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I had some issues with the length of a 4 rotor and originally thought I could do as much as 400-425 whp with a streetable 3 rotor. Only got to 397, but am happy with that. For me its the instant response and consistent throttle response of NA that's attractive. Plus, I have never had any issues with reliability. And, I have had the 3 rotor since 2009. A lightly tuned NA 4 rotor should easily do 425-450 whp or more.
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I'm not trying to start a fight with you, for some reason this whole sticking with oem and REW stuff for a 4 rotor that isn't going to take advantage of their ports (na), and then settle on less than best in class parts for such a large undertaking is just plain...weird, and wrong. Now, if it's just because the dude wants to, have at it, I'm taking issue with the justification being thrown around so here goes:
Originally Posted by arghx
(Post 12384353)
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. |
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Johnny needs to figure out the target torque curve. WIthout knowing that you can't define the intake port closing timing (i.e 4 vs 6 ports, and porting on top of that), the runner length, or whether you want to use pulsation effects in the manifold (ie a plenum).
https://cimg9.ibsrv.net/gimg/www.rx7...e249e0599b.png This is from Mazda's own research from 1982. It's really no different than a piston engine with fixed cam timing. Later closing - more high rpm power, worse low end torque. Bigger isn't always better, shorter runners aren't always better either. There is no variable intake manifold runner length option here unless you can somehow shoehorn in an S5 VDI system, and I doubt that would be optimized. The 89+ and Renesis VDI were not designed for 4 rotors (duh). You've got to pick an RPM point of peak VE and go with it. Of course it can breathe over 7k with later intake port timing and short ITB's. There's no debate there. But you're going to take a hit in low end torque. Mazda went through this 40 years ago when they designed the early 6 port + plenum system. You've got to give something up. https://cimg5.ibsrv.net/gimg/www.rx7...eab8d114fe.png ITB's are not a slam dunk. ITB's and short runners hurt low end torque. They add complexities to tuning and streetability. Just because it's been done before doesn't mean it needs to be done again. If you can get a six port system + plenum going like on a 84-88 13B you'd get a broader torque curve, and in that case you need to make FC irons work. Now I wasn't aware that someone had successfully used the BMW actuators for Rotary ITB's. Has anyone actually done that or was it just a retrofit on a different piston engine? Last I heard Electromotive was under consideration for the ECU in this case, and as far as I know electronic throttle isn't even an option for their most expensive unit. If somebody has already figured out ITB electronic throttle on a rotary with 4 ITB's, it would be the first I had heard. So what are the goals? Target idle speed? Acceptable fluctuation under accessory load? Acceptable warm up behavior? Lowest acceptable starting temperature? Target peak torque rpm? Target peak power band? Emissions and fuel economy - ok with open venting the charcoal canister and PCV ? running cat or no cat? Obviously premix is required here and secondary air (air pump) is off the table. Tip in fuel control - do you care how rich it goes on tip and tip out (has implications for acceleration enrichment tuning) ? Do you want to have wideband feedback control (full time closed loop) ? If you ask me, if you want the broadest torque curve, you've got two options: plenum with single throttlebody and 4 port, or plenum with single throttlebody and 6 port. |
Originally Posted by gracer7-rx7
(Post 12384413)
Not to derail the conversation but... what chassis and race org/class is this car being built for? I'm hoping to see it on track :)
It's an older John Finger chassis with an FD body. It had a 2 rotor in it competing in NASA and now it'll have a 4 rotor competing in either Super Production or GT-X with SCCA. Here it was at Buttonwillow shaking down the suspension with the old powerplant https://cimg8.ibsrv.net/gimg/www.rx7...c785faa5e6.jpg Any more questions on it means I should probably do a build thread but I'm pretty bad about stuff like that. Back to Johnny's 4 rotor build. . |
Originally Posted by gmonsen
(Post 12384395)
I had some issues with the length of a 4 rotor and originally thought I could do as much as 400-425 whp with a streetable 3 rotor. Only got to 397, but am happy with that. For me its the instant response and consistent throttle response of NA that's attractive. Plus, I have never had any issues with reliability. And, I have had the 3 rotor since 2009. A lightly tuned NA 4 rotor should easily do 425-450 whp or more.
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You know my opinion already but Ill post here. Start with the two REW blocks, spend the little bit extra for the S5NA rotors to have them lightened and scalloped. You will need minimal new internal seals. Dont skimp on electrical and alternator. Make sure oil coolers are overkill, spend a lot of money and time on tuning. Keep it simple where you can with trans, streetable clutch, rear diff. Work out the few kinks when you get it back that you are more then capable of handling then enjoy. You are sending it to the right place and I think it will be a really enjoyable car for your intentions.
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DJ... As I said above regarding eshaft wobble, when Barninger gave me the car to drive to DGRR in 2011, he didn't have it properly balanced and the bearing spun on the third rotor. That is the only problem I have ever had with the motor since 2009, although I only have about 10,000 miles on the motor. That includes Ihor running some pretty extreme dyno runs. Other than Barninger's screw-up, the motor has been bullet-proof.
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Johnny, what is the motivation for keeping it in an FD body?
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Originally Posted by lt1_rx7
(Post 12384915)
Johnny, what is the motivation for keeping it in an FD body?
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Originally Posted by lt1_rx7
(Post 12384915)
Johnny, what is the motivation for keeping it in an FD body?
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Originally Posted by djseven
(Post 12384943)
Have you seen a FD lately? They get sexier daily.
and other chassis... have fun with it! build a mid-engine component car! SL-C? |
Just ran across this pic. Pretty neat UIM
https://www.rx7club.com/attachment.p...1&d=1292095973 |
This is just something I keep thinking about and probably won't work at all or not the way I am thinking about it. Myself and others are using ITB's and one ITB per housing with runners that split off or "Y" to service both the primary and secondary intake ports. There are a lot of issues with the lengths of the runners to each port and diameter of the runners and where they split off. I and others are using something like 50mm ITB's.
I wonder if it wouldn't make sense to run separate ITB's for the primary and secondary ports. So, with a 4 rotor, you would have 8 ITB's. (Probably motorcycle ITB's, where you could size them small enough.) One larger and one smaller per rotor. Different length runners and different diameter runners to optimize flow. The primaries need runners about 14-15 inches long, IIRC. The secondaries' runners should be shorter and as straight a shot in as possible. Using throttle-by-wire controls and a really good ECU, like a MOTEC, this setup would make more power -- ceterus paribus -- and it might provide a lot smoother transition. |
1 Attachment(s)
Interesting that you mentioned ITB. I was just looking at these today.
Attachment 746440 The plan is still to use parts from a REW but I’m going to sell the REW rotors and going use S5 NA rotors as some of you have mentioned. I am pretty sure I am going to order the two new engines, eShaft and counter weight in January. |
Originally Posted by Johnny Kommavongsa
(Post 12385801)
Just ran across this pic. Pretty neat UIM
https://www.rx7club.com/attachment.p...1&d=1292095973 |
Hey, Trey. How about some pictures or video of your 20b?
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I need to get some more videos of it... weather just hasn't been playing nice lately...
in the mean time, enjoy this pic from when i had it detailed... https://cimg2.ibsrv.net/gimg/www.rx7...71bca156d4.jpg |
Originally Posted by gmonsen
(Post 12388077)
Hey, Trey. How about some pictures or video of your 20b?
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t-von... I knew you had some trick stuff, Trey, but how about a video of you driving it? Just love to hear it.
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Originally Posted by gmonsen
(Post 12388314)
t-von... I knew you had some trick stuff, Trey, but how about a video of you driving it? Just love to hear it.
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t-von... i'm a Tray too... so this can get a little confusing! hahahaha
i need to sort out a significant oil leak in my car... and hope for decent weather again soon... edit: did find these from the first running after the most recent re-install: https://drive.google.com/open?id=19S...lJ1yznD5v0Yko3 https://drive.google.com/open?id=19N...Ugb6cvOsjbNB4g |
Funny we Trey's had the exact same problem when I 1st fired mine up too. The oil filter pedestal I made was leaking badly. Sadly that wasn't the only leak. Intake and coolant leaks have been my biggest problems. That's why I cant wait to pull everything down and re-engineer the whole setup now that I actually know how to fab and what the hell I'm doing. When I look at my current setup, I think to myself "what the hell was I thinking". Lol!!!
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That vacuum line to the FPR is hurtin' for a squirtin'.
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