Forward Facing Plenum

[Dorifta]

saw this on skylinesowners.com and wondering if anyone has done it before to give me an idea of the time involved. Looks like a solid days work for the experienced. I cant wait to do it to increase throttlle response which all front mounts suffer from,

Whats the verdict

http:/www.skylineowners.com/forum/showthread.php?t=70143http://www.skylineowners.com/forum/showthread.php?t=70143

how do u post pics, I select add image and it asks for the url of the image

[cruzin33]

It wouldnt be to hard but its really not worth it as the plenum is designed to flow from the middle not the frount. The best option is to buy a greddy or plezman plenum that have been flow tested.

Some pics of my cut and shut job plenum that came with the car, very neat work but still i took it of the car

Dave

[Dorifta]

It wouldnt be to hard but its really not worth it as the plenum is designed to flow from the middle not the frount. The best option is to buy a greddy or plezman plenum that have been flow tested.

Some pics of my cut and shut job plenum that came with the car, very neat work but still i took it of the car

Dave

Any reason you took it off the car, im thinking of doing it because I hate the lag in throttle response most front mounts give you

[GUN_METAL_GTR32]

i have heard from some ppl that these r no good because it makes the air mixtures uneven towards the back.

if u know what i mean

+ plazmaman and greddy have great plenum that look really f**king good so y wouldnt u just get one of them?

[Dorifta]

i have heard from some ppl that these r no good because it makes the air mixtures uneven towards the back.

if u know what i mean

+ plazmaman and greddy have great plenum that look really f**king good so y wouldnt u just get one of them?

everythings relative, but i believe there excessively overprice and I dont like bling, I like the stock look

Edited October 4, 2009 by Dorifta

[turael]

it leans out the back cylinders. either get a flow tested one, or don't do it.

[GUN_METAL_GTR32]

everythings relative, but i believe there excessively overprice and I dont like bling, I like the stock look

u can get them black dude

and i think the plazmaman and greddy ones are well priced unlike the hypertune ones lol

[Mr500]

it leans out the back cylinders. either get a flow tested one, or don't do it.

please explain your theory on this. pressure is the same at all points in in the inlet manifold.

the only way the rear cylinders would run lean is if they did from the factory.

feel free to prove me wrong though.

[SiR_RB]

ive herd that there isnt a problem in running the plenum like this

anywayz can anyone do it? im very interested to get it done, better yet anyone got one for sale?

let me no

thanks

[EJD001]

Im getting a custom plenum made, he is building it to retain all the factory options. Will let u know how it goes once i get it done

[89CAL]

I think theres a debate on the pressure being equal across all cylinders during boost. Theres for and against arguments from what i remember, be interesting to see for real what actually happens within front facing plenums (using stock manifold) under boost and vacum conditons.

[mad082]

please explain your theory on this. pressure is the same at all points in in the inlet manifold.

the only way the rear cylinders would run lean is if they did from the factory.

feel free to prove me wrong though.

not exactly. the pressure is higher where the airflow is hitting an object and being forced to change direction. if your statement was true then airplanes wouldn't fly.

what happens when you foward face a stock plenum is that the air is coming into the plenum is flowing in and hits the back of the plenum then flows down towards the rear cylinders. the air then flows around the plenum and into the other cylinders from there. not exactly an even flow. what you end up with is number 6 being lean (gets more air) and number 1 being rich (gets the least air). you may still get an afr the same as what it was with the stock manifold, but since that is simply an average of all 6 cylinders you don't know what is actually happening with individual cylinders.

this is the reason why front facing plenums will usually have the inlet facing at a bit of an angle. if they have no angle then the airflow is going to directed mainly at the rear cylinders, and if they have too much of an angle the airflow will be directed into the front cylinders.

[Mr500]

not exactly. the pressure is higher where the airflow is hitting an object and being forced to change direction. if your statement was true then airplanes wouldn't fly.

what happens when you foward face a stock plenum is that the air is coming into the plenum is flowing in and hits the back of the plenum then flows down towards the rear cylinders. the air then flows around the plenum and into the other cylinders from there. not exactly an even flow. what you end up with is number 6 being lean (gets more air) and number 1 being rich (gets the least air). you may still get an afr the same as what it was with the stock manifold, but since that is simply an average of all 6 cylinders you don't know what is actually happening with individual cylinders.

this is the reason why front facing plenums will usually have the inlet facing at a bit of an angle. if they have no angle then the airflow is going to directed mainly at the rear cylinders, and if they have too much of an angle the airflow will be directed into the front cylinders.

incorrect. 6psi is 6 pounds of pressure on every square inch of surface area. RBs have equal volume runners, that means that each runner holds the same volume of air being fed from the plenum. the same volume of air, under the same pressure fed through the same size hole will funnily enough flow the same amount of air as the next hole.

planes fly because there is a speed differance over the aerofoil. the air is forced to travel faster over the top of the wing by the convex shape being a further distance to cover then the concave bottom. this creates a high pressure on top of the wing and a low on the bottom. the low pressure tries to equalise with the high, acting on the bottom of the wing, pushing it up.

i dont think nissan would have spent millions of dollars developing the SR20 engine to have lean as No 4 cylinders.

what you are saying would be true if we where talking about NA engines but as soon as you add boost it throws it all out the window.

the engines i work with are 27ltr, twin turbo V12s that make around 1000hp at 30psi, carrying 100 tonnes of rock up a steep hill of around 2km in length for 12hrs a day in upto 45deg heat. the outlet of the aftercooler is right at the rear of the engine, around 1.5mtrs from No1 cylinder compared to 5cm to No12 and AFRs are the same across ALL cylinders.

[mad082]

incorrect. 6psi is 6 pounds of pressure on every square inch of surface area. RBs have equal volume runners, that means that each runner holds the same volume of air being fed from the plenum. the same volume of air, under the same pressure fed through the same size hole will funnily enough flow the same amount of air as the next hole.

planes fly because there is a speed differance over the aerofoil. the air is forced to travel faster over the top of the wing by the convex shape being a further distance to cover then the concave bottom. this creates a high pressure on top of the wing and a low on the bottom. the low pressure tries to equalise with the high, acting on the bottom of the wing, pushing it up.

i dont think nissan would have spent millions of dollars developing the SR20 engine to have lean as No 4 cylinders.

what you are saying would be true if we where talking about NA engines but as soon as you add boost it throws it all out the window.

nissan designed the plenum to be foward facing, so they spent the money making sure it was right. the designed the rb20/25 plenum to be side facing, so cutting it open and making it foward facing makes any designing they did pointless. the did all the design to take into account the air coming in from the side and designed the position and length of the runners around this info. going and positioning the inlet in a totally different position and direction renders this designing somewhat useless.

you are somewhat correct in your statement that 6psi = 6psi everywhere, however once you take into account other things like turbulence and air speed it isn't so simple. if it was as simple as what you say (6psi = 6psi) then there would be less gains from putting bigger turbos on. also the end tank design of intercoolers wouldn't make any difference to airflow. even how much throttle you use wouldn't make as much of a difference because you can make full boost without using 100% throttle, but using 100% throttle allows the most air through and gives you the most power because the air is travelling faster.

what the air is doing inside the plenum dictates how much air actually goes into the cylinder when the valves are open. if 6psi simply meant 6 psi and that was all that mattered, then you could just stick a mailbox on there with 6 pipes coming out of it and it wouldn't make any difference to performance and all the companies would be wasteing their time and more paying people to design technical manifolds that flow well and deliver equal airflow.

and why bother with proper intercooler piping? why not just weld up some rectangular downpipe with 90 degree corners (note i said corners note bends). it will still presurise to 6psi, and that's apparently all that matters.......

the engines i work with are 27ltr, twin turbo V12s that make around 1000hp at 30psi, carrying 100 tonnes of rock up a steep hill of around 2km in length for 12hrs a day in upto 45deg heat. the outlet of the aftercooler is right at the rear of the engine, around 1.5mtrs from No1 cylinder compared to 5cm to No12 and AFRs are the same across ALL cylinders.

well good for you........ do you want a medal?

[joeyjoejoejuniorshabadoo]

these are the facts:

there ARE people running cut and shut front facing plenums without problems... yet

BUT

there ARE people that have blown up no6 due to leaning out with a cut and shut

now... the fact that multiple people have blown up the same part using the same plenum setup tells me something... mebbe its not the best idea....

the fact that psi should be even in a pressurized environment goes out the window as an argument when people start blowing up motors, regardless of how much you think it SHOULD work, real world testing has shown it CAN and DOES fail

its a cheap and nasty approach to blinging out your engine bay.... the difference in lag will be undetectable.

i have 300rwkw seeing full boost of 21psi by 33-3400.... the stock plenum is fine.

and i'm not just being a ponce about expensive parts here. i have a cut and shut plenum on my 4age as a temporary untill i put in ITB's (although that's a 180 deg no a 90 deg)

[paulR32gtr]

what you are saying would be true if we where talking about NA engines but as soon as you add boost it throws it all out the window.

Oldish thread but hey things move slowly in the fab section.

My 2c - NA engines at sea level are already running at 14.7psi - atmospheric pressure... just because 6psi boost is higher than we are used to walking around in doesnt mean that the flow characteristics are out the window.

[crack]

planes fly because there is a speed differance over the aerofoil. the air is forced to travel faster over the top of the wing by the convex shape being a further distance to cover then the concave bottom. this creates a high pressure on top of the wing and a low on the bottom. the low pressure tries to equalise with the high, acting on the bottom of the wing, pushing it up.

close. high pressure on the bottom of the wing, low pressure on top of the wing. high pressure on top of the wing would bury the plane in the runway

[ISL33P]

just a quick note, air pressure may be the same by air flow is completely different.

if you go on some of the theory some have mentioned here, a straight pipe will flow the same as a pipe with a 90deg bend and that is simply not the case.

the cut and shut plenum would have nothing to do with cylinder 6 leaning out. quite the opposite, if you were to flow test a cut and shut plenum, i could almost guarantee that the last cylinder is one of the lowest if not the lowest flowing cylinder of them all, and therefore a richer mixture. this would have more to do with the turbulence being experienced at the back of the plenum.

i remember reading somewhere (not my words) that the leaning out of cylinders has more to do with coolant flow and coolant temperatures at the rear of the engine more than anything else.

i recently purchased an egt kit which is currently on a customers car for some logging and once i get it back, i will be looking for another car to do some logging on and compare not only this theory but the theory behind standard and aftermarket plenums and the dis/advantages they may have.

Ariel

[mad082]

just a quick note, air pressure may be the same by air flow is completely different.

if you go on some of the theory some have mentioned here, a straight pipe will flow the same as a pipe with a 90deg bend and that is simply not the case.

the cut and shut plenum would have nothing to do with cylinder 6 leaning out. quite the opposite, if you were to flow test a cut and shut plenum, i could almost guarantee that the last cylinder is one of the lowest if not the lowest flowing cylinder of them all, and therefore a richer mixture. this would have more to do with the turbulence being experienced at the back of the plenum.

i remember reading somewhere (not my words) that the leaning out of cylinders has more to do with coolant flow and coolant temperatures at the rear of the engine more than anything else.

i recently purchased an egt kit which is currently on a customers car for some logging and once i get it back, i will be looking for another car to do some logging on and compare not only this theory but the theory behind standard and aftermarket plenums and the dis/advantages they may have.

Ariel

i don't think that the AFR mixture is going to be affected by coolant, etc. however the amount of detonation, resulting in cylinder failure can be affected by coolant temps. higher coolant temp around that cylinder = more detonation caused by hot spots in the cylinder, resulting in damage.

and i would still say that the cut and shut plenum will flow higher to number 6 than number 1. but if you want to flow test one and prove me wrong then feel free. but number 1 cylinder is farthest from the inlet as far as airflow is concerned, despite being the closest distance wise.

[ISL33P]

both afr and egt's will both be directly reflective affected of the temparature in the cylinder, otherwise you wont have the detonation

does anyone have one of these floating cut and shut plenums about....i am curios to test one?

come to think of it, i have a complete spare r33 inlet, i will make one and and test it by the end of the year...i have plenty on at the moment so it will have to take a back seat for the time being