The problem I'm trying to solve right now is the higher than expected backpressure I'm seeing. A smaller AR housing will make that worse but a larger compressor wheel may well improve it. I think the spoolup/response penaltly will be minimal . Remember I've done the same swap in reverse 62 - 58 and saw no real gain in response from that . Only difference this time around is that the compressor wheel will be a 11blade billet vs a 6x6cast blade.

Ok, I suppose there must be other factors involved that I don’t have a grasp for then. I hope you get the result you’re looking for!

Here is the rear scroll backpressure on the current setup at 10psi boost pressure . FYI

https://cimg9.ibsrv.net/gimg/www.rx8...8e7ca3f3f4.jpg

First lump in pink afr curve is 4000rpm , second lump is 6000rpm.

Can't figure out what the wild swing is between the two .... doesn't correspond to any valve opening. Probably the wg opening too far for an instant , but why it happens fairly consistently at that point is baffling.

Front scroll:
https://cimg2.ibsrv.net/gimg/www.rx8...69e845e366.jpg


Here is the corresponding boost curve:

https://cimg0.ibsrv.net/gimg/www.rx8...6cc917bf08.jpg

I can’t tell what’s going on that crammed full of way too much info graph. If there’s a data point you want me to see why not just show it specifically or just put it into text?

Whatever, hope you figure it out. Seems like there is some greater issue that’s the problem based on what your saying. None of it adds up in my book, but good luck.



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There are only two parameters displayed !

Green line is pressure , pink line is AFR (vs time) . The other lines are just alarm limits for the failsafe gauge.
The gauges and the numbers displayed to the right are all taken from where the blue line intersects the chart.
All the logs are taken at WOT from 2500 through to about 8000rpm

You can see turbine backpressure reaches 18psi on both front and rear scrolls. Boost pressure is 10-11psi . I would like to get backpresssure down to just above boost pressure .

But on graph you have to move around over to the scales to see what the values are, which I’m also on my iphone not a pc. Try to remember that you know what the graphs/scales are as compared to someone who never looked at it before. I’m a mechanical engineer. For me graphs have a purpose for trends and such, but I always prefer the log data. I wouldn’t post a whole log to make you dig into it. I’d display the important piece or two.

Once you open up the above on your PC you will see that they are quite simple charts.

I don’t use a pc for the forum.

I can't imagine browsing the forum on a mobile device.

Generally don’t have any issue using it in pc mode, I typically would ignore graphs in general even on a pc. Seriously over/mis-used, but that’s just me.

Yes ..... yes it is.

By studying and understanding the BW turbine CHART above, I am confident the larger compressor will reduce back pressure on the turbine and not have a major negative effect on spoolup.

Of course it will because that’s always the case with the both the pros amd cons that come with it. However, imo you have a larger problem somewhere else that’s being ignored by a side dodge rather than addressed properly. Assuming everything from CAI to exhaust ports is setup and operating properly then there must be some prevalent issue in the manifold/wastegate/exhaust setup that is not optimized properly.

Those basic turbo sizes and end results for 2-rotor are well documented and known. If your similar system can’t get similar results then it can’t really be the turbo sizing ...




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Possibly true.......... but at this early stage you can't ignore that it's still on par or better than any other setup you can compare it with .
This manifold design is still experimental but there are a couple of things about the above charts that give me some confidence that it is working well.
Firstly the slightly higher pressure on spoolup on the turbine side paired with the siamese. That effect is what I was hoping i would get .
Secondly , the pressure from that point on is fairly even between the two scrolls . So there is no major imbalance happening = good .
With a comp wheel properly matched to the turbine I expect improvements everywhere . We will see.

I suppose that depends on which setups you’re referring to and what the judgement parameters are. IMO there hasn’t been too many of what I personally consider competent Renesis low mount builds in general.

Once I’m past getting my race RX8 back and going again I had been considering getting a second one and doing the BW EFR 7163 setup I had discussed a while back. My goal isn’t so much max power, but low end torque, explosive response, and zoom-zoom driveability around 350 rwhp max.

I'll look forward to seeing this and finally getting to discuss it with you after you have some real world experience.

If you make anything close to 350 with that turbo without blowing the engine ...i'll eat my hat . :)


I'm fairly confident that this turbine has NEVER been paired with a 76mm comp. wheel before on any engine , let alone a 2 rotor.

Yes, I could be completely off base on that because my only involvement is through the discussion here rather than hands on experience with it. I completely defer that to you.

WRT the 7163 that’s the peak number @ 47 lbs/min i.e. only short time there before shifting. It’d be full E85, high boost, and reduced rev limiter (not 9000). It was proposed by other people on RX7Club too, but REW. You know that I understand the difference. My goal and direction would be much different than what you’re doing on many levels. Those are just words though. It doesn’t necessarily mean better etc. Just a very different direction

Below is a dyno of a similar concept using the next size up BW 7670 EFR on an REW, which is going to move more air up high, but was otherwise making 350 rwhp and 410 lb/ft at 4400 rpm or so with a nice fat torque curve leading up to it. I’m not trying to build a high revving turbo setup. I want quick and zippy right off the line. 4-port with an import 5-spd rear side housing (US was auto-trans housing bolt up only) might even make more sense


https://cimg9.ibsrv.net/gimg/www.rx8...a35ac59a09.jpg



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You wont get the same spoolup or power that an REW gets (even on E85) but it will def. be an interesting setup nevertheless.

You have to remember that it’s the next size down (faster spool) and has a more unique blade design which is going to help offset that some. Also shooting for lower power overall too. I would use the 0.85 V-band turbine housing with external WG. Manifold would be interesting if I can get it all positioned properly. No UIM eother. Would put a plenum right on the LIM flange with v-type IC venting out hood and v radiator venting down. My piping between turbo-IC-LIM would be over 50%+ less in length/volume than anything else too.


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I think you will learn a lot by doing this. If there is one thing I've learned over the years with this engine ..it's .........expect the unexpected.

If I were trying to achieve 350 with quick spool ....I'd go for the 7670. I can see why you would want the 7163 for the housing sizes ..... (same reason I went with the turbo I did) but I think you would regret going so small.

Semi related :
https://www.facebook.com/rotarypatent/

While I respect your opinion, I disagree with it.

I won’t need either ....

1. the larger physical sizing; biggest issue on a low-mount configuration

2. or the higher and more efficient top end mass flow range; 5-spd trans & 3.90 gear on a “dedicated super zippy, ultra-responsive, high lowend TQ, 7000 rpm redline street car, not race/track/the only thing bigger than my rwhp# is my forum bragging car”, that comes with the 7670 turbo.

My goal still seems to be eluding you, but is the opposite of why most people go turbo. So I understand in general why it doesn’t compute in some people’s minds. It does compute for the desired end result though.

It’s pretty simple really; think of an FD3 Twin Turbo with 100 more whp, much faster response, without all the transitional surge and complication of the twin setup in an RX8 chassis. That’s probably the dream car most of us wished Mazda had offered in 2004 ...

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Perhaps this is where it doesn’t add up for some people. Let me be clear, 350 rwhp is not the goal. I think it can get there no problem, but that’s all. I don’t intend to be at the redline much or at least not long periods of time. I don’t race on the street. What I want is to be able to just push the throttle in high gear to easily cut and slice my way through the typical urban traffic jungle mess. For people who enjoy driving it makes life much easier and happier when you have that level of power and control rather than sit there and being stuck dealing with it.

I wouldn’t say this except you’re the one who brought up turbo sizing and where you’re at now. This just my opinion, but I disagree that sizing is your issue. The issue is what I perceive to be flaws in the general concept and applied design of where your overall configuration is. What I think isn’t really relevant though. As long as you end up happy and satisified with your car & efforts then that’s all that matters.

Otherwise I’m going to start a dedicated thread on my proposal and stop interjecting on this thread about your car.
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I really do get what you want to achieve .
However , the Renesis has been an extremely difficult engine to make big power on . The same issues that cause that will hamper you greatly in achieving your goal even though you will be flowing much less air.

There may be flaws .............. BUT .............. and it's a big but , there is no other design out there that performs better . You don't seem to be grasping that.

If you say so ...