RB20 Cam lift

[JH32]

I've been searching around on this forum and skylinesdownunder, and can't find what I'm looking for.

Basically, I want to run HKS 256 inlet with 8.8mm of lift and HKS 264 exhaust with 9mm lift.

Is this possible without changing valvesprings / machining the head ?

At what point does one have to change the springs or machine the head ?

Cheers

[V8eta]

I thought it was suppossed to be anything over 8.8mm you had to machine but apparently the apexi cams for the rb20 are 8.9mm so im not to sure, 9.0mm might be a little to much.

[Sydneykid]

I've been searching around on this forum and skylinesdownunder, and can't find what I'm looking for.

Basically, I want to run HKS 256 inlet with 8.8mm of lift and HKS 264 exhaust with 9mm lift.

Is this possible without changing valvesprings / machining the head ?

At what point does one have to change the springs or machine the head ?

Cheers  

Are they RB26 cams or RB20 cams?

[JH32]

v8eta: cheers for that mate ... just that someone told me once that i could use cams up to 9mm lift, and then a workshop suggested to me the other day that 8.8mm might be the limit :confused:

sydneykid: I haven't ordered the cams yet, but I will when I find out what lift I can use. I'll order them for my RB20DET.

[Sydneykid]

v8eta: cheers for that mate ... just that someone told me once that i could use cams up to 9mm lift, and then a workshop suggested to me the other day that 8.8mm might be the limit :confused:

sydneykid: I haven't ordered the cams yet, but I will when I find out what lift I can use. I'll order them for my RB20DET.  

OK, the questions sounds simple but it's not, the particualr issue here is PCD. If the camshafts have been ground with standard PCD, then 9 mm lift may need a slight (very slight) touch up on the clearances. There are pictures on other threads on where to machine, but is is bloody obvious when you have the cams in the head. Don't be afraid, it's a die grinder and about 1 minute per lobe.

If the PCD is smaller than standard, then ~9.2 mm is OK. But you will need to check your valve lash clearances as there are geometry issues with using smaller PCD cams. These may require offset followers to correct the geometry.

Bottom line, don't just grab the first pair of cams you see with the highest lift that say you don't have to relieve the head. My recommendation is, make sure you get standard PCD cams.

The second issue is hydraulic followers, I personally haven't had any success with cams over 9 mm lift in RB20's. I end up with follower rattle every time, probably because the engines have done a lot of k's and the followers are worn and leak a little.

Hope that helps

[JH32]

Thanks very much for your help Sydneykid.

So if I got a pair of 8.8mm lift cams I should be ok ?

One thing though, what does PCD refer to when talking about cams ?

[Sydneykid]

So if I got a pair of 8.8mm lift cams I should be ok ?

One thing though, what does PCD refer to when talking about cams ?

Re 8.8 mm lift, I have used a number of GTR cams in RB20's and they work fine.

PCD = Pitch Circle Diameter. In a camshaft it generally expressed as the distance from the the centre of the camshaft to the point of the lowest lift, valve closed, sometimes called the heel. The point of the highest lift, valve open, sometimes called the toe. The lift of the camshaft is measured by subtracting the heel (distance from the centre of the cam) from the toe (distance from the centre of the cam).

Reducing the PCD of a camshaft is a trick used by camshaft grinders to get more lift. Instead of building up the toe they take some off the heel, the follower takes up this loss of PCD (if it can), so you end up with more lift.

A few simplified examples;

1. Standard camshaft

Distance from centre of cam to heel = 6 mm

Distance from centre of cam to toe = 14 mm

Lift of camshaft = 8 mm

2. Reduced PCD camshaft with higher lift

Distance from centre of cam to heel = 5mm

Distance from centre of cam to toe = 14mm

Lift of camshaft = 9 mm

Will not require machining of head as toe is 14 mm from centre of camshaft

3. Standard PCD camshaft, but with higher lift

Distance from centre of cam to heel = 6mm

Distance from centre of cam to toe = 15mm

Lift of camshaft = 9 mm

Will require machining of head as toe is 15 mm from centre of camshaft

4. Increased PCD camshaft with higher lift

Distance from centre of cam to heel = 7mm

Distance from centre of cam to toe = 15mm

Lift of camshaft = 8 mm

Will require machining of head as toe is 15 mm from centre of camshaft

I have never seen a #4 for an RB but it is possible, so I always check the PCD quoted by the cam grinder.

Hope that helps

[JH32]

That's excellent, thanks heaps for that Sydneykid !!

[Roy]

So JiMiH, got thsoe cams sorted.

Im looking at ordering ASAP the following Tomei cams:

Inlet - 260/8.8mm , Part no. 1411260088

Exhaust - 270/8.8mm , Part no. 1412270088

I have adjustable cam gears to go with these puppies, should i just go 270 inlet as well or 260 both inlet , exhaust?

Im erring on perhaps sticking with 260s, but no-one botls cams into RB20s, lol, instead they bolt RB25s in:)

[DoughBoy]

Get the 270's all round Roy! Even if they give you reduced bottom end torque, the lope at idle will make women swoon and babies cry!

p.s. your car spends more time at idle than anything else!

[Roy]

Get the 270's all round Roy! Even if they give you reduced bottom end torque, the lope at idle will make women swoon and babies cry!

 

p.s. your car spends more time at idle than anything else!

You know what? You are right...LOL. Even if i aint quick at least my car will look and sound tuff? Response is for wimps, my top end is is going to make my ears bleed

[blackfink]

Anyone got any idea how much these tomei cams are? and where they can be sourced for a reasonable price? ie not with 200% profit margin thrown on.

Thinking of a pair of 270 ins/outs. for an rb20 as well..

[Roy]

Anyone got any idea how much these tomei cams are? and where they can be sourced for a reasonable price? ie not with 200% profit margin thrown on.

Thinking of a pair of 270 ins/outs. for an rb20 as well..

Im waiting to hear back from Greenline re-delivery times

see...

http://www.greenline.jp/catalogue/bcpartli...=R32B&intake=FI

[JH32]

Roy let me know how it goes ... I haven't ordered my cams yet.

Was going to do it last week but ended up getting a new exhaust manifold instead as I still wasn't totally sure which cams I would order. The Tomei 260/270 idea does sound good though.

Are you getting new valvesprings with those as well or just keeping the standard ones? I've heard that with the Tomei cams the uprated valvesprings aren't totally necessary.

[Roy]

Meh, upgrading the valve springs is for ppl that do things the proper way. :Oops:

Will see how it goes. No one can give me credible / reliable information concerning modding an RB20 so have to go on a fact finding mission.

If the std springs are no good then since i have a spare head i may do some DIY porting and put new springs in that, then swap over the cams and heads.

But im hoping that the cams will be fine with std sprigs

LOL th ebefore and after figures will be intersting

[JH32]

They will indeed, and I'm definitely very interested in seeing them.

That's the thing with the RB20 ... not many people have really done a lot to them. Well, it appears not on these forums anyhow. So hard to get reliable information for these engines.

[Roy]

It sux, even when speaking to workshops, it seems RB20 owners never really bother doing anything to them simply because it is so easy to get better power out of RB25/26/30s.

But it aint an R32 GTST without an RB20, and im hoping my car will be a quick R32 GTST with only the RB20, but cams are about as far as im willing to go. If i need springs to make them work then ok.

[R31 POWER]

Excuse my stupidity but are there any Jap cams that WILL bring on power earlier?

[Roy]

From my understanding of old school love of the V8 it all comes back to cylinder filling. Short duration cams are good for maintaining good cylinder filling at low rpm but as revs rise they can cause a restriction. Up top it would choke two fold as you have a turbo strying to stuff extra cfm inot the cylinders.

Vice versa, big duration cams give good flow at high rpm but poor cylinder filling/velocities at low rpm. Throw a turbo into the mix and the physics of cylinder filling seem the be masked by sensibly sized turbos. Not saying that cams still dont result in power, but the good old turbo masks alot of inefficiencies/tuning of inlet manifolds, exhausts and even cams selection.

So im guessing to bring on power earlier you would want as much lift as you can muster with minimal increase in duration. How that pans out with your turbo selection and power band who knows, id love to know the cam specs of the GMS R31 GTS-R used:thumbsup:

DISCLAIMER: Im no engine building guru. The above is my basic understanding of internal combustion engines, even the above could be flawed.

[black_32]

i bought some cams off a guy from a 33 gtr he told me he had some in his and they worked well but i put them in and it ran like a heap just wonderin if ne 1 had tryed this btw i hve an rb20