Show us some pics of the kit car already!!

You mentioned maybe stock intake and exhaust on the Reni are compromised. Not so - Mazda did an excellent job designing them. Perhaps the bad rep is from people that have expected to make big gains by replacing OEM parts with aftermarket performance parts and getting very minimal gains.

Without knowing the scope of your project, you might also consider swapping some of the rx-8 wheel/brake/suspension components onto your existing chassis.

 

The OP stated he is not going fuel injection, hence he cannot use the OE intake. The exhaust is irrelevant as you are limited by the 90 degree port shape, hence no exhaust really makes a difference in power. I wouldn't really call that an excellence in engineering from Mazda

 

Gotcha, I assumed he meant piping - different story for ports.

More on the proposed custom intake - height restrictions aside, could a custom intake manifold (albeit with carbs) produce enough of a performance improvement over stock intake to make the effort worthwhile?

 

Sorry, I didn't make myself clear...

I am sticking with fuel injection... those are Jenvey IDA throttle bodies in my OP - not carbs.

The only reason I am contemplating junking the stock intake is because I don't think I have suficient height in my engine bay. If it fits, then I will likely stick with what Mr Mazda intended and see if I can utilise the stock ECU.

If not, then it will be an aftermarket manifold and ECU.

 

The donor...

 

The patient...

 

I've been thinking about this overnight Brettus.

My logic was that the RB manifold fitted directly with IDA throttle bodies, velocity stacks and a straight-to-air filter would be far less restricted than the stock intake assembly and would likely flow air faster into the engine.

I can understand there being a loss of torque by losing the APV's, but I wouldn't have expected a significant loss of HP by ditching them. As I said before, I would have hoped for some extra power at the very top of the rev range.

I've had a search around the forum, but can't find anything that explains the workings of the stock intake in great detail. I don't doubt for a second what you're saying - it's just that I know the square root of nothing when it comes to rotaries. Was hoping you could find the time to explain it to me.

 

I've been following this. I was thinking it had to be a Lotus 7 clone.

 

This may help with your intake questions.



And here is a video or the LIM which houses the APV, VDI and SSV valves. The VFAD is located in-front of the air box behind the bumper but is just another fresh air intake valve that opens under when certain criteria are met.

 

Thanks very much for that! Really interesting!

 

So many replies without an actual answer to your questions!

In a kit car like ours the renesis is a much better fit than a REW. All you have to do is find a reliable standalone ecu unless you want to use the rx8's hubs, wheel speed sensors, abs etc to retain the factory one.
There are some options out there, some better than others of course.
The OMP can be operated as a stepper motor. Build a small circuit and tie it to the rpm signal, job done.

The oem intake manifold is both a sweet piece of engineering to get some power down low for an heavy car... and a bit restrictive if you want to run high rpms. It doesn't choke the engine but it's still sub-par when coupled to a longer exhaust manifold.

A couple of throttle bodies (one per rotor) will also make tuning much easier, less intake valves to deal with! just remember that you have 6 injectors installed on a returnless fuel rail.

Let me know if there's anything else you might need to know. I thought about swapping a renesis in my westfield for a while but then decided to keep the hayabusa engine since it's a much better fit and is way lighter.

 

Serious question: Why would you have to retain the wheel speed sensors and abs? Would not having them introduce a limp mode?

 

It would only trigger annoying CELs for the most part, the real problem comes with using a pcm that's so integrated into a car (dash, radio, fuel system, abs etc) into a car that only really needs "spark and fuel control" with a mechanical accelerator. Those things would send the car in limp mode and he couldn't tune his way around such problems.

There's almost no room behind the dashboard and the whole wiring loom would be too heavy, just like the stock engine with the stock intake and exhaust manifolds.

 

Hmmm

 

Thanks for the input BSE... given me something to think about!

 

You will lose power below 6000 and it will be the same above 6000 if the aux ports are open all the time . Those ports will reduce the efficiency of the intake stroke by allowing leakage at low rotor speeds.
At the top of the rev range you will lose a little by not having the VDI but may gain some of that back by having a free flowing intake .

 

Cheers Brettus!

 

With properly sized throttle air horns you won't even waste much below 5k rpm... and the power you are going to see is going to be more than enough to get the car moving.