Hi all,

I've recently been planning on what to do with my next project, which will be a NA FC3S.

So far, I have been focusing on engine mods which at the moment im leaning towards; full bridge port, as well as ITBs - this post is focused on the latter.

iirc, someone had recently posted a thread which is very similar to what I'll be asking however with multiple questions being asked it seems there was no reply to one question I was also wondering about.

*please bare with me as I've been interested in ITBs for a few years now but this is the first time of which I'm seriously considering using them - so I have a lot to learn.

So, my question... obviously with the 13b only have 2 rotors, this means most people (with an exception of a few examples i've seen online) naturally run twin ITBs. I was hoping to turn this project into a mix between a show car, yet still having the power to back the looks.

I was wondering if theres any way to run quad ITBs as IMHO, I believe these look alot more aesthetically pleasing than twin ITBs, and if not - would it be possible to essentially run quad horns into twin ITBs (so 2 horns per ITB).

I have been searching forums for a while with some good info on ITBs but little info on quad setups. I have also seen someone has a few youtube videos on their DIY quad setup which I intend on watching through ASAP, but I've decided to ask here in the meantime.

Thanks all,

Ben

 

i'm not sure it matters of you have 2 vs 4 ITBS, as long as you get the sizing right.

there aren't any off the shelf manifolds for a 4 ITB setup, as far as i know

 

easy enough to make, the question is do you stage the secondaries either with a second DBW controller or vacuum/solenoid Renesis-style
.

 

Here ya go
buyer beware though. I've never heard of these guys and their only other online presence seems to be on facebook and wordpress.

 

That's a good point! Since your reply I've been gradually learning and understanding more information regarding how to stage the secondaries. I found quite a few people didn't seem to like using a DBW (it seems some people say it doesn't feel so good when driving - however I believe this could be down to improper installation/tuning), and the vacuum/solenoid method is giving me a hard time to wrap my head around how I could make that work & I'm struggling to find much information about how to implement it in the ITBs system!

However, since researching through the rx7club forum again for more posts on ITBs (it seems every time I go through the posts again I'm really starting to understand them as I keep picking up more knowledge upon the topic), I found someone who actually made an intake manifold for the FC, which is 3D Printed out of nylon and paired with Honda CBR600RR Bike ITBs interestingly. On top of this, included in the kit is a 'Throttle cable with firewall adapter' and a 'Throttle correction adapter'... so now I'm wondering if me having to sort out how to stage the secondaries is still an issue.

I'll read up more about the kit however I may end up emailing him and ask if I need to worry about staging the secondaries.

(Link to the kit if anyone is interested: 1989-91 NA Mazda RX-7 ITB Adapter Kit)

 

Thanks for your reply!

Coincidentally, I just came back onto the forum to share that I had found a quad ITB kit made by JAFA Engineering (The same manufacturer of the kit which you had just shared). Very interesting design as I believe I read it is 3D Printed out of nylon - This is the kit I found which is similar to the one you linked JAFA Engineering FC Quad ITB Kit.

As for credibility however, I have only just come across them too, but their website, ebay shop and so on seems quite legitimate.

Thanks again!

 

To stage motorcycle ITB's, you have to alter the linkage. It's not one continuous shaft, but four that are connected by a linkage, they can be removed individually. They tie the throttle bodies together to get vacuum, port on each one connecting to a single, with check valves. You can buy vacuum pots from Summit, find a way to separate the two outside ones from the centers, and put them on a common, vacuum operated shaft. As I said, you have to modify the throttle shaft end linkage that engages the next ITB.

I bought set considering this same thing and, it's still sits on the shelf in the garage.

 

DBW isn’t cheap, but can be done. Jenvy and others offer the motor drive for that purpose. The difference is you can control a secondary pair via DBW-PWM relative to rpm and load. You can phase the vacuum pots in a similar way, but only open vs. closed.

AT Power offers one on their bladeless TBs, but those might be better suited for vacuum pots like on the Renesis SSV secondaries; no restriction in the flow path.

What I failed to think of though, for vacuum pots it requires a single TB at the front feeding the intake runners in a plenum. Otherwise having your secondaries suddenly snap WOT without any control might get exciting …
.

 

I was going down the road of like a Holley vacuum secondary. Lock out cam, restrictor pill to slow the opening.

 

that tends to be different because I haven’t seen a 13B 4Bbl intake manifold that dedicates the 4 intake runners individually to to each carb barrel opening. You could build one though, yet some people on here think it won’t work regardless based on their experience. The big difference between these 13B engines and the Renesis is the impact of overlap port timing vs. none at all on the Renesis. Yet even the factory intake manifolds managed to configure the secondary pulses to compliment each other. It might require a lot of effort to find out, and then maybe not be successful in the end either.
.

 

the RB holley intakes are IR and the holley, and its EFI throttle bodies are all setup to do primary/secondary.
so you can have a bolt on 4 ITB setup that is progressive, it just won't look like it.

 

yeah I came back to say my memory was bad on that point, they mostly all have dedicated runners

 

I think I need to clarify this. My idea was the inline four ITB with the secondary's divorced from the primaries, and using a second shaft, operated by a vacuum pot, that operated like a Holley vacuum secondary carburetor.

The secondary's on those don't snap open (tiny vacuum orifice) and don't open in part throttle high vacuum like cruise (lock out cam).

I never pursued it but, had pretty much figured and sketched it out.

 

A long long time ago I saw a porsche ITB kit used, or one bank/side of it at least. They ran the primaries through the center throttle and the secondaries each had their own runner. Man, I wish I could remember where I saw it, probably old youtube in 240p.

 

If the only reason you want a quad ITB setup is aesthetics, then that's really the only benefit for you over a dual setup. Sure, there may be some theoretical gain by fiddling with staging, but I've never seen any dyno or performance comparisons for quad versus dual ITB's anywhere. Also, there are very few (1, linked in this thread) off the shelf manifold options for a quad setup and it costs more than a dual manifold and Jenvey throttle body combined.

I've had ITB's on a stock port 13b and a peripheral port 13b, both with a dual set-up. The stock port dyno'd at 178whp on a 98k mile engine with the 5th/6th port actuators removed, and the peripheral port made 270whp with low compression on the rear rotor. Both of these engines used the same 48mm Jenvey DCOE Throttle body and only two ID injectors for simplicity. Drivability was great once tuned.

All this being said, I'm not trying to dissuade you from what you're attempting to do. As someone who's stubbornly stuck with NA ITB setups on rotaries, I've learned to save money where it counts for the amount of horsepower you get in return lol.

Edit: I realize now this post is over a year old...

 

I modified the Holley that I use as a throttle body to open all four barrels equally at the same time. You don't really WANT a progressive linkage. My Holley has 42mm throttle plates so it's kind of like the dual DCOE setup that TWM used to sell, with something between 40 and 45mm DCOEs. It's a little too small because datalogs show that I start to build vacuum at WOT at higher RPM.

I also have a TWM manifold but DCOEs are expensive and my Holley was free.

Racing Beat manifolds are independent runner. I have one for my 4 port 13B. I picked up an off brand manifold for a 6 port that had a plenum, presumably so that a Holley could work without extreme recalibration. A couple pounds of epoxy fixed that

 

 

you don't just have the option of vacuum vs dbw, there's also just the option op true mechanical secondaries.

i am working on a quad intake for my RX-4 and the throttle blades work purely mechanical
they're now designed to open around 50% throttle

 

Why?
The point of ITBs isn't really more power, it's more throttle response. Having primary/secondary action defeats the purpose.

 

cause you'll have high intake velocity on the primaries for cruising and none of the "negatives" of the secondary bridge at low rpms

the vintage Rotary Engineering DCD setup had this feature and everyone loved it for a half-bridge streetcar
I've replicated this setup with my own custom manifold but hadn't ported the engine yet but it was such a great setup for the streets
i want to convert to EFI and basically run the same type of setup
and if i would want to run all 4 at the same time it's only a matter of changing the linkage, which can be done in 5min

 

I've gotta say, this Anniversary Racing Factory quad ITB FD set-up is the 1st rotary ITB set-up that has ALL the ITB aesthetic.

has that coveted tractor tip-in throttle sound.

 

That's been the complete opposite of my experience with a bridge ported engine, though. Velocity doesn't enter into it, the issue is vacuum during the intake stroke pulling exhaust gases up from the next rotor face during its exhaust stroke.

When playing with a primary/secondary manifold (FC intake) on a half bridge engine, I found that drivability improved the more I reduced vacuum on the secondary side. I replaced the secondary idle stop with a long screw and found best drivability by setting it so far open that the engine essentially idled with air from the secondaries and through the primary fuel injector air bleeds, the primary was completely shut at idle. While road tuning with a friend driving, he even noted how much better it kept driving after every underhood change I made.

That's why with a full bridge I just eliminated any pretense of primary/secondary action at the throttle body. You don't want the engine to run a high overlap port against a closed throttle, all that does is increase the amount of exhaust gases that get pulled into the intake port to dilute the airflow.

I also need to quash the idea that bridge ports are a high RPM thing. They are very much not, they increase midrange power to an intense degree. When I half bridged my T2 engine it had the effect of shifting peak power 1000rpm LOWER and it dramatically increased power under 5500. With my full bridge, I can and do drive it all the time below 2500.

 

i can understand where you're coming from, I'll see what happens. the way I'm building it i could change things up and have the secondary bridge act as if they were the primaries, or just run all 4 at once.

i do know it also depends on the intake and exhaust port timing
Its been a few years, but when i started out this restoration journey i had quite a lot and long conversations with Logan Carswell about what i wanted for my engine setup.
he then provided me with custom porting templates and a custom header for this, i trust his knowledge that things will perform the way i had envisioned.
but either way I'm not really stuck in my way and have options to change things if needed