Jump to content
SAU Community

Cut And Shut Plenum

AMR33

By AMR33,
in Engines & Forced Induction

 Share

Recommended Posts

  • Replies 101
  • Created
  • Last Reply

Top Posters In This Topic

Popular Days

Top Posters In This Topic

Popular Days

Popular Posts

Ben C34
Ben C34

Maybe we need a pro and cons list. pros less pipe work easier to change plugs cons unknown effect on air distribution better chance of a defect then it's just a matter of weighing it u

ARTZ
ARTZ

but bro, a bunch of internet people just told me it wouldn't work with no factual evidence to back up their claims.. how can you argue with that? reading through some toyota forums and they have the

ARTZ
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

Posted Images

GTSBoy Grand Master

GTSBoy

Posted
Posted

I am not going to try any more. I am not an internet theorist. I am an engineer whose work rather deeply involves aerodynamics, particularly flow in ducts. You can tell when someone who doesn't know abotu air flow at all starts posting abotu this stuff because they start talking as if boost has something to do with it (ie there's a difference between turbo and NA air flow - which there isn't really until you start getting into the detail of flow inside the ports in the head). Or they start to carry on about how their tuner didn't notice X or Y, but when asked if the tuner had individual exhaust temperature probes, the answer is always "no".

Cut open the upper plenum of an RB, or an old 7M, or even the plenum off a 2J or SR20. Look at the strange lumps and bumps involved in the casting on the inside of the chamber. If you can't point to a bolt or other clearance issue on the outside of the plenum as the reason for a bulge on the inside, then it's a fair bet that some switched on OEM engineer put that lump there to alter the air flow inside the plenum to achieve a goal of some sort - probably to balance the flow between runners. There is a hell of a lot that goes into designing this stuff properly that people who are uninformed of it would never imagine is possible. I spent $100k of CFD computer and engineering time doing a plenum design job for a kaolin calcination kiln to get the air into the process in the best possible way. Alright, I didn't spend the money. The client spent the money. I did the work.

ARTZ Grand Master

ARTZ

Posted
Posted

That's nice that you are educated GTSboy im sure your mummy is proud of you too...

But believe it or not I do know about the lumps inside the plenum and what they are there for..and i didn't even finish high school. :woot:

I also know there is plenty of cars around making power with these plenums so unfortunately your argument, while somewhat "educated" is not really being proven 100% correct yet

Now the only point I was trying to make is that there is alot more pressure in the plenum of a boosted car than that of a NA..i don't remember ever hearing of an NA car blowing the welds on the intake...doesn't it make sense that this pressurized air is going to make its way out of or into any opening (hopefully the valves) that it can make its was into...

Now while.it might not technically be the most efficient way of doing things it seems to me that it can indeed work well enough as I am yet to hear of an engine that blew up just because it had a cut n shut plenum...

GTScotT Grand Master

GTScotT

Posted
Posted

Without individual cylinder temperature probes it would be difficult to know if its working right or not. The AF at the tailpipe is basically an average across all 6 cylinders, and you need the temp probes to tell you which is literally running hotter (leaner) than the others.

In this case I know there are cars where this is known to work FINE, and others where it is not so fine.. I am unsure on the verdict for an RB25.

What I do know is I am about to start fixing a car with this EXACT plenum cut and shut job. I will take photos when I do... The motor has been looked after but has gradually spun a bearing AND fried the fire rings on one or more cylinders. I am looking forward to seeing the piston crowns once I crack it open... I am fearful that some cylinders will present leaner than others.

I will report back in due time. If anyone is specifically wanting to know about this (long term) and doesn't hear back from me in 3 months drop me a PM and I will update my findings at that stage.

GTSBoy Grand Master

GTSBoy

Posted
Posted

But believe it or not I do know about the lumps inside the plenum and what they are there for..and i didn't even finish high school. :woot:

Now the only point I was trying to make is that there is alot more pressure in the plenum of a boosted car than that of a NA..i don't remember ever hearing of an NA car blowing the welds on the intake...doesn't it make sense that this pressurized air is going to make its way out of or into any opening (hopefully the valves) that it can make its was into...

Now while.it might not technically be the most efficient way of doing things it seems to me that it can indeed work well enough as I am yet to hear of an engine that blew up just because it had a cut n shut plenum...

Responses to the various paragraphs in your post.

1) OK, then do tell what you know about the function of these lumps and bumps.

2) No. Wrong. Pressure has NO EFFECT. Air flow is air flow. Until you can grasp that, you are labouring under a massive misapprehension as to how this stuff works. Sure, the absolute value of the static pressure in a flowing gas will change the gas properties a bit, which will tend to influence the thickness of the boundary layer and a few other such things. But it does not change the nature of the flow patterns at all. Not one bit.

3) A motor does not have to blow up to be working not as well as it could if the plenum were working properly.

GTSBoy Grand Master

GTSBoy

Posted
Posted

No. RBs are "freaking easy to kill" when you do things the wrong way. Limiter bashing is the wrong way. Smashing ceramic turbines into the engine is the wrong way. Leaning out on old fuel pumps is the wrong way. Revving them hard without dealing with the oil pump drive or the CAS scatter is the wrong way. Randomly upsetting the flow into the inlet manifold runners is the wrong way. Sure, some people's bodgy mod might work OK. Others might not. Unless you've properly tested the result of a mod to the plenum you can't claim it is fine.

I could suggest a lot of mods to plenums that I would be happy to implement without testing because it is a very fair bet that they won't upset the flow. Making the plenum very large, for example, will almost certainly do nothing bad for distribution. Might not be great for response, but that's not the point. Making it smaller, or randomly aiming the incoming air at some other point in the plenum are not what I would call sensible without an instrumented test afterwards. Hell, I wouldn't even trust a Plasmaman type plenum unless they could show me that they'd done some reasonable testwork during development (and preferably that they'd had problems with distribution on some prototypes and found solutions to them - it's hard to trust "we got it right the first time"). Sure, there may be a big installed base of engines out there with Plasmaman plenums on that you can point to as proof that it works......but I'd still like to see at least one of them report all the exhaust temps (and show that the injectors were all within a little margin of each other and there were no cylinder trims in effect) before believing that they aren't all limping along with some flow distribution problem that is being masked by the tuning.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • GTSBoy
      R34 Gtt Wheel Offset Advice

      By GTSBoy · Posted

      I think my main complaint with your idea is that there is a veneer of idealism spread across it. You want the simple numbers to make it easier, but all they will do is make it easier for someone to come to the wrong conclusion because the fine details will kick them in the nuts. As it is right now, the tiny bit of arithmetic is NOT the obstacle to understanding what will fit and what will not fit. The reality of trying it is what determines whether it will fit. If you had a "standard rule" that R34 GTT guards have that magic 100mm space from the hub face to whichever side you were worried about, and someone said "excellent, this wheel is only 98mm in that direction, I'll just go spend $4k on them and jam them on my sick ride".....they would just as likely find out that the "standard rule" is not true because the rear subframe is offset to one side by a fairly typical (but variable) 8mm on their car and they only have 92mm on one side and 108 on the other.
    • Kinkstaah
      R34 Gtt Wheel Offset Advice

      By Kinkstaah · Posted

      It still combines inches with mm, especially when you have .5 inches involved, and mm and inches that can go in either direction. This would give a clear idea on both sides of the rim, right away, with no arithmetic. Even better if somebody gives you the dimensions of the arch of multiple cars. i.e GTR may be 125mm, a A80 Supra may be 117mm, or something along those lines. Yes, you can 'know' that going from a 10in rim to a 10.5in rim with the same offset moves both sides about 6mm, but you still have to 'know' that and do the math. Often it's combined. People are going from 9.5 +27 to 10.5 +15. You may do the math to know it, but if it was going from (I had to go look it up to be sure) 241mm/2 - 27 - 93.5mm from the center line to (more math) 266/2 - 15 (118mm) from the center line. Versus 93mm vs 118mm. It's right there. If you know you have a GTT with 100mm guards you can see right away that one is close to flush and the other absolutely won't work. And when someone says "Oh the GTR is 120mm" suddenly you see that the 10.5 +15 is about perfect. (or you go and buy rims with approximately 118mm outward guard space) I think it's safe to say that given one of the most common questions in all modified cars is "How do offsets work" and "How do I know if wheels will fit on my car" that this would be much simpler... Of course, nothing will really change and nobody is going to remanufacture wheels and ditch inches and offset based on this conversation :p We'll all go "18x9+30 will line up pretty close to the guards for a R34 GTT (84mm)" but 'pretty close' is still not really defined (it is now!) and if you really care you still have go measure. Yes it depends on camber and height and dynamic movement, but so do all wheels no matter what you measure it for.
    • GTSBoy
      R34 Gtt Wheel Offset Advice

      By GTSBoy · Posted

      But offsets are simple numbers. 8" wheel? Call it 200mm, near enough. +35 offset? OK, so that means the hub face is that far out from the wheel centreline. Which is 2s of mental arithmetic to get to 65mm to outer edge and 135mm to inner. It's hardly any more effort for any other wheel width or offset. As I said, I just close my eyes and can see a picture of the wheel when given the width and offset. That wouldn't help me trust that a marginal fitment would actually go in and clear everything, any more than the supposedly simple numbers you're talking about. I dunno. Maybe I just automatically do numbers.
    • silviaz
      R32gtr sputtering and stalling

      By silviaz · Posted

      Ah ok interesting to know.
    • Kinkstaah
      R34 Gtt Wheel Offset Advice

      By Kinkstaah · Posted

      Sure! But you at least have simple numbers instead of 8.5 inches +/mm, relative to your current rims you do maths with as well, and/or compare with OEM diameter, which you also need to know/research/confirm..
×
×
  • Create New...