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This is mostly just a theorycrafting/hypothetical discussion thread. So let's not waste time arguing whether such a build would be worth the time/effort/money/etc... However, let's assume it's going to be a Renesis-based 3 rotor instead of a true 20B. So unless a custom side-ported "thick" center plate is created, the center rotor will probably flow slightly less than the outer rotors. In other words, I'm assuming it's going to be a "short" engine where the center rotor is housed by 2 standard intermediate side plates. Or perhaps Anyway, I bring this up because a 3 rotor is a naturally larger engine and thus has more wiggle room in terms of turbo sizing/selection. Of course, it would largely depend on one's specific goals, ranging from dyno queen to OEM-like spool. This means there's no true right/wrong answer. I simply want to get people's opinions on the matter. Therefore, let's keep things civil and respect each other's ideas.
Basically, let's say Santa Claus gifted you a hypothetical "20B-MSP" out of the blue and an additional ~$10k cash for a turbo and supporting mods. What would you do? What would be your intended goal for such a motor? What size turbo would you put on it? Maybe a twin-turbo setup instead? Or, perhaps you'd opt for a centrifugal S/C (e.g. Rotrex) instead since the 3rd rotor would already be providing extra torque throughout the entire rev range. Or maybe keeping it N/A would be preferred? Let's just treat this as just a fun "what's your dream 3 rotor setup" exercise. Looking forward to hearing what everyone has to say!
Also, the reason I want to discuss a side-ported 3 rotor as opposed to a conventional peripheral-ported 3 rotor is because I'm curious as to what implications that may have on the rest of the build and how such choices may differ from the various 20B builds of the past. For example, a conventional 20B would have 3 exhaust ports, with no ideal way to utilize a twin-scroll setup. Whereas, a "20B-MSP" could potentially have a 4-2-1 manifold, right? Of course, I'm well aware of the superior flow potential of the traditional peripheral-ported design. So if that's more your jam, feel free to say so. But that's also been done numerous times, so I'd love to see some fresh perspective. If you feel a "Renesis-based" 3 rotor is too restrictive, then by all means, go ahead and describe your ideal traditional 20B build instead. For example, a compound turbo setup would almost certainly be impossible with the restrictive side exhaust ports, but much a more likely prospect with peripheral exhaust ports. Or perhaps something like what Brettus envisioned, in which only the center rotor is PP while the outer rotors are not.
For reference, Rob Dahm recently fitted a new G42-1450 onto his 3 rotor, which was partially the reason I brought up the topic. I personally think that's too big, but that's just my opinion...thoughts?
It’s a lot of words to say you don’t understand turbo selection for a rotary application, but I can respect it finally being said. So here’s one perspective.
Ultimately you have to pick a power level and calculate out the flow required to achieve that; there are some general equations laid out for it on a rotary. Which is different than a reciprocating piston engine due to the difference in how they pump. In general a rotary engine is only going to make approx. 0.77x whp what a piston engine will make on the same compressor flow and is going to need much more turbine as well.
So if you know 400 whp is made at a particular point on the maps with a 2-rotor and you want to make 600 whp with a 3-rotor, then just multiplying those points by 1.5 and then seeing what turbo you need to achieve might be a good place to start, right? Which it requires approx. 54 lbs/min to achieve 400 whp on a 2-rotor and it’d be preferred for that to not be at the extreme right side of the compressor map.
Then for 600 whp, maybe 120 - 130 lbs/min compressor max flow at roughly 2.5 Pr at the far tight of the map. Doing similar on the turbine side, around 40 lb/min in that same Pr range. Or roughly a Garrett G42-1450 that you think is too big despite the person you chose to match up against your own experience level is no rookie wrt turbo rotary engines. A knowledgable rotary enthusiast wouldn’t bother building a 20B turbo for anything less than 550- 600 whp as a general rule of thumb. He’s probably shooting for 700+ whp though and it’ll probably need the max 1.28 A/R turbine available to not choke.
All this assumes you have flow maps, which is why those tend to be a bit more critical for a rotary application. From there you can roughly correlate 200 whp @ 27 lbs/min per 0.65L rotor linearly to a general WHP and flow requirement for a 1/2/3/4- Rotor configuration. The Pr is a bit trickier depending on how well the total package flows from air filter inlet to tailpipe exit. For the general enthusiast power level being discussed, the 2.0 - 2.5 Pr range is going to work.
As for the 3-rotor Renesis, I’d like to think that given recent discussions some people might have finally concluded that trying to build a combination overlap + non-overlap Renesis hybrid is not likely to pan out very well. It’s easy to dream when the reality of being awake can magically not come into play. Regardless of which way you go on choosing one design concept over the other, my own view is that it makes zero sense to do it with a Renesis configuration over the previous 13B, particularly for PP. It will be a lot of money for a mediocre result in comparison.
I seriously looked at the 20B RX8 currently FS on here with the 20B already in it, but needing a rebuild/refresh; my estimate is that it needs at least another $15k minimum to get it up to spec from where it presently sits. Probably $20k would be more realistic for a worst case cover the bases scenario.
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A 9180 1.45 is only good to about 650 whp and then hits a wall around 7000+ rpm on a real 20B, not seeing that in a Renesis version. Part of the issue is those large BW ceramic turbine wheels are rpm limited and if overrun will catastrophically disintegrate. Several threads listing these results over on Rx7club. With a BW it needs one of the larger 400SX-E turbos imo.
funny that I posted this 3 or so weeks ago, didn’t just pull a rabbit out of my hat and am not sure where the Dahm reference is coming from since I don’t follow him at all; respect his experience and all, but am not a fan of youboob attention seekers:
105 lbs/min @ 3.0+ PR and only 0.6 efficiency, but still peak speed limited and especially so compared to the other turbos I mentioned
you could make it work down there for reasonable power and good torque, that’s probably why it wasn’t chosen for the reference being made.
I wouldn’t choose it unless there was no choice due to fitment reasons. Supposedly a G40 is coming, but if choosing today I’d be more inclined to to the SX400SE or G42 other than just what was stated at the beginning; it really depends what the target power level is.
Then for 600 whp, maybe 120 - 130 lbs/min compressor max flow at roughly 2.5 Pr at the far tight of the map. Doing similar on the turbine side, around 40 lb/min in that same Pr range. Or roughly a Garrett G42-1450 that you think is too big despite the person you chose to match up against your own experience level is no rookie wrt turbo rotary engines. A knowledgable rotary enthusiast wouldn’t bother building a 20B turbo for anything less than 550- 600 whp as a general rule of thumb. He’s probably shooting for 700+ whp though and it’ll probably need the max 1.28 A/R turbine available to not choke.
Just to clarify, I wasn't trying to imply Rob Dahm was inexperienced or "doing it wrong" by any means. After all, I wouldn't be following his YouTube channel if I didn't have respect for the guy. Just that his goals for his 3 rotor differ from what I have in mind. If you look at the following graph, the turbo he was using just before switching to the G42-1450 doesn't produce full boost (~15psi) until around 5k rpm. Let's say the G42-1450 provides a 500-1k rpm better spool than w/e turbo he was using before. It would still not be fully spooled until after ~4k & change. Basically, the only thing I was trying to imply w/ that statement regarding Rob Dahm's turbo choice was that it's kind of a big turbo w/ noticeable turbo lag. Now, I'm not saying that's the wrong choice or anything. It's probably exactly what he needs for his goals. I guess my overall question w/ the topic is less "what's the correct turbo size?" and more "what's your goals for a 3 rotor?". Anyway, I just wanted to make sure my earlier comment wasn't misinterpreted as bagging on the guy or anything.
Originally Posted by TeamRX8
was slated for Q1-2021 release, on a mild 20B maybe ...
I'm pretty sure the map you posted was that of the G40-1150. The G40-1000 should be this one: (look at the text at the bottom of both graphs)
edit: Btw, here is a comparison map for the EFR 9180 vs 9280:
P.S. I am well aware the choice of turbo is largely dependent on the power goals of the build. So I guess, that is what I'm truly asking. What would your goals for a 3 rotor be? And with said goals, what turbo would you pick?
Me personally...I would want more low-mid range than most 3 rotor configurations. Hopefully, see full boost by 3-3.5k rpm. Cuz honestly, what am I gonna do with 700, 800, 900, or 1k+ HP? I'd be content w/ 500-600whp.
No, I was riding you some, but doing my best to not go overboard
What you’re missing in that example is they maxed the turbo out. What were my words at the start; what is the target power level?
How do you propose a higher power level without going to a larger turbo? Without knowing the specific details though (didn’t watch the vid) it could be that they went with a loose A/R knowing it was a stretch, but a larger turbo with same or tighter A/R might not be any worse lag, possibly better, with better top end power not being tapped out.
706 hp @ 15 psi means it flows pretty good as I also referenced wrt Pr. Again not having looked at the details, it must be a pretty good BP or PP. Those give up low end rpm for high end tq and power. It’s more a result of that then turbo choice, though turbo choice plays into it because those configurations don’t go well with EMAP. So that requires a larger turbo with loose turbine.
9180 vs 9280; only difference is the larger compressor; same turbine. i’m not so sure it will flow any better up top if the turbine is choking before it get’s to where that higher flow will come in.
so I did go take a look; the latest vid shows him running a half-mile standing start race with the G42-1450, stated 161 mph at the finish lighting up the tires in every gear
edit: probably will be closing in on 900+ whp, and you think he needs to be more concerned about improving spool. Was probably only pushing 800 hp for that 1/2 mile speed with a rough tune and soft throttle foot.
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No no, my issue wasn't really the turbo selection itself. It's evident his choice of the G42-1450 is great for his application (e.g. half-mile runs). My point was that a turbo that size would make any application that sees sub-4.5k rpm suffer, that's all. That actually seems to be the trend w/ almost all 3 rotor builds in general. I guess people just really love big numbers. For example, I recall you've had your eyes on the G25-660 (or was it 550?). My thought is basically, why aren't there more 3 rotor builds w/ that kind of turbo sizing around? In other words, a 3 rotor that's fully spooled by 3k rpm.
What's 800+ whp got to do w/ anything? I never said that to be the min requirement. The Rob Damn thing was only mentioned initially as a reference, nothing more...I'm not even talking about his build atm. Besides, why do you yourself want a G25 sized turbo on a 2 rotor? And with what would be so wrong w/ using that same line of thinking on a 3 rotor?
It only demonstrates your complete lack of understanding on the subject overall starting from my first post in this thread.
Why choose that build for your basis if the intent is the complete opposite? It’s just more uniformed arguing over a subject you have little understanding of beyond reading and attempting to mimic. Just as your posts in the UK turbo thread do indicate. You’re not fooling anyone knowledgable, just noobs more inexperienced than yourself.
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It only demonstrates your complete lack of understanding on the subject overall starting from my first post in this thread.
Why choose that build for your basis if the intent is the complete opposite? It’s just more uniformed arguing over a subject you have little understanding of beyond reading and attempting to mimic. Just as your posts in the UK turbo thread do indicate. You’re not fooling anyone knowledgable, just noobs more inexperienced than yourself.
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Choose what build? If you mean Rob Dahm's, I only mentioned it because watching his YouTube video inspired me to make a thread, nothing more. It was not meant as the focus of the topic, just a little something to get the ball rolling. You seem to be very affixed to it for some reason, as well as dodging questions and throwing insults at the same time. Whoever's right or wrong is beside the point...there's literally no excuse for that kind of attitude. Even if someone claimed "1 + 1 = 3", insult and ridicule is never the appropriate response. I assume you are an adult, please act like one.
So anyway, lemme ask you: What would your goals be for a turbo 3 rotor? Assuming you still desire a G25 based turbo for a 2 rotor, would you want a similar powerband on a 3 rotor? In other words, nothing more than 1.5x in displacement. Or would your goals differ due to it being a 3 rotor? If so, why? Assume cost-effectiveness need not be considered due to Santa Clause, as mentioned earlier.
I wouldn’t waste my time attempting a Renesis 20B even if you were paying for it out of a magic well with an endless flow of cash for the reasons stated in the existing thread where this should have been posted instead rather than starting a new thread on it.
which again, you bringing up the Dahm engine build; which is a heavily ported real 20B with non-staged semi-PP and as a result will never have any power below 5000 rpm regardless of what turbo is on it, only serves to call you out for the uninformed time-suck noob that you are.
@TeamRX8, whether you like it or not, you are a veteran member of this community and thus much more representative than most people here (such as myself). Your hostile and immature behavior is an utter embarrassment to the community you represent. What do you hope to achieve with that condescending attitude anyway? I would be ashamed if I were you. It is such a disappointment to see that the vibe here is filled with such negativity. The video you posted even states that if you have something to say, then say so respectfully. Did your parents never teach you any manners or basic human decency? I was originally eager to reach 10 posts so I could make a thread, but now this place feels much less welcoming with the toxicity you bring to the table. I sincerely hope someone can prove me wrong about this place.
04-17-2021 | 01:29 AM
