Cam Question

[DaveB]

Hi all,

I've been doing some research on Tomei Poncams for the NEO/R34 RB25DET.

Would it be accurate to summarise?...

- there are 2 styles of Tomei cams available for RB25's - Poncam (lower duration, lower lift) and Procam (higher durations available than Poncam, higher lift). The version I'm interested in is Poncam as it doesn't require valve spring upgrades etc.

- the style I'm interested in, Poncams, are available in 252 degrees and 260 degrees

- 260 degree cams require adjustment of valve shims to increase clearance to ?(.45mm or whatever it is Tomei specify) whereas 252 degrees don't?

Basically I would like to know from those who have fitted Poncams (to any version RB25 really):

- if you've gone for 260 degrees or thereabouts, how liveable is the idle, in an auto? (ie. does it stall easy, need to set idle over 1,000rpm etc?)

- anyone with 252 degrees, much improvement? much difference in idle?

- is shimming required? If not, is this something which could be attempted as a DIY? (I know, tuning would be required)

- at what power level might one see a decent benefit, and is head porting necessary?

cheers for any info

[wolverine]

I have 260 deg poncams.

There is a slightly lumpy idle but it idles fine.

The car was shimmed to 0.45mm but this has created slight lifter noise. I would go with a skinnier clearance. Some people have checked it and left it factory shims (I don't know what clearances they end up having).

The 260 deg seem to make the car better everywhere but I would still suggest you will get better value for money out of turbo selection/change. At the time that we decided to change them there was conjecture about the lift and duration of the factory cams so I sucked it up and changed them.

Factor in labout to get to them, removal, new cams, new shims ($200+) and tuning vs new sexy time turbo (sorry watched Boral last night).

[KiwiRS4T]

^^^tend to agree. In order to improve flow on a n/a motor it is necessary to change cam profiles and port and polish heads. Its much easier (and cheaper) just to get a bigger or more efficient turbo. Of course once you are getting well over 300kw then headwork and cams come into it again as does better manifolds. Retaining the stock cams and vct with an adjustable exhaust cam gear will give you adequate tuning options near to the limits of say a GT3076 on an RB25.

[darrinspencer]

I use to run type B 260deg poncams when I had the smaller 380ps Apexi turbo on and 250rwhp.

Probably a waste of time with that turbo. I removed them and sold them

Probaly could put them to better use now with the gt3076.

I did not re-shim.

[DaveB]

Thanks guys. I should have mentioned that my turbo is a GCG high-flow (I'm not sure what that makes the internals - 3071 or 3076? or somewhere in between). Wolverine I guess you had a manual when you changed cams? I would be interested to know how the idle affects an auto, whether it's too drastic and stalls etc. Sounds OK though.

So at ~250+rwkw, which I hope to be in a couple of weeks after a tune, will I see any benefit or, at the limit of the turbo already, will it not help?

[KiwiRS4T]

Hi Dave

If you make it to 250awkw I think you will be surprised just how fast the old Stagea gets along! I think you already have a Z32 afm - can't remember what injectors? Do you have a Just Jap turnflow front mount or a Blitz? Intercooler could become a limitation. You could spend $5k on Poncams and headwork. If you sold the GCG and got a Gt3076 even with a low mount you could make near 300kw for around 2K or get a 6boost manifold with external wastegate and crack 300!

Or even without the 6 boost - see the following page esp post 662 663 675 680 for some outstanding results from a Hypergear turbo tuned by Trent at Status Tuning!

http://www.skylinesaustralia.com/forums/Rb...html&st=660

[wolverine]

I can't spell when in a hurry it seems (try Borat not Boral, labour not labout).

The cams will achieve what you want as well it will idle fine even with an auto. It should increase your midrange and top end by about 10-15kw. If you don't re-shim and just replace the cams plus a few gaskets it won't be that expensive.

One of the new GTX3071's might be an option if you want more power and more midrange but then you need intake, oil/water and dump pipe changes. I would caution you on going too large on the turbo front as you start going backwards with response on the street.

[dirtyRS4]

All is correct ^^^. Ask Tangles he has proven figures with these in. Compare results.

Edited November 29, 2010 by dirtyRS4

[DaveB]

Thanks for the replies all Rob I have been having issues making power and I now know why (the compression/detonation issues) so I'm only guessing at 250Rwkw ( = ~ 230awkw?) after the next tune since an R34 made 280rwkw with a manual and a GT3071. I'll be installing 600cc Deatchwerks injectors and a 2nd-hand Z32 I've had sitting around for a while (picked it up for a bargain). I've also upgraded my sidemount intercooler; that was a lot of work but worth it. Sidemount should be good for 500+hp now with less than 1/10th PSI pressure drop through the core so this shouldn't cause too much of a limitation.

Certainly if I achieve anything like 250kw at all fours, I will be happy In that case, I don't think the extra 10-15kw of poncams is going to entice me to spend the extra ~$1,000. I was just interested to know if this extra power could be realised using the same turbo.

[DaveB]

Hmm you're right about those Hypergears Rob. I'll have to checkout which state Status is in Though I am mainly interested in turbo mod's which will fit under the factory heatshield.

PS cheers for the help freighting the CAS sensor too; I have changed it and it is running fine; unfortunately that isn't the issue with my pinging though. It does however suggest pretty stongly that a NEO RB25DE sensor is the same as a RB25DET. Someone with FAST probably already knows this lol.

Hi Dave

If you make it to 250awkw I think you will be surprised just how fast the old Stagea gets along! I think you already have a Z32 afm - can't remember what injectors? Do you have a Just Jap turnflow front mount or a Blitz? Intercooler could become a limitation. You could spend $5k on Poncams and headwork. If you sold the GCG and got a Gt3076 even with a low mount you could make near 300kw for around 2K or get a 6boost manifold with external wastegate and crack 300!

Or even without the 6 boost - see the following page esp post 662 663 675 680 for some outstanding results from a Hypergear turbo tuned by Trent at Status Tuning!

http://www.skylinesaustralia.com/forums/Rb...html&st=660

[dirtyRS4]

TBH i have to agree with Bob. Do the rest first. IMO at this stage you have to ask yourself what is the outlay for such little return. 10-15kw in the mid range. Choosing an apropriate turbo specification and manifold is the key. Remember it becomes more expensive and smaller returns as you squeeze kw out of the motor.

Edited November 29, 2010 by dirtyRS4

[DaveB]

TBH i have to agree with Bob. Do the rest first. IMO at this stage you have to ask yourself what is the outlay for such little return. 10-15kw in the mid range. Choosing an apropriate turbo specification and manifold is the key. Remember it becomes more expensive and smaller returns as you squeeze kw out of the motor.

Absolutely; seems like good advice. Though I have kinda done everything else (or will have by this time next week) and the prospect of 10-15kw more midrange is kinda appealing (I am, of course, assuming a price for poncams well under $1,000 which means the expense and ease of install compares favourably - for me anyway - with a turbo upgrade).

However from some brief research, talking to people who've done it and my own intuition, I'm thinking that torque at low-rev's would be affected. So I think the best choice for a heavy vehicle like the stagea would be either stock cams or maybe 252's (type A's) since they still have the higher lift which should help.

Edited November 29, 2010 by DaveB