R33 Intake Plenum

[StockyMcStock]

see now that is a good looking job there - pity you're in perth i could have used your fabricator to do another one.

how much did it cost to get done?

Edited October 5, 2005 by StockyMcStock

[stR33ter]

NUTHIN

MATE DID IT FOR ME

BUT HE NO LONGER WORKS AT THE SHOP WHERE HE DID IT

[Evan_R33]

Dude i say do it. everyone can talk sh*t all they want, but untill you just up and do it to see you will never know! I reckon that everyone is overthinking the whole situation. What are we looing at? 1000hp no, so i don't think it's gonna matter! i mean all that inlet runner crap! point is shorter pipes= good bigger throttle body = good! so i say just do it!

[33SOM]

Here we go again.... I predict 10 pages??

[bilbo117]

i have been long looking up this. A standard plenum modified will lean out on cylinders 1 & 6. but i believe this would only be an issue in high flowing applications.

this is the latest plazmaman plenum for the RB25det and autostyle claim to have gotn 208rwkw with exhaust and 12psi.

i believe the main benefits of an aftermarket planem are

-less heat

-less piping

-greater volume of inlet manifold

-smoother airflow

there is no doubt in my mind any plenum modification/upgrade wouldnt give more horsepower over the factory item. but at the cost of reliability???

[Sydneykid]

increased throttle response/better spool will be down to the shorter piping without a doubt. tried and proven over and over again.

Not be me, I have proven exactly the opposite time after time. Even some simple primary school maths kills that arguement.

How can removing 2 litres of volume from the (shorter) pipework and adding 3 litres to the plenum result in improved response? And that's assuming equal pipework diameter.

The most important air volume for response is the amount between the throttle butterfly and the valve, ie the more air you put between the TB and the valve the worse the response. In fact this is more important for immediate response than the volume of air between the turbo and the TB. That's why GTR's have the TB's close to the valves. Think about the extra distance (volume of air) between #6 and the TB when you move it to the front.

How can replacing 63 mm inlet pipework with 75/80 mm pipework result in improved throttle response? The volume of air inside the 80 mm pipework is 61% greater than the 63mm pipework. You don't get a 61% shorter inlet by having the throttle body at the front of the plenum. So you must have slower throttle response because there is more air in the inlet system in total.

Until you have measured the internal volume of the complete inlet system (pipework, intercooler and plenum) and can prove it is less, then no one with any modicum of sense will believe that there is anything but a loss of response.

Save you time, I have done it, about 2 years ago and published the results on this forum.

here is an example of 4 intercooler setups and pipework we have actually used;

1. R33 GTST Standard Intercooler and standard R32 GTST pipework

150 rwkw = 27 lbs of air per min @ 13 litres of i/c & pipework

2. Supra Intercooler and matching 63mm pipework

180 rwkw = 30 lbs of air per min @ 15 litres of i/c & pipework

3. Standard GTR GTR and 63/75mm pipework

250 rwkw = 40 lbs of air per min @ 21 litres of i/c & pipework

4. Greddy 600 X 300 X 115 and 80 mm pipework

400 rwkw = 60 lbs of air per min @ 28 litres of i/c & pipework

If you look at the numbers you can see that the rate of air flow and the volume of I/C and pipework have a fixed relationship (27 = 13 , 30 = 15 , 40 = 21 , 60 = 28).  This is not an accident, I designed it that way.  The reason is I wanted to keep the throttle response as close what it was when the car had 150 rwkw, because I though that was very nice response.

The theory I followed was, the more power the engine produces the more air it needs.  Thus if I keep the increase in the volume of air inside the inlet system in the same proportion as the power increase, then the throttle response should stay the same.  This is based on the engine using the air in the same time frame.

So when people say they fitted a FMIC and have not noticed any less throttle response, my response would be, that is what I would expect.  As long as they went from 150 rwkw to 180 rwkw.  On the other hand, if there was no power increase then it would be simply physically impossible for there to be no decrease in throttle response.

The problem of poor throttle response arrises when you have a 220 rwkw engine with a 28 litre inlet system.  This is something I see way to often.

So get out your calibrated container and measure the internal volume of the entire inlet system, apply the appropriate calculations and compare it with the above. It's the only way you are going to win me over, and anyone else who can add up.

cheers

[33SOM]

But wouldnt larger intercooler piping work the same as an exhaust system? Less restriction = more flow. More flow = more air. More air = more power??

Just my thoughts

[bilbo117]

wow. but just as u have power gains witha front mount, wouldnt u also have them with an aftermarket plenum? hence a better throttle response? from wat u said, this would happen with a larger increase in power and slight increase in volume? correct? im learning heaps here....

[ISL33P]

stocky - it is done individually on each cylinder once temps have stabilisied after several dynos runs to keep consistency.

sydney kid - i proved this on my own car where pipe diamter stayed the same during all mods. only thing that changed was pipe length and plenum volume. i had greater torque (proven by a dyno) and throttle response (proven by increased fuel efficiency) with a (very) large plenum volume and short ic pipes than what i did with a std plenum and same size pipes but longer in length.

but in the end each to their own as every person you ask has a different theory, i just go from what i know and has worked for me and customer and friends cars in the past.

[Sydneykid]

sydney kid - i proved this on my own car where pipe diamter stayed the same during all mods. only thing that changed was pipe length and plenum volume. i had greater torque (proven by a dyno) and throttle response (proven by increased fuel efficiency) with a (very) large plenum volume and short ic pipes than what i did with a std plenum and same size pipes but longer in length.

but in the end each to their own as every person you ask has a different theory, i just go from what i know and has worked for me and customer and friends cars in the past.

<{POST_SNAPBACK}>

What the hell has fuel ecomomy got to do with throttle response?

I believe the greater torque, but that's a static measurement not transient response.

So you kept the same pipe diameter but shortened it. What if you have left it the same length and reduced the diameter? Same effect, up to the restriction limit of the pipework. I could argue that the pipework was too big in diameter and by shortening its length you simply covered up for the fact that is was too big.

This is not "theory", it is simple mathematics. If there is more air between the turbo and the inlet valves, then it takes longer for that air to flow into the engine at the same power level. That means the throttle response is worse.

Is the problem here that you haven't measured/compared the internal volume? So you have no idea what improvement you have made. In fact you may have gone backwards, you don't know because you haven't measured anything that will tell you whether you have or not. You have measured a number of other things, but not one of them actually tells you whether you have done the right thing or not.

It may seem like I am picking on you personally, but I am not. I get this sort of statement from people all the time about front mounted plenums/throttle bodies. The engine makes more torque so therefore this mod is a good thing, but that is simply rubbish. It makes about as much sense as "the new plenum has removed restrictions and I got more boost". Nope, if you remove restrictions the boost goes down, not up.

If you want to have a front mounted throttle body/big plenum because it looks good, that's a quite valid reason. But don't kid yourself that that it is going to give you more performance/better throttle response on an internally standard RB20/25. Spending the same amount of money on other parts (say cams) will give a higher hp per dollar result. On the bang for buck stakes, changing the inlet system on an internally standard RB20/25 is pretty poor value.

cheers

[Sydneykid]

But wouldnt larger intercooler piping work the same as an exhaust system? Less restriction = more flow. More flow = more air. More air = more power??

Just my thoughts

<{POST_SNAPBACK}>

Not if the pipework is already of sufficient size and so does not have any restriction. It only helps when the pipework is too small.

wow. but just as u have power gains witha front mount, wouldnt u also have them with an aftermarket plenum? hence a better throttle response? from wat u said, this would happen with a larger increase in power and slight increase in volume? correct? im learning heaps here....

We are not talking about only power gains, we are talking about throttle response. The dreaded lag between when you put you foot down and when the engine accelerates. If there is more air between the throttle body and the engine then you have more lag, unless the increase in power = the increase in volume. Adding 50% to the volume means you need to add 50% to the power, and that simply didn't happen. So the throttle response MUST be worse.

Think about it, you have a throttle body that is ~250 mm away from #1 and ~900 mm away from #6. To get away from that obvious issue is why Nissan equiped GTR's with multiple throttle bodies. If they could have saved that amount of money and achieved the same throttle response, I am sure they would have stuck a single throttle body on there.

If you want to test the lag effect of pipework and intercoolers on throttle response, try running the pipework straight from the turbo into the plenum. You won't believe how fast the engine responds to every little tickle of the throttle.

It isn't that complicated when you think about what it is that you are trying to achieve, and then spending the time, money and effort on something that will actually help in achieving that target. There are simply better/more effective ways to spend your ~$1500 than on a plenum upgrade.

cheers

[R31Nismoid]

But wouldnt larger intercooler piping work the same as an exhaust system? Less restriction = more flow. More flow = more air. More air = more power??

Just my thoughts

Its like a 2kg milo tin vs a 500gram milo tin

if you have the same amount of air, the 500gram is smaller and moves the shit faster.

The 2kg tin is larger, the volume of it all means the same amount of air has to fill the space, or more air is required

Filling space means slower moving. Slower moving it a cost to response

thats my average joe understanding anyhow

[StockyMcStock]

all good reading and a cracker of a thread guys!

i'm not too worried about improving my power output, or my throttle response with a plenum change. i just need a front-facing plenum because of space restrictions. modding the standard one and keeping the AAC stuff at the rear is the best option i can see, as i will be running a powerFC which uses this stuff for cold starts etc.

if i could get a custom plenum that incorporated all the AAC gear, then i might consider it. but modding the standard one just appears to be the best way about it at this point in time.

[ISL33P]

increased throttle response/more torque/less lag all increase fuel economy with the engine reaching a better level of efficiency than previously (whatever that may be).

how would you explain hp/torque increases on a car with exactly the same pipe lengths and diameters and the only difference being change in forward facing plenum design ? This has been done and the results are quite interesting. They do reflect some of your comment with volume affecting throttle response, but at the cost of power. Time will tell with more results coming soon.

sounds like you are only kidding yourself if you think plenums dont increase hp, doesnt matter if the car is internally standard or not. Internals have no effect on engine performance, they are only modified for durability, not performance. Cams will enhance power but generally at a cost of bottom end performance (depending on what cams you get). So an increase of airflow per cylinder will not increase hp ? i beg to differ and that is exactly what a plenum should do.

as for bang for buck, cams and adj cam wheels will set you back more than one of my plenums ($900*) and i would like someone to see what results they get. They may not be a brand name but have outperformed brand names in the past and will continue to do so at a bargain price. My RB30ET plenums compared to bigger names for one and my 2JZ compared to Veilside is a prime example (sorry about the free plug, just giving examples) CA18 is a completely different kettle of fish as no-one makes them like myself (hence customers CA18's in Europe making 500-600rwhp with them).

as for airspeed, let the turbo (upgrade) sort that out. Many people have asked that question in the past and it is all relative to engines efficiency as per my first paragraph.

no offence taken at all sydneykid, this is what forums are all about.

stocky -aac can be retained, i have dont it with nearly all different plenums i have done.

Edited October 5, 2005 by ISL33P

[Sydneykid]

increased throttle response/more torque/less lag all increase fuel economy with the engine reaching a better level of efficiency than previously (whatever that may be).

how would you explain hp/torque increases on a car with exactly the same pipe lengths and diameters and the only difference being change in forward facing plenum design ? This has been done and the results are quite interesting. They do reflect some of your comment with volume affecting throttle response, but at the cost of power. Time will tell with more results coming soon.

sounds like you are only kidding yourself if you think plenums dont increase hp, doesnt matter if the car is internally standard or not. Internals have no effect on engine performance, they are only modified for durability, not performance. Cams will enhance power but generally at a cost of bottom end performance (depending on what cams you get). So an increase of airflow per cylinder will not increase hp ? i beg to differ and that is exactly what a plenum should do.

as for bang for buck, cams and adj cam wheels will set you back more than one of my plenums ($900*) and i would like someone to see what results they get. They may not be a brand name but have outperformed brand names in the past and will continue to do so at a bargain price. My RB30ET plenums compared to bigger names for one and my 2JZ compared to Veilside is a prime example (sorry about the free plug, just giving examples) CA18 is a completely different kettle of fish as no-one makes them like myself (hence customers CA18's in Europe making 500-600rwhp with them).

as for airspeed, let the turbo (upgrade) sort that out. Many people have asked that question in the past and it is all relative to engines efficiency as per my first paragraph.

no offence taken at all sydneykid, this is what forums are all about.

stocky -aac can be retained, i have dont it with nearly all different plenums i have done.

<{POST_SNAPBACK}>

Quick clarification to start off with. I refer to the standard internals of an engine as a bench mark of its power handling capablity. An example, my rule of thumb limit for RB25DET standard internals is 450 bhp. I have not found 1 bhp from changing the RB25 inlet manifold/plenum when the engine produces 450 bhp or less (ie; has standard internals). Over 450 bhp there are a number of advantages to be had in changing the inlet system. The way I put it is "if you have standard internals, there is nothing to be gained from changing the inlet system on an RB25".

I have been hearing about this and that inlet manifold/plenum increasing bhp on RB25's (at less than 450 bhp), but I have never seen it. Not once have I seen or been able to produce a power increase from ONLY changing the inlet manifold/plenum. Every time I dig I find that other things have been changed at the same time Boost was increased, or ignition timing was tuned, or A/F ratios improved, or a larger intercooler, or a bigger turbo etc etc. When just the inlet manifold/plenum and nothing but the inlet manifold/plenum was changed I have NEVER EVER seem a power increase. The truth is I have seen plenty of power decreases on our dyno.

Then I get out my bucket of water and measure the internal volume, all fail the internal volume test, they have greater volume than the standard inlet manifold/plenum. That inextricably means a loss of throttle response at the same power output.

Then I stick it on the flow bench and compare it to the standard inlet system and find that both have almost zero restriction at sufficient airflow to produce 450 bhp. In fact I have tested up to airflows equaling 550 bhp and found amost zero restriction in the standard inlet system. I am not the only one, Zenitani, for example, have produced a numbewr of 500+bhp RB25's with standard inlet manifolds/plenums.

The bottom line, until you produce a before and after set of dyno results (with nothing elses changed) I won't believe that your inlet manifold/plenum gives more power than the standard inlet system on an RB25 up to 450 bhp. Until you produce a set of volume tests that prove that the internal volume is less than the standard inlet system, then I won't believe that your inlet system gives improved throttle response. Until you produce a set of comparative flow bench tests that show your inlet system has less restriction than the standard inlet system I won't believe that I wouldn't be waisting my money buying one.

CostsThe last set of RB cams that I bought cost $450, there are currently 3 sets advertised on the forums for less than $900.

http://www.skylinesaustralia.com/forums/in...c=86468&hl=cams

http://www.skylinesaustralia.com/forums/in...c=89339&hl=cams

http://www.skylinesaustralia.com/forums/in...topic=84077&hl=

I have no doubt that if I spent $900 (or less) on almost anything (cams, adj exhaust cam pulley, split dump, intercooler, Power FC, power porting the manifolds, more thorough tuning etc etc) I would get a power increase far in excess of what I would get from changing the inlet manifold/plenum.

I have similarly challenged every inlet manifold/plenum manufacturer that claims a power increase from fitting their product (only) to an internally standard RB20/25 to prove me wrong. Nothing would give me greater pleasure than for you to be the first, at least I could then buy and recommend an inlet manifold/plenum that is actually worth spending the money for an internally standard RB20/25's.

cheers

Edited October 5, 2005 by Sydneykid

[StockyMcStock]

hmmm..... so you can do plenums with the AAC valve on the rear eh? i might be interested in one of those.......

[MacGuyver]

The R33 that Autosalon magazine tested the Plazmaman plenum upgrade on was internally stock BUT they were also upgrading the intercooler, BOV and pod filter at the same time. So all their power and torque increases in the test would've come from these? It was the same kit as the one tested in Autostyle that bilbo117 mentioned above.

"Mmmm, unexplained bacon."

[r33_racer]

Reading SK's posts gives me goose bumps....you can feel the intensity just glowing from the post....FLAWLESS VICTORY!

I love reading this stuff.....its soooo good. Gives me the experience i need to be the best internet mechanic around....haha. God im a tool

[ISL33P]

i am happy to supply a plenum for a car producing 450+hp and see what it does, on one condition, its is tuned before and after by the same dyno operator on the same day (see beow), preferably one unknown to both the cars owner and myself to save any "fundging" of figures on anyones behalf.

the challenge is up to you to prove me wrong.

in regards to the tuningmwhy wouldnt someone change the tune to take full benefit of the mods, its like changing a turbo and not doing anything else. The only benchmark you can use if boost level. If a car is tuned to its peak and produced xxxhp at yypsi what is wrong with tuning the car with the new mods with the same yypsi and air/fuel ratios and use that as a basis for any improvement in the cars peformance. If people were to take your philosophy on board, we would all have all the mods in the world with standard computers, injectors exhaust etc ......... ????????? whats the point of that.

r33 racer, you just stick to your internet mechanics and you will go a long way

[r33_racer]

haha...yeh not really an internet mechanic (fabricator actually) have enough real ones in the household. But i admit you can learn ALOT from reading these forums. Dad never believed in the net, but now if we get stuck on the race car its 'Michael can ya pm sydneykid about this or about that and see what he reckons?' Ive gotten to the point now where im worried about annoying him cause im always asking him about race car stuff. anyway...

I can see the point your both making about the manifolds and its been argued forward nad back a million times before. Always good to see though, something new is always bound to show up.