Rotary20B

G'day,

Just wondering how many na 20Bs there are around and what specs

I'll start


Car: '84 S3 RX-7

Engine: 20B extend port (stock turbo rotors)

Exhaust: 3-2-1 extractors into single under drivers seat, 2 1/2" pipe into a single 3" straight through SelectMaz muffler

EFI: Microtech LTX12

Diff: Stock S3 with 4.4 gears

Gearbox: 12A Turbo

Power: 245 rwhp @ 8300 rpm on a Dyno Dynamics

bcool

Car: 86' GXL

Engine: Stock block 20B

Exhaust: Custom Header 3" back to a Flowmaster Y and split into the stock TII catback (I also have an electric 3" exhuast cutout right after the header for track days)

EMS: EFI Technology Race 2.0 ECU

Diff: Stock TII rear

Transmission: Stock TII

Power: 240 @ 7000 RPM

RETed

Customers car...
More info in other threads in here.

1986 FC
Stock 20B - never been opened
Haltech E6K running in "V6" mode firing a trio of FC leading coils through an MSD DIS-4
Custom 3-into-1 header, 2.0" primaries
4" single muffler split into a pair of 3" mufflers
FC turbo trans
FC turbo rear diff

232hp at the wheels on a DynoJet
190-195 lb-ft torque


-Ted

Rxmfn7

iTrader: (4)

Hmm.. forgive me if I sound a bit unimpressed, but are you guys happy with those numbers? I see you are all using stock 9.0:1 rotors and the stock intake, which is less than optimized for N/A applications, but still. There are 2-rotor FCs that are cracking 200WHP on stock ECUs with just piggyback fuel controllers. I'm heavily looking into an N/A 3-rotor setup for my FD, which would be built from the start with intentions of staying N/A ( 9.7 rotors and ITB setup, huge streetport, possibly bridge), but I would not be happy with any less than 350RWHP.. but seeing these numbers makes me wonder if that is even possible.

SMonty

if you go rotary you better go turbo, all that work for a 3-rotor and you only have mid 200 rwhp is not worth it. 2 rotors are in the high 400's. i would've kept the 2 rotor and spent the money on turbo stuff, but instead i went with a v8

Jager

iTrader: (10)

Those #'s are still with 9.0 rotors and no work other then usually intake and exhaust. It'll be like taking a stock TII, taking off the turbo and adding a header. Gains really wouldn't be that great would they (less then 130HP)?

9.7 rotors, ITB, and a well build bridge in theory is good for 350+ HP. PM Kahren and ask him about his 20B build ideas.

Jager

iTrader: (10)

And 3 rotors can go higher with alot more torque.

Rxmfn7

iTrader: (4)

There have been 700RWHP+ 2-rotors, whats your point?

Jeff20B

iTrader: (13)

Interesting topic shift as I am now looking into a future turbo upgrade. My plans are to tear down my stocker and see which shaft it's got. It is #756 but has an oil pressure reg change to the later, higher pressure type. The oil pan gasket surface was scratched up, so maybe it was a factory warranty rebuild? Well, at least the ROPR was changed.

Is it normal for an early 20B to have over 100PSI at cold idle? Sounds like possibly an FD ROPR to me.

I hope it's got a later shaft. If it does, it'll get a large single and moderate boost (heh, we'll see). For now though, I'll run it NA in a 1st gen after it's rebuilt with a street port and turbo sleeves.

Kahren

iTrader: (13)

bridge? what bridge? it should do 350whp with a streetport, header, itbs and a decent tune with 9.7 rotors, well see soon enouf...

Jager

iTrader: (10)

Oops, sorry cowboy.

:O What EMS will you be running Kahren?

Rotary20B

Mine was done on a Dyno Dynamics, which read 15% less than dyno jets and other American dynos

It is making more hp then one of the countries best IPRA cars here, big dollar 13B bridgeport, and kills it for torque (was run on the same dyno at the same time)

I've had big port 13Bs for the last 8 years and can tell you, the extend port 20B kills it.

t-von

iTrader: (8)

First off the tiny 1.3 L rotary isn't going to have know where near the power band or even the reliability of the larger displacement 20b at that power level. You can't even compare to 2. All things being equal, which engine do you think is going to last the longest?

t-von

iTrader: (8)

To each his own. Not everyone wants to build an engine that has to rely on boost to actually be fast. Mid 200 rwhp from a NA 20b will easily last you many thousands of miles. Also turbing is an easy upgrade that can always come later.

t-von

iTrader: (8)

GtoRx7 is a perfect example!

rarson

^ Exactly what I was about to say. 350whp has already been accomplished on an N/A 20B.

Rxmfn7

iTrader: (4)

My post was in response to SMonty's comment about there being 400HP 2-rotors.. Im on you're side hombre

t-von

iTrader: (8)

My bad I guess I was more relating to your first post on this thread when you seemed unimpressed by some of the NA numbers being posted.

slidingsky

its a stepping stone. the na is kinda 4 fun. of course there are much bigger plans. far more than any 2 rotor can do. Getting the stock turbos piped in didnt seem worth the effort, plus it was to see what it would do na.

bcool

Thats exactly my story, its fun right now to play around n/a, see what it can do. Its super great for autocross right now, almost kinda sad i'm slapping a GT42 onto it.

rarson

Lol... just switch to drag racing. I'm sure you'll still love it with the GT42!

RETed

For a stock internal block with the stock intake, that was dead-on what my estimate was.
The header is not optimized.
We built the car like that just as a "intermediate" build.
The car is getting turbos slapped on it soon.
I estimated the power output to be 230 to 250.
We would've went higher, except we found out the damn air filter was too damn small - the AFR's jumped up one full point when we removed the air filter.
Oh well, we ran out of time.

There is NO 2-rotor that'll make close to 200 lb-ft of torque, period with similar mods.
If hp #'s are all that you are looking at, then it would stand to reason you are disappointed.


I have never seen one - stock internal block, stock intake.
I've only heard of Kahren's build which uses a custom intake to hit over 190 at the wheels.


I dunno why you're so hung up on horsepower.
It's the torque that makes this motor unique.


-Ted

Rotary20B

To give you an idea on a comparison, on this same dyno, decent street driven 13B bridgeports with IDA Webers were making no more than 180rwhp.

The 13B Bridge Port that did 238 was an all out race car, quad throttle body injection, lightened high comp rotors, all the good gear, very low friction driveline & built by one of the best engine builders in Australia. These engines alone are rumoured to cost around the 20k mark. So to do a conversion for a little over half that cost, and beat those numbers with a totally streetable engine natuarally aspirated is pretty impressive I reckon.

A decent 13B extend will run around 150 rwhp at the very best on a dyno dynamics, so yeah.. 245 rwhp from a 20B extend port, using stock intake & low compression turbo rotors and a stock S3 driveline I am pretty damn happy with.

Will see what difference the intake makes.

t-von

iTrader: (8)

I hate to say it, but those are some weak numbers for NA 13B bridges over their.

Rotary20B

Once again.. our dyno's do not read as high as American dynos

http://www.twinturbov8.com/dynostuff.htm