What supercharger did you use? Was it a positive displacement SC? Do you plan to ever go back and finish it?

 

It's an Eaton M62 positive displacement with electronic clutch which is from a Mercedes SLK 230.

Regarding finishing it. I have a 20b and I have a bone stock FD that needs an engine. So I'm torn between which car to put the 20b in. I could put the 20b in the twincharged car and use its motor in the stock car. Or make the stock car. 20b and complete the twincharged car as it is today.

 

So many great choices! I hope someday to see the twincharged car finished and see how it turns out. I thought long and hard about adding a whipple to my 20b. Still might someday, but torn between 4 rotor and supercharged 20b. Or just keep driving the car as is and actually enjoy it after so many years.

 

The 6758 actually came in .49 and .85. Compared to the 8374 I have lying around, the exhaust housings of the pair of used indy 7163s seem tiny, can only image the .49 housing would fit in your palm. They're smaller than the production version - v band inlet takes 2 1/4" tube v 3"(?) in the normal .85. The outlet side uses the same v band, but looks smaller at the wheel, but has a much more pronounced bellmouth exit. Was toying with the idea of a Feed style twin turbo manifold, as they were intending to limit inlet area to the same size as the stock twins in the competition class here, if you ditched them. If limiting the 8374 to the same degree, expected the tips of the compressor to go sonic if you restricted the inlet by more than half they wanted - providing the turbine didn't disintegrate first!

With the old Lancia S4, and the steam powered electronics used there, was expecting a turbo and supercharged car to be a certainty by the 90s....still waiting in vain!

 

well I'm not sure an Indy engine is comparable given 2.2L capacity, 12,000 rpm RL, narrow powerband, and only 1.6 Bar boost; then there's the mastery of developing a system that can operate between series to parallel flow paths but ok ...


also power level that was around 600 hp and through these turbo changes is now heading to 900 - 1000 hp soon.

 

High rev 2.2L V6 is about as close as you are going to get ti rotary dynamics in the piston world...

The ID of the inlet on my efr 7163s is 2".

That is the old standard size for turbo runners that would taper or merge down to T4 divided flange.

Turblown efr manifolds are 1.5" ID and taper down to the T4 divided flange.

Put two 6758 or 8163 exhaust housings side by side and compare it to the T4 flanged divided efr exhaust housing and you can see why two of 7163 0.85AR exhaust housings even with their little 63mm exhaust wheels flow as much as a 83mm exhaust wheel in a 1.25AR housing.
which is two steps above the largest 80mm efr exhaust wheel in the largest 1.45AR efr exhaust housing.

 

I’ll concede on AR with some reservation. I had considered 2x phi swallowing capacity, but it didn’t seem to match up between some real world twin vs single comparisons. That may just be due to the flow dynamic of the smaller compressor. Which the 7163 compressor just doesn’t work due to the dynamic differences of the 13B at lower rpm unless you sacrifice with an electronic boost vs rpm scheme to keep out of surge for half the powerband. None of the other comparable EFRs for a twin fitment provide any relief of that. So for both fitment and functionality the S252SXE stands out imo. Which was only my point from the start.

I’ll give you a good deal on a new 7163 with all the options including an additional 90* compressor housing though

 

I already got a couple 7163s, just need a good deal on a pot of gold to work on the rest of the set-up.

I really dont think a 2 rotor could send a single 7163 into surge without antilag.
I would try it out with the T4 divided housing if you are looking for a badass 400ftlbs torque/350rwhp turbo.

 

There was a guy who put one on a Renesis 6-port RX8 and quickly went through several engines. It spooled almost immediately. He subsequently deleted everything he had online about it. It just depends what you’re shooting for. Nobody is going to try and get 30+ psi boost on a single, but dual in parallel is going to be in surge until around 5k -6k. 2.6PR is exceeded very quickly (19 lb/min) and the surge line is angled back sharply. S252SXE (7070) is already at 3.0PR by 18 lbs min.

if you layout a 13B like they did in this 2.0L thread post I think you’ll see what I mean

https://forums.vwvortex.com/showthre...#post111477498

 

I haven't punted on weighing everything and since I don't have a hanging scale (or stripped REWs for that matter) I can't just pick up a 20B to get a gross weight from one I'd give a few individual weights. These are rounded to the nearest pound for ease of visualization, when I finish collating everything and throw it on a spreadsheet that I'll share you'll see everything to the nearest whatever it gets formatted to :P

Also the goal is a differential, not really to get ultra precise at the moment.

Part | 20B | REW

Eshaft | 25 | 14
Big Iron (includes gear) | 38 | 0
Intake Manifolds (Elbow to engine) | 31 | 21
Rear Iron (No gear) | 25 | 25
Center Iron | 26 | 26
Front Iron (No gear) | 24 | 24
Housings | 42 | 28
Rotors | 27 | 18

Total | 238 | 156

Diff | +82 | -82

Honestly this is a bit closer than I had thought it would be based purely on handling the parts individually and unfortunately I don't have a set of FD twins or a stock NA cast exhaust manifold to extrapolate what the exhaust side of both engines would be. That said I'm still very confident that an NA 20b in stock form would have been heavier from the factory than an REW as I dont believe the turbos, manifolds, and intercooler would weigh 82lbs + whatever the NA 20bs exhaust manifold would have weighed.

I could be completely full of **** and wrong though, I'm open to insight and please let me know if I'm forgetting anything of merit :P


Edit: I'm also aware that there are more parts that need to be weighed for a more accurate total such as tension bolts (20Bs with their extra thick set will fall further behind by a few lbs I estimate), gland nut (20b has a bigassed one), solenoids, waterpumps etc and I'm intentionally leaving off AC/PS and alternator.

 

dguy... Thanks for weighing all that. Helpful. I think you discuss the difference nibbling at the edges so to speak. Let's assume the exhaust manifolds between the 13b and NA 20b are of equal weight. If that were true, then the weight of the twin turbos and the intercooler get subtracted from the 82 pound difference you came up with. That difference then will be about zero. And, through all of this discussion, it should be clear that my "custom" 20b is actually a bit lighter than the stock 13btt.

 

No, it wont be, the turbos themselves don't weigh 50 or even 40 lbs, and the intercooler CERTAINLY doesn't weigh 30-40 lbs. I believe I've seen them weighed previously though can't recall specific weights and the intercooler with piping is ~10lbs based on the old FD weight thread. I dig your powerplant and I'm stoked it at the weight savings you've achieved via tubular manifolding and simplification but the point of contention here has always been what and why Mazda chose to go twin turbo over a 'big block' NA 3 rotor and the truth remains that a factory NA 3 rotor would definitely been heavier, and most likely heavier further forward of the centerline of the front wheels which are both completely at odds with the spirit behind the design of the rx7. In my opinion.

I also wonder if they would have gone with a larger volume of substrate in the cat given the 33% increase in displacement and potential scrubbing required even under low load/speed.

 

the 20B has a precat and then it has a Y and TWO FC style main cats

 

the 20B manifold is 50% longer, its going to be 50% heavier, it needs to do a third rotor.

 

jpfd3s... You're absolutely right. I had presumed that they would not have needed the same type of manifold or downpipe for an NA motor as for the TT 20b as installed.

Okay. Okay, guys... Disregarding the manifolds and downpipes and whatever, but taking dguys weights for most things having a difference of 82 pounds and subtracting 32 pounds for the twins and 10 pounds (?) for the intercooler, that basic weight difference would be 40 pounds plus whatever differences there are in the exhaust manifolds (and whatever else). Whatever the difference ends up being I think any "modest" weight gain would have been worth it then and now. If the installed NA 20b would have added 100-150 pounds, but made 300 hp, had slightly better performance, and been far more reliable, it would have been a better decision in my opinion.

Truth is that, while I have a strong view on all this, I just wanted to build an NA 20b and have the car weigh what it did with the stock twins and did that.

 

Coolest setup imo. Wish CA didn’t have crazy emissions laws or I would start saving pennies right now.

 

+1, if i did another 20B it would be NA, the noise is worth it...

as a complete aside, my friend has a 20B Cosmo, and it is just awesome, however it is NOT a sports car and there is nothing about it that is lightweight.

 

I've driven 20b Cosmo's and they need the twin turbos I think for the torque needed for a bigger sedan. Very nice cars, though. Wish we had gotten them here.

 

Speedhunters recently featured a JC Cosmo at the Tokyo Auto Salon: Garage Yamaguchi's 20B-PP Mazda Cosmo - Speedhunters

I'd love to see more of them on the road here. There must be a modern transmission that can bolt to the 20B.

Also, could a variable-geometry turbo work with a new rotary engine?

https://www.carsguide.com.au/overste...y-turbos-68205

 

Awesome car.

 

the funniest thing about the Cosmo, today is how small it is. its a big car in 1989, but in 2020 its teeny.

 

You are just so right. My wife and I were talking about how much smaller and lighter cars were back then much less comparing todays cars with those produced before 1975 or so. Like a Chevy Nova...

 

20b JC is still a 1600kg car. Not exactly lightweight. Seems slightly eccentric to chuck a rowdy N/A 20b in one .

 

I think maybe it would make sense if that one was originally a 13b. But if it already had a turbo 20b, then it doesn't make any sense.