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Custom Plenum & Cam gear adjustments

Chris32

By Chris32,
in Engines & Forced Induction

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Beer Baron Grand Master

Beer Baron

Posted
Posted

It's quite possible that the 'custom' plenum is just a step backwards from the stock one. Is it just the plenum, or a whole new intake manifold (inc. runners)?

I've seen some pretty poor looking custom plenums on RB25s and I'm sure some of them would have been a step backwards from the stock one.

Richard

Chris32 Veteran

Chris32

Posted
  • Author
Posted
It's quite possible that the 'custom' plenum is just a step backwards from the stock one. Is it just the plenum, or a whole new intake manifold (inc. runners)?

I've seen some pretty poor looking custom plenums on RB25s and I'm sure some of them would have been a step backwards from the stock one.

Richard

Its the whole nine yards, and fundementally looks fantastic, a pic is attached of it

Just not sure if the exahust cam timing adjustment is holding the whole thing back or not, or what exactly is casuing the problem

Chris32 Veteran

Chris32

Posted
  • Author
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yeah, he has already been contacted etc

I am sure I read somewhere about someone putting on a Greddy and a custom plenum and having to drop back the amount of advance/retard on there adjustable cam gears

Just trying to find out who it was.........

Chris

Beer Baron Grand Master

Beer Baron

Posted
Posted
Its the whole nine yards, and fundementally looks fantastic, a pic is attached of it

Just not sure if the exahust cam timing adjustment is holding the whole thing back or not, or what exactly is casuing the problem

Yeah, I agree that plenum looks nice. I think a little research is in order to find out why you guys went backwards with it.

Richard

Targa Tom Proficient

Targa Tom

Posted
Posted
G'day all,

posting as a question for a mate who is having a few probs -

Custom plenum installed and the car has gone backwards in power quite a bit, I read somewhere the other day (cant remember where, I read so much) that guys who have put Greddy/custom plenums and who have had adjustable cam wheels had to adjust these to suit the new plenum and airflow charactersitcs

ie they have been set up with tha standard plenum etc, and have had to be changed quite considerably to get a good result

Currently the exahust cam wheel is retarded 4 degree's (from memory) - engine is a RB25, which was making around 270rwkw on the stock plenum

Can anyone help or suggest what the problem may be  

Chris

I used to race karts. Way back when I had a fairly fast DAP T75.... Anyhow one night it was going stong (as they do when lean) and it put the rod through the bottom of the crank cases.

A guy came to me in the pits and offered the price of a new engine for the barrell and head.

We did the deal and by Wednesday he was on the phone "I just measured this barrell and it is Stock!!!"

"I know mate,"I replied" dont, stuff with it. The next meeting I blew him off down the shute.... "WTF I said??... "Oh I just fixed up the ports he said....

Lesson for me... Unless you have gut loads of cash to spend on R & D, leave it alone...

Who believes beer made in a garbage can is as good as the brewery makes??? When you pay for the the name you pay for the research....

Anyhow, I'm sure after countless hours (what cost) you cobber will get it to be something OK... How much are those trick Jap items again??

Hope it improves without being a WAFTAM Chris,

Good Luck

TT :/

Trust33 Grand Master

Trust33

Posted
Posted
If I remember rightly it has RAM TUBES.:/

The plenum has a ramming problem then.Could be overcome with a ported head,cams & match ported manifolds to realy get things flowing?Or do you think that i have just gone too far and left the saine answer. :cooldance

Sydneykid Grand Master

Sydneykid

Posted
Posted
The plenum has a ramming problem then.Could be overcome with a ported head,cams & match ported manifolds to realy get things flowing?Or do you think that i have just gone too far and left the saine answer. :cooldance

Ahhh no, the problem is distribution, not all cyinders get the same airflow at all rpms. A cam upgrade works the same on all cylinders, so it doesn't fix the distribution. Ditto porting, matching etc.

So there are 2 ways to overcome uneven distribution, the first is to design the plenum to even out the airflow. Not easy, aerodynamics is a very tricky science, Nissan spent millions to get the standard plenums right. The second is to compensate for the different airflow by programming the ECU to supply different amounts of fuel to each cylinder. This keeps the A/F ratios in the safe zone and makes more power as you don't have to run one cylinder rich in order to overcome the one or two lean cylinders.

Hope that helps:cheers:

Targa Tom Proficient

Targa Tom

Posted
Posted

And you don't expect anything sensible @ 11pm on Friday Night...

The guys that design these items for OEM do have a fair idea. While I concure with skids diagnosis, it is like grinding a cam to suit your inefficient plennum. Sounds like a WOFTAM to me... Imagine setting up A/F readings on all six cylinders... I have enough drama getting the one average right. Also imagine the turbulance the inrush of air has to go through by passing up to five velocity stacks (if that is what is being used).

Anyhow each to their own, I get "I told you so's from my tuner and crew cheif all the time.

TT

Trust33 Grand Master

Trust33

Posted
Posted

So the A/F ratios are hard to keep at a constant at any given rpm....So when a car is tuned with aftermarket ecu they really only try to make an A/F average accross the entire rpm range as good as they possibly can.So in cases like this it is not the tuners fault that it is not making the power it's the plenum design......

Maybee a fatter mid section in the plenum to give it time for the A/F ratios to even themselves out and a splitfire coil pack to burn the extra air and fuel quicker making its way into the cylinders...

Im not at all knowledgeable about this process so go easy....

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