RB25DET Greddy Plenum

[APA]

very good points skid.... yeah i was 99.5 percent sure that the subzero plenum was not a full replacement unit i pretty sure some did a flow bench test on the two hmmmz must search the forums

adrian

[Remix-]

Please don't let this turn into a shit fight of what plenum is better. I am purely buying this plenum for simplicity in intercooler piping and to make it easier to get to my spark plugs/coil packs etc. This thread is for discussion of what is needed to be done to install the Greddy plenum.

Cheers fellas

[Kaido_RR]

hey gtst89,

i am having no luck with neugun looks like no-group buy from there, Mod You cars' is getting back to me on a price and my other supply is out for the night so i will get incontact with him 2morrow.

Like i said i have a price of $1300 if we get alest 5 people this inc everything shipping,tax, custum etc

[lukevl]

Att: SK! I want one because it makes my eyes hurt looking at the standard Rb25 inlet! Honestly its that bad I'm considering switching over to a GTR head because I have a GTR inlet.

If I run the Greddy plenum I will have like a metre less inlet length won't I? My main preference with the car is to have minimal lag. You mentioned using a U-turn right in front of the throttle body. it look kinda rough, what are your experiences with that? What about that fugly throttle body relocation to the front of the plenum?

[Trust33]

Your right the sub zero plenums bolt to the origional runners..

[skid]

sorry guys no intensions of causing a shit fight, just trying to give yous some information that might help yous decide what yous want to do.

[Trust33]

skid i think they made their minds up allready..Its greddy or busssst.

[Big B]

Hi fellas i,m a first time poster. What i was wondering are the coolant lines running through the throttle body really necessary? wouldnt it be heating the air back up slightly after the i/c has done its best cooling it down.

[Sydneykid]

Hi Guys, I'll keep this brief as there are plenty of threads on this exact subject.

I have tested the standard RB25DET inlet (inc throttle body) and it shows ZERO resistance at airflows equivalent to 450 bhp on the flow bench. Since 450 bhp is my rule of thumb limit for standard internals, my suggestion is always to spend your money on something else (other than a plenum) until you have upgraded the internals. Simply because it is a waste of money, not to mention time.

Don't get me wrong I am not saying that Greddy plenums are crap, although the airflow distribution is not perfect. What I am saying is you will get a better result from spending your $1K plus on other things.

An example, for around the same money I will get a much larger power increase from a set of camshafts. Porting the cylinder head, polishing amnd matching the combustion chambers will give a larger power increase. A better turbo will give a larger power increase. A better intercooler will give a larger power increase. A Power FC will give a larger power increase. A decent exhaust manifold will give a larger power increase. Hi flow cat, cat back exhaust etc etc. There are plenty of better ways to spend your money.

As for response, I have compared the amount of air held in the standard manifold and 120 degree style pipework to a Greddy plenum and its pipework. The difference is less than 1.5 litres. So do the numbers;

2500 cc X 5000 rpm / 2 (4 stroke) = 104 litres per second

So saving 1.5 litres represents 1.4 hundredths of a second

That's not a lot of lag to save with reduced pipework

A set of cams, a port and polish, Power FC, exhaust manifold, will all reduce lag much better than that.

Bottom line, after you upgrade the internals is the time to THINK about upgrading the plenum.

Hope that helps:cheers:

[G0DF4Th3R]

that does make sense actually, we dont all have the deepest pockets so what SK is saying that there are much better 'bang for your buck' upgrades out there...

i wouldnt know what you guys have on your cars and what sorta power levels ure chasing btw

[fresh]

u can get ur throttle body moved on the stock plenum for $250, woudn't that be easier ???

[lukevl]

Thanks SK. I didn't have Greddy plenum to measure so that helped me a lot. Good job once again

[-=BoganRice=-]

if anyone can get incontact with neugun as i am having problem

this was the article for the SR20DET greddy plenum if I'm not mistaken ??

[-=BoganRice=-]

I just got one for my car ... having fun installing it too lol ...

[ookami]

very good points skid.... yeah i was 99.5 percent sure that the subzero plenum was not a full replacement unit i pretty sure some did a flow bench test on the two hmmmz must search the forums

adrian

subzero can do the short runner ones too ... I believe they simply cut the standard runners and attach the plenum to it.

I would have to say the topic of plenums is rather opinionated. If you don't want to spend a big amount of cash on your car simply leave this area alone and make do with the mods in other areas. RB25 Aftermarkets plenums have very little power increase for those still running the stock turbos as the stock plenum will out flow the standard turbo. The standard plenum from what i have read starts to run out of breath once you get up around the 350rwhp. The general rule of thumb is for every PSI of boost increase your meant to see approx 7-9 hp (providing all other areas of the engine are efficent, obviously differs from turbo to turbo too.). But once you start to make over this hp mark the power increase as to each PSI of boost pressure added decreases.

Runner length also plays a big part in engine response and behavour. The longer the runner (providing the runner has decent flow properties), the slightly less engine response (read:lag). The shorter the runner the quicker the engine responses. The longer runners however increase capacity of the plenum system so to speak which inturns gives the affect of a much larger plenum that what is actually there which means higher HP support.

In my opinion cast plenums are always much stronger than the sheet metal fabricated ones. While some sheet metal ones can give no problems at all they still have the potential to split and fail. I have heard of a story of a sheet metal fabricated plenum blowing apart while on a dyno and doing damage to a vehicle. This is almost a worse case scenario though. Usually if anything do go wrong the plenum would crack around the welds if at all.

Another issue with aftermarket plenums is the positioning of the bell mouths (if any) and even air distrubition. This has the potentional to cause more problems than its worth. Personally when i see a standard rb25 plenum with the throttle body cut and moved to the front of the plenum i shudder. The standard plenum was not designed to have air enter from this point so air distribution inside plenum would not do ideal and could cause one or a number of cylinders to recieve a vastly different amount of air to others, which in turns causes leaning.

I'm not going to say which plenum I think is best as they all have their good and bad points. I have a Greddy plenum on my R33, it was on there when i bought the car so I'm kind of biased, but that doesn't necessary mean its the best plenum.

[SLY33]

ookami, you say longer runners give more lag? I thought the factory runners are long to provide good off boost response and better drivability, i dont think it has a lag issue. Especially since SK has said that the extra length of cooler piping on a standard set up only has 1.5litres of extra air, the extra air a std plenum will hold compared to a Greddy one would be a sparrows fart.

great post SK, i like the idea of doing the plenum to improve the look and convenience of accessing plugs etc, but like you say its sure not worth over a grand just for that! how often do people need to pull plugs?! the factory setup can look very neat when the right parts are detailed.

sorry author this thread is off track.

[ookami]

it's not lag thats noticable in lightly modified cars its a lot more noticable in the cars with upper size turbos and even then it won't be very noticable.

[Sydneykid]

ookami, you say longer runners give more lag? I thought the factory runners are long to provide good off boost response and better drivability, i dont think it has a lag issue. Especially since SK has said that the extra length of cooler piping on a standard set up only has 1.5litres of extra air, the extra air a std plenum will hold compared to a Greddy one would be a sparrows fart.

great post SK, i like the idea of doing the plenum to improve the look and convenience of accessing plugs etc, but like you say its sure not worth over a grand just for that! how often do people need to pull plugs?!  the factory setup can look very neat when the right parts are detailed.

sorry author this thread is off track.

Be careful, there is a lot of difference between the air before the throttle body (as in the pipework & the intercooler) and the air between the throttle body and the inlet valve.

[GeeTR]

YEah,

"The longer the runner (providing the runner has decent flow properties), the slightly less engine response (read:lag) "

Mmm was of the thinking, longer runner length, purely equated to better cylinder filling at lower engine speeds, ( that 15” column of pressurized air, stored in the runner able to quickly vent into the chamber on inlet valve open ) causing Better response. Course at higher air speeds the longer runner becomes a bottle neck, where the shorter option does not.

Lets maybe not get into the relationship of runner length and harmonics, with positive pulse tuneing.

… I thought

What was the topic again?... sorry gtst89

[skid]

just check the wiring for your idle controll valve ect. you might have to lengthen them. mine have been lengthened, but a mate fitted one and recons you dont have to.

hi boganrice and i just finnished fitting his Greddy plennum, you do have to lengthen the idle cont valve wiring. my other mate forgot that the vehicle he fitted the plennum to had previously had an aftermarket plennum.