Cut And Shut Plenum

[ARTZ]

exactly ,when you cram enough boost into anything its going to end up in the goddamn cylinders regardless of what sort of plenum you have on it or how many millions was spent designing it....

[scotty nm35]

I agree to some extent Artz, but I have seen dangerous hack jobs out there that scare the hell outta me. Can you imagine what may happen if one let go on an unsuspecting driver? Especially if map sensored...

[WMDC35]

That's no good Scotty, you'll probably be doing the cutting & shutting?

[scotty nm35]

I refuse to do them, as I don't have an oven large enough to pre-heat the plenum for decent penetration, and for the exact reason I mentioned above. Even welding in a secondary injector boss on my plenum was stressful enough for me.

[Soundboyracer]

Personally I find you guys over thinking such a small matter, to each their own

[GTScotT]

Actually they are debating whether or not it would nuke the motor if run like that for long enough.

So I'd say they aren't over thinking anything.. Its a good topic.

[Joshbigt62r]

I can't agree enough with GTSBOY. Just my opinion and I'm far from a engineer. But Nissan made things the way they are for a reason. Cut and shut is a no go. Plazmaman FTW....

Josh.

[Kinks]

lol...fair enough..in this industry its another shitty RB motor that's gumma die sooner or later anyway...

With an attitude like this it's no wonder people kill motors.

"Cut and shut plenum she'll be right mate"

"The air will get in there somehow it'll be right mate"

"Give me a rich power tune she'll be right mate"

"I fitted one and my engine is 'fine' mate"

As an engineer myself I feel sorry for GTSBOY in this discussion. When you are actually designing something properly, "she'll be right" is an omission you don't know what the f&ck you're on about. He's doing his best to share knowledge and coming up against "let's bolt these 2 things together and see what happens".

RB's have a lot of margin in the design, that's why we see unopened RB25DET's doing 300rwkw all day long. If done PROPERLY there is no reason why this can't be reliable and have good longevity. But stick a shitty plenum in it, do a quick tune at 10:1 that ends up washing down the bores with petrol and you end up with a motor that eventually dies. It's the margin that lets you "she'll be right" it and you will get away with it.. for a while.. but the engine is not happy.

[ARTZ]

Ok..

Lets discuss. "Nissan designed it that way for a reason"

Nissan designed alot of things for a reason, most of which are modified by some of you at some point...so maybe we should stop modifying everything!

Anyway I will gladly retract any argument and admit they are omissions of my lack of knowledge, when I see some factual evidence that these plenums are detrimental to engine health which it seems none of you are yet to provide..

And for the record "she'll be right" Is commonly referred to reference a job done right ..unless of course you have a stick firmly implanted in your rectal area then it becomes a term associated with those who make themselves feel better or try to prove their point by the putting down of others..

I am not here to attack anyones character,I am simply providing another point of view

[Kinks]

Ok..

Lets discuss. "Nissan designed it that way for a reason"

Nissan designed alot of things for a reason, most of which are modified by some of you at some point...so maybe we should stop modifying everything!

Nissan's priorities and the enthusiasts' priorities are somewhat different. Nissan wants to sell as many cars as possible and get as little warranty work in return, and they also have to pass pesky legal things like emissions and safety legislation. Fuel economy is also an important part of a car's marketing. Enthusiasts want to get as much power out as possible, so a lot of those compromises Nissan makes goes out the window.

My point is that when you throw a cut and shut plenum, big turbo and some random injectors onto an RB, go to your tuner and pay as little as possible for a tune because you spent it all on mods, that you shouldn't be surprised that maybe the tuner gets close to your power goal but your emissions are woeful, so's your fuel economy and the motor doesn't last anywhere near as long as it should.

The big problem with cut and shut plenums is upsetting the balance of airflow between cylinders. Of course, if you simply throw fuel at the motor so that your average AFR is rich then the leanest cylinder (typically #6 since the air has momentum and will tend to flow along the back wall of a front-facing plenum) will still be OK. But the engine is definitely far from optimised. This is where it comes down to "doing it right" with the proper knowledge and just slapping a bunch of parts together with a power figure in mind and nothing else. As GTSBoy has said, invariably when people say "FFP works" you ask them if they've had individual cylinder EGT measurement on their exhaust manifold and the answer is "no" - they just threw enough fuel at it to keep it more or less happy and moved on to the next customer.

[AMR33]

What GTSTboy, Kinks and others who agreed with them said is all plausible, but again so are the arguments which disagree. To say that Nissan designed something for a reason and thats that is nonesene as far as I am concerned. The last RB25 was built what, almost 2 decades ago now and the requirements and market undoubtedly changed by now. Almost every part on a nissan is replacable with aftermarket parts these days and some can simply be modified as is the case here.

The bottom line is this, unless someone has proven results on a dyno accross the rev range, no argument on here is substantiated. This is a really good discussion and if anyone has something else to add.........C'MON DOWN!!!!

[GTSBoy]

I have seen two RB20s that died rather nastily with the same cut'n'shut plenum. After the second death, when the third engine went into the car, some thermocouples were installed into the exhaust manifold and some rather frightening differences in temperatures demonstrated. These differences were not linked to the injectors (as these were swapped around and also cleaned and flow tested as part of the ensuing paranoia). And when an unmolested RB20 plenum was put back on (with a Gibson style pipe to hook it up to the cooler piping on a temporary basis) the temperature differences all went away.

This was 16 years ago. The science hasn't changed since then. The only thing that has changed is whether the bodgy mod to the plenum gets the lucky angle or the unlucky angle. Whether the throttle body is set to swing one way or the other way, or any of a half dozen other reasons why one hacked plenum won't work at all while another will.

[wolverine]

Asking the opinion of 9 idiots and 1 expert doesn't tip the argument in the favour of the majority.

[LTHLRB]

As much as Cut n Shut are uneasy on the eye and look like they will do bad things to your engine

They seem to be working pretty well on some cars... Yeah it isn't a skyline or a rb20/5/6 BUT they've been proven to support a bucket load of power and able to run some pretty decent numbers.

Id still never ever EVER use one on my engine.

Edited August 21, 2013 by LTHLRB

[Kinks]

Asking the opinion of 9 idiots and 1 expert doesn't tip the argument in the favour of the majority.

indeed, also see my signature.

[scotty nm35]

And when an unmolested RB20 plenum was put back on (with a Gibson style pipe to hook it up to the cooler piping on a temporary basis) the temperature differences all went away.

^^ this.

[WMDC35]

What GTSTboy, Kinks and others who agreed with them said is all plausible, but again so are the arguments which disagree. To say that Nissan designed something for a reason and thats that is nonesene as far as I am concerned. The last RB25 was built what, almost 2 decades ago now and the requirements and market undoubtedly changed by now. Almost every part on a nissan is replacable with aftermarket parts these days and some can simply be modified as is the case here.

The bottom line is this, unless someone has proven results on a dyno accross the rev range, no argument on here is substantiated. This is a really good discussion and if anyone has something else to add.........C'MON DOWN!!!!

the people that design this stuff know what they're doing, the stock manifold still works well at over double it's original power, and is debatable whether even the performance designs work better, but it's all good anyone can hack it up and improve it?

it seems that the people against it only have proof in what has been seen in the past so have no interest in experimenting with it

so far the argument for it is it's going to be boosting hard so doesn't matter?

i'm surprised there's even people still talking about wanting to do it, refer the pros & cons list earlier in the thread

[Dose Pipe Sutututu]

2 mates cars run a cut and shut one has 300kw other has 360kw both running for 2-3 years tuner noticed decreance in intake temps but no leaning on cylinders.

I have one I am about to throw on mine as in a 180sx the crossover section hits the bonnet etc

did he have 6 wideband 02, one on each of exhaust ports? If not how can you tell if one cylinder is running leaner than the other

[GTScotT]

did he have 6 wideband 02, one on each of exhaust ports? If not how can you tell if one cylinder is running leaner than the other

Individual temperature probes on each exhaust runner (off the head).

Hotter is leaner. Simple as that.

[Kinks]

i'm surprised there's even people still talking about wanting to do it, refer the pros & cons list earlier in the thread

That's the problem with ignorance. Some people just keep re-stating the same point of view until people with actual knowledge get frustrated at the lack of rational discussion, throw their hands in the air and give up.

Then the ignoramus thinks they've "won" and continues to spout rubbish ad nauseum.

This thread will continue until all the people with technical knowledge have given up and all we have left is "my cousin's left handed inbred sister's boyfriend's VL commodore made 400hp with a cut and shut plenum so it must be OK".

Whatever.