Custom Inlet Plenum

[RB- ajsx]

hey everyone

spoken to a few people about installing a custom inlet plenum (thanks to bullet32 for the manifold! ) on an rb20 with a stock ecu.

half the folks said, "it will lean out your rear cylinder. make sure you've got an aftermarket computer" the other half, "shouldn't make a difference. air pressure is air pressure"

if i did have an engine management system that allowed to tune individual cylinders, it'd want to be a pretty nuts engine then yes?

and isn't air pressure always going to be air pressure?

cheers.

[neofenrir34]

some different manifold's will cause the rear cyclinders to lean out not good if you are going to case big power levels if you are after some companies that make flow tested manifolds i would suggest plazmaman.com or hypertune.net. just for a start.

plazmaman only really does inlet plenums

Edited October 1, 2007 by neofenrir34

[RB- ajsx]

i'm not chasing big numbers at the moment, and if i was i'd certainly have an aftermarket ecu

here's a pic of the plenum

any thoughts?

[skybarge]

to sort the leaning out problem, get the injectors flow tested

put the largest flowing injector in the 6th cylinder, second largest in the 5th etc all the way to the lowest flowing injector in the 1st cylinder

should fix the leaning out issue

[datto260Z]

Pete at Autotech wasnt worried with mine with a powerFC, so i dont think its that big a problem, 250rwkw...

[Bullet32]

You wont have a problem if you get a Power FC, Microtech, Haltech etc. because these will allow you (or your tuner) to rich up or lean out your mixtures and get it running right.

That plenum came off a Gtst that was making over 300kw at the wheels and the engine was about 300,000km's old when he decided to take the plenum off, so I think you'll be fine.

[MIVEC]

Is changing the plenum a worthwhile modification? Or something to only really consider when most other options have been done?

And is the primary purpose for changing the plenum for better/quicker throttle response?

[RB- ajsx]

turns out the plenum didn't fit anyway hahaha BUT danny (performance garage) is taking the throttle body off it and attaching it to my original plenum, essentially the same thing but to fit my RB20

i will eventually get an aftermarket ecu (thinking GReddy Emanage or Haltech. Anyone had experience with one of them?) spoke with danny and it should be fine till then. not going to be driven much in the meantime anyway.

Is changing the plenum a worthwhile modification? Or something to only really consider when most other options have been done?

And is the primary purpose for changing the plenum for better/quicker throttle response?

depends. if you're looking at mods that are value for money there's no point as there are other modifications that will give you more power. yes you'll get more torque i'm just setting the base down as i have plans for the engine later. plus i HATE the stock RB20 inlet plenum setup (**waits for fans to start lighting torches and grabing pitchforks** )

[Bullet32]

Im sorry to hear that it didnt fit AJ, I was sure that the RB20 and 25 were compatible.

Glad to hear that youre still going to use the RB25 throttle body though.

[RB- ajsx]

haha don't sweat it actually ended up saving money. the custom pipes i would've needed to suit the stock plenum would have cost about $200-$300. this new custom plenum will be about another $100 maybe $200

is there a difference in the throttle bodies? haha didn't even notice

[sprinterboy]

if i did have an engine management system that allowed to tune individual cylinders, it'd want to be a pretty nuts engine then yes?

and isn't air pressure always going to be air pressure?

cheers.

Air flow... it's all about how much air you can move and how fast you can move it. the more bends and twists and changes in pipe size will make a difference.

[ISL33P]

air pressure is one thing and air flow is another.

although air pressure can be constant between cylidners the air flow is not. it is affected by a large number of factors, but as mentioned before, the less bends the better. aerodynamicswithin the plenum play a major factor and not something that can be shown on a flow bench, but more on autocad style programs which simulate different circumstances of air flow/pressure. all this and then throw in air speed and plenum volumes and the fun begins......

more pressure = more airflow (in general*)

more air flow = more power (with the right amount of fuel of course)

then again you can have

more airflow @ less pressure (due to less restriction) = more power...and this is what a correctly designed and fabricated plenum should provide.

* more pressure can sometimes produce the same amount of air flow at a lesser pressure since an orifice can only flow a certain amount of air regardless of pressure. basically, at some point the air "banks up" and can not get thru