I've seen at least a couple of people on here know a bit about fluid dynamics and intake modifications and im looking for some input/views on my plenum modifications. These were done before the car was exported from Japan. There's basically a full depth extension on each side of the plenum. Why would someone do this? I've read before that turbo charged cars benefit from a plenum of at least the same volume as the engine. Does anyone know what the volume of a standard plenum is? One side appears to be slightly larger than the other, is that an issue? Any educated views on whether this could be considered an improvement over the original or not are appreciated
You would think for someone to go to that much trouble and to do such a nice looking job thet would have a fair idea what and why they where doing it.
looking from a volume standpoint what looks like the larger side is also the side of #6 runner which is considerably smaller,
As above. My thoughts exactly as to why ones larger then the other. If you're curious to check the volume of each bank, perhaps affix some perspex to where it would bolt onto the lower plenum and block off the bypass tube. Then fill with measured water. Im thinking there would be more volume in the plenum compared to the displacement of the engine.
agreed... three litre engine... 1.5 litres per side... the standard plenum as got to be way more than that anyway. maybe it was more about air flow, or how they thought they could improve it (like you first indicated).
Good thinking, although im not sure if it would actually help that runner flow more air as it's not increasing the size of the runner although as Medallion Man says it may increase the flow back there and force more in? Isn't the runner you're referring to number 5, the one closest to the driver on RHD? I thought the firing sequence went: Windscreen 5 6 3 4 1 2 Front of car Yeah that was my plan so im hoping someone knows the volume of the standard plenum so I can work out the difference. Yeah maybe it flows more air to the back cylinders
Volume of standard runners by rough calculation is approx 1680cc each side This is a rough calculation and doesn't take in to account irregular shapes etc or the fact the the drivers side has a hunk missing from one corner. It wont be more than 1680cc each side though and could come down much closer to 1500cc by the time it was measured properly. If I still have the parts from the plenum I chopped up not so long ago I can tape it up and weigh them, fill them with water and weigh again giving a pretty accurate volume based on the weight of the water added. I would say looking at the shape and size of the additions there has been roughly 50cc - 100cc added to the volume so that actually goes further away from the 1500CC mentioned above. The crazy Tasmanian is the one to talk to about this in detail though and he will bring much technicality to the discussion, as to the exact thinking of the person that fitted the additions - a little tricky to say, blatantly obvious reasons are to make the car go better by increasing the plenum volume and/or changing its shape slightly. Maybe find someone who can read Japanese and go hunting Jap car forums to dig up an old thread?? :rofl:
There was a thread posted a while ago that linked us to some savvy info regarding the volume and length of intake runners to coincide with the requirements of the engine, and its optioned none oem parts. Perhaps this manifold was designed to flow more, for a hot engine? Nothing else special about your donk?
Yes Piston #5 is on our drivers side (RHS) at the fire wall but I thought our plenums and lower manifold were a crossover design so RHS plenum fed LHS pistons
That's right. The plenum runner on the drivers side of the car, closest to the firewall (ie above pot 5) feeds the 6th cylinder. ***** As for the tech side of things, the stock plenum serves 2 purposes- 1) The plenum where air is stored and drawn from to go into the engine via the intake runners, 2) the runners themselves which are extensions of the intake ports on the heads. Plenum volume: I've read that for 4-6 cyl engines can benefit from 0.8 to 1.5 times the engine cpacity (ie 2.398 L to 4.497 L for the 2,998 cc VG30DETT). For V8's and larger, the recommendation is less than those multiplier figures. There are exceptions with this for the big V8's where blowers can cause problems to the engine without significant plenum volume to soak up the pulses from the blower. Inlet runners and airflow: in straight 6's like the RB's, the throttle is on one end and the last cyl is on the far end. The front cylinder in cases like this get on average less intake airflow than the one at the far end. I've read that the close cyl will gety approx 3% less air, while the far cyl will enjoy 5% more than average. For the VG30, this is similar to the far, so called 'problem' cylinders, which may actually get more flow, as the air actually has inertia as it is being rammed past the throttle body, into the intake plenum, then being syphoned down into each runner. This is why I reckon nissan lopped a huge chunk off the back of the plenum. Likewise with the RB motor plenums, they taper down towards the back to counteract this fact. The other idea is to have the air go thru the throttle, then have the plenum expand out to slow the airflow down, so that the front cyl can get a better share of the intake airflow. Bellmouths: The intake plenum has bellmouths integrated into the runners. Idea is to have a smooth transition for the air, and there are specs (which I cant recall) as to how spaced the bellmouths should be to the plenum. If you really wanted to modify a plenum, cutting each plenum half longitudinally and working on the runners would be a good option, but like everything, we are talking poofteenths of benefit versus hours of welding up the bellmouths and die grinding them to the right shape, with flow-bench tests in between. Intake runners: As mentioned, these are a extension of the intake ports on the head... when you look at them, they are the main place where flow can be directed down the throat of the upper and lower plenum, past the bifurcated intakes, down past each valve, and into the combustion chamber. Inlet runners can be geared to tweak the power curve, but alwys remember that at the end of the runners, most of the time you have a whopping big intake valve stopping airflow, and causing all sorts of disruption and pressure waves as air is deflecting back aginist a closed valve, and attempting to get laminar flow for that brief moment that it is opened on the intake stroke (and part of the exhaust stroke). The main idea is that long runners increases lower RPM power, shorter runners increases the top RPM power, and runner diameter influences max top HP.... in other words, you can't cram too much air thru a small diameter pipe, having a long pipe influences the velocity of the air to allow lower RPM power (sort of like ram air), and short stumpy runners have less restriction to flow up high in the revs. So your Dyno Zed would benefit from short trumpets hooked right up to the lower intake plenum into like a coffin-box style plenum, whereas a good daily driver has massive runners, like nissan engineered. You can tell the thought on these things, as each runner is probably pushing 50cm long, from intake valve back to the bellmouth on the plenum. The idea with the runnner also, is that you dont want too short a runner as the turbo won't bo on spool, and you can't afford the loss of power down low with too-big a runner diameter. Match your diameter of your runner to the HP you might expect from the engine, as the runner length tends to rock the whole curve about this point. All in all, this info is good to know, but I have no freaking idea what the tuner was doing when he welded up that abberations of a plenum. The stock design is not that bad, it works well up to 1000HP (the Z1 silver convertible still has a stock plenum), and worst case, getting it extrude-honed to smooth out the inseds is probably the best you'd need to do for most of us here with a serious engine. For Joe Blo in his shed with a boost controller and an appetite for destruction, the stock plenum will do everything you want, plus more. /epicpost
To be honest I wouldn't even bother with extrude honing the plenum, get in there with the appropriate tools and sort out the worst of the lumps etc and leave the rest alone. (boundary layers etc etc etc) Stock plenum is fine, tinkering with it is just for fun, looks or bragging rights more than anything.
I spent hours smoothing mine out ..but extrude hone is better ..takes out the lumps/bumps via flow ! .
Too right. The honing fluid follows the same path as airflow, so will over time, hone it out to how it wants to flow, as opposed to how a human thinks it should flow while grinding it out. With extrude honing though, you are limited to the wall thickness of the plenum casting. While anti has dabbled in this for other reasons, there is probably only a few mm all round you could take out before you start running into other problems (cracking etc)
and you know what staggers me is that the british in WW2 took the standard spitfire engine from say 1000HP to over 2000HP over 5 years by supercharging yet without all our modern flow bench stuff, whizbang testing electronics etc truly amazing and not even injected but force feed SUs
Entire plenum is only around 3-4mm thick, you can't make any significant changes to how the air will flow without a substantial amount of work - better to start with a scratch built design if you really want to dabble in this. There are no bell mouth entries for the runners, the hunk missing of the RHS rear corner is for clearance for the clutch master cylinder and the funny shape for number six runner is to give access to the heater hoses. The only stuff that's worth removing from the inside of the plenum can be done within an hour or so, it's really not that hard. How much does it cost to get it extrude honed? It's not a commonly used process here in NZ, I'm not even sure if anyone even bothers at all. I think we need to remember that while Nissan spent a fair bit of time and money designing the plenum it's not a thing of perfection, it's a production part with significant compromises built in to save costs and assist with construction and maintenance (to save more costs).
Why does this stagger you? Our plenums are made for power curves throughout rpm ranges. You don't need much of a 'runner' if the engine sits at 3000rpm all day and doesn't change. Plus you reken you could get a bit more outta a 27l engine nowadays if you threw modern tech at it? I hope so.
There is all custom pipework but to be honest I don't think it's going to be any better than stock. You may have seen me ask MungyZ in another thread if intake pipework is only as good as it's smallest point which actually goes to just under 2" if I remember right so I think that's less than stock at a single part of each intake. I have what I think are HKS intercoolers that have their own pipework that attaches to them and brings the inlet and outlet up to the level of the headlights, not sure if you can see that with the pic i've uploaded. Im not overly familiar with stock piping but im pretty sure it wouldn't fit. I know the bay looks gash, it's in the process of being changed There was full custom tubular steel manifolds linked across the back of the engine to a single external wastegate and screamer. I will take some pics tomorrow of them unwrapped as they are alot more impressive. One of the previous owners clearly spent alot of money on the car or had the skills/facilities to do it them self. Regardless of the effort/expense that went into it all I don't know if they flow better than some of the current off the shelf items so in due course i'll get them flow tested. There was also an HKS Vein Throttle Convertor to replace the MAF and a Greddy unit that fired a 7th and 8th injector into the intake piping just before the throttle bodies at a pre determined rpm and throttle position. Those items have both been removed as it's quite an old skool setup for more power. Gotcha, never realised that looking at it, thanks The replacement engine apparently has the lower plenum and heads ported. After holding a manifold gasket to the exhaust outlet im dubious so i'll explore further with the lower plenum. Yeah that is pretty amazing, so is the fact that the Messerschmitt used to fire through the bloody prop blades! Mungy and Mitch thanks for the info, it's all a very interesting read. Any views/opinions on the manifold/wastegate setup are very welcome, cheers guys
looking at your pics that engine has had some serious money and effort put into it. I would suggest you dont have the turbos and dumps it was originally set up for either, It has extra injectors by the looks of those intakes onto the TB's and a huge amount of custome bolt on work. I believe that was running some serious boost at one stage and possibly serious turbos to match. Just my opinions though.
Looks like once upon a time that thing was a serious weapon It's age shows though like you say with the extra injectors etc all being very old school technology from back in the days prior to anyone fitting bigger injectors and a new or reprogrammed ECU as common practice. Nice twin plate clutch on there and the manifolds would be like a lost treasure to some of the Z fans I'm sure, screamer pipe is a big no no in most places now though - easy enough to fix that Did you ever crank it up on a dyno and see what it could do? Cam gears etc - could be quite the weapon if updated a little
