Putting a Renesis in a Kit Car
 

Hello all,

I'm UK based and have a kit car that needs a new engine.

It was an ageing 4-cylinder Ford unit in there, but I decided I wanted to put something a little different in it, so after a little time thinking about it, I settled on a Renesis.

I picked up my donor car the other day - a 2004 6-port model. It had 55k miles on it and drives pretty well. It starts from cold and hot. It has a little panel damage, so I got it really cheap at auction (£700 / $1000).

My plan would be to strip the engine, transmission, and diferential, and transplant them all into my car. The finished weight should be around 550kg (1210 pounds)... less than half the weight of the RX8.

I understand how the wankel engine works, but I'm not fully up to speed with all it's intricacies... this is where I'm hoping you guys will come in handy!

I have no emmissions restrictions, so I plan to use the follwoing 'IDA' style inlet manifold parts from Racing Beat, so I can junk the standard inlet system and reduce the height of the installation.

RX-8 Engine Carburetor/Manifold Adapter Plate for RX8 - Racing Beat

Weber Intake Manifold 48/51IDA for 86-92 13B 6-Port - Racing Beat

I will then add a set of Jenvey 50mm 'IDA' injection throttle bodies...

TA body 50mm Single - Jenvey Dynamics

And then a standalone ECU.

I will also change to a lightweight flywheel.

I do not require a catalytic converter and there are no 'packaging' restrictions in my engine bay, so I can be as invetive as I like with the header design!

So that's kind of that!

I've also picked up a spare 6-port engine that I plan to pull apart, learn from, and then rebuild. I guess I could do with some pointers as to what to aim for in my rebuild. I don't want forced induction (230-or-so ponies in such a lightweight car is more than adequate). It seems to me that the induction and exhaust on the Renesis are quite compromised (?). Bearing in mind that I do not have to meet any emmission limits, would it be worth sealing the side ports in the spare engine and changing over to peripheral ports? Would the car still be reasonably reliable and would it remain civilised at low revs?

That's probably enough from me just now... I have loads of questions, but I'll ease into it!

Thanks for reading and I look forward to your input!

Should of got a REW

Something that has become a big issue for conversions like this is how to oil the apex/corner/side seals . It has been established that if you use premix only , over a short period of time the corner seals will dig into the land on your exhaust ports .

You need to find a way to control and utilize the omp to get acceptable engine life.

Cheers carbon... what would your reasoning be for the REW (bear in mind I'm a newbie!)?

1/ see my post above yours .... ;)

Thanks Brettus... I've seen that the aviation guys seem to be getting closer to cracking an RPM based OMP. I'd planned on taking my cues from them.

Same reason most Rx8 owners wish they had one, in most peoples mind it was a much superior design, more reliable, more potential etc.....

REW was designed for power, RENESIS was designed for emissions.

The REW doesn't use an OMP?

Thanks... I'm off to google the REW LOL!

If it bolts up to the 6-speed Renesis transmission, then I can easily change!

I juts went for the Renesis as it seemed to be the one that made the highest NA power.

If you need NA stick with the RENESIS, not sure what the end use of this car is.

For comparison,

REW; More engine management/ mod-ability present. potential for 350-400WHP @10PSI, not much reliability issues 80-100K miles

RENESIS FI; Only 2 choices for engine management/ mod-ability limited. Potential for 300-330WHP @10PSI, reliability drastically reduced 30-60K miles

Yeah... I want to stay NA.

The car is purely for playing with on the highways and then the occasional track-day, so 'driveability' is very important.

A big toy!

Just out of interest, what is it that makes the REW more reliable over the Renesis?

I meant .... the inability to rely soley on premix . But it seems you have that covered .

I think it would be a good choice if you can get that sorted .
As that RB manifold doesn't cater for the APVs- you will lose a lot of power under 6000rpm !

Renesis has side exhaust ports...and this configuration appears to be having issues with the heat and side seal life. As well as much shorter apex seals

The REW had a peripheral exhaust port...and less side seal issues with the heat

Power wise though the Remesis does well NA...and as long as it stays within the NA parameters it seems to be less of a problem. The issue is when we try and stuff 3-4X the exhaust flow out the 90 degree port....:)

I don't mind a drop in low-to-midrange power (bear in mind the car is a lightweight and doesn't need much to get it moving). Am I right in thinking that the RB manifold would be likely to make more at the top end though?

Thanks!

Highly unlikely - the stock manifold also has VDI (variable dynamic Intake) which gives the engine a nice little kick from 7200 on .

Would there be any way to get better NA results from the REW? Can you mix and match some of the Renesis engine components with it to increase compression, etc?

Thanks - that info could save me a bit of money! I would only be looking to junk the standard intake as engine bay height is my only restriction. If it all fits under there, then I can stick with it if there are no great gains to be had from going aftermarket.

I guess that really restricts my ECU choice though as there are a lot of valves and clever gizmos on the OE intake... you mentioned there are two that can do the job - any pointers on what they are?

Keep in mind that you have an ECU on hand for no extra cost that can, and has, run that engine :) It shifts the electrical challenges to dealing with the other stuff, like wheel speed sensors, immobilizer, etc... but considering that you have the complete donor car, you have every module already paired with the ECU that is on hand and all of the sensors that go to those modules, so those challenges wouldn't be insurmountable. Tuning would be as simple an an AP or MazdaEdit.

Just something to consider.

Thanks RIWWP. Are the AP and MazdaEdit both ECU piggybacks?

No, they are flashing tools that allow you to edit the ECU tables directly and then upload those changes up to the ECU ROM.

Thanks very much! I'll look into them!

But ................... has anyone ever run the ecu outside of an 8 before ?

Not to my specific knowledge. :)

It's still a free option to at least try considering that the donor car has every component and sensor that the ECU is looking for already on hand. The challenges would be different than an aftermarket ECU, but comparing them, I would think that the challenges of using the factory ECU would be easier to solve and cause fewer engine reliability/driveability problems.

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 :dunno:

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...

https://www.rx8club.com/members/scot...2171-39186.jpg

The patient...

https://www.rx8club.com/members/scot...re-a-39183.jpg
https://www.rx8club.com/members/scot...re-a-39185.jpg
https://www.rx8club.com/members/scot...re-a-39184.jpg

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.