks for thetip rev210. I get my car done at industry prices, i.e. what they charge someone else in the industry, not retail. My mate does alot of race cars and can get good work done at very cheap prices. Even for parts I tend to score big time, with my OS Giken Twin-plate costing just over a grand fitted.

I always tend to shop around because the prices can vary so much, but this guy has so many contacts that he can get anything done cheap, but he only uses the best.

I'll probably stick with the hydraulic lifters, as I'll only run mild cams without too much lift.

See'ya

[Merli]

Originally posted by GTS-t VSPEC

Hi Merli,

Thanks for the advice, do you think shotpeening the rods will be enough? And what about the crank, just polished and balanced?

Do the adjustable cam gears make much difference on factory cams?

Sorry for all the questions, but its good to know some people have already done some of these things and to get as much info as possible, before making a big mistake.

See'ya:burnout:

I am getting an RB26 Crank, RB26 Rods (which I will shotpeen, linish and crack test), ARP rod bolts, and Forged JE or Tomei Pistons...

I have an HKS GT3040 and I gained between 5-10rwkw all the way through the rev range on my standard RB25 cams by adding HKS Adjustable Cam Gears... By far the best benefit from fitting these Cam Gears was that it allowed the turbo to spool up 200rpm earlier, which made a huge difference in the driveability of the car...

I will be swapping over to RB26 solid lifters, because the hydraulic lifters have been known to fall over at over 8000rpm (I want a 9000rpm redline)...

Cheers.

[GTS-t VSPEC]

Hi Merli,

Sounds like a good setup, very similar to what I am proposing. How do you find the GT3040, it is what I am planning on using, but what is the drivability like and when does it spool up?

Are you planning on do camshafts aswell, or are you waiting to see how it performs?

See'ya:burnout:

[Merli]

Originally posted by GTS-t VSPEC

Hi Merli,

Sounds like a good setup, very similar to what I am proposing. How do you find the GT3040, it is what I am planning on using, but what is the drivability like and when does it spool up?

Are you planning on do camshafts aswell, or are you waiting to see how it performs?

See'ya:burnout:

The HKS GT3040 starts spooling at 2500rpm, and has 1bar at 4000rpm... I love it because I can cruise around in it, and it's just like driving a 2.5L N/A engine, and doesn't vent the BOV, and doesn't attract that much attention from the cops (as little as a Skyline could, anyway), but when I floor it, all hell breaks loose

I shall take my own advice and hold off on the camshafts until after the internals go in... There's no benefit in doing them at the same time as the internals, as cams can be dropped in without removing the head anyway.

I have sourced RB26 camshafts though, and will be removing NVCS, which I'm not too happy about.

[GTS-t VSPEC]

Merli,

Wow, I thought the GT3040 would have more lag than that, but it sounds like I was on the right track for what I want. I will hold off on camshafts aswell, probably just adding adjustable cam gears on factory cams once I have the internals in.

What duration and lift camshafts are you considering? I was told that 256/264 gives a nice streetable setup, but other have told me to go for 264/264, whats your opinion? The other thing I was told was to get camshafts that remove the NVCS, I'm not sure the logic behind that do you?

Anyway thanks for all the advice, I can't wait to put the forged pistons in etc. Are you overboring the engine to lower the static compression of fitting a metal headgasket?

See'ya:burnout: