R33 Intake Plenum

[GTRgeoff]

I'm afraid the onus is on the manufacturer to prove his product. The basis for improvement must be without other modifications. At a later time you can then explore the limits of your product. Tuning for each system provides no insight and proves nothing.

The fact that pressure increases in a larger manifold is a direct function of the Bernoulli principle of P1.V1=P2.V2 so as velocity decreases in the larger chamber, pressure increases. With boost pressure read off the plenum all you are demonstrating is the change in volume, not some magically discovered boost made out of thin air (hey I thought that was good ).

Are you using software to model the system and making iterative changes to achieve a best solution or just trial and error on a piece of hardware? It always helps to be able to find a steady state solution to the Navier-Stokes equations through a high end product such as Fluent before welding and grinding. Not that you won't, but you usually overlook something, or compromise trying to solve a niggling problem.

Anyways, good luck but I'm with SK all the way with this type of issue.

[Dump_Pipe]

i've modelled a few similar things at the labs at uni, all very interesting stuff to have a look at. in reality, a plenum with 6 runners and pulsing valve openings is just too complicated to model in any kind of accurate way. the best way of testing them is simply to put them on an engine and change things until you're happy with it.

measuring EGT's out of each runner is the best way of measuring charge distribution.

feeling the response change is the best way of measuring throttle response.

so it all comes down to: "does the product work?" and "has my engine blown up because of it?" not to mention "did it actually give me more power, or does it just look good?"

EDIT: stupid people leaving their SAU accounts open on my computer! this post was by StockyMcStock.

Edited October 7, 2005 by Dump_Pipe

[GTRgeoff]

Yeah I did aero for my thesis and was lucky ?? enough to be about the only person in the country to put an armoured vehicle in a wind tunnel, but even after modelling with ANSYS they still wanted the tunnel work. Cost a bloody fortune. Could have had several more seats for the cost. I know that for the expected customer base the cost-benefit analysis will rule out specifically buying seats of Fluent etc but that's why you contract the experts. Doing limited development and testing will only result in a limited product unless you get lucky, but a pro would eat up a basic manifold design even with a frequency change over the valve timings and the increasing boost figures. There are just too many clever people on the forum to try to pretend that you don't need some engineering rigour. Sure looking the goods will get the bling buyers but a screwup will come out pretty quick.

As for response, the only appropriate way is to use accelerometers. Seat of the pants can be too subjective, much like judging hot and cold.

[ISL33P]

gtrgeoff - what is the point of changing components and not making the necessary adj's to suit. would you not get a new tune if you installed new injectors, turbo or cams etc ? please, think about it. would you get more power from installing 1000cc injectors on a stock engine and make more power, i think not, most probably the opposite and this is the reason why after each modification people tune their cars to get the best from it and the saem reason why dyno's are so popular.

tuning does give insight amnd very good insight at that. for eg, if a car is able to cope with more timing thanks to the mod, where before it couldnt, wouldnt this be to the advantage of the modification and therefore a benefit of carrying out the modification, just like a decent intercooler does complaed to standard ones.

your response would be appreciated.

i am happy to supply a plenum to anyone for free for dyno testing if they would like to provide their car as a test dummy. any takers ? this will shut anyone, including me, if results aren't there and put an end to any and all arguments on this topic.

[TurboX]

I STILL just like the look of mine

BUT SK, what if I do some mods to it to increase the airflow inside and even it up with dividers as shown by the lines in the below pics?? At the moment it is just one large plenum with some longer dividers at the entrance to each port.

[GTRgeoff]

Unfortunately mate you are not quite getting the point of baseline comparisons. The items you refer to are essentially active or dynamic components within the system, each responding to different control systems be they timing, boost or pulse width or a combination of those and useless without system accomodation, while the plenum is a static element that won't change it's characteristics over the sample range from minimum to maximum flow at static throttle openings. With that in mind, it would be logical to establish a baseline performance datum and then compare directly against that on an otherwise completely standard engine. I would suggest the only difference from standard would be the FMIC install that will remain throughout all testing.

Once that is completed you can then run a number of other baselines at differing performance levels of modification. So for each setup you have the standard then aftermarket plenum using the same engine maps tuned on the standard plenum (obviously a different tune for each setup). You can then later make minor tweaks but they are not really indicative as the more time spent improving a tune is simply tampering the results. Doing the same for the standard plenum would probably give similar results but not many return to the dyno to fine up the tune. Of course you want something for your dollars spent on the shiny new plenum so off to the dyno and hey presto, a bigger number. We all know the tricks tuners know to keep customers happy and returning for bigger numbers.

Of course it sounds like a lot of work, and it is. It has to be so you can then say without prejudice just how your design is an improvement over the standard plenum. Without this level of rigour then there will always be doubt, but don't put the emphasis on proving your product on the members of this forum in some thinly veiled challenge to protect your honour and integrity or prove you wrong. The costs would be significant and are your burden to shoulder to establish credibility. You provide the comparisons in a reviewed piece of literature under controlled supervision. That is the way of the professional world.

The alternative of course is to admit that perhaps your research is not complete, nor is the product fully tested, but fitted to the standard plenum it flows X kg of air at certain pressures as compared to the stock plenums performance. This would allow a cheaper alternative.

I suggest to you that a plenum is simply a settling and distribution chamber and works well up to the established maximum flow rate for the plenum which is in excess of what most are running daily - 350rwkw being the generally accepted limit and virtually unusable on the GTS25t with its rear suspension setup. What SK states on throttle response is also established throughout industry so that leaves you in a market open for 2 things. Convenience/elegence of installation and maximised flow at very high engine output. So if your egt's are similar up to that number you are matching the standard item. If you continue well beyond your are then satisfying the drag/dyno crew for big HP. If you don't improve throttle response or degrade it then you lose the track racers.

I naturally wish you well in your endeavours as we need Aussie product developers, but there are many pitfalls and traps to avoid and the first is unsubstantiated claims.

[ISL33P]

Still dont agree with that theory - then the same would go for intercoolers, exhausts, exhaust manifolds which are all static ??? - but anyway. I am after a top half of a rb25 plenum for flow testing if anyone is willing to let me borrow one for a week or so and then i will return it.

Plenums can be made to suit any application, whether it be for outright hp (which is the most popular) or good throttle response for a circuit/street car.

Time and real world figures (not theory) will tell.

As i currently dont own a rb25 (just a rb25/30 in the build), and as i said before i am happy to supply a plenum to anyone for free to do comparisons.

[GTRgeoff]

It's not theory but fundamental engineering in the pursuit of real world figures. The same will apply for those items and not surprisingly (and as suggested by SK) they will produce immediate and quantifiable improvements for a far greater cost/benefit ratio.

Without the subjective repeatable baseline tests your just making up your so called improvements to suit your own marketing.

I'm not just trying to rag you but suggest some ways to demonstrate the benefits of your product. I'm not about preventing you from marketing your stuff, just proving it works as suggested. I believe section 52 or thereabouts of the Trade Practices Act requires that you do this and not attempt to mislead your potential customers, so without the baseline tests, and if proven that it doesn't magically improve the performance you could be committing a breach of the Act. While my current role is policy and implementation of technical integrity (that is engineering and trade quality management) across the ADF my background is mechanic, fleet engineering management, weapons systems acquisition project management and weapons systems engineering and development including guided weapons. I simply cannot expect the same rigour of a small concern as I would of our organisation but there has to be some effort that is acceptable from an engineering perspective. I've had a couple of small businesses as well so i can appreciate the costs involved. Free advice and possibly prevention of future law suits. It only takes the time to read and understand then apply some of the recommendations. If you can't understand so as to agree then there is little hope for broad acceptance of your product.

[ISL33P]

just an update for all those interested std rb25det inlet manifold flow results

1 256cfm

2 260 "

3 283 "

4 290 "

5 259 "

6 260 "

overall 505cfm thru the tb

% variance of upto 14% between 1 & 4. overall variance -4.5% - +8.2%

my plenum results will be a couple of weeks away. will be measured using same flow bech and test vacuum