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RB26 Idle Quality With Tomei Poncams

GTR32

By GTR32,
in Engines & Forced Induction

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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

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https://www.sau.com.au/forums/topic/42148-rb26-idle-quality-with-tomei-poncams/
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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.

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