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Rb25 Non Vct Cams

RB25_Zenki

By RB25_Zenki,
in Engines & Forced Induction

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RB25_Zenki Contributor

RB25_Zenki

Posted
Posted

Hey guys.

Long story short I have decided to delete VCT out of my RB25. At the moment I have HKS cams in it and a HKS adjustable cam gear on the exhaust side. So I need a new cam on the intake and another cam gear. The Problem I have is when I bought my motor I was told it had aftermarket valves and springs in it. but the old owner of the motor didn't know to much. So now im going to get a new set of cams im not sure what I should do. Is it worth taking the head to see if it has valves and springs and if it does I can go bigger cams or should just slap the same size cams back in it but non VCT.

Just want to hear people opinions on the situation?

Thanks

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https://www.sau.com.au/forums/topic/442178-rb25-non-vct-cams/
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Dale FZ1 Veteran

Dale FZ1

Posted
Posted

8.9mm is about the limit before you would need to lift the head and have it machined for clearance if you went for higher lift.

You will find that the likes of Kelford, Camtech, and Tighe can supply fixed cam profile that's compatible with hydraulic lifters.

methz Proficient

methz

Posted
Posted

Im in a similar boat, ive got camtech 272s 9mm lift with after market valves/springs, I asked for the 272s to be drilled to suit vct, but im thinking about going down the route of ditching the vct and putting an adjustable intake cam gear on and putting some overlap on the cams and retuning to suit. any ideas from ppl with experience? I mean most setups around 500atw mark aren't using vct, so why should I?

Dale FZ1 Veteran

Dale FZ1

Posted
Posted

Broadly speaking, I suspect the factory had emissions/economy targets to reach, and their design brief required smooth usable torque from 1500-4500rpm. VCT plays a big role in hitting those marks.

Someone chasing 500rwhp has targets that don't really include emissions or economy, and the engine is likely to spin between 4500-8000 depending on cubic capacity. Strong low rpm torque may not be a high priority and lets face it between 3-4000 an RB25 or 30 in the 500rwhp range will be making significantly more mumbo than most. Would you notice the lack of VCT in that area? Probably. Would it be a big loss? Probably depends on how frequently you actually access the potential.

For a 100% race use I'd think a well matched fixed cam, properly dialled in would be viable and remove one layer of complexity. For 100% road use and with a set of VCT cams it would be hard to think why you would ditch them other than to have a play.

  • Like 1
Mick_o Grand Master

Mick_o

Posted
Posted

Where did you read that most people making around 500 aren't using vct?

As Dale said if its street only VCT for the win. If not if its living life up in the rev range fixed cams will be fine.

But seriously sacrificing low down torque driveabilty and turbo response for a lumpy idle is just plain homosex :/

nicksamaniac Collaborator

nicksamaniac

Posted
Posted

Fyi -I have a non/pre vct head on my 30, at standard cam timing there is alot of standoff/reverberations coming out the intake at low rpm under load, and it lacked low end torque for it. I've had to dial the intake cam quite a bit to get low end torque and boost to come on lower in the rpm range.

But at the expense of high rpm performance, it now falls over abit up high.

I believe that Vct helps to overcome this, and helps to provide a wide power band on 1 cam profile.

Piggaz Grand Master

Piggaz

Posted
Posted

^^^ then why would you even consider ditching it? VCT is your friend.... Unless you like the "nothing, nothing.... BOOM" delivery, then go for it.

At the end if the day, our cars are not light with short stroke, small capacity engine with relatively low wish comp ratios with tallish gearing . Monster cams and throwing away VCT are only going to make them harder to drive on the street.

If you don't want it, I'll buy it off you and put it on my engine :P

  • Like 1
Piggaz Grand Master

Piggaz

Posted
Posted

I gave camtech a call today and they said go with 268 cams exhaust and intake and 9.00mm lift. I hope my car has springs in it. if it doesn't would my motor still hold up?

You'll just valve float which will limit your boost and or rpm.
Piggaz Grand Master

Piggaz

Posted
Posted

A set of suitable valve springs will hardly break the bank.

$600 for my springs and Ti retainers. Retainers were actually lighter and fit better than the 2 x more expensive jap crap.

Once again, jap shit fails - won't buy jap again.

nicksamaniac Collaborator

nicksamaniac

Posted
Posted (edited)

$600 for my springs and Ti retainers. Retainers were actually lighter and fit better than the 2 x more expensive jap crap.

Once again, jap shit fails - won't buy jap again.

No offense intended, but you just made me lough out loud! You do realise your engine is jap built? (but I do understand what your saying) Edited by nicksamaniac
Piggaz Grand Master

Piggaz

Posted
Posted

No offense intended, but you just made me lough out loud! You do realise your engine is jap built? (but I do understand what your saying)

Lol. Rightio mate. I'm not talking OEM parts, I'm talking what often is expensive stuff, aftermarket gear. I'll give you an example.

HKS step two valve springs used with an aggressive custom made cam valve floated at around 5500 at 20 psi on my own engine. Pulled them out along with the mega dollar Jun Ti retainers and put in a a set from camtech. Not only did it not valve float but the retainers fit the spring much better, also 1/3rd the price!

Exhausts, you'd be crazy not to get a custom one made. It'll fit better and not really be much more expensive.

Nice pretty sard fuel rail - doesn't have a seat for the injectors to but up against. Waste of cash.

Tomei manifolds - not worth the box they came in as they crack. I've personally done two sets and a mate has one off an Evo currently holding down the concrete in his garage. Cracked to hell.

That's only a few examples.

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