256 RB25 Poncam experiences plz .

[boostn0199]

Idle is basically same you cant really tell cams have been changed. Performance wise when I put them in 6years ago on 98 it made gains in the mid and 10kw up top and response remained the same. 

[Dose Pipe Sutututu]

2 minutes ago, boostn0199 said:

Idle is basically same you cant really tell cams have been changed. Performance wise when I put them in 6years ago on 98 it made gains in the mid and 10kw up top and response remained the same. 

you can force it to brap a little, as I've explained earlier

nothing braps as good as a set of 272+ lol

[discopotato03]

From Tomei USA .

R33 RB25DE(T) Early .

Inlet   8-68 so 8+68+180=256 , Lobe center 120 deg .

Cam actuator pressurised I assume 28-48 .

Exh 63-13 so 13+63+180=256 , Lobe center 115 deg .

The way most people look at the figures its 8-68 63-13 , or (I'm assuming)  28-48 63-13 cam actuator pressurised . 

Overlap 8+13=21 degrees .

Cam actuator pressurised I assume overlap timing is 28+13=41 degrees , so not surprised ole 25 won't idle in this state .

 

A .

 

 

 

 

[zebra]

So if you go off tomei's advertised duration at 1mm of lift which is 220deg for both inlet and exh and using a 115deg lsa.

 

My calculator says

 

Camshaft Calculations - Lobe Center / Duration

Your Tomei 256 has an Overlap of -5.00 degrees and has in Intake Duration of 220.00 degrees. The Exhaust Duration is 230.00 degrees. Your Lobe Separation Angle is 115.00 degrees. The Inlet Cam has an Installed Centerline of 120.00 degrees ATDC. The exhaust cam has an Installed Centerline of 110.00 degrees BTDC.

 

So no overlap at all. Infact both valves are closed for 5 degs of crank rotation

[zebra]

Interestingly...that differs a lot from tomeis cam card. But my calculator has no way of allowing for vct on the inlet

[Dale FZ1]

End of the day, they can  be a handy improvement to "whole of engine package" - with a few riders.

Not much point under the 300rwkW mark - change turbo spec and/or add boost.  Or change fuels if not on E85 (and yes we know you are on some home brew Adrian).

Expect some change to idle sound, but no real change to idle quality.  You can/would play with the fuelling and ignition in a couple of cells depending on what you want to achieve in that area

Possibly a small lift in useable rpm ceiling before it noses over, and slightly softer down low.

Probably an increase in fuel consumption - if this grind gives some increased overlap over OEM for scavenging then that's to be expected.

For road use only, and if you're hell bent on best fuel economy, not much point.  But it's kinda fun to play a bit and see for yourself.  Worst case scenario, go back to stock cams for a known quantity if you're not happy.

 

 

[discopotato03]

50/50 E70/P98 - E35 . 

Problems atm confirmed this afternoon - leaking exhaust valves on no2 and when cams come out will see if it has bucket issues or valve/seat probs . Hoping in a way that head comes off tomorrow so top end can be freshened up . This 163K/20 yr old RB25 breathes absolutely zip when running with filler cap off so bottom end should be good . 5 of the 6 plugs looked mint though no so much on 2 . The opportunity exists to refit the standard cams and Id be interested to hear what Stao thinks of std vs Poncams in a 33 spec 25DET . Will probably leave the Tomeis in because a few things like better turbo and injectors have changed since those cams went in - 70K back .

I don't know how long the valve issue has been there and probably blamed some of its antics on the larger side feeds I ran before the ID750s went in . Car ran like a dog today with a weak stalling idle made worse by using AC and headlights (defog in heavy rain) .

Will know more tomorrow cheers  A . 

 

[Dose Pipe Sutututu]

Temp fix, increase idle duty and the values of the proportional and integral of the closed loop settings. 

At least car won't be "like a dog"

[discopotato03]

Did everything possible brain wise , derivative gain/proportional gain/anti stall gain all maxed . Mucked around with stepper base position and idle screw and all the conditions to do with closed loop idle and idle ignition timing . 

This is a mechanical issue and when fixed should make the tuning part much easier .

 

[Dale FZ1]

So you have been running the aftermarket cams already, for a considerable time?

[tridentt150v]

I didn't really feel any difference, but I changed my turbo to a high flow at the same time so was hard to tell. But standard cams are often set up for pollution control so are generally softer for a longer burn. The 256 cams are probably what Nissan would have wanted to use if ADR's etc didn't dictate otherwise.

[AngryRB]

Amazing this thread had so many responses, usually be, try search button etc

[t_revz]

Maybe cos Adrian typically searches and is very informative

[discopotato03]

Bit more of the puzzle .

Turns out that head and cams was done for me 8 yrs ago , one I bought 2nd hand off Wolverine . Was ported and fitted with Ferrea OS exhaust valves and wire rings fitted in grooves in the heads deck just behind the gaskets fire rings . Also got 33 Poncams and head decked for a 9.2-9.3 static CR .

Once removed and stripped the problem was found to be worn exhaust valve guides some quite badly . Obviously the inconsistent issue was exhaust valves sometimes lining up with their seats and sometimes not . Obviously when they didn't decent running went out the window along with erratic idle speed and quality .

So all exhaust guides replaced and all seats and valves resurfaced , spring heights and tensions reset . Heads deck is perfect and will go with a new genuine Nissan head gasket , actually all genuine gaskets and seals . Manifolds were port matched last time .

This time around going with Sydneykids recommendation to retard the exhaust Poncam 2 degrees . They found in their day that this gave a little more power and fractionally more boost at around 3200 revs fine tuned on the dyno . My engine builder doesn't like aftermarket cam pulleys so they are going to set the crank pulley to 2 degrees and alter the std exhaust cam pulley to allow it to line up with the std marks - basically 0-2 adjustment and can't damage anything if it moves .

With luck it'll be together and running tomorrow so I can redo all the idle and cold start stuff and retune all the light load low to medium speed ranges . Then it will be going back to Scott at Insight and quite likely be final tuned on straight 98 ULP . For how I drive these days I don't think I'll need the ethanol any more .

If I ever do another RB the plan would be an RB30 with an RB25 Neo turbo head for the valve train updates . Anyone got a complete standard Neo top end in good nick for sale ?

More soon , cheers A .

 

     

[zebra]

Sounds way to complicated... just buy a tomei cam gear and be done with it.

 

Because f**k pulling the radiator out and balancer off for timing adjustment 

[KiwiRS4T]

+1 for adjustable cam gear.

I can see now in a few years the new owner of your car posting about his timing marks not lining up!

[GTSBoy]

Adrian always like to find the hard way!

[discopotato03]

Hardly , if it was being sold which it isn't they'd be told the story and if all else failed to fit a std pulley . If they were smart they'd find a way to mark the cam and pulley before disassembly so they could get it right . The way it is now if it moved it fails safe - provided it didn't spit the bolts out . Personally I think setting the crank where you want it (+2deg) and having the cam lined up on the std mark is way to go but to each their own . Also this engine has new belt bearings seals and water pump so shouldn't be coming apart any time soon . 

Have to get if back to Insight for tuning probably with a better fuel pump and maybe a bit higher base pressure for those EV14 injectors .

Hunt will be on for Neo head and a decent tall short block .   

[zebra]

And what if you go backwards when advancing the cam?

[Dose Postman STFUU]

brap brap brap bro