Anyone looked into building one of these? They've caught my interest quite a bit.
Audi R8 Lemans Engine
One sexy Kinsler manifold
The purpose behind them is very simple. As we all know, when you throw air into a plenum at high velocity a lot of times the cylinders will be fed different amounts of air because much of the air tends to push toward the back of the plenum. The dual plenum allows air to be pushed into the first plenum, and then move through a small opening into the second plenum which causes the air to equal out and supply all of the runners with the same amount of air. If this doesn't make sense, this should help illustrate.
Gains seem to be fairly small, only netting 5-10whp up top, but there are some pretty big midrange gains.
this place sells a kit to DIY....audi has been doing this since the 90's and a bunch of VW guys have done this for some time.....idk, but it never really caught on. all the high hp people do what you guys do, and only some people do the dual plenum, and they were never high hp builds.
personally, i'd rather build a manifold that incorporates a barrel throttle into the runners. the dual plenum would certainly be good for equalizing flow, but i don't think it would be as critical with a b-t because you could draw the air from anywhere... just tuning it would be a challenge.
thats cool, i have never seen those befor but the principle seems pretty sound but in reality i feel like it would be hard to get all the details right without doing flow testing of different designs or using those velocity computer illustrations.
1991 Galant Vr4. (1900/2000) built 2.4, built AUTO, PTE 6776, 40 PSI, E85
Miller Syncro-wave 200.
These were what I actually wanted to develop at first, but after comparing construction costs and fabrication time to the other they lost. It took a LONG time to get a airflow path through a normal side inlet intake to have equal air distribution, but after I found that path it ended up being a more economical setup.
I may just put one of these dual plenum manifolds together someday for fun Will have to wait till my semester is over though, I'm backed up as it is.
BMCRace.com Intake Manifolds, Flanges, Collectors and More! Click Here!
Just seems like a lot of the applications that this is used on is road race application, and from what I've been seeing mostly is that the overall whp increase is minimal on the top end, but mid range gets a pretty nice fat increase. Haven't seen much on big turbo drag cars though.
That type of design is really meant for equal air distribution, so the gains are always better response and midrange power. Cylinder distribution is very important for road race applications, when useable power vs fuel economy is a key to winning. I noticed this type of manifold design can really allow the car to run leaner and safer (due to good air distribution among each cylinder), however, it doesn't quite necessary gain more overall power though (so it doesn't quite gain power based on HP vs PSI of boost).
Here's a plenum made by Jenvey, and is meant to go along with their ITB's:
Looks like we have all run across familiar ground when researching dual plenum manifolds . Some of the following has already been touched on RE: airflow, distribution, gains(or not) when using the manifold, etc.
Anyway, here is a copy and paste off another forum about my attempt at a dual plenum intake manifold (with a couple edits).
-The car is a dedicated autocrosser (SCCA DSP).
-Non Honda FWD , SOHC 12valve 2.2l I4 turbo. Dynoed at 145hp/195ft-lbs to the wheels (just like the sales brochure said...yeah, they rated it atw instead of the crank...I dunno either :/ ).
-Turbo is small, so boost starts sub 2000rpm, full boost @3000.
-Torque comes on _hard_ and fast, then tapers off as the turbo runs out of huff at higher rpms (makes the car "quick", if not "fast" if you get my drift)
-Increasing power levels in this engine sees huge corresponding torque gains as well. Fun, but problematic.
-Since I cant swap the turbo in SP, and knowing the wheelspin issues associated with FWD and metric assloads of torque....the plan was: (1) to lean towards high RPM gains as much as possible, even at the expense of the low/midrange power(theres plenty there already). (B)Modest power gains..200hp atw is the target. Again the goal is to keep the torque levels manageable. I need traction, not tire smoke. (III) Make life as easy as possible for the small turbo. Its working hard already, it shouldnt have to fight to get rid of exhaust gasses and if a better intake manifold makes for more precise engine tuning, perhaps more gains can be had without having to lean on the turbo.(quattro): Profit??
Which brings us to...
why a dual plenum manifold? Couple reasons....The stock manifold was built to live for the lifetime of the car and it shows. Its a lot of sturdy, cast, heavy aluminum. I really dont need that kind of overengineering (coolant passages, EGR passages) for the car in this project, so anything that can be done to cut weight is a good thing.
I get to use something other than the stock TB. Lets face it, the stock throttle body is not only, er...."complex", but theres also a limited amount of "upgradability" that can be done with the twin (40/44mm) butterflys.
Lastly...eh, why not? Its a good way to see if I can extract some performance from a "better" designed manifold (provided I know what I am doing...which probably isnt the case ).
With that in mind, here are the parts i used to make the new manifold..
Its a twin plenum sheet metal manifold Kit from Jasper integration(predominantly VAG folks). Pre-bent and formed for welding.
The lower half of the stock intake manifold was used to save time in fabricating new flanges and runners. The coolant and EGR passages were removed (er..ignore those "whoopsies". They will be fixed later. My "fabricator" needs a talking to...yeah, thats it )
I cut the runners down as short as possible without cutting into the space of the fuel rail.
Ford 4.6l throttle body. 68mm to start with the ability to be punched out to 70mm if needed. Its simple, readily available and has plenty of aftermarket (if you want to go beyond what it can provide).
Heres the preliminary fitup. Still need the TB flange needs to go on and some other odds and ends need to be fitted.
The finished product.
A couple things... the stock mazda TB cam instead of the ford item and had a small aluminum tab welded to mount the throttle cable.
So again..."why a dual plenum intake manifold?"
First, Im going to admit right up front that I did a _lot_ of guesswork on my part so I may ultimately be proved wrong in the end, but nothing ventured right?...
OEM intake manifolds tend to be built with an eye towards cost and longevity. Components tend to be built with so much leeway (in terms of performance) that most consumers will never likely encounter the inherent inefficiencies brought about by cost vs design compromises. Once you start turning up the wick a bit and moving things towards more performance based applications, those compromises start to show. Depending on how the manifold is shaped, airflow can be uneven across the runners. You can have a kind of "first come, first served" situation and a runner gets "starved" of air more than the others.
The idea behind the dual plenum design is to equalize the amount of air each of the runners see. The initial taper increases the air velocity as the air charge moves towards the end of the plenum, the central slit that separates the two plenums is 110% of the area of the throttle body (theoretically this should not be a restriction). The secondary plenum is sized to the to the engine (in this case 2.2l) and gets fed along its entire length evenly through the central slit. The runners should then get an even distribution of air. Its based on a design called the lehmann(sp?) manifold.
Now heres why I said there was a lot of guesswork on my part...most of the info I have mentioned, uneven distribution of air across runners, blah, blah, blah...comes from the naturally aspirated engine world. On forced induction engines, being positive manifold pressure, the flow dynamics are..a bit different. Sure, theoretically flow is flow so its all the same...but not really...its all a bit difficult to pin down. So Is it worth all the trouble to hash out the "truth" of the matter, just so I can justify a dual plenum manifolds use for an application like mine? Im not sure.
The dual plenum design is very favored in the motorsports community, specifically rally cars(from the old group B cars to todays WRC cars) and sportscars (like the Audi R8/R10). Heres the thing though, the bulk of those cars seem to be built around rules that call for restrictors (SIRs) that limit the amount of air that can enter the turbos. There are a lot of smart people working in motorsports whose job it is to extract the very maximum possible under restrictive rulesets. It very well could be the case that this manifold design is better suited to a "restricted" engine than an "unrestricted" engine. Ill tell you what, if the motorsports community has the data(and they do), they arent sharing. Its been very hard to find real numbers regarding flow dynamics in the ACTUAL fields these manifolds are so favored in. Ergo, the guesswork on my part.
Another thing...Ill be using the stock turbocharger, lightly bumped up in boost to reach the awe inspiring goal of...200hp. For such a (relatively) low HP application, Ill probably not even see the full gains from the efficiency a dual plenum manifold can deliver. Theres a bit of math to consider as well, and it can be exacting, but looking at my scenario in a pragmatic fashion, it didnt make sense to chase the numbers to the .0000000000 decimal place. I figure if I get things close enough..main chamber volume, taper, chamber separator area % vs TB area, runner length, etc.. in the 95-98 percentile area, Ill probably get most of the benefits and it certainly cant hurt....I think. So you can see why, with all this guesswork and fudging of the numbers, that all of this high zoot engineering may not have even been neccessary. But who knows?
One thing I AM sure of....the new manifold is much lighter than the stock piece (ill have to get a stock manifold to check the actual weight difference).
Here is an interesting discussion on this type of manifold on Hybridz.org
My feeling coming away from all this is that the dual plenum intake manifold is probably a more of a specialist item....under the right conditions/circumstances/parameters, its the right tool for the job, but not so much of a universal/"all things for all conditions" item.
PS: Fully dressed stock manifold = 25lbs. Fully dressed dual plenum manifold = 10lbs (and it wasnt that expensive either).
Tony, informative as always. That seems to be the conclusion that I've been coming to. Big midrange gains and mostly geared towards road racing, rally, etc. Not really a huge drag racing application here, so it may not be great for my personal car, but maybe something for a future project.
Oh absolutely it looks cool! Remember kids...if you cant _be_ good, then youve got to at least _look_ good. (Its cool, no applause necessary....Im here to help )
The manifold is installed in the car but I still have to get the engine tuned at a shop....eventually (money tree is uhhhhh, just a little bare right now). I did get things to where the car can idle on its own though. One thing thats immediately noticeable....man is the induction noise loud. Yay for harmonic resonance . Its no wonder OEMs do everything they can to stamp it out.
I've made a few of these, the latest being one for my VVL Nissan engine. I was previously using ITBs and an older high port DE head so I can't compare before and after. I'm a firm believer of the technology and you would be hard pressed to find any top level professional turbo engine in either circuit race or rally/rallycross that doesn't have a similar plenum design (the design dates to the early 80's).
To answer your specific question, I don't know where to find one off tapered cones. It took a good 2-3 hours to make it on a slip roll and it would be great to find someone who makes them.
My current one is a little different than more common types and is a rear entry, allowing a bit longer runners and a larger plenum in a confined space.
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