Jump to content
SAU Community

RB26 Idle Quality With Tomei Poncams

GTR32

By GTR32,
in Engines & Forced Induction

 Share

Recommended Posts

GTR32 Rising Star

GTR32

Posted
Posted

The benefits of cams and adj pulleys seem to be well known. However, a NZ based tuner with a shop on Silverwater Rd in Sydney (some of you will know who this is) has suggested that idle will be lumpy and there will be an increase in lag using either or both. Cams are 250/260 9.15 mm Tomei PONCAMS.

They seem to know their stuff, can anyone comment based on experience?

Regards

Link to comment
https://www.sau.com.au/forums/topic/42148-rb26-idle-quality-with-tomei-poncams/
Share on other sites
meggala Grand Master

meggala

Posted
Posted

yeah the idle might be a bit lumpy and there might be a bit of lag associated but the amount of power you generate when on full boost will be higher.

there are pro's and cons to doing cams.mostfactory cams are a compromise due to the need to meet emissions standards.

meggala

Warpspeed Experienced

Warpspeed

Posted
Posted

A very great deal depends on how the cams are timed in the engine when they are installed. Each cam could be either advanced or retarded and the resulting valve overlap could be set either narrow or be quite wide.

Factory cams have very little or no valve overlap to keep idle emissions within legal limits.

How much overlap you can get away with on a turbo engine depends mainly on total exhaust back pressure, which in turn depends on turbine size and a/r and how much noise you want to make. It is all relative, and it is not really possible to give advice.

I think you are going to have a lot of other problems long before the idle goes really lumpy on a turbo engine. If you overcam it, it is not going to run well unless you really uncork the exhaust side, then it will be very noisy.

So decide what you want. Do you want just a bit more on road performance, but still keep it reasonably quiet ? or do you want balls to the wall top end horsepower only, and noise is of absolutely no no concern.

Too many guys fit bigger cams then find out it is laggy and unresponsive. They then fit a huge exhaust and find it then runs really well, but is cop bait. The usual conclusion is that the original exhaust was limiting performance and had to go. Nobody ever thinks that the engine did not go because it was overcammed, it is always the exhaust that is the problem not the cams.

Everyone has their own ideas about all of this, and what is acceptable and what is not.

Whoneedstherapy Veteran

Whoneedstherapy

Posted
Posted
Those cams will not be overly lumpy... Just reduce the overlap a little bit and it'll idle like a stocker.

As merli mentioned, these cams can be sorted out if you don't want them to be lumpy, but then again there is a customer of that certain tuning shop that has those cams and has them dialed in to be a little on the lumpy side. You can definately go either way and i personally would not discount the cams because they are going to be lumpy. You can have big cams without having problems with idle. It all depends on how there setup.

GTR32 Rising Star

GTR32

Posted
  • Author
Posted
Those cams will not be overly lumpy... Just reduce the overlap a little bit and it'll idle like a stocker.

Thanks Merli;

These cams are very mild, if the overlap is reduced won't it negate their effect? I'm assuing you mean do this using the adj pulleys? I'm also thinking that the duration will affect idle more than overlap, which I can't do anything about.

GTR32 Rising Star

GTR32

Posted
  • Author
Posted
As merli mentioned, these cams can be sorted out if you don't want them to be lumpy, but then again there is a customer of that certain tuning shop that has those cams and has them dialed in to be a little on the lumpy side. You can definately go either way and i personally would not discount the cams because they are going to be lumpy. You can have big cams without having problems with idle. It all depends on how there setup.

Hi Aphex;

As always, it's in the tune...I think that the a good tuner with a PFC will be able to overcome any lumpyness, particulary with such a mild cam. That shop doesn't seem short on experience so it would surprise me if they'd base their views on one customer but you never know.

Hopefully someone using these cam specs will appear.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi guys, I have already replied to GTR32 in a PM, but I was discussing this with the race team guys at EC on the weekend and they had a good chuckle over it. We all reckon 256 degrees is very mild, in fact we stood around the R34 GTT (that has these cams in it) and a standard cammed R33 GTST and no one could pick the difference at idle. At 4,000 + rpm it was a different story though.

Scooby Veteran

Scooby

Posted
Posted
Hi guys, I have already replied to GTR32 in a PM, but I was discussing this with the race team guys at EC on the weekend and they had a good chuckle over it.  We all reckon 256 degrees is very mild, in fact we stood around the R34 GTT (that has these cams in it) and a standard cammed R33 GTST and no one could pick the difference at idle.  At 4,000 + rpm it was a different story though.

Proof of the pudding. Assuming other aspects of the cars were comparable, did the cams contribute to lag in the R34 GTT?

Scooby Veteran

Scooby

Posted
Posted
Hi guys, I have already replied to GTR32 in a PM, but I was discussing this with the race team guys at EC on the weekend and they had a good chuckle over it.  We all reckon 256 degrees is very mild, in fact we stood around the R34 GTT (that has these cams in it) and a standard cammed R33 GTST and no one could pick the difference at idle.  At 4,000 + rpm it was a different story though.

Assuming other aspects of the cars were comparable, was the R34 GTT less responsive? Were the cams dialled in with pulleys?

Sydneykid Grand Master

Sydneykid

Posted
Posted
Assuming other aspects of the cars were comparable, was the R34 GTT less responsive? Were the cams dialled in with pulleys?

Both have;

*the same spec turbo

*GTR intercoolers

*one has a HKS POD filter, the other a Pipercross panel

*exhausts are different brands and the R33 is 3" while the R34 is 3.5"

*no adj pulley on the R34 (we found no average power gain from fitting it)

*both have Power FC's

*the R34 has a PFC boost control kit, the R33 has an Autospeed twin Norgren valve based boost controller

The R34 (with cams) makes more power EVERYWHERE than the R33, on or off boost , it makes boost earlier, has higher average power and higher max power. So it is certainly more "responsive" in my opinion.

It is worth noting that the R34 RB25DET has solid lifters, so it uses the Tomei 260 degree Poncams. With hydraulic lifters (as in R33) they recommend using 256 degrees.

Hope that answered your questions.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Kapr
      RB20DE NEO smallbox clutch.

      By Kapr · Posted

      For once a good news  It needed to be adjusted by that one nut and it is ok  At least something was easy But thank you very much for help. But a small issue is now(gearbox) that when the car is stationary you can hear "clinking" from gearbox so some of the bearing is 100% not that happy... It goes away once you push clutch so it is 100% gearbox. Just if you know...what that bearing could be? It sounding like "spun bearing" but it is louder.
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      Yeah, that's fine**. But the numbers you came up with are just wrong. Try it for yourself. Put in any voltage from the possible range and see what result you get. You get nonsense. ** When I say "fine", I mean, it's still shit. The very simple linear formula (slope & intercept) is shit for a sensor with a non-linear response. This is the curve, from your data above. Look at the CURVE! It's only really linear between about 30 and 90 °C. And if you used only that range to define a curve, it would be great. But you would go more and more wrong as you went to higher temps. And that is why the slope & intercept found when you use 50 and 150 as the end points is so bad halfway between those points. The real curve is a long way below the linear curve which just zips straight between the end points, like this one. You could probably use the same slope and a lower intercept, to move that straight line down, and spread the error out. But you would 5-10°C off in a lot of places. You'd need to say what temperature range you really wanted to be most right - say, 100 to 130, and plop the line closest to teh real curve in that region, which would make it quite wrong down at the lower temperatures. Let me just say that HPTuners are not being realistic in only allowing for a simple linear curve. 
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      I feel I should re-iterate. The above picture is the only option available in the software and the blurb from HP Tuners I quoted earlier is the only way to add data to it and that's the description they offer as to how to figure it out. The only fields available is the blank box after (Input/ ) and the box right before = Output. Those are the only numbers that can be entered.
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      No, your formula is arse backwards. Mine is totally different to yours, and is the one I said was bang on at 50 and 150. I'll put your data into Excel (actually it already is, chart it and fit a linear fit to it, aiming to make it evenly wrong across the whole span. But not now. Other things to do first.
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      God damnit. The only option I actually have in the software is the one that is screenshotted. I am glad that I at least got it right... for those two points. Would it actually change anything if I chose/used 80C and 120C as the two points instead? My brain wants to imagine the formula put into HPtuners would be the same equation, otherwise none of this makes sense to me, unless: 1) The formula you put into VCM Scanner/HPTuners is always linear 2) The two points/input pairs are only arbitrary to choose (as the documentation implies) IF the actual scaling of the sensor is linear. then 3) If the scaling is not linear, the two points you choose matter a great deal, because the formula will draw a line between those two points only.
×
×
  • Create New...