hi, i have a 6port rx8 block that i can get for a fair bit of money, im thinking of putting it in my 78 rx4, to replace the old 12a. the question is. can i user the 12a gearbox, clutch (stronger one of course) and perhaps the 12a front cover. my plan is to open upp the block, rebuild it, and if possible, give it much bigger ports (i have no experience with the rx8)
and run it with a racecarb and dizzy ignition. is this possible?

 

I know the Renesis uses a similar clutch to the T2, in fact they may be the same part. I don't know if the 12A front cover would work. A few guys have swapped in a Renesis but they went EFI.

You can't port a Renesis much. The intake ports are huge compared to the old n/a engines--they're basically maxed out from the factory, and there isn't a whole lot of room before you hit the water jacket. The exhaust ports are on the side housings and can be tweaked a little bit.

I've never heard of anyone running a carb on a Renesis, but if you did that you are basically killing the entire intake system that allows it to make power at such high rpm. The Rx-8 intake system opens in five (yes 5) stages: primary port, secondary port, aux port, variable manifold runner system, variable intake pipe length.

 

better off using a much cheaper 6 port FC engine versus the renesis. more work making the renesis work and more custom parts required.

 

well, as i stated above, im getting the block dirtcheap so no need for an older engine.
how much would i loose on not using the stock intake system (im only getting a shortblock, so i would have to buy everything)
if i can reach 200+ hp with a carb and alittle massaging of the exhaustports im happy (might ad a supercharger/turbo in the future)

 

You are starting with the wrong engine...

 

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it's the same displacement of any 13B so no real gains over any previous engine there.
the porting will gain minor improvements, mainly to keep the power flowing up to redline versus the previous 13B engines which tapered off early, porting fixed that for the older engines.
going to a carb is a kick in the nuts for the engine, loss of horsepower over trying to make the complete engine fit and work as it was originally intended to work.

your ONLY benefit at this point over any previous engine is the 10:1 rotors and side port exhaust which help scrounge up a more thorough powerband, but with a carb? nope, low end is going to suffer, especially without the tuned variable length intake which worked directly in conjunction with the side exit exhaust to get it anywhere near the 215 BRAKE horsepower level that mazda claimed(and that we know is false).

we're just trying to save you some headache, the engine's configuration is setup to work exactly how it sits in the 8, once you start stripping everything off the block it is not a renesis anymore and will not come close to the power that it originally put out, especially with a garden hose in the intake aka carburetor...

if you got a great deal on it then by all means, attempt it if you want but keep in mind there is no readily available intake or exhausts for the renesis like there is for the earlier 13B engines which can make nearly the same power. better off flipping the renesis to buy an early 13B and purchase a carb and intake kit to toss onto it if you're dead set on a simplistic design(not better in this case).

all you're attempting with this is a showpony motor to say "i did it". alot more work for marginal results.

 

like everyone says it'll go into the car easily, the stock Rx8 clutch and t2 clutch are the same, you could buy the automatic counter weight and use a NA flywheel/clutch too.

the 12a front cover will fit, but you have to also change the water pump, and you loose the crank angle sensor too. be much better to do some kind of bracket that lets you keep the Rx8 stuff.

also like everyone says there isn't much to do with the ports except smooth things a little, the renesis already has the biggest intake ports short of a PP engine (14.5cm3 vs 20 for the PP and like 7 for the FD). the exhaust has a lot of area too, but i'm not sure it flows all that well?

the 10:1 rotors seem to hurt power, in any combustion engine the chamber shape has a HUGE impact on power and emissions, and it seems that the 10:1 rotor ends up with a shape that doesn't work for power.

rebuilding is probably a good idea, all of the Japanese tuners start the Rx8 tuning with a rebuild....

i have yet to see an Rx8 engine without the stock intake, so no clue what it would do powerwise...

 

i hear that the 6 port renesis is already maxed out from the factory, but what about its weak little brother, the 4 port renesis?

im kinda curious what could done with its ports :O

 

You can try Goopy Performance...
They have modified 12A front covers that will fit onto a rennesis engines and use a front engine mount, CAS and or distributor. They also have a ways to use a older style 13B oil pan and older style water pump assembly. They also have modified intake manifolds for carb swaps. If you want something that bad there is always someone who can do it.

 

while i tend to agree with most of the advice/thoughts everyone has given in this thread, i'll say this: only you can decide what's best for you and your situation. you said you're getting the bare block for a good deal, then take it. as long as you're good with less than Rx-8 performance from the engine (not necessarily the Rx-4 itself), then i say go ahead with your plans.

as said, the Renesis is already a big streetport when compared to 6-port of old. there's a pretty good thread by Rotarygod or Charles Hill (i can't remember who started it) over at Rx8Club. it shows pretty well what you can and CAN'T do. i hope you (or whomever ports it) is careful and vigilant. the water jacket is there and waiting to bite you!

as for going with a carburetor and distributor (also as said before), power, but more importantly, the powerband will suffer comparatively. as mentioned, a LOT of work went into making the intake system on the Rx-8 and that's where most of the performance magic happens. however, i don't see why you shouldn't do it if that's what's best for you. for all the people that have wasted perfectly good 13B-RE's with nonsensical builds, you at least have the option of scaling up once you collect the right parts to do so.

my only personal thought on the carb issue is for you to make sure cost is not your motivation - meaning you're thinking it will be cheaper, because i doubt it.

 

similar question to the stated above have an s5 6port I'm swapping to rx8 before I purchase the 13b msp I would like to know if the 6p0rt intake would fit even with minor mods. any help would be appreciated

 

welcome to the board.

the first question would be, why? there is zero benefit to that whatsoever. better just to wait until you get the MSP.
if the 6 port intake would fit what? the MSP block? not sure what you're asking.

that said, it won't fit an MSP block. they have completely different flanges/templates.