hi again ! I recently asked a question abaout bolting a 3rd gen tb on a 20b uim and thnks again for the responce I have also been thinkin about ITB for my street ported 20b N/A with 9.7 rotors , my quetion is are they worth the money ,time and effort? or will the 20b intake be better over all? I havent driven a 20b with ITb so I cant compare the two, will the ITB lose torque down low ? will it be noticable? recommende TB size? sorry for all the questions but where I live there no other rotaries let alone 20b's with ITB for me to test drive. as far as exhust and headers I ca n get these made locally no problem ,what length and diameter should the primaries be and is a 3' or 3.5" better ?
Thanks

 

if you can afford it, go ITB. They are the ****. hands down. performance and driveability benefits.

 

I heard ~50hp can be picked up with ITBs up top for the 20b.

 

driveability benefits are mainly due to the near instant throttle response.
you need to have a good tuner who knows how to work with TPS data though, or else you will get just the opposite; bad driveability.

 

ITB will effect part throttle drivability in the low range power unless you incorporate a secondary shutter valve system. The factory tb has delayed opening of the secondary throttle plates. It's engineered this way so that all the air goes through the primary runners at cruise. With all the air flow through the primary ports, the air velocity stay higher. The positive effect of this is the engine is able to cram more air into the combustion chamber and make more torque at cruise. You loose this high velocity flow in the low range with ITB's because now you have air flowing through both the primary and secondary runners. This combined flow slows the air velocity into the engine down low. The RX8 has electronic secondary shutter valves that open at around 3,800rpms so up until this point, it's only the primary ports doing all the work. Some say that the renesis doesn't have much low range punch. I beg to differ as it's very responsive and has more low end torque than any NA 13b Mazda has ever produced.

 

The RX8 is an overweight pig to begin with. Good points though.

 

Yep, the large custom single TB is really for all-out power, i.e. crazy amount of CFM of airflow generated with big turbos, no way is it ideal for your set up.

Great point, t-von. I'll add a little of my experience to this: it'll also matter here, the size and shape of the primary and secondary intake ports. If both the primary and secondary ports have identical opening/closing, the benefit of going to a ITB will even be greater, you'll likely have more power almost through out the entire rpm range. Otherwise, the "staged" factory tb will more optimized for low-end power.

Gordon, do you know what kind of porting you have?

 

t-von is headed pretty much in the right direction with his rx-8 analogy. If you are going to consider placing ITB's on your ride for an NA setup then it's time to break out the calculator and start crunching some numbers. Over the years Mazda has made some incredible advances in intake manifold design for these engines. Take a look at what they did with the 787B intake. Variable intake geometry translated directly into what they produced on the NA FC's with the VDI system. It wasn't practical to build a system for production like the racecar so they settled on the VDI. Look at how they treated the air flow at low, mid, high rpm and how engine load played a roll. If i were to design a system from scratch for ultimate HP AND drivability I would start with a single TB that was about 1/3 bigger than the primary throttle on the NA FC and run 3 equal length "long" runners collected to a chamber just after the primary throttle. I would then run 3 ITBs to each of secondary ports "shorter" than the long primaries. I would then like to experiment with equalizing the port runners at a specific distance to come online at a specific rpm and load, much like the VDI on the NA FC's. This would of course be ideal for street/performance and drivability.

Mazda has done some pretty remarkable things with their intake tuning by utilizing various resonance and wave forms. I'd love to have the resources at my disposal to "try" these ideas out. I'd also like to develop the mathematical and engineering expertise to crunch the numbers on the port diameters and lengths in order to have a more refined "idea" before i tried to implement them :-)

Ray

 

this thread delivers.

 

You would probably love the intake I built for my NA 20b. It has the long runners for the primaries and short runners for the secondary's and 3 throttle bodies. I fabricated my own secondary shutter valves to be controled by a vacuum diaphram and operated at whatever rpm I want. I don't have pics yet (well atleast till I get it running 1st). Gotta make sure it works the way I know it will b4 I start a thread. Project is about 95% complete.

 

Absolutley!

keep me posted on the happenings with it. How did you calculate your tuned runner lengths? Helmholtz equation, some other mathematical logic, or just what looked right?

Are you going to design a way to equalize the runners near peak rpm? Rotarygod had an elightening post a few years ago regarding mazda's use of the Helmholtz equation in designing their intakes.

http://www.rx8club.com/showthread.php?t=5710

Ray

 

Please keep us posted on the 90mm single throttle body conversion I am very interested so see the results

 

Gordon did you run the stock 20b elbow with that air filter?

 

No fancy mathematics or anything. Just my general knowledge from all the research I've been doing for the past 5yrs and the experiments I've done to my 91 NA 13b vert. I will tell you this, my primary runners are much longer than the 20b's. This is only phase one of my project. My current goals is to create the most torque I can get at the lowest rpm possible for now. Max power I will worry about in phase two which I'm already in the process of fabricating.

 

Well there's your problem. The Greddy elbow has a 2 1/2" point of entry. It's too restrictive to be used as a NA elbow for top end and should only be used for turbo applications. It looks like yours was modified to have a 3" entry? Think about Bernoulli's principle and see what's happening. At your engine top end, the air is flowing really fast past your air filter and into that pipe b4 your Tb. Then it slows down as it enters the larger chamber and 90 degree bend of the Greddy elbow. To help make top end, you should never have air slowing down as it enters the TB. Should be the other way around like a ventury. Experiment and save yourself some time and money by cutting the greddy elbow near the flange. Then have someone weld on a 4" aluminum pipe so you can attatch an air filter. This is one of the things Logan did with his cosmo 13b that helped make 230rwhp with side ports. The stock tb is proven to flow well. You just have to eliminate the restriction in front of it. That 90mm tb will cost your some bottom end as I stated above with you loosing delayed secondary control.

 

good point. even a stock NA FC has a 3" I.D. intake duct, for the PP they want 4-4.5"