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Renesis side port/peripheral port exhaust hybrid...
Naturally Aspirated Performance ForumDiscussion of naturally-aspirated rotary performance. No Power Adders, only pure rotary power!
From the "12A" to the "RENESIS" and beyond.
I've been thinking a lot lately about N/A. Specifically, I’ve been thinking a lot about a “high powered” 2 rotor build to swap into a smaller, lighter weight chassis. So, I’ve been doing some research...
My research has taken me far and wide. At this stage, I’m of two mindsets: one is optimistic and hopeful of achieving an “ultimate” build, and the other is more realistic, and feeling if it were possible it would have already been done.
So, the first mindset...a hybrid engine utilizing the MSP side port exhaust irons, coupled with GSL-SE peripheral exhaust ports. Some may ask “Why?” - the answer is simple.
The Renesis, or MSP rotary engine is the most powerful naturally aspirated rotary engine ever produced. 238 flywheel horsepower is by far the greatest output Mazda has achieved without turbocharging. So, naturally this was the first place to look. Add to that the parts are dirt cheap and engine/transmission combo’s can be had for $1,000-$1,500 all day long and this looks attractive.
Then, you find out that modifying the engine with anything short of FI has yielded virtually no increase in horsepower. Why? The general concensus is the Intake is perfection - supplying enough air to support 300-400 horsepower. But, the side ports are extremely limited and you can’t open them up like you would with a peripheral exhaust port because you run the risk of damaging the coolant passages and ruining your engine.
The intake is the key, but the exhaust is the limitation. So, introduce peripheral exhaust ports and your problem is solved! It seems so very simple but then, nobody has a running, working car with this configuration.
I believe that many who have gone down this road with anything Renesis based are long gone because they are always chasing the holy grail of FI power. At the end of the day, the side port exhaust is still present though and you’re still going to have failure due to the extreme heat and stress placed on the spring/seal. However, an N/A build would not have EGT’s anywhere close to as high and as a result, would most probably remain reliable.
If this hybrid engine were to be developed for N/A application, it could be the key to a 300 bhp two rotor, naturally aspirated engine. The intake manifold is supposedly sent from heaven and if we can get more exhaust gases out, then porting the intake would yield true performance gains where previously were impossible.
Personally, I have a target of 230-250 whp in mind, with a two rotor build. Could this engine be the key?
Oh, and I’d just like to add real quick that I’m fully aware this configuration would most probably require a standalone ECU with inputs for the stepper motors and actuators in the intake manifold to work properly, and the drive by wire, such as Motec or Adaptronic.
There is also the need to work out the OMP. I’ve considered using a factory pump but in all likelihood if I’m using a sophisticated standalone, I may be able to run an OMP with it and utilize a separate reservoir for the Idemitsu that I premix in my FD. Then of course you could just premix, like I do already but my goal is to eliminate that need in the FD one day as well.
On a side note; if someone here has any numbers on losses from ditching the electronic intake manifold design on the Renesis, in favor of a simple intake manifold or ITB setup, do share. If my powerband shifted higher or I lose a few HP here or there, I’d be open to this as an option because it would save me having to really splash the cash on a high end Motec, as an example and run something more conventional that would be cheaper and perhaps sort of worth the cost savings for a few HP less.
The MSP is off by about 100hp from the powerful naturally aspirated two rotor engines produced by Mazda. The MFR engines were in the 300-320 range, and that isn't a marketing-inflated number.
They had SMALLER exhaust ports than anything else they made. Mazda put an excessively large angle of diffusion i nthe exhaust ports of street car engines to curtail noise at the expense of flow.
Exhaust ports do not need to be very large, the flow is supersonic. Getting air IN is always the problem.
The MSP is off by about 100hp from the powerful naturally aspirated two rotor engines produced by Mazda. The MFR engines were in the 300-320 range, and that isn't a marketing-inflated number.
They had SMALLER exhaust ports than anything else they made. Mazda put an excessively large angle of diffusion i nthe exhaust ports of street car engines to curtail noise at the expense of flow.
Exhaust ports do not need to be very large, the flow is supersonic. Getting air IN is always the problem.
Ok, so you’re suggesting the Renesis exhaust flow capabilities are sufficient?
What sort of porting and other modifications did those engines undergo? Personally, I do not want to go J-Port or Peripheral Port. A bridge is the furthest I’d be comfortable with cause I do want the engine to last and I don’t want the powerband to be only between say 7,000-11,000 RPMs. I’m not looking to build a race motor, but instead a street plus kind of car with an emphasis on balance.
Is this even possible with a two rotor? Gordon has a street port on his 20B and has achieved 352 whp. A two rotor may yield 2/3 of that? I’d be cool with 225 whp with a two rotor...
Powerband on my bridge is whenever the tach is on a number. It's been a long time since I had my peripheral port but it was similar. Anybody who's driven a peripheral port will tell you that at anything over 2000rpm they embarass a stock engine. It isn't that they only make power at the top end, it's that the torque is high and it never falls off, so there's no incentive to not use all of the RPM the engine is capable of using without blowing up.
IIRC, the pointy end of the stick in Australia's Improved Production bridge ports is around 400hp at the crank. IPRA rules specify that the intake port may not extend past the periphery of the rotor housing, meaning they aren't even allowed to run relieved rotor housngs. Of course this is with extremely scienced out intake and exhaust tuning, and noise levels higher than would be acceptable on the street.
There are a few guys with standard Renesis side ports making over 200whp, you might be able to get pretty close to your goal without doing a bunch of crazy internal mods. Plus 200whp in a lightweight car like an FB would be a blast. For 220+ whp you'll have to get a little more crazy. I really like how driveable Peejay's bridgeport is. Seems to have power everywhere and be really mild to drive. Spend some time checking out his youtube channel, you might want to go the way of the bridgeport as well. http://www.youtube.com/izzmus
Almost everything anyone has heard word of mouth about NA rotaries and power is wrong.
Race engines usually aim to put peak power as high in the rpms as is reliable for the application as Horsepower (work done) increases with rpms; its in the definition of Horsepower (the time component).
That doesn't mean rotaries with overlap naturally make peak power high in the rpms- that is relative to many factors.
Rotary overlap adds power at all rpms at wide open throttle.
Small intake ports peak power at lower rpm that large intake ports.
Later closing intake peaks power later than earlier closing intake.
Big part of rotary overlap magic is from the exhaust port velocity and even that supersonic flow. If you add side exhaust ports you are limiting the exhaust driven effects of overlap.
Overlap is measured by in how many degrees of rotation the intake and exhaust ports are open together on the same rotor face.
That isn't the magic of rotary overlap though! "Overlap" is just an engineering term it is some number in degrees.
The magic of rotary overlap is the geometry/proximity of the rotor tip; that is the physical relation of the rotor face you have measured overlap degrees on and the next upcoming rotor face. The peripheral exhaust port creates a very effective siphon flow on the intake.
It has less relation to piston engine overlap for this reason.
The high velocity of the peripheral exhaust port helps this siphon flow. If you lower exhaust velocity by adding side exhaust ports the benefits you reap from overlap will suffer.
Supersonic flow nozzle effect. Another engineering term.
Even though every engineer will tell you that you need to avoid supersonic flow in an engine as it creates the supersonic nozzle effect which limits flow, supersonic flow does important tasks for the rotary.
You size your peripheral exhaust port so it "chokes" flow at your desired peak hp to get supersonic flow because the dynamic sonic component of the exhaust pulse (and reversion pulses) cannot travel through a supersonic fluid back into the engine and the nozzle effect increases pressure which is what you want to increase the siphon effect of overlap and to push your exhaust down the exhaust pipe Yes, you can raise your peak hp goal and make the exhaust port flow more to suit, but you are going to have to get the new larger port to "choke flow" as well to get the full benefits of overlap.
So basically, like Peejay says- you want the smallest exhaust port possible to support your power goals.
Thank you all for your input, especially Blue for the technical explanation. Unfortunately, these concepts aren’t familiar to me so I found myself nodding my head while not fully grasping the information.
I understand that the biggest power will be had from the PP engines. However, I don’t feel like that’s the best option for me because of the obvious issues relating to longevity and noise. The intention is to have a street car after all, one that I could go on a date with the wife in...
So, I’m wondering if Bridgeport may be the better option but I’ve found it hard to find concrete numbers. Peejay, do you have numbers for your setup? What should a 13B bridgeport, with ITB’s and standalone make?
I saw some interesting thread on Rx8club with a 13B-MSP bridgeported but as is normally the case, it was kind of inconclusive about power output. The owner said he felt it was stronger but it was also rebuilt, so you can’t be sure with butt dyno’s here...
Unfortunately, the owner never got photos of the bridge before they sealed the engine up but he claims its a small bridge. From the videos he posted there is definitely some overlap but to your point Blue, with a side port exhaust, the overlap benefits may be minimal.
You size your peripheral exhaust port so it "chokes" flow at your desired peak hp to get supersonic flow because the dynamic sonic component of the exhaust pulse (and reversion pulses) cannot travel through a supersonic fluid back into the engine and the nozzle effect increases pressure which is what you want to increase the siphon effect of overlap and to push your exhaust down the exhaust pipe Yes, you can raise your peak hp goal and make the exhaust port flow more to suit, but you are going to have to get the new larger port to "choke flow" as well to get the full benefits of overlap.
So basically, like Peejay says- you want the smallest exhaust port possible to support your power goals.
Is there a good references for the calculations needed to figure out what the max port size for hp is? This is something I'd love to play with if possible. I'm sure there is more to it than flow testing the port and calculating max CFM required to max X power. I'm assuming it more of a try something, tear down, make changes approach, but had to ask if there is any data or references of people doing this.
Couple more questions for the smart kids in class...
So, I had two thoughts today as I was driving around my FD.
First, I said to myself: “Self, why are you trying to piece together some experimental hybrid engine for potentially boat loads of money?” - so I thought let me just settle on a damn bone stock Renesis and be happy with just having a rotary in a modern Miata chassis. I mean how cool is that right?? And, if the damn thing fails on me, I’ll just rebuild it with a street port and oil mods and push something in the 220-230 whp range, which is what I set out to accomplish anyway.
But then, I thought: “Well, what if I swap in a Renesis and decide it’s just not enough power one day?” I can’t boost it, well cause it’s a Renesis and we all know they are ticking time bombs when using FI.
So, I thought maybe I should instead do some kind of N/A build in an REW so if I chose to add more power down the road, I could simply buy a small turbo charger and slap it on there. If I had a Renesis, I would have to scrap it and buy a whole new engine basically and might have to refabricate engine mounts, as I am not sure if they both would fit the exact same way...?
This brings me to two questions. One, assuming I built an REW for NA, how much could I expect to see? At least 200 whp?? Could I get close to the 220-240 mark without a bridge or PP?
And two, if I utilize Renesis rotors with their higher compression ratio, would it be worth it? They’re cheaper than REW rotors after all. And I understand they have a special design that affects the timing in the side port — will this have any effect in a peripheral exhaust port housing? Assuming I modify them to accept the REW apex seals, will they have any other detrimental effects, or should I just find some S4 or S5 NA rotors and be done?
Nick
Last edited by Brilliant7-LFC; 11-27-17 at 09:22 PM.
Is there a good references for the calculations needed to figure out what the max port size for hp is?
No, the only thing we know for sure is the Mazda Factory Race rotor housings have a good starting point for the exhaust size (which are really hard to get now) and the modified production rotor housings exhaust port starts out too large (throat volume not face timing) and make less power.
An NA stock port 13B-REW will get you around 160-180rwhp depending on peripherals and with a street port you can get 200-230rwhp depending on peripherals.
Again, check out the Anniversary Racing page for 4 port builds since the only 6 port they ever got was the Renesis.
The cheap easy way to make NA power is 13B-REW block, $200 Holley style intake, $200 injector-less 4150 throttle body, $150 boost hat, aftermarket primary rail with 2,100cc primary injectors only and a decent stand alone ECU, $200 ebay race (uncollected) stainless headers, a good 2-1 merge and some length of pipe to play with primary tube length and some dyno time.
The bonus is you get a really simple light engine this way as well at around 240lbs with race accessories (stock 13B-REW with full accessories is ~425lbs by comparison).
This set-up can do 180rwhp on stock ports or 230rwhp on street ports.
You can switch it up for forced induction and bump the fuel pressure up to 70psi (or start at 70psi on NA build for an easy transition) and you have fuel for a bit over 400rwhp. If you want more fuel you have to go to a $$$ injector style 4150 throttle body or switch back to stock style intake manifolds.
Renesis rotors
These are not balanced from the factory, so you have to have them balanced as an added cost (not a bad idea for any rotor set)
They do not fit regular apex seals so you have to have the apex seal slots machined
Benefit, if you are street porting you can open the port earlier with the revised side seal location and the rotor is beveled for earlier opening
Benefit, they are light and higher compression so the engine feels snappier revving and faster rev matches on shifts
If you are planning forced induction in the future, save your $ and keep the 13B-REW rotors and buy a nice EFR turbo instead.
I was under the impression that a 13B wouldn't reach those types of levels of power even with a street port. I continually heard 180-200whp for a 13B was pretty much the max without going to PP or Bridgeport. If what you're saying is true - and I'm sure it is - then I will probably go that route as it gets me very close to my power goals, but doesn't pigeon hole me into a potential problem down the road. I like that.
As for the setup you recommended, how will the car idle with 2,100cc injectors!? If I understood you correctly, the setup would be simplified to two injectors total. I got feedback from people concerning idle with my FD only using 1,000cc primaries...?
The Renesis rotors are still interesting to me... I am wondering if the benefits will outweigh the costs though. The rotors themselves are a little cheaper perhaps than REW rotors. However, the additional cost to machine the apex grooves and have them balanced would probably negate any cost savings for the rotors themselves. The upshot would be that I would have the higher compression ratio and have the "snappy" throttle response and perhaps a bit more torque, like you alluded to. I don't fully understand how the beveling affects performance if you're using a peripheral exhaust port housing though. Will the beveling change the timing enough to introduce overlap with a street port??
Lastly, I read about the grooves in the coolant passages in the housings and that it was a bonus for cooling on certain S4 or S5 housings and the Renesis housings. But they can be machined as well?
I'm thinking for the build, perhaps this would be the optimal N/A build for my purposes:
13-B REW block (iron, front and rear covers)
13-B S4/S5 housings (for coolant passages)
13-B MSP rotors (machined for apex seals)
13-B MSP or REW eccentric shaft?? (not sure which would be better here but I'm thinking the MSP because it was designed for a higher rev limit?)
13-B MSP counter-weights
Balance rotating assembly
With this configuration I don't believe I will need any oil mods that are common with the Renesis because I'll be using the REW block which already has the higher pressure regulator. I may need to have the eccentric shaft modified though, as I thought I saw that in a Renesis rebuild video I watch recently.
Last question, are there better guys to do the porting for an NA build compared to an FI build, or is it the same; air in, air out? Could I just roll with the Racing Beat template for example and be done?
Thanks guys, and especially Blue!
Nick
Last edited by Brilliant7-LFC; 11-28-17 at 01:03 PM.
As for the question of switching to FI one day; if I were to ever get that itch and do it, I would only be looking to make bout 350whp or less. The NC chassis is so light and so small that I feel it will be easily overwhelmed and in turn, ruined by too much power. So, I doubt I'll even want that and if I did, it'd be either stock twins or like you said a smaller EFR setup.
Nick
EDIT: Quick question here...any thoughts on ac compressor? I wonder if the NC Miata has the same basic dimensions as the RX-8. I'd prefer to use all modern A/C components due to the need to retro for R-134 with older FD components. I wonder how that would work...maybe an RX-8 front cover and water pump would make it easier to then use the RX-8 compressor and hook up the NC's lines to it...? Hmm need to figure that out as well, but that's for another day.
Last edited by Brilliant7-LFC; 11-28-17 at 01:17 PM.
People are doing it with the Injector Dynamics ID2000 (2,100cc EV14 injectors) and I haven't heard of any problems.
I don't fully understand how the beveling affects performance if you're using a peripheral exhaust port housing though
The bevel on the RX-8 rotor is on the upper part of the rotor flank that opens the side intake ports only. This is a rear rotor for instance.
Lastly, I read about the grooves in the coolant passages in the housings and that it was a bonus for cooling on certain S4 or S5 housings and the Renesis housings. But they can be machined as well?
Yes, as shown in this picture I machined the grooves in S5 FC and FD rotor housings (which are basically the same) with a drill press and a dremel bit.
Could I just roll with the Racing Beat template for example and be done?
If you use the RX-8 rotors you will want to make your own street port template (could base it off an RX-8 template for the bottom of the opening line). Otherwise you won't have the early intake opening that the revised side seal location allows.
Standard production Mazda side port rotary opens the intake at 32 degrees after bottom dead center a the earliest (keeps both side seals on the side housing).
Mazda production street port (as done on early Cosmo sport 10A rotaries) opens earlier at 24 deg ABDC (drops leading side seal into intake port as street ports do)
RX-8 13B-MSP opens intake 0 ABDC with the combination of earlier opening port from moving the side seals on the rotor and the bevel on the rotor (drops leading side seal into intake port and shoots trailing side seal over a short gap on the bottom of the port).
If you do use the RB street port template you will want to touch it up as the leading (dropped) side seal tips will wear against the side housing because they have too large a radius on the top of the opening line (I verified this when my friend bought the template).
If you are having to pay someone to do the work you should probably just save money and buy a brand new 13B-REW from Mazda for ~$4,000 and run it stock. This will limit you to ~200rwhp with all the right peripherals NA, but it will be cheap and reliable.
EDIT: Quick question here...any thoughts on ac compressor?
Sounds like weight to me.
NC Miata sounds like weight to me as well.
FD RX-7 is a slightly narrower car (57.5" track width VS NC 58.9" track width) and can be the same weight as NC Miata easily.
Most raced out stripped NC Miata I have seen with $$ in CF doors etc was 2,000lbs which is what a similarly stripped non caged FD weighs (see XP class FDs).
Base FD weight is 2,700lbs for an R1.
Race NA engine saves 150lbs off that.
2,550lbs for a full weight stock R1 NA rotary FD versus 2,400-2,600lbs for an NC Miata (depending on year, how much gas and trim package).
The NC Miata has a lot less creature comforts, etc to delete to lose the weight versus the FD when you start to reduce weight from this stock spec as well.
If you're trying to idle a peripheral port low and lean, 2200cc injectors will be the least of your problem. I ran 4 of them on a large streetport turbo 13BT and was able to get an idle of around 13:1 at 900rpm. Any leaner and it'd stumble, but FWIW, it would run without misfire at different load cells and less pulsewidth, I think 13:1 was just as lean as my engine preferred with the amount of overlap it had. The current 2200cc injectors (ID2000s, Bosch NGI-2s, etc) have very load dead times and are pretty damn stable at very low pulsewidths. Injector Dynamics was also nice enough to fully map their characteristics for several different ECUs which takes the guess work out of it.
So my mind is racing and I’m trying to process everything. I don’t have the time to put my thoughts together this moment. I’ll put together a reply tomorrow.
For now, I’m curious to hear your thoughts on why this guy is only looking at 185-200 whp with a half bridge? I am operating under the premise of 220-230 whp with a 13B and street port. I wouldn’t want to go through all the trouble of piecing a motor together and getting it ported to fall short by that much...? Is this result typical?
Well, a half bridge isn't even a real engine option for NA rotary- so I can't help you on figuring out what that guy is doing. Only thing more ludicrous would be a 6 port half bridge.
You have to have all your ducks in a row to get over 200rwhp on a streetport.
You can easily piece an NA street port motor together and only get 150rwhp, but chances are if it was correctly assembled in the most basic sense (clearances ok and not damaged) someone else's careful, methodical and thorough hands can get it to over 200rwhp with the right parts and tuning.
Over 200rwhp is not typical for an NA rotary, but people have gotten 215rwhp on a 4 port motor from as little as street ported exhaust and intake ports, and ported stock S5 TII intake manifold, headers and tuning. Meaning, its not magic either.
So, first, I failed to mention originally that I REALLY would want an ITB setup for this motor. I think it adds some "prestige" to the build, some amazing sound and should unlock a few horsepower as well. I don't know if it would be "worth" the cost from a power perspective...but it would be worth it to me overall. I saw some Borla setups that looked like they would work with the holley style 4 port manifolds that you recommended and that I've seen around. Is there one in particular you'd recommend?
In saying that, I think the build is doable with everything else I mentioned? Remind me which rotor housings came with the grooves in the coolant passages from factory...?
13-B REW block (iron, front and rear covers)
13-B S4/S5 housings (for coolant passages)
13-B MSP rotors (machined for apex seals)
13-B MSP or REW eccentric shaft?? (not sure which would be better here but I'm thinking the MSP because it was designed for a higher rev limit?)
13-B MSP counter-weights
Balance rotating assembly
With a street port and these components, with supporting exhaust mods, the 220whp mark looks doable, it would seem.
To your comment about the weight of the NC, I am absolutely not interested in building a track car. This car would quite possibly never see the track, aside from an HPDE or autocross. I live in Florida and absolutely need AC. And the FD comparison, while valid because we're on an RX7 forum, is not really applicable cause I already have an FD and have gone a different direction with that build. I don't really see myself owning another FD unless I one day found a 100% stock car that I wanted to keep as a collector's car. Which probably won't happen...
The only real question I have is whether or not you think the "special" porting needed on the intake ports will be worth the trouble and coupling that with the RX-8 rotors? Or, are we talking 2whp and just using the 9.7:1 rotors from the NA 2nd gen's will be the better way to go?
Also, the REW was turbocharged from factory and so there are coolant and oil lines that are normally run. Maybe it would be better to use a different base engine...?
First in my posts I kept referring to After Bottom Dead Center when I should have said After Top Dead Center when referring to intake port opening
Second, here is a picture that sums up the 1,000 words I could waste talking about difference between 13B-MSP port opening and older 13Bs.
Third, apparently Rick Shaw has also experimented with hybrid 13B-MSP and 13B engines. This post of one for sale says this bridge ported intake unit with both side and peripheral exhaust ports did 35KW over what a stock RX-8 dynos. We can extrapolate that to 180rwhp + 47hp = 227rwhp. https://www.rx8club.com/australia-ne...sydney-264419/
So, first, I failed to mention originally that I REALLY would want an ITB setup for this motor. I think it adds some "prestige" to the build, some amazing sound and should unlock a few horsepower as well. I don't know if it would be "worth" the cost from a power perspective...but it would be worth it to me overall. I saw some Borla setups that looked like they would work with the holley style 4 port manifolds that you recommended and that I've seen around. Is there one in particular you'd recommend?
Holley 4 port manifold and 4150 throttle body is an ITB set-up.
I understand you want the look of individual throttle bodies and velocity stacks on the wrap around manifold.
Traditional ITBs are a pain in the *** to make an intake box with fresh air feed for and to synchronize, but people do go "Ooooh, ITBs!" when they see them.
13-B REW block (iron, front and rear covers)
13-B S4/S5 housings (for coolant passages)
S6 rotor housings are the best as they have better chrome, teflon impregnation and an improvement in the cooling passages
13-B MSP rotors (machined for apex seals)
13-B MSP or REW eccentric shaft?? (not sure which would be better here but I'm thinking the MSP because it was designed for a higher rev limit?)
The 13B-MSP one has tapered rear main bearing area and is a tad lighter.
13-B MSP counter-weights
Balance rotating assembly
13B-MSP main stationary gears/main bearings
I don't really see myself owning another FD unless I one day found a 100% stock car that I wanted to keep as a collector's car. Which probably won't happen...
I offered the weight and size comparison between NC Miata and FD simply because I went down this road of thought as well (rotary NC Miata).
I came to the conclusion that an FD with comparable engine and level of interior (stock to stripped) does not weigh significantly more than an NC Miata and would be really slow (relative- S2000 slow, not stock Miata slow) with an NA 13B compared to even a stock FD with reliability mods.
So, it follows the NA 13B NC Miata would be really slow as well and can't fit near as much wheel and tire as the FD.
I guess I can understand wanting a $20,000 rotary swapped NC Miata over a $20,000 FD with the turbos taken off.
A faster than stock Miata would probably impress people more than a slower than stock FD.
The only real question I have is whether or not you think the "special" porting needed on the intake ports will be worth the trouble and coupling that with the RX-8 rotors? Or, are we talking 2whp and just using the 9.7:1 rotors from the NA 2nd gen's will be the better way to go?
Special porting isn't necessary with the 13B-MSP rotors on 13B side plates, it will just make more power because it adds overlap. How much more power? IDK- I would guess probably around 10-20hp over traditional street port on an NA 13B.
Also, the REW was turbocharged from factory and so there are coolant and oil lines that are normally run. Maybe it would be better to use a different base engine...?
13B-REW will require two block off plates for the turbo oil return passages and a bolt and crush washer for the turbo oil feed over a factory NA 13B. The coolant routing doesn't come through the rotor housings like the old 13B turbo engines.
First in my posts I kept referring to After Bottom Dead Center when I should have said After Top Dead Center when referring to intake port opening
Second, here is a picture that sums up the 1,000 words I could waste talking about difference between 13B-MSP port opening and older 13Bs.
Third, apparently Rick Shaw has also experimented with hybrid 13B-MSP and 13B engines. This post of one for sale says this bridge ported intake unit with both side and peripheral exhaust ports did 35KW over what a stock RX-8 dynos. We can extrapolate that to 180rwhp + 47hp = 227rwhp. https://www.rx8club.com/australia-ne...sydney-264419/
Holley 4 port manifold and 4150 throttle body is an ITB set-up.
I understand you want the look of individual throttle bodies and velocity stacks on the wrap around manifold.
Traditional ITBs are a pain in the *** to make an intake box with fresh air feed for and to synchronize, but people do go "Ooooh, ITBs!" when they see them.
S6 rotor housings are the best as they have better chrome, teflon impregnation and an improvement in the cooling passages
The 13B-MSP one has tapered rear main bearing area and is a tad lighter.
13B-MSP main stationary gears/main bearings
I offered the weight and size comparison between NC Miata and FD simply because I went down this road of thought as well (rotary NC Miata).
I came to the conclusion that an FD with comparable engine and level of interior (stock to stripped) does not weigh significantly more than an NC Miata and would be really slow (relative- S2000 slow, not stock Miata slow) with an NA 13B compared to even a stock FD with reliability mods.
So, it follows the NA 13B NC Miata would be really slow as well and can't fit near as much wheel and tire as the FD.
I guess I can understand wanting a $20,000 rotary swapped NC Miata over a $20,000 FD with the turbos taken off.
A faster than stock Miata would probably impress people more than a slower than stock FD.
Special porting isn't necessary with the 13B-MSP rotors on 13B side plates, it will just make more power because it adds overlap. How much more power? IDK- I would guess probably around 10-20hp over traditional street port on an NA 13B.
13B-REW will require two block off plates for the turbo oil return passages and a bolt and crush washer for the turbo oil feed over a factory NA 13B. The coolant routing doesn't come through the rotor housings like the old 13B turbo engines.
Seeing that info on the hybrid build that makes ~227whp, I'd say that rules it out for me. If that's a bridged motor and it's making that relatively low level of power, than I'm not interested for all the added work and having to go down a road that very few have been...
OK, so based on all the information we've gone over, it seems the best option would be:
13B-REW S6 block (with coolant passage mod to housings)
13B-MSP Rotors (with machined apex seal groove)
13B-MSP Eccentric Shaft
13B-MSP Counter Weights
13B-MSP Main Stationary Gears and Bearings
Balance assembly
I guess we could simplify by saying: "Rensis rotating assembly with REW block".
As for the ITB topic, yes you're 100% right and I am fully aware that it will cost me more and be more difficult to tune...but I want it man. To me, this build would be all about wow factor. Who the heck has seen an NC Miata with a rotary in person before? Hell, there's maybe only a handful online. So, the wow factor of the ITB's means something to me. I don't want a soul to ask me if it's carbureted...there should be zero doubt that this is a bad *** EFI, N/A build. That's my thought on it.
Your conclusions in regards to chassis choice are spot on. The more research I do, the more I'm confident I may be able to get this thing done for more like $15k, but the overall premise is spot on. The NC Miata's dyno out between 110-120whp stock. So, to see about double the power in this little car and have it rotary powered is just the best thing I can think of. How cool is that? I love the N/A powerband and doing that in a small car, with an open roof and still be able to take it on dates with my wife, or go to the beach...it's awesome. The FD is past that point. It's too fast and too scary for her. In the long run, an FD will always be worth more than an NC Miata, but having an NC with the "right" power level and remain balanced is a real draw for me.
The reason I say maybe $15k by the way is I've discovered the RX-8 and Miata were built on the "same frame". The RX-8 is longer but most everything changes over. The RX-8 brakes for example, which are larger and more powerful are a direct swap. So, this would naturally mean that any BBK for the RX-8 would also fit the Miata. The rear diff has the exact same bolt pattern and the diff mount bolts in as well. So, it's things like this that encourage me and make me feel like I won't have a ton of fitment issues requiring fabrication and extra cost.
If your estimate is correct about the MSP rotors with the S6 housings, than perhaps the configuration we've worked out would yield close to 250whp with a true ITB setup, as well. To me, 250whp is like the holy grail. If I could reach that with a street port I'd be so damn happy. My assumption, and again I am so unfamiliar with true NA tuning, is that the exhaust tuning will be important. But, with a street port, I probably won't HAVE to make it stupid loud, right? If it does need to be stupid loud to make the power, perhaps I can utilize an electronic cutout for the exhaust, pre-muffler or post resonator to quiet her down when I'm with the wife...?
First, I think a rotary powered NC would be a hoot. Or an NA or NB frankly - I'd do the earlier ones personally - but a proper roadster with a rotary would be great.
Second, 250whp with a streetport 13B is possible. It's not easy or cheap but Dave Lemon of Mazdatrix apparently had one of his SCCA EProd engines in the 280 (flywheel) HP range with a Weber IDA and 42mm chokes (class rules) and I've heard tell that Rob Warcocki is making a couple HP off of 300 (at the flywheel) in his GT3 car (no induction restrictions)
The problem is you seem to be equating "street" port with some concept of street manners - smoothish idle, wide powerband, ability to accept mufflers.
This is a mistake.
I have not seen A/B dynos to prove this, but having built and driven EProd engines, it's going to be far more of a lightswitch powerband than bridgeports or peripheral ports. To get those sorts of power levels you need to optimize everything to an inch of its life, which means that the ports don't really have the gas velocity to work at low RPM, and frankly you're fighting for every bit of overlap you can get so it's not going to idle well either. Pretty much the only reason to build a street port engine like that is if you're not allowed to build a bridge or peripheral port.
If you poke around you can find the 13B-RE 1st gen RX-7 that Defined Autoworks made that's doing about 230hp at the wheels on a street port with a very well optimized (a lot of testing time in short) combination. I think that's about the limits before you're pushing things too far - fighting for that last 20hp is going to cost you. All that said though, I don't think 230hp at the wheels on an NC (or NB/NA) would be boring.
11-25-17, 11:25 PM
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