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who has custom intake plem??

06-05-2004, 02:32 AM
afternoon every1......

i would like to know if any1 here has a front facing intake plem or a custom made job for there 25det and are willing to let (us) have a look at it as i wish to make my own but not sure if i should do the whole top intake out of s/st or just cut and weld the standard 1??
so any picture's would be great as it's just to get a fair idea of what other people have done.
thank you

ps....is there a noticable performance upgrade having it done other then it tidying up the engine bay?

06-17-2004, 03:35 PM
front facing is worst. It does not distrubte the air evenly.

06-18-2004, 02:14 AM

06-19-2004, 04:57 PM
Expect no big gains from a different intake manifold. certainly not when you're using a turbo. You could use it to increase torque at low revs but you need quite some space for that.


06-19-2004, 09:09 PM
Expect no big gains from a different intake manifold. certainly not when you're using a turbo. You could use it to increase torque at low revs but you need quite some space for that.


R33 GTS25t.

T41B Turbo, front mount, 650cc injectors, Bosch 044 fuel pump, Nismo raising rate fuel pressure reg, 1.2 bar - 240rwkw. (321hp)

Greedy intake plenum add same everything else including throttle body - 266 rwkw (356hp)

06-20-2004, 12:35 AM
Yes, intakes make a huge difference.

06-20-2004, 02:28 PM
From the graphs i have seen (made with Gt power suite) a different intake doesn't change a thing. For NA engines it can make nice power gains but for turbo's...no

And razor 35 hp at what rpm. it can make a difference if you change the whole intake manifold from filter to valve. But a plenum change makes not much of a difference. (or the stock intake is just one huge mistake on intake technique)

I've run some simulations, i did quite some research on intakes and pulses and i'm not impressed by the advantages in combo with a turbo.


By the way there is some difference between a plenum and an intake. The plenum is the 'reservoir' which the engine can take air out (bigger plenum mkaes it look like the engine can breathe like it breathes without any filter or other obstruction.). The intake is the whole package. Kleks (or what the you call it.) can make some difference.

06-20-2004, 04:50 PM
I have seen as much as 50hp change from one intake to another, in Supercharger, and Turboed applications. Yes, they can and do make a difference. But, it also depends on what you are starting with.

06-20-2004, 06:07 PM
I have seen as much as 50hp change from one intake to another, in Supercharger, and Turboed applications. Yes, they can and do make a difference. But, it also depends on what you are starting with.

Yeah what you start with. and it also depends on the end power. thus percentages. 50 hp on 900 hp isn't much of a difference. I'm talking about small engines (1.4-2.0 litres)

Pulses (is what we talk about mainly) are dampered(sorry for my bad english) in combination with pressure. The best i've seen is a pressure rise of 0.05 bar. (1.4l Turbo with a special designed/custom made intake.) problem was the engine went completly dead at 2300rpm.

Other then stock intakes are usefull if someone with knowlegde has worked on it.


06-20-2004, 11:54 PM
I was reffering to engines with less than half of that power, but I am also talking about V8s.

Your speaking from what you know, and I am speaking from a totally different type of knowledge. Yes, you can change intakes on a turboed engine with less than 400hp, and you can see a rise of 50 hp depending on the intake.

06-21-2004, 01:37 AM
Derby its very, very manufactor and engine spefic as to what sort of gains can be seen by an inlet manifold change on a forced induction engine.

Nissan has a reputation as a builder of very strong engines. Its quite clear that most of thier R&D work has gone into engine strength and lots of boost to over come weakness's in the flow capablities of the head and manifolds.
Also remember that the RB series of engines (whats being discussed in this thread) are based heavily on an engine orginaly designed in the 50s by Mercedes.
Its intake design has been little changed since the 80s, and it was done at a time when Nissan did not have a lot of spare money to spend on refining an intake. What they had worked, extremly well, they didn't need to improve on it.

However as it happens technology and industry knowledge has improved a lot since 1988, and there are now aftermarket manifolds that are signifcantly better than the orginal, and will yield quite noticable gains.

06-21-2004, 06:24 AM
all right i'll give up.

But i want to know one thing. These gains in power(50 hp) are that 50 din HP's or are that 50 marketings HP's?

No offence,


06-21-2004, 12:13 PM
Derby Also remember that the RB series of engines (whats being discussed in this thread) are based heavily on an engine orginaly designed in the 50s by Mercedes.
Its intake design has been little changed since the 80s, and it was done at a time when Nissan did not have a lot of spare money to spend on refining an intake. What they had worked, extremly well, they didn't need to improve on it.

What makes you say this Moppie? I don't recall the Merc having a DOHC head, "bearingless cam journals", oil pump mounted to the front of the crank, 4 valves per cylinder to mention a few. Saying that is like saying the BA16 is based on the Ford Flat head 4.

Also Nissan did refine the intake since the 80's. It change quite a bit though the R32 and R33 non-GTR intakes are simular they infact are not the same.

Darby unless you know what the non-GTR intakes looked like on the R32, R33 series it is hard to envision an aftermarket plenum would make. The intakes curl upwards back over the top of the head with a single inlet feeding into a rectangular shaped manifold then 6 runners curling downwards to the head. The inlet is dead centre on the long side of the rectangled chamber. If you were to look at the design it is simple in theory but not practical in making efficeint power.
The factory intake on an SR20DET motor is a good example of how an intake plenum should look, though it is still not the best of design.

Looking at a GTR intake plenum it uses 6 throttle bodies instead of one single one found on 99% of cars. This is what the aftermarket ones copied to bolt onto the other RB series motors. Only the GTR was designed for "high performance" not a family sedan nor a sports car, but true supercar status.

I'm short on time this morning but will endevour to explain it a bit deeper when I get home from work tonight.

06-21-2004, 01:37 PM
Despite your effort to explain the shape size and form of the intake, i still can't make a picture out of it. (my fault).

Every designer has his own interpretation of a good intake.

The best i've seen is the intake of the BMW V12. I'll look to get some pics.

And what about exhausts. then i mean from valve to catalyst?

I'm looking forward to a more deep explanation, RazorGTR


06-22-2004, 02:56 AM
It took me a while to find decent pictures to post up to show you just pathetic the non-GTR intake manifolds really are.

Here you can see the inlet pipe to the throttle body which then mounts to what is described as the front of the intake "plenum". Notice the rectangular shaped box that feeds the runners. You should also now see which cylinders are going to be fed the best volumes of air based on volumetric calculations/force/pressure. Now this picture is of an N/A GTS but the intake is the same on the base turbo models.


Here is a good picture though I had to blow it up quite a bit of the intake runners split.

What a proper plenum will give you is better distrabution of pressure vs volume. Good inline mainfolds will be larger at the front end and smaller at the back end. This is to prevent more air entering the back cylinders vs less to the front based on pressure/volume.

The GTR Plenum comes close but the back is still too big compared to the inlet hence many top cars go to either the Trust, Top Secret, or Veilside plenum.

A common unknown problem with the RB motors is the non-GTR's always run leaner on the #3 and #4 cylinders, while GTR's are natorious for #6 and sometimes #5 being the leaner ones. This is not theory but reality, as when you check the plugs for leaness or most noticably pistons for detination it always will show up on these cylinders first. Some say it is the fuel rails but if that was so, then all the RB motors would be leaner on the same cylinders.

How much of a difference a plenum would make on other motors, I can't say as honestly I've not studied them as close as i have on the RB motors. I do know that intake manifolds on V8's is critical in getting them to run properly on all 8, this makes the same sence in this case we are discussing. The runners on a 4 bbl intake make or break the manifold, same applies here except it isn't the runners as much as the holding or expansion chamber of the intake. A square or rectangular shaped one will never be as effecient as one that is smoother with a better overall delivery system designed into it. I would venture to say the system Nissan came up with for the non-GTR is more due to the engine configuration more so than a performance orientated design. On the turbo models the small factory intercooler is located in the left front between the inner guard and the bumper at the bottom. The piping goes in and back out in a small area then preceeds back over the mid section of the motor as you can see from the pictures.

Some guys have tried to cut the throttle body mount, patch and weld the factory intake body, then cut and weld the mount onto the front of it to simulate a proper plenum. They do this when the run an aftermarket front mount to avoid coming either back over the top of the fan, or replum it back across the front of the car behind the new front mount to tap into the existing pipe work. I've yet to see any gains from this though some claimed it. To me the air is trying to litterally travel 90degs down the runners, this would make for large amounts of turbulance, while a poper plenum would have the inside guide rails if you will, to guide the air into the plenum runners then into the head.

Hope this helps clarify it a bit more.

06-22-2004, 03:02 PM
I believe I begin to understand you.

A intake as I think it should be made. (better is a variable intake but that quite hard to draw)


The runners are blue. The runners should be the same length. The turn must be gentle. The begin of the runner should be rounded to avoid turbulence.
The plenum (bubblegum)should be about ten times the displacement. But that is quite hard to make under todays hood.
The green pipe is for connection with air filter/intercooler/turbo

It looks like the NA gts intake but without the 90 turns.


06-22-2004, 10:20 PM
I'll do one up in Solid works and take some screen shots.

What software do you use by chance?

06-22-2004, 10:38 PM
I didn't read too deeply into the thread so forgive me but I thought this was a pretty cool idea for non RB26's:



06-22-2004, 11:33 PM
Very simular to some of the other custom built one's I've seen. Not a too bad of a job but looks like they went a bit overkill on the welding.

06-23-2004, 11:40 AM
I didn't read too deeply into the thread so forgive me but I thought this was a pretty cool idea for non RB26's:


That intake is a nice try but the runners are to short. And the plenum is to small. It cannot hold much air.

don't get me wrong it is a good intake. but it looks like it was some 10-minute-intake.

(But i have to admit there isn't much space for something better)

@RazorGTR Love to see your picture/drawing/design
It took me 3 hours to draw this. And the bents in the runners was new to me.

I use Autodesk Inventor 8. Very, very userfriendly


06-23-2004, 12:47 PM
Shorter the runners the better:)

06-23-2004, 01:24 PM
WRONG. (no offence)

The longer the runners the better(which isn't true for all applications). The runners on the pic of the nissan 2500. are way to short for the rpm range the engine can reach. those runners are usefull for F1 engines (reach 19000 rpm)

With longer runners u can use natural physics to fill your cil.

Has to do with pressure waves. But you already know that.


06-23-2004, 02:28 PM
WRONG. (no offence)

The longer the runners the better(which isn't true for all applications). The runners on the pic of the nissan 2500. are way to short for the rpm range the engine can reach. those runners are usefull for F1 engines (reach 19000 rpm)

With longer runners u can use natural physics to fill your cil.

Has to do with pressure waves. But you already know that.



Shorter the better, but yes they can be too short. Just trying to get a rise out of you:) I'll get into this disscusion when I have more time. Its been pretty good so far, and everything has been well written. Good to see some tech stuff in here. Big thumbs up :iceslolan

06-23-2004, 02:54 PM
While in some cases longer runners are better, in turbo or supercharged cars where the intake system is pressurized it isn't as critical. Actually the more turbulance you create in a natrually asperated application the better. This helps atomize the fuel better.
In injected cars, let me rephrase that, port injected cars air turbulance is a bad thing. The injector amtomized the fuel or is suppose to. It injects a fine mist instead of dropplets like in TBI or carburated.

On a plenum the idea is in a round-about way, to store air under pressure so when the intake valve opens there is sufficent air mass to fill the cylinder. Now in a high reving engine or one that has a large capacity this becomes more relivent.

Space is also a consideration, and along with flow and design. There are many theories and calculations on this. A smother transition will always fill a given volume better than one that is filled with turbulance when under pressure. At vaccum though this is changed. It is hard to explain but when tested with smoke filled air into a glass jar you would see what i mean.

06-23-2004, 05:13 PM

I really like this discussion as well, So keep up the good work.


I as fas as i know the bigger the plenum the better. The bigger the plenum the better turbulence is turned into quite air (colisions (crashes) with other aotoms/moleculs). Also for the engine it looks like it is sucking air from a room where the pressure is pressure at sealevel. It can suck air without any obstruction( airfilter, badly designed box to plenum pipes)Therefor the plenum must contain air for more then one cilinder to keep the pressure the same as the surroudings. Like a Common rail diesel.

by opening the the inlet valve a pressure wave (negative -) is travelling into the cilinder. by closing the cilinder a pressure wave (positive +) is bouncing upon the valve. This +wave is going back to the plenum where it returns as a -wave back to the valve. It bounces back on the closed valve and it travels back to the plenum still as a -wave. By entering the plenum the sign (-/+) switches (here from - to +) and begins he travel to the inlet valve as a positive wave.
Now the engineer who works on the intake has to get the +wave at the inlet valve as it is 1 mm open.
In case of my car I have to get 9 meters (29.52747 feet)of runner (one runner 4 in total) under the hood to get more torque on the by my desired(there is something wrong on this word) rpm (2500).
The pulses (positive/negative wave) travel at 343 meter/s (0.2131303 mile per second) at 25C (77 Fahrenheit) and every 20 C that the air is hotter the speed raises 11m/s so lets take an air temperature of 65 C the speed of sound is 365 m/s at this temp. (0.2268005 mile per second). 7000 rpm is 116 rps. Every 720 degrees a combustion. So every 720 degrees the intake valve opens once. So from those 116 rps the inlet opens 58 times (please people correct me if I'm wrong. It is late for me). I pick a cam that is used for an NA Renault Alpine (I got the data on my desktop... everybody is lazy sometimes :smile: ). Every work process takes 1/116 seconds (0.008620). From every work process the inlet is 255 degress open. so the inlet is closed for 720-255 = 465 degrees. That is 0.005567 seconds. So a +wave(back) a -wave (to) a -wave (back) and a +wave(to the valve) has to travel in 0.005567 second. The speed of sound is 365 meter per second, so the inlet has to be 365*0.005567 = 2 meters (6.56166 feet)(that is a lot...) long to have advantage of the pressure waves in the inlet. This advantage is used for this rpm but it also works when the inlet is already open. (not when closed of course) So it works for something more then one rpm. This creates a mountain landscape in a graph.
(This is all just an example, I took the time for this but it still can contain mistakes)
It also works on the 3500 rpm. but the pressure waves have to travel 4 times (up and down). But the effect is less cause of efficiency.
This is all for NA engines. I still don't know how it works for turboed engines. I think it works the same because of the natural effect. But if someone thinks different please let it know.

No offence SkylineUSA but shorter runners work only for high reving motors. Like F1. The best would be a engine without any kind of runners...

I hope this clears something up. This however is not the only way to desing runner length. There are two other ways to come to a runner length. The art is to combine all of them.
Most of todays intakes are designed around the exhaust. The exhaust works on a similar way. But there are also some other things that work on a exhausts. Cause of the change between negative effect and positive, the intake is designed to compensate for the negative effects of the exhaust.


06-23-2004, 08:48 PM
Just so you guys know I stuck the thread because it is one of the BEST on intake systems bar none.

Darby that is well and truely over my head. While i understand the basic principles and theories you've reached a new platto, good on ya!

From what I've been able to dig up on the top hp cars using forced induction, ie turbo in this case, the shorter the runners and size/shape of the expansion chamber does make a difference. While what i can explain is turbulance, but not the indepth you have. It seems from what I've been able to find a larger frontal area of the plenum and sloping down to a smaller rear section is what seems to be the go for these application. The area I do agree must be able to support much more than what the individual cylinder capacity is. This is without a doubt common sense in the intake world. While I'm not designer for intakes, I go by what I see the top cars using.

To be able to squeeze 1,400+hp out of a 2.6 - 2.8 litre motor they all seem to use the same basic shape plenum. Keep in mind all these cars are using extremely large front mounted intercoolers there for the intake charge temp is greatly reduced. What you don't want is the air inside the intake system to be there long enough to then again re-heat up. This in fact would negate cooling the intercooler is doing and you get no gains.

In keeping with the high rpms for a mass produced turbo motor to rev to 8,200rpms factory you then can see why the shape, size, and runner lengths are what they are. HKS, VEILSIDE, JUN, TOP SECRET, etc all use plenums of nearly identical shapes and configurations. All have cars making extreme amounts of power using gas (race gas but still gas).

Most high performance plenums I've seen for the RB series motors are extremely thin. They would be in the area of 1.5mm - 2mm thick. Why I have not idea other than weight savings.

Something else has been sitting with me. You've memtioned the "shockwave" effect of the valves opening an closing, while that would be an issue with an N/A engine, when you have the intake system under constant pressure this would be reduced. Air compresses only a given amount, and even at that the amount the valves would move I honestly can't see it making that much of an impact on a forced induction small capicity engine. The larger N/A motors with very large lifting valves, which are also much larger would make a lot more sense.

06-24-2004, 05:48 AM
@ RazorGTR:
Thanx for the the compliments.

What I calculated was mentioned for a NA car. NA cars have serious trouble to get enough air into the cilinder. And most of the NA cars don't have an intercooler. So warming up agian is ot much of an issue. For turbo cars with large coolers it is better to have a small plenum. That is something i never thought about really.

I'm gonna comment on this later on the day. Have to work a little more, while i'm think of what you said. Could you post a pic of an HKS intake (or veilside or jun doesn't matter really)?


06-24-2004, 10:31 AM
@RazorGTR (and the other that follow this)

The intake you describe (big plenum at beginning and smaller at the end)must be the best there is cause it is used on many engines. Plenum size is the big questionmark. I looked for some relations ships between power, cilinder fill rate and plenum size but there is none (as far as i have seen). Some people talk about ten times the displacement, other only two times.

looking at what other designed thought is almost the best way to learn. (asking and discussion the design is one little step better, but it is hard to find the people who really know stuff)

What i forgot to tell about runners is that they have to be (i think you call it tapped) bigger at the entrance and smaller at the cilinder head. This depens on the material used and the turbulence it is creating close to the side of the runner.

About the speed of sound in pressurized enviroment. The speed slows down at greater pressures. So for a turbo engine the runners can be shorter to have advantage of the pressure waves. Found on the net (learing new things all day is fantastic... :smile: )
In mediums with very high densities indiviual particles have greater inertia and they are less responsive to the interactions between neighboring particles. So at greater densities sound waves will move slower, if all other factors are equal. Thus, a sound wave will travel nearly three tmies faster in Helium gas as it will in air; this is due to the lower mass of Helium particles as compared to air particles.

about the time the wave is working in pressure. I can't find any relation to a life time of a wave in pressure. I know that a pressure wave is dampered when travelling through the runner. ( advantage of waves works for 16 sign (-/+) chances) i wanto believe the wave is canceled earlier but i can't find any proof of it.

The wave is made by closing the valve. The force the wave has is determent by the speed the valve closes. Force is slightly influenced by the size of the valve. (a big valve houses in a big runner in the head. if the big valve is placed at the end of a small area runner the force will by greater by cause of turbulence the effect will soon be away.) So a steepper cam has more influence on the 'lifetime' of the wave.


06-24-2004, 06:34 PM
i read on a issue of turbo magizine.....a toyota supra gaining around 72 bhp
on a vielside plenum......geez thats a lot or hp gian..
but then agian thats with a larger trottle body too :)

06-25-2004, 05:42 AM
it is quite hard to compare these things. Maybe was the x brand intake very very bad. And what is the gain in percentages?
It is all relative


Nizam Abdool
07-25-2004, 03:07 PM
Interestingly guys, the newer version of the Nissan NEO inline sixes found in the HC35 Medalists for example have the same config. as the older RB20's except that they have a "Y" shaped piece of piping as an addition upstream the rectangular box so that air entry is now at two separate points not one....In effect smoothing and redirecting the flow a bit...

07-25-2004, 05:56 PM
So for a 4 cil 16v it has 8 runners instead of four right.

That is what i've seen on a Opel over here. Really don't believe in that stuff. The area of resistance is greater. So is the air speed. That is two times bad...


04-22-2005, 12:07 AM
I joined this club here cause I was just plain fedup with all the bull that you guys repeat, quote, say and just simply invent. Let me dispell a couple of them....as a matter of fact let me introduce myself. I have the most powerful rb25 in the U.S. My friend has the most powerful rb26 in the U.S. You guys repeat so many times that the rb25 bottom end is good for max 500hp. bullll.. I make over 900 for over three years on the stock bottom end plus I had a 120 shot of spoolup nos, hows that for strength?. Secondly I rev the engine to 9500rpm hows that for strenth? I have blown four head gaskets 2 oil pumps 2 tubos 3 rear ends and damaged my syncros for third and fourth and finaly due to abuse and oil leakage thru valve seals damaged all my pistons to where you can see the rings and thru all this my engine stillran and my block is 90% as if still new, Hows that for strength. I have gone from third @9000rpm missed fourth landed back in second not one effect on the engine this engine is the god of engines. I dare anyone to show me by experience a stronger engine. This by the way is the neo engine... please stop talking if you are guessing.

10-17-2005, 08:03 PM
if you changed up your plenum, thereby adding more air, wouldnt you have you step up your injectors just to keep from running lean? or is it small enough of a change just to not worry about it? maybe thats where some of these people are gaining some of the extra horsepower.

10-17-2005, 10:01 PM
Its not going to be much of a gain.
But there will always be variables.

04-30-2006, 10:27 AM
it's all about effiency with turbo there will be positive pressure and the idea is get whatever psi you want into your cylinders,and evenly across all cylinders at the same air temp. bigger phleum means less preasure drop in the phleum while smaller fills faster and less air just sitting there. Also while air is entering your cylinder air is also entering the phleum. Rpm is also gonna have a big equation as to how things go not to mention valve timing, size, lift and duration. It's simple to see research goes into it so your homemade hack job probably isn't gonna be better than aftermarket just cheaper(not to mention it has a good chance of hurting performance). Also it depends what RPM your looking to get better efficency at. The change you see in your power depends on the rest of your engine. boost, i/c pressure drop, and a bunch of other stuff. I was also wondering is it better to have 2 boost gauges one after the i/c and bov and one before? the one after would be just for your data loging and keep u informed.

06-18-2006, 11:46 AM
@ driftkingz: About bigger/smaller plenums, I tried to calculate what the influence was with a plenum the size of 5 time the engine capacity. The plenum is made from aluminum. Assuming the air entering the plenum is 60 degrees celcius.(140 degrees fahrenheit) and the plenum it self is 100 degrees (212), an rpm of 3000 revs/min a 2.6l 6 cil. engine. That means that the air has a temperature difference of 40 degrees with the plenum. But the plenum that contains 13 liters (ambient air pressure. With boost the density increases and also the amount of energy needed to heat the air) of air is with and engine speed of 50 revs a sec empty in 0.2 seconds. That is not much time for the air to heat up. Besides that new air is coming in all and aluminum is not a efficient heat radiator. Too bad space under the hood is limited.

Luckily todays systems of vvti-l solves a lot of problems concerning intakes. :wink:


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