GTR Forum banner

21 - 37 of 37 Posts

·
Registered
Joined
·
700 Posts
Well it flows almost as good as a RB26 head, bigger inlet valves aren't that dear and it already has a variable inlet cam. All you need is a v-tec controller to run the selenoid and a bit of faffing.
 

·
Registered
Joined
·
3,720 Posts
hipogtr said:
It only modifies inlet cam timing and, from memory, I believe the working range is 90-130 degrees ATDC. Maybe Bean or Abbey can confirm this?
Yes, it's inlet cam only and the range is 85-135 degrees.

I love threads like this where someone asks a perfectly reasonable question - and there are all kinds of opinions from people who've never even seen it but they somehow know how it can be done cheaper or better.
Somebody show me another way to have made the difference in power and torque characteristics that hipogtr got by installing the Vcam and adjusting the tuning to match because I'd love to see it....
I've never seen any other street car perform like Hipogtr's car - it's drivable everyday, has full trim, 100% reliable, can do 200 mph and still has fantastic response and low down ability. If anyone has a car to match it then they can say that the Vcam is not worth it.
 

·
Registered
Joined
·
1,969 Posts
Bean,
Maybe it's because some of us are sceptical. V-Cams, or at least the concept has been around for a number of years. Later GTS's have it as standard, for example, as do many Toyota's, BMW's, etc. It is rumoured Nissan wanted to fit it to the GTR (NVCS) around the NEO time, but decided not to. Why?
For those that don't know what v-cam does, it is basically like having an automatic vernier cam gear on your inlet cam. Playing with a vernier cam gear on any car will replicate exactly the figures of the v-cam at one area of the rev range, with a sacrifice at the other end(s). Unfortunately with a vernier wheel, you have to choose a position, and lock it. The v-cam advances /retards the inlet cam automatically as the revs change. Any tuner will tell you there is an ideal cam dial in, adjustments from there will only make a small difference further up or lower down in the rev range. Unless I'm mistaken, the V-cam doesn't finely adjust the the cam angle, rather moves it from max one way, to max the other in an instant. So hardly a sophisticated device. I don't often hear of people dialling in more cam when at Santa Pod, or track days, and then re-setting the cam timing back again for road use, even though it is a simple two minute job with a 4mm allen key (well, if it weren't for the cam cover).

Fitting an RB25 head on a GTR is not a silly idea, if you want a cheap V-cam. Also as mentioned previously, you used to be able to get a cam gear with centrifugal adjustment, which is a 1/10th of the price solution, and as it adjusts in small increments with engine speed, so is more 'intelligent' than the v-cam.

For ultimate hp, a V-cam would limit the amount of lift and or duration choice to perhaps 272's or lower (as mentioned by HKS), and I would imagine lower than 9.5mm lift (without recessed valve cuts into the pistons). The higher the duration cams the more effect this will have on the power curve, and driveability, but it won't allow 280+deg cams, the ones that really need something like this.

If you want a high (not drag spec) power, daily driver, with max possible response, and you've got all the other usual mods, and still want more, then perhaps the v-cam is the way to go. Oh, you do need £4500 spare in your pocket too.

I'm sure when Abbey have done all the tests, Mark will comment on the differences. It will be interesting to hear his thoughts on when the V-cam becomes worth it. I am placing my money on it being well down the list.

Not all of us believe the hype from the big tuning co's
 

·
Registered
Joined
·
2,170 Posts
The thing is here is that this comment sums up Chris' situation perfectly...

If you want a high (not drag spec) power, daily driver, with max possible response, and you've got all the other usual mods, and still want more, then perhaps the v-cam is the way to go. Oh, you do need £4500 spare in your pocket too.
Still interesting reading for someone like myself with limited teccy knowledge!
 

·
Registered
Joined
·
6,129 Posts
I saw Marks new engine the other day .... I almost made a very embaressing mess (LOL !) ;) I'm quite envious, and would love that lump in my car. Hopefully he managed to get it finished for all you guys to see at J.A.E. this weekend.
 

·
Registered
Joined
·
1,986 Posts
Nisfan,

I believe the V-cam allows fine adjustment against revs. It's not simply a case of swinging from min to max. At least not on the limited edition V-cams. Virtually every tuner car in Japan is currently running one of these.

To be honest, I can't see the V-cam pro being any different to the ltd. as it's not far off the price. There were rumours that the production V-cam would only have a single adjustable crossover point but the ones Bean and Gio have are constanty variable.

Regards
Nito
 

·
Registered
Joined
·
1,969 Posts
NITO said:
Nisfan,

I believe the V-cam allows fine adjustment against revs. It's not simply a case of swinging from min to max. At least not on the limited edition V-cams. Virtually every tuner car in Japan is currently running one of these.
Well that clears that up, goes a little further into justfying the cost in my books, but only a little.(as that is a fair bit more complicated than an on/off type adjustment)

Regarding what Jap Tuners have on thier cars, well, they are more about business and to a degree hype. If it is seen to be more desireable, they will make sure they use it, or at least appear to be using it. Doesn't neccesarily mean it works. The Japanese market seems very fickle to certain concepts. One car co. brings out rear wheel steering, then they all have it. Now the RWS craze has gone very few Jap cars have it fitted.

If HKS or anyone for that matter replicated the Honda V-Tec, for an RB, now that would be good. That short of F1 style pneumatic valves, is the best by far.

One last thing, the range 85 - 135 ATDC degrees, what a load of bull. Thats the cam range, not the adjustment range given by the V-cam. The v-cam will only give perhaps 6 (cam) degrees in either direction on top of the normal cam range. Much more than that, and pistons and valves have a little get together.
If you make a product, be truthful about the figures, not skew it into making someone believe a stock cam will act like a 270deg one, at top end.

Hipo,
Was anything else done to the engine/tuning other than a fitment of the V-cam. The results shown are way more than I would have expected. 150hp @ 6000rpm. Was the exhaust cam timing changed at all.
 

·
Registered
Joined
·
1,969 Posts
Hipo, I see you mentioned a fitment of a screamer pipe, and some fine tuning. Was this done in conjunction with the v-cam between the before and after results?
Once the v-cam is fitted, can it be locked off? would be good to see dyno results with v-cam locked in central position vs. unlocked.
 

·
Registered
Joined
·
700 Posts
NISFAN said:
Bean,
Fitting an RB25 head on a GTR is not a silly idea, if you want a cheap V-cam. Also as mentioned previously, you used to be able to get a cam gear with centrifugal adjustment, which is a 1/10th of the price solution, and as it adjusts in small increments with engine speed, so is more 'intelligent' than the v-cam.


Not all of us believe the hype from the big tuning co's
Thats why I am sort-of going this way. I am fitting GT-R externals (2 x R34 Turbos and throttle bodies with Reinick pistons) to my GTS25t ot tt as it will be. So how does the V-cam actually modulate the cam - electric or hydraulic and how does it acheive this technically ?As you say the range of operation cannot be great otherwise the pistons will close the valves! Does any one know the actual differences between the RB25DET pre & post NEO spec ?

I think Nissan didn't bother with VVC on the RB26 because of the costs involved or maybe they just felt if it's not broken why fix it.

I for one take everything the tuning companies say with a pinch of salt. Aftermarket stuff is never as good as factory racing dept tackle, and is always way overpriced. To some extent I get brassed off listening to people saying it's got Trust this, HKS that and Apexi the other and Mr XXXX took several thousand pounds out of my wallet to fit it all for me and set it up. For sure there is some repectable tackle available from Tuning co's, Jun pistons are made by Cosworth, Trust gearboxes are made by Quaife, Farndon probably make a lot of the a/m cranks - but fashion doesn't warm to these names.
 

·
Registered
Joined
·
2,110 Posts
NISFAN said:
Was anything else done to the engine/tuning other than a fitment of the V-cam. The results shown are way more than I would have expected. 150hp @ 6000rpm. Was the exhaust cam timing changed at all.
Besides the pieces that I mentioned earlier (i.e. screamer pipes, ECU retuning, and VCam) nothing else of relevance was changed. I already ran 272s both IN/EX prior to the VCam going on. The overall tuning (both ECU and VCam setup) is what made the biggest change. I'll stress again that the baseline run we are comparing against is a neutral map (i.e. no ECU tuning optimizations) without VCam. Consequently, you are right in saying that the gains are more than you would expect in a real back to back comparison. This was the first thing I mentioned in my first post.

NISFAN said:
Hipo, I see you mentioned a fitment of a screamer pipe, and some fine tuning. Was this done in conjunction with the v-cam between the before and after results?
I fitted the screamer pipes after the first run (which also didn't have the VCam). That is, the original curve does not have the benefit of screamer pipes or optimized tuning. I had a lot of backpressure in my exhaust stream at the top end due to the rerouting of the external wastegates into the exhaust for emissions. Its clearly obvious in my other dyno graphs. Consequently, some of the impact on the new curves from 6,000rpm upwards must be attributed to this change.

NISFAN said:
Once the v-cam is fitted, can it be locked off? would be good to see dyno results with v-cam locked in central position vs. unlocked.
I agree that it would be good to see this. Hence my requst to Mark (Abbey). I believe you can lock/switch off the VCam effect after you've installed it, however, since a complicated interaction exists between the VCam and the engine tuning, doing it that way will not give you the results you're after. What you really want to see is a compare between an optimized tune without the VCam and an optimized tune with it. For example, as you mentioned, without the VCam you will be setting the vernier pulleys differently - this clearly impacts the curves in a non-VCam situation.

Having said all this, IMHO, modifying at our level is not an investment decision - its simply entertainment. If you can afford to play, make the most of it!

Cya O!
 

·
Registered
Joined
·
3,720 Posts
NISFAN said:
Bean,
Fitting an RB25 head on a GTR is not a silly idea, if you want a cheap V-cam. Also as mentioned previously, you used to be able to get a cam gear with centrifugal adjustment, which is a 1/10th of the price solution, and as it adjusts in small increments with engine speed, so is more 'intelligent' than the v-cam.
Never said it was a silly idea - in fact I said if you can show me a way to get the results that I've seen from the Vcam another way then I'd love to see it.
 

·
Registered
Joined
·
1,986 Posts
Bean,

Does your car run a screamer pipe or is the external gate routed back into the exhaust?

Thanks
Nito

btw. both your cars look fantastic on Dino's Blog. - Congratulations!
 

·
Registered
Joined
·
172 Posts
get JUN high lift cams set. cheapest in the market..
 

·
Registered
Joined
·
3,720 Posts
NITO said:
Bean,

Does your car run a screamer pipe or is the external gate routed back into the exhaust?

Thanks
Nito

btw. both your cars look fantastic on Dino's Blog. - Congratulations!
My ears say - definitely not routed back into the exhaust :D
 

·
Registered
Joined
·
7 Posts
RB211 said:
Does any one know the actual differences between the RB25DET pre & post NEO spec ?
Ive read that the NEO has a different turbo with a plastic compressor wheel. I'm trying to learn more about it, if anyone knows make/model of the neo turbo let me know.
 
21 - 37 of 37 Posts
Top