Street Friendly NA 4 rotor
2 Attachment(s)
There are probably a few other 4 rotor FDs in the states but Rob’s and David’s are probably the most discussed and recently another turbo 4 rotor build emerged at SEMA.
Rob is in the process of building an AWD Turbo 4 rotor. Attachment 746539 David has a track oriented turbo 4 rotor but I haven’t see a street friendly non tracked NA 4 rotor FD. Attachment 746540 When I say street friendly, here is what I’m thinking
Engine setup would be
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Any reason not to use S5 NA rotors? Would be nice to have the higher compression.
Would also be cool (but a CRAZY amount of work) to somehow put 2 S5 intake manifolds together to have the 6-port and VDI. Also the 89-91 NA's had an 8000 RPM redline. I don't see any reason not to use the higher redline. Being NA the engine will be much less stressed than a turbo version. Dale |
Originally Posted by DaleClark
(Post 12384059)
Any reason not to use S5 NA rotors? Would be nice to have the higher compression.
Would also be cool (but a CRAZY amount of work) to somehow put 2 S5 intake manifolds together to have the 6-port and VDI. Also the 89-91 NA's had an 8000 RPM redline. I don't see any reason not to use the higher redline. Being NA the engine will be much less stressed than a turbo version. Dale And yea using the two s5 intake manifolds would be cool but complex. |
Depending on your fab skills, I would say it's possible to have a street friendly 4 rotor, but from what I understand, one part is the complexity of shaping an OEM side port based intake manifold. Of course, if you're spending the money, why not go big or go home? Another concern of course is packaging as the 4 rotor extends out really far forward. I'd be extremely interested in seeing someone achieve such a thing, personally.
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In the scheme of things this isn't a project you can save money on, it's going to be a LOT of money. Just the e-shaft would be some serious money. Also custom fabbed intake manifold, an ECU that can run the thing, you're probably looking at $30k easy. Not to mention getting it all tuned so it not only runs well and safely but is streetable with good manners all through the power band.
Really it's like doing a turbo 4-rotor but just saving some of the turbo costs associated. Price would also go up if you wanted a more exotic intake manifold - variable length runners or ITB's for example. Dale |
The primary concern is cost vs benefit. If you're going to spend the money to turn-key a 4 rotor setup, you're not saving much to go N/A or streetport. It's a negligible cost difference (in the grand scheme of things) to go turbo p-port with a lot of power specific benefits (roughly 3-400 additional RWHP). Even if you truly want just a street motor, you'd be better off with a turbo in either case.
The secondary concern is practicality. It's essentially a fully custom setup to run a 4 rotor; this means a lot but I'm going to focus on one particular hangup for the 4 rotor design: The side port 4 rotor sucks. It will make almost no power for what you're investing (see cost vs benefit concern). The side port 4 rotor uses much smaller primary ports for both intake ports. You don't have the benefit of the much larger secondary port on the engine such as every other useful rotary engine. If you look at the 3 rotor, it has a "fat iron" because it has the much larger intake port designed into that iron to balance the center rotor to match the end plate intake ports. The "fat iron" of the 3 rotor also holds the stationary bearing, which is less of an issue for this discussion. The similarly designed short crank 3 rotor, also has the same, less than desirable, side port design; which is why almost all of them are configured for turbo p-port intake setups. If money was no object, you'd probably still not want a side port N/A 4 rotor engine design due to the lackluster performance. So that brings you to the p-port N/A 4 rotor, which is where almost all of your streetability is lost to begin with, the p-port. So then you're left with the turbo side port 4 rotor, which is still not perfect but probably the most streetable setup you could go with but expect roughly 3 rotor power numbers for a much higher price tag. If you're going to build a 4 rotor, you build it with a turbo and a p-port configuration because the cost is absurd to build one at all; You're going to want that extra power if you're investing a small fortune into it. Either way, you're probably not going to be daily driving any of these configurations, so build a turbo p-port monster and enjoy the sweet sound of a proper 4 rotor. |
Copeland... It kind of matters what he wants as en end result. I have an NA 20b that makes close to 400 whp. A 4 rotor NA would easily make 450-500 whp. Turbos would make a lot more power, but that might no be his goal. It certainly wasn't mine.
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Originally Posted by Copeland
(Post 12384084)
If you're going to spend the money to turn-key a 4 rotor setup, you're not saving much to go N/A or streetport. It's a negligible cost difference (in the grand scheme of things) to go turbo p-port with a lot of power specific benefits (roughly 3-400 additional RWHP).
Not following this comment but I'm assuming you meant to say, "you're not saving much to go N/A or Turbo"You have a valid point on, if you are going to do this, might as well go p port and turbo. I do think a p port would be cool and I think they sound awesome. It’s just not something I’m going to want driving around town. Same thing with boost, I love a boosted car but for this setup, I think a NA would be best as its less complex. Less heat, no wastegates, no additional oil and coolant lines, no intercooler, etc… |
I think you're going to be doing so much custom fabbing that sticking to REW parts just because you can get 2 kegs new will net you next to nothing. With regards to your redline it depends completely on how many bearings you're going to shove in there for support/to prevent shaft roping. I'm currently fitting one of Logan's peripheral port 4 rotors into a tube chassis with an FD body.
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Here is my idea which makes side port and preserving some of the FD chassis balance easier.
Use two crate 13B-REWs side by side in the engine bay. I measured and they fit but you have to dry sump them and turn them spark plug side down. Have an inboard boat engine shop make you a twin engine to transmission adapter (its what they do). You can use a standard short exhaust manifold to a single turbo on each engine (EFR 9180 iwg would be nice and simple) and a custom vertical short runner intake to plenum (modified 4cyl piece) on each engine with dual lever/shaft linked TBs. The downpipes would be a headache, so probably easiest to reverse mount the turbos and bring the DPs forward and into cats/mufflers down where the radiator would normally be. A sheet stainless duct over the top of the exhaust guides air from the front bumper over the exhaust, but dumps under the car in front of the engine (like radiator waste heat) and/or through a Vmount style forward hood vent. muffler exit either side on front bumper just ahead of wheel well. Bonus with reversed turbos you can use the Feed style cowl vent hood to feed pressurized fresh air to turbos airbox against the firewall. Liquid to air ICs in the plenums (so might as well use Cobalt SS plenums with their superior Laminova IC cores). Rear mount radiator for engine and IC where gas tank and muffler was. Ducted inlets from under the car and rear of rear wheel wells and exit through a mesh screen moulded into the rear bumper cover or a diffuser set higher in a trimmed up rear bumper. Gas tank moved into race car fuel cell where storage bins were (you make expanding foam in trashbag mould of the space and they make you the fuel cell). Cover that in sealed sheet metal above with nothing in rear seatbelt holes below and its safe and legal for racing too. Steering rack must be rotated so input shaft is forward and steering shaft must be extended to run over the engine and then use a steering quickener style coupling to bring the shaft and rack together in front of the engine. It would look tits with the top mount turbos/plenums and could use standard engines, 2 rotor ecus, base maps and turbo kits (So, all known quantities), the 600lbs of engine would be where the original 420lbs of engine were instead of 300 in stock location and 300 in front of that like an inline 4 rotor. You want AC too? Ugh, put that with the rear radiator and use an electric AC pump *somewhere*. You know what? Might be easier and cheaper to buy the white Scoot 12A based 4 rotor car since streetable emissions passing 4 rotor was their goal with that one. Sure, it might not make much power, but it is a 4 rotor and the shorter 12A based 4 rotor is a nod to preserving chassis balance. |
I wanted to comment that Copeland is a little off on the side port 4 rotor being a waste or low power etc. I’m a massive fan of street ports for their low idle etc. but holy crap does this engine pull without the turbo boosting. And i haven’t even attempted to clean up the tune much.
But i think op messaged me privately. The issue I see is that you have to do the bearing mod if you pull the parts from two REWs. And the center iron definitely should be a tall port for the same concerns Copeland had. Mines billet on the awd engine. So poet matching is pretty solid. Going to buikd my second motor into a semi p na motor. Or turbo it down the line. Idk. But I feel like one of the unspoken benefits as billet blocks come alive is the weight savings. It makes a 4 rotor less of a burden in your street fd. The 3 billet aluminum irons knocked 100 or so pounds out of my engine. I don’t remember exactly. But it was substantial and my 4 rotor weighs the same as my 3. Just a late night brain dump |
I think Logan from Defined Autoworks offers several different pre-built 4 rotor engines. Last time I checked, he has a couple of "mild" more street oriented engines on his website.
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Originally Posted by gmonsen
(Post 12384095)
Copeland... It kind of matters what he wants as en end result. I have an NA 20b that makes close to 400 whp. A 4 rotor NA would easily make 450-500 whp. Turbos would make a lot more power, but that might no be his goal. It certainly wasn't mine.
Isn't yours setup a p-port motor? I'd argue that's where a lot of the complexity lies in street manners, it's very tough to make a p-port setup streetable. If not, it's still impressive but not a good comparison since you have a fat iron 3 rotor which the 4 rotor will not benefit from due to the skinny intermediate plates. I just don't think a significant investment on a 4 rotor would be worth 450-500rwhp when a 13B turbo can make that on pump gas. Yes, you can probably make the 4 rotor more reliable, but I can also rebuild that 13B 10+ times for less than a 4 rotor cost.
Originally Posted by Johnny Kommavongsa
(Post 12384107)
Thanks for the feedback.
Not following this comment but I'm assuming you meant to say, "you're not saving much to go N/A or Turbo"You have a valid point on, if you are going to do this, might as well go p port and turbo. I do think a p port would be cool and I think they sound awesome. It’s just not something I’m going to want driving around town. Same thing with boost, I love a boosted car but for this setup, I think a NA would be best as its less complex. Less heat, no wastegates, no additional oil and coolant lines, no intercooler, etc… I understand wanting less complexity but I'm just being realistic and pointing out the cost to power is hard to justify for most people when the 13B turbo makes similar power with decent street manners. I'd even argue that the 13B turbo has less complexity than a 4 rotor, of any kind, brings. Don't get me wrong, I'd still love to see you build one.
Originally Posted by rdahm
(Post 12384172)
I wanted to comment that Copeland is a little off on the side port 4 rotor being a waste or low power etc. I’m a massive fan of street ports for their low idle etc. but holy crap does this engine pull without the turbo boosting. And i haven’t even attempted to clean up the tune much.
But i think op messaged me privately. The issue I see is that you have to do the bearing mod if you pull the parts from two REWs. And the center iron definitely should be a tall port for the same concerns Copeland had. Mines billet on the awd engine. So poet matching is pretty solid. Going to buikd my second motor into a semi p na motor. Or turbo it down the line. Idk. But I feel like one of the unspoken benefits as billet blocks come alive is the weight savings. It makes a 4 rotor less of a burden in your street fd. The 3 billet aluminum irons knocked 100 or so pounds out of my engine. I don’t remember exactly. But it was substantial and my 4 rotor weighs the same as my 3. Just a late night brain dump I'm sure the side-port 4 rotor still pulls nicely but for comparisons sake, your car is likely to have different transmission and axle gearing than stock and the butt dyno is a tough comparison to use. Edit: I'm only saying the side-port 4 rotor is a waste, when compared to a similar p-port 4 rotor. It is essentially only a couple percentage points cost difference between the two and the power gains are significant. The power gains are due to the skinny intermediate plates restricting intake side-port size. |
Makes sense thxs for the info Copeland. I remember seeing your car at DGRR and that thing looked rowdy.
And thxs to Rob and others for chiming in. Still interested in hearing others feedback. Any feedback on slide throttle vs ITB or plenum? Cable vs drive by wire throttle? Mechanical vs electric water pump? |
A proper side port 4 rotor could be built with billet plates.
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Originally Posted by Gilgamesh
(Post 12384196)
A proper side port 4 rotor could be built with billet plates.
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Originally Posted by dguy
(Post 12384118)
I think you're going to be doing so much custom fabbing that sticking to REW parts just because you can get 2 kegs new will net you next to nothing. With regards to your redline it depends completely on how many bearings you're going to shove in there for support/to prevent shaft roping. I'm currently fitting one of Logan's peripheral port 4 rotors into a tube chassis with an FD body.
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Johnny and I have spoken about this build and I've been recommending him to make it as mild/OEM as he can. Don't even play the power game is what I've argued.
My recommendation is basically side port 4 rotor with the two REW blocks if he can make it fit. Just use the stock rotors and stock seals. If wet sump won't fit then dry sump, but if you can make wet sump work then do it. Johnny mentioned using Xcessive LIM's as a foundation for a manifold or fabricate. Either way, use a single throttlebody and common plenum with common vacuum signal. -- Not many big builds have rubber mounts and idle like stock. -- Absolutely no ITB's. No Plenum - no vacuum signal, Alpha-N tuning only. Yuck! -- electronic throttle preferable but if not, install an idle speed control valve at least. I know there are romantic notions about throttle cables on this forum but they've been out of production since 2008. -- [gasp] use a simple exhaust manfiold and even consider a muffler and a high flow cat... -- simple cooling system --no expensive drivetrain and transmission hassles --PCV and evaporative purge solenoids! Yes you heard me! no catch can to check, no vapors smell on a hot day! Just like a normal car. Bet you've never heard someone argue for those before. Keep the stock charcoal canister and purge solenoid and PWM control it like a normal car. No turbos = no knock, no secondary injectors or huge fuel systems needed either. Stock red line saves cost and complexity and risk. You just need a trigger wheel on the crank and could probably get away with batch firing it. Cooling system is nowhere near as difficult as with boost, no need to fit the turbos and intercooler stuff. Big power 4 rotor will just spin tires and be a one trick pony (which is why Dom's car is going the AWD route, and why try to copy someone else?) 6 port irons and VDI aren't worth the trouble, if you could even fit them. Then you're stuck with two throttlebodies and Alpha-N or other complicated tuning and idle control. WIth this style setup you get better low end torque vs ports with very late closing and huge overlap. It's not going to dyno a whole lot but it will be different and it will be torquey and it can be more comfortable and quiet. |
Originally Posted by arghx
(Post 12384229)
Johnny and I have spoken about this build and I've been recommending him to make it as mild/OEM as he can. Don't even play the power game is what I've argued.
My recommendation is basically side port 4 rotor with the two REW blocks if he can make it fit. Just use the stock rotors and stock seals. If wet sump won't fit then dry sump, but if you can make wet sump work then do it. Johnny mentioned using Xcessive LIM's as a foundation for a manifold or fabricate. Either way, use a single throttlebody and common plenum with common vacuum signal. -- Not many big builds have rubber mounts and idle like stock. -- Absolutely no ITB's. No Plenum - no vacuum signal, Alpha-N tuning only. Yuck! -- electronic throttle preferable but if not, install an idle speed control valve at least. I know there are romantic notions about throttle cables on this forum but they've been out of production since 2008. -- [gasp] use a simple exhaust manfiold and even consider a muffler and a high flow cat... -- simple cooling system --no expensive drivetrain and transmission hassles --PCV and evaporative purge solenoids! Yes you heard me! no catch can to check, no vapors smell on a hot day! Just like a normal car. Bet you've never heard someone argue for those before. Keep the stock charcoal canister and purge solenoid and PWM control it like a normal car. No turbos = no knock, no secondary injectors or huge fuel systems needed either. Stock red line saves cost and complexity and risk. You just need a trigger wheel on the crank and could probably get away with batch firing it. Cooling system is nowhere near as difficult as with boost, no need to fit the turbos and intercooler stuff. Big power 4 rotor will just spin tires and be a one trick pony (which is why Dom's car is going the AWD route, and why try to copy someone else?) 6 port irons and VDI aren't worth the trouble, if you could even fit them. Then you're stuck with two throttlebodies and Alpha-N or other complicated tuning and idle control. WIth this style setup you get better low end torque vs ports with very late closing and huge overlap. It's not going to dyno a whole lot but it will be different and it will be torquey and it can be more comfortable and quiet. I don't understand the push to save what amounts to a few hundred dollars on using stock seals from new REW kegs on what will amount to be at least a $40000 project after labor (I'd say north of 50 to be honest). This doesn't make sense nor does pushing for REW irons, housings, and rotors for that matter. The amount of machining required to fit stationary gears and bearings in the irons negates all savings and you also have the option of just running things like PAC performance aluminum pieces and for the cost of this project overall just run lightened NA rotors. Also Alpha-N with MAP compensation using a vacuum manifold run to each ITB is completely streetable given some finesse during tuning, even on a peripheral port. With regards to the other bits, I think you're oversimplifying the ease of staying 'oem-ish', though I do agree with keeping modern emissions controls, real mounting components, and a reasonable exhaust. All of these things are totally doable, just don't kid yourself that you're saving anything by sticking with a couple OEM blocks. BTW, these fuckers are bigger than they seem, and even if you've seen one in person you wont appreciate it until you try to shove it in a chassis: https://cimg1.ibsrv.net/gimg/www.rx7...481d54c1ad.jpg https://cimg7.ibsrv.net/gimg/www.rx7...d39d39cc60.jpg https://cimg8.ibsrv.net/gimg/www.rx7...6aaf41ac71.jpg P.S. I can't stress this enough: I'm not saying you can't do it, nor am I saying don't try. |
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the reason you go with the OEM blocks is because the parts are actually new. All this stuff about lightweight this and clearancing that, what's the point if it won't breathe over 7k? Sure you could if you do the whole ITB/velocity stack with big ports for high rpm breathing. The 6 port systems you could probably get working if you really want to, but now you've got to deal with n/a irons and controlling the ports etc. VDI is out of the question because you can't make that UIM work.
With ITB's and big ports your low end torque takes a hit, you've got to balance 4 throttles by turning screws, and you've got half the carburetor experience at that point. You can't run electronic throttle, you can't run an idle valve, you'll probably have to open vent the evap canister and PCV system (catch can), your MAP signal is questionable. Yes you can run Alpha-N, but why bother? You can use some aftermarket seals but the stock ones work fine. Sure the 9.7:1 rotors would be a small benefit if you want to go that route. I think we all have a different definition of street cars and streetability. I'm judging by the standards of a stock FD, and a stock FD is basically awful by modern car standards due to its rough and unstable idle, poor HVAC, etc etc. Everyone else is judging by the standards of a typical peripheral ported race car. Only Johnny can decide what the goals are. |
I'd love to see you build any kind of 4 rotor setup so let's start off with some suggested (or at minimum, required to look at sections). I'll try to focus on the non-engine specific things to consider, I'll touch on the oil pump though.
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It will be a lot of work but it can be done. I just suggest you look at your budget before digging too far into it, it will add up quickly. This was why I brought up cost vs benefit, it's going to be hitting on some unfavorable ratios by the end of it. |
If you're doing NA 4-rotor and staying at 350-400 I don't see needing to do a trans/diff upgrade. Turbo 4-rotor, yes.
Room is going to be a big issue for sure. 4-rotor is just damn long. I think Scoot in Japan did a 4-rotor with 12a housings/rotors, that would knock 40mm off the length of the motor. Dale |
2 Attachment(s)
Thanks for the consideration items Copeland.
I don’t think I will be making more than 450 with the current setup that I’m thinking so I’m hoping the trans and diff will be ok. I think a lot of the issues with them breaking is how hard one is on them. Didn’t think about the fuel tank but you have a good point. I don’t foresee myself putting a whole lot of miles on the car. The furthest drive we ever do at once is to DGRR which is about 200 miles. I probably average 5k miles a year on the FD. I could see myself doing a brake upgrade in the future. Alternator, I need to figure out what Rob and David are doing. Check out how the alternator is mounted on the scoot car and how Logan did the Alternator and PS on his 3 rotor build. Would be neat to try and do something similar. Attachment 746537 Attachment 746538 The scoot car started off as a 12a but now has 13b parts The Rotary Dream Is Well & Truly Alive At Scoot - Speedhunters |
Here's a few shots of my alternator on the 3 rotor. I wanted to retain the airconditioning.
https://i234.photobucket.com/albums/...psskrvtqng.jpg https://i234.photobucket.com/albums/...ps5gxqfztx.jpg |
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