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dguy... I've seen your build. Going to be a great track car!
Stay with me a minute on the weight issue and I think you'll see my point in comparing the weight of a 13btt and an NA 20b. Let's "convert" a 13btt into a 3 rotor NA? You subtract the twin turbos, their piping, actuators, and the intercooler, and its associated piping. You add the weight of 2 more runners, 2 more coils, plus the weight of a 50% longer e-shaft and bearings , another rotor and its housing, and a thicker plate. Assuming a productionized version, the weight of the original stock 13btt and the converted 3 rotor are going to be just about equal. But I think that, given the engineers focus at the time on saving weight, they would have made these parts for a 3 rotor as light as possible. I would think they could easily have gotten the car to 2900 pounds or under. You are correct that I can't take the weight of my motor as a standard on the weight issue, if thinking in terms of supposedly heavier cast production parts, but mine weighs about 2925, which is negatively effected by all the sound deadening, full leather interior, and metal instead of plastic interior parts.
dguy... I've seen your build. Going to be a great track car!
Thank you, it belongs to Wayne Graham and has since graduated to a real engine (turbocharged, I finally got my way even after I was coerced into speccing and converting the original NA 3 rotor to a supercharged powerplant
Stay with me a minute on the weight issue and I think you'll see my point in comparing the weight of a 13btt and an NA 20b. Let's "convert" a 13btt into a 3 rotor NA? You subtract the twin turbos, their piping, actuators, and the intercooler, and its associated piping. You add the weight of 2 more runners, 2 more coils, plus the weight of a 50% longer e-shaft and bearings , another rotor and its housing, and a thicker plate. Assuming a productionized version, the weight of the original stock 13btt and the converted 3 rotor are going to be just about equal.
See, I just disagree with that. I don't consider myself an expert though I do have access to literally every single part we're discussing that was designed and implemented by Mazda as well as examples of more modern and one off construction. The engine would not have been lighter had they had to follow their design ethos. I do not disagree that it COULD have been lighter and CAN be lighter when designed today, I'm saying that it WOULD not have been given the way we know that Mazda designed and built things in that era.
I have a couple more 20Bs that are more stock as well as a few that are disassembled that I think I'll weigh sometime (maybe even tomorrow) I think that people will be amazed at the extra gravity in the multi piece e-shaft, thick center irons and other extra hardware thats there. Im also curious to see what the thin 20b irons weigh compared to REW irons.
Agreed, that’s more or less what I was trying to convey too.
Back to a twin setup, packaging aside it’d be kind of cool to see a 13B with dual BW S252-SXE turbos (uniquely a 7070 sizing) that has the combined potential of 108 lb/hr at 30 psi. Heard through the grapevine that an aftermarket v-band inlet turbine housing with higher AR is coming for it. Currently you can only get that in 0.83 AR. Pretty much a rainy-day dreamers idea though.
almost off topic, but the JDM tuners went through a twin single turbo phase in the late 90's early 2000's, and its complex, but it works. the poster child are the KSP cars (FC and FD) full bridegport with HKS 3037's, they were in the 700rwhp range. FEED did a couple too, there is a sinister looking black FD that was like 600hp.
these days you can buy a single turbo that is a better sizing for that kind of hp, and its simpler to plumb it, and much cheaper (you don't buy two of everything), but its also less cool...
I remember there was a 20b triple-turbo car some tuner did. Plumbing nightmare.
Kevin Wyum back in the big list days was trying to do a dual aftermarket turbo setup, I don't think it was sequential but just 2 smaller turbos. I want to say someone on the forum got the car and posted about it at some point, supposedly the setup worked pretty darn well. He was thinking about making it as a kit before his untimely passing. He's the guy that did the big ASP intercoolers.
You add the AR of each exhaust side to get the full turbo AR. So the 0.83 plus 0.83 is a 1.66AR.
Learned that from the Yamaguchi FD book as well.
Another thing to remeber is you add the surge lines of each turbo compressor together.
Combine those two factors and you can see why parallel twins have garbage low end power. Even if you go smalm on each tuebine AR you are surging the compressors when they try to spool on the low end.
But EFR 7163 has some compressors with really good surge lines. Even added together the surge line is better tha efr 9180 singe and can flow more.
The mixed axial and radial flow exhaust wheel is the wildcard with the rotary though. Mazda testing showed the rturbo strongly prefers radial flow on the rotary. The "impact" turbine wheels for rotaries are heavily skewed toward radial flow.
But EFR 7163 has some compressors with really good surge lines. Even added together the surge line is better the efr 9180 singe and can flow more..
and this is why it was done.. in 1999, when his was more common, they were either maxing out the T04R or living with the big laggy TA45/T88 turbos.
also all most of these setups are on 550-700hp cars, so it made sense. things have changed though, and not only do turbos come in more sizes, but people are building milder engines to do more street/mountain driving, so you don't see these twin setups anymore.
The dual 7163 vs 9180 is especially relative because both those turbos came directly from Indycar.
Honda went with the big single 9180 while the other manufacturers used twin 6758 turbos for their Indycar engine programs.
Indycar/Borg Warner developed the 7163 as the replacement 6758 and disallowed the big single having appeased Honda with the now improved twins performance.
So what I want to know is...
if you twin 7163 on a big bridge to spool it, run the exhausts parallel but the compressors serial for an insanely good surgeline and no exhaist choking-
what hapens when you max the serial compressor flow at ~400rwhp and then whack the compressors into parallel flow for more cfm potential?
Does power stay the same and then rise since the cfm output jumps when psi at the compressor drops (so stabilizes)?
Obviously there are packaging and tuning concerns, but they somehow managed to do it on warranteed cars. Some kind of electric supercharger / hybrid would reduce the parasitic load at low RPM.
Also, have you guys seen this? I wonder if Mazda has already gone down this road of inquiry:
people are building milder engines to do more street/mountain driving, so you don't see these twin setups anymore.
The move toward lower hp, but better spooling and more reliable motors has been great to see. Always wondered why there hasn't been as much experimentation with superchargers. I don't remember what happened to Colin's turbocharger/supercharger setup. Talked to Logan Carswell about doing a 3 rotor supercharged and think he may have built one or may still be working on one.
That video is a guy who doesnt understand how a rotary works explaining how to " improve" it to other people who dont understand how a rotary works.
The trailing sparkplug hole is already a small hole covered by the apex seal so there is minimal air/fuel loss as he proposes with the slot. Just the volume of the gap from sparkplug face to apex seal blows back into the intake stroke.
The larger leading sparkplug hole is carefully positioned so that the exhaust stroke pressure is the same as the compression pressure when the apex seal passes it, so there is no/minimal leakage.
The relationship between pressure of the compression stroke (amount of air) and the pressure of the exhaust stroke is constant because combustion pressure is set by the amount of air (compression pressure).
Ive posted the diagrams for this before from the book on the development of the Wankel engine.
"The Wankel Engine" Jan Norbye 1971
The ridiculous depression on the tips of the rotor instead of the middle. Again, he findamentally doesnt understand how the engime works.
The rotor tub is a transfer port, it has to be there or there wont be any air/gas at the leading tip of the rotor to push it around. Where the combustion force pushes on the rotor is a result of ignition timing and the air/fuel rushing through the transfer port in the rotor propogating the flame front.
Mazda has played with the shape to tailor when peak combustion pressure occurs (leading deep recess, trailing deep recess and what we have now middle deep recess).
The move toward lower hp, but better spooling and more reliable motors has been great to see. Always wondered why there hasn't been as much experimentation with superchargers. I don't remember what happened to Colin's turbocharger/supercharger setup. Talked to Logan Carswell about doing a 3 rotor supercharged and think he may have built one or may still be working on one.
The second iteration of the 3 rotor chassis I've been building was running a somewhat custom Vortech/V-1 framed centrifugal setup at 18 PSI and it was pretty 'meh' in my opinion. On paper it seems neat but driving it exacerbated all the negatives that get thrown at rotary power bands and didn't give access to the torque we were looking for on corner exit to keep up with big v8s and v10s. I'll admit though I never liked the idea and may not have given it a fair shot with transmission/gearing development to keep it on power the compressor is also less than optimal for what we were doing but it was the only thing I knew of that was readily available even with the step up mods we had done to the gearbox.
On a side note I realized I wanted to be a bit more thorough with weighing some parts so I didn't get around to the whole shebang though I did quickly throw an REW e-shaft on a scale and then a 20b. On this scale (I didn't get any of the good gear out, this is a shipping scale so exact weights may be off, I was more interested in the differential) the REW shaft weighed in at 14 lbs and the 20b weighed in at 26, the 20b was wrapped in cardboard so lets say 25. ~78% increase in weight in the crank shaft alone. I'll bust out some Longacre scales and weigh more 20b vs REW stuff as soon as I can.
Yeah, for purely supercharging if you want low rpm torque it would have to be a positive displacement supercharger for low rpm boost and if you wamt it to make any power it would have to be huuuge.
Might as well just strap a other rotary on top of your rotary to make the power.
Centrifugal supercharger has the same compressor surge line issue as a turbo, so you cant just gear it to spin fast at low engine rpm for boost- will surge.
Combined with a tirbo for top end boost a smaller (still big by piston standards) positive displacement supercharger or a small centrifugal geared for low rpm boost would work.
But you thought Mazda's sequential turbo system was complex? Now you've got all that and a mechanical drive for the SC to maintain as well.
Hell no, might as well go with custom larger sequential turbos (not stock hybrid) since the ecus/programming are there to control it and its well documented how to run and maintain a sequential turbo system.
Pretty sure that two turbines at 0.83 AR are not equivalent to 1.66 AR. Or at least that’s not making sense to me from a flow potential perspective, but perhaps I’m not looking at it clearly. I looked around and couldn’t find a clear answer.
I think that's just what Colin did. Turbo down low and supercharger up high. He had it running, but I am not sure where he went with it.("twincharged" is his handle here?)
The AR is a RATIO used as a unit of measure calculated from the Area of the cross section of a turbos exhaust passage divided by the Radius that cross section is from the center of the exhaust wheel.
So, its a constant ratio.
Twin turbos double the Area cross section while maintaining the same radius to the center of an exhaust wheel.
Double the Area per (same) Radius. Double the AR.
The 3rd gen Yamaguchi book spells this out as well.
Easy way to think of it.
Undivided 1.00 AR T4 exhaust housing.
Divided 1.00 AR T4 exhaust housing.
See how each volute of the divided housing is half the total area of the 1.00 AR undivided volute.
Divided 1.00 AR exhaust housing is actually a 0.50 AR plus 0.50 AR exhaust housing.
An even easier way to think of it-
Look at the Borg Warner exhaust side flow chart. Each exhaust housing can flow that much exhaust. Two of the same exhaust housings combined flow is twice as much as a single housing.
Not a stupid question.
Both volutes of a divided turbo exhaust housing are designed to flow the same with the exhaust wheels they were designed around.
This means they usually arent perfectly symeyrical where the scroll slot meets the exhaust wheel.
Some divided (dual entry) housings are not divided all the way to the exhaust wheel, but instead collect right before it to avoid the difficulty of even flow.
Then you have dual AR turbos like S4 TII thay have one tighter AR meant to be open all the time and a looser AR meant to open at later rpms.
They are not meant to be run on a divided manifold.
Well I looked at some non-rotary single vs twin comparisons and they don’t work out that way. You have to remember that each turbine on a twin setup is smaller than a single divided turbine. So that’s not a direct correlation.
Try this perspective instead; you’re not going to get 375-400 whp out of each 63mm or 70mm turbine with a 0.50AR on a rotary application, lol. Because what we’re talking about here is a 2-rotor with twin turbos making 750-800 whp. I’m thinking a 1.06AR isn’t even big enough with a 63mm turbine. You can probably make it with the 70mm turbine as you directly experienced.
One other point, the EFR 7163 is not favorable to high boost at low rpm. If you lay the S252SXE (7070) map over it you’ll see that getting up to 30+psi boost needed to generate the needed power level, that the S252 is going to handle it a lot easier where the 7163 is going to be way out in surge early on. Which I was already evaluating both for another application and came to that realization early on. The largest AR for the 7163 is currently only 0.85 too. Which I already have a complete new EFR 7163 setup and was a bit bummed. When originally purchased I was only going for 20 psi, which keeps it out of low rpm surge.
However, after looking into those non-rotary comparisons it’s pretty clear that with modern technology today that a single big turbo is the way to go. It will be way more cost and hassle to built a twin setup without any advantage, just as other people already stated earlier.
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Had a friend YEARS ago that had one of the very few twin charged 1st gen MR2's in the US.
The 1st gen MR2 was available with a supercharged 4-cylinder motor. HKS developed a kit that added a turbo onto it with a whole lot of plumbing. The supercharger had a magnetic clutch like an AC compressor so it could come on at low RPM and spin the turbo up and then the SC would disengage and let the turbo take over for high RPM. It actually worked pretty well except for the skinny tires on the MR2, it was just a smoke show.
It's obviously a plumbing mess and adding a lot of weight and complexity.
The supercharger had a magnetic clutch like an AC compressor so it could come on at low RPM and spin the turbo up and then the SC would disengage and let the turbo take over for high RPM. It actually worked pretty well except for the skinny tires on the MR2, it was just a smoke show. It's obviously a plumbing mess and adding a lot of weight and complexity.
That's very interesting. Basically the same thing Colin was doing. Just too complex.
I drove a supercharged 1st gen MR2. It was great! (The later ones grew too big and too heavy for my tastes.)
Yeah. That's what my twincharged setup does. Turbo blows through the positive displacement supercharger. It has a clutch (like an AC compressor), so it turns off when the turbo overpowers it.
It's still on the car, never tuned as I needed to wire in a new ECU (old electromotive was ok for its time but firmware needed to be upgraded and I wasn't going to spend any more on it) and then life happened haha.
Even without much tuning, the supercharger worked awesome. I don't have dyno numbers but it gave it immediate low end grunt (better than stock sequential twins (I've driven a fairly stock FD with bolt ons making about 300-325whp).
I never finished the tune for high end power and ironed out the crossover of the supercharger disengaging. So no real data on how well the overall system works from beginning to end.
I think you are exactly right that trying to make 400rwhp on 7163 with 0.83AR is going to be like trying to make 800rwhp on two 7163s each with 0.83AR.
Could be done, but few people would lean on a set-up that hard for 400rwhp when there are much more reliable ways to get 400rwhp.
People do decide leaning on a set-up that hard is worth it for 800rwhp. Not many ways to get 800rwhp on a 2 rotor.
We know from Indycar that they considered twin 6758 equal to one 9180 in power. I believe they switched 0.60AR to 0.85AR depending on course layout on the twin 6758s.
Indy car considered twin 7163 with 0.85AR an improvement in power over twin 6758 and single 9180 with a slight reduction in response over the 6758s with the 0.60AR
That is why I like the idea of using both exhaust sides in parallel and using the compressors in series at low rpm for the great surgeline and then parallel for high rpm.
Application would be relatively high boost at low rpm while keeping each turbo operating at low boost where they are efficient (pressure ratio is multiplied through serial compressors) and then lower boost at high rpm when in parallel mode.
Bridge port to spin the turbos at low rpm.
Intercooler per turbo so 1st stage is intercooled before going through 2nd stage when in serial compressor mode.
I think it would have a broad usable powerband.
Shoot for over 400rwhp and under 800rwhp
Streetport and 8374 is probably a way simpler and better idea though if 500rwhp is enough. Especially if Turblown gets their variable geometey housing working where ot switches from one volute at 0.60AR to both at 1.20AR.
12-30-19, 07:04 PM
