Okay, disclaimer here - I am an ex-V8 Ford Solo II racer. I know my way around a V8 and common carb induction systems used for a V8 in roadracing and Solo II. I want to know if I can apply some of that logic to a rotary.

My question centers around the use of an intake manifold that has a common plenum for all of the intake ports on a rotary to draw from. I have never seen this kind of arrangement in an off the self intake. Instead what I am seeing are intakes that separate the rotors from one another so that either a single venturi feeds each rotor (Single DCOE or IDA). Or intakes that split a 4 barrel carb so that the primary and secondary venturis feed both intake ports for each rotor via a transfer slot under the carb (factory Nikki manifold). Or different still a Racing beat manifold that provides 4 separate ports for each venturi in a Holley carb.

So, what happens when entire area below the carb is opened up? Would this allow me the rotate a Nikki 90 degrees to solve float pivot issues in road racing?

Hey Sterling.....have you tried this???

Thanks

 

Good question, curious to hear the answers.

If it makes you feel better, I had a Holley 600 and the manifold for it. Ran it like that, then got a 1 inch spacer. Forgot what all happened, but it sucked enough for me to go back to non-spaced.

 

I think the book "How to Modify your RX-7" has some theory on this... Been a while, but I believe there's some issue with oscillation, because of the two-pulse cycle. I'll have to go read it again.

It makes mention of a "Dynamic Effect" intake system, which apparently does what you're asking about, and was used on 1987 fuel-injected 13B's to get a slight supercharging effect due to the oscillations. Doesn't go into great detail, though, and no mention if it would work as well on a carbed intake.

All their high-performance carb mods they cover use the original one-chamber-per venturi set arrangement.

 

Been there done that with both a streetported 13b using a racingbeat intake and a n edelbrock and on my supercharged 7. A standard holley or edelbrock get improved idle charactistics, throttle response and midrange with an open spacer. 1" is all that's needed, bigger shows no further improvements.

 

"So, what happens when entire area below the carb is opened up? Would this allow me the rotate a Nikki 90 degrees to solve float pivot issues in road racing?"

What issues? Bogging on hard left handers?




.

 

This happens sometimes - not really a big problem as long as I keep after the float levels and fuel pressure between races. I have an ISC prepared Nikki on my IT racecar. It is esentially a stock carb with no choke or emissions - Sterling makes one for this application too. It is all that we are allowed to have in Improved Touring.

If Nikki, Mazda, or who ever, would have built that carb with floats that pivoted like a center hung holley - life would be better. With an open plenum....may be I could get there.

 

Interesting....was the carb still oriented the way the Racing Beat manifold normally mounts the carb?

 

Hmm, interesting. When I had it on mine it sucked at idle and cruising.

 

All in the tuning

 

Would boosting change any of that? I would assume so, since it is being forced down instead of sucked down. Then again, you are not boosting 24/7... I hope

This will be an interesting thread, subscribed.

 

Here is a nice thread:


https://www.rx7club.com/1st-generation-specific-1979-1985-18/open-plenum-intake-manifold-223100/

And nice link as well!

http://www.nellump.net/peri/epi/firs...keOptions.html

 

Now you understand the direction Mazda went in when they switched to fuel injection. From the 13B-EGI training manual for the GSL-SE (which is admittedly a 6 port):





Mazda continuously improved upon taking advantage of this effect in 4 port engines though:



4 port FC3S manifold on left, 4 port FD3S manifold on right



4 port FC3S manifold cut in half.

These are both designed to take advantage of the "dynamic supercharging" effect.

 

the s5 intake manifold is known to show 2-3 psi of boost on stock engines at WOT.

 

That's exactly what I was going to mention. As long as I don't get too agressive with the fuel pressure, I don't experience that issue. Was a real pain in the **** before I figured that out...

 

interesting links up there ... funny how sometimes you feel like you live on this forum and still not know anything

 

Just thought of something. If you rotate it 90*, then you will have the same problem as before, but now when you hit the gas or the brakes.

 

True, but I think this can be dealt with how the bowels are vented. On a Holley you can install vent baffles and longer vent tubes to control this issue.

Anyway - lots of great stuff to consider from everyone

Thanks for the input

 

That's interesting... makes me wonder if I should start looking for a S5 manifold for the S4 engine I have...