it must be the camera angle, but it looks like the flange for the block is cockayed, but I can't believe you of all people would do something like that

 

43" primary length seems quite short compared to what RacingBeat recommends. Although, that just means you will only get a torque peak at 1 RPM point instead of 2. For PP cars they recommend around 96" primary length with bridgeys being as long as 110"... Pretty hard to package that and also fit resonators and mufflers. I'm going to try to get as close to 110" as possible on my car when I build my exhuast but I imagine I'll have to compromise for shorter primaries to fit enough muffling.

http://www.racingbeat.com/mazda/perf...gurations.html

 

It's the angle at which the pic was taken. The flange is cnc machined, and machined flat after the header was welded, fits perfectly



Yes, I've seen that page, and it makes sense. This is a page from an older competition manual (Which assumes a PP engine):



Note that it recommends a 2300mm exhaust length. This is a page from a SAE paper about optimizing a rotary engine for racing:



Note, at 6000 rpm, 2300mm is the sweet spot to be.
Also, it runs a 370mm long intake, same as I am running at the moment.


However, that said. The 787B doesn't run an exhaust that is anything like that length, it's much shorter. This is a picture from another SAE paper, it's not a 13B but a 500cc test engine, which may make a little bit difference.



That engine seems to like shorter headers. But who knows what a 2300mm header would do.
It does run a way shorter intake, at 170mm. I think the intake and exhaust pipe length somehow needs to "match" each other at some sort of ratio or something.


I may try longer headers, but I want the exhaust quiter aswell, which is why I made them shorter and added a premuffler. I just heatwrapped and fitted the exhaust. It's pretty quite at idle, but way raspier and sharper sounding when on the throttle. I like to think it's because of all the pulses and resonations happening in the header, but it's probably because I didnt want to spend a boat load of money on the premuffler and got something cheap.

 

230 cm is about 9" for us Americans and, that is one short header.

 

Roughly 90".

2.54 cm per inch.

 

Lol! My bad.

 

Lots of rotaries in Australia and New Zealand also run long primary lengths but Defined Autoworks header is somewhere in between a short and a long system... I'm hoping I'll be able to pick a length that allows me to have a resonator and big muffler at the back and then change intake lengths until I find what makes the best power under the curve. Could be an interesting dyno day when it eventually happens...

 

nice build

 

Did you make the collector yourself or is it an off the shelf item? I was sort of eyeing the Vibrant Performance 2-1 collector but haven't decided yet

 

Euhm John builds them from tubing

 

Beautiful work, love the harmonic study. I've had a question burning at the back of my mind for months; why not use a single intake runner to two rotors in stead of running individual runners? I'm assuming that the rotors are still in pairs 180 degrees apart, peak air velocity should be evenly timed, the main runner could be larger diameter to increase flow, half as long for proper resonance, it would be easier to build and take up less space under the hood.

Just a thought, great build!!!

 

Indeed, maybe I'll do the same


Like damic said, maybe it myself, as I like to save a buck, The vibrant one looks nice


Not really sure how that would work harmonic wise, but at high overlap engines you don't want that, because exhaust gasses from one rotor could get sucked in the intake caused by the vaccuum of the other rotor, so you want to keep the runners seperated, which is why you don't really want short runners and a plenum on these engines, but ITB's instead.



Soo today I spend another day on the mazda , I pulled out the microsquirt ecu, and fitted the ms3x ecu in there , I had to make a new engine wiring loom, so the job took me all day, but it's running!

Made some pretty good improvements!, It's running sequential injection now, which helps. Also increasing all the lag settings helps a lot. Normally the ecu smooths all the values, at the cost of response. Not a big deal if you have a plenum, but with ITB's I couldn't get the response tuned. With the smoothing removed it's much more responsive, drives much better on the street.

Dual widebands are in, but not working properly, because I've got 2 different controllers, and it's only possible to enter one set of calibration values, so one of the two sensors is always off. I'll order another controller, so they both are equal.

Engine is beginning to make some power. AFR's are still rich at 1:11 at full throttle, EGT's at around 1450F, so there's probably a bit more in there if I lean it out a bit.

First I want to work on the intake though. My datalog showed peaks of 160F intake temp , so that's on top of the to do list. I've got a trackday planned next friday, so fingers crossed I can finish it before then!

 

agreed. we can tell what worked for certain combinations, but thats about it.

the 787B header is fairly short, but it also looks like a bigger diameter. it is likely that there is a packaging concern there.

i do agree that the intake and exhaust seem to need to match, but to what isn't certain

 

TrackDay where? Rely John °F 71°C is pretty hot for a intake, air taken from under the bonnet?

 

Going to zandvoort . Hopefully I can get this thing ready by then, if not, I'll take the E36 beemer.

Yes, the intake temp is pretty bad, but to be fair, the weather has been pretty hot. Yesterday when I got in the car all the temperatures were already reading around 48C, just from the car sitting in the sun.

Anyway I did start on the cold air intake, hope to get it done before friday:






Old stacks and baseplate on the right, new one on the left. I'll need to get some materials in to finish it. New velocity stacks are about 20mm shorter, as I wouldn't mind moving the peak power up a few rpm (currently at about 7200-7500-ish).

For a filter I actually tried fitting a stock S4 airbox, as I think it would actually work fine, but for some reason I have a turbo radiator, so the snorkel doesn't fit. So I'll probably end up just running a hose to the front of the radiator, and fit a universal filter there.

 

Can't you make a full hood width snorkel, normally there's enough space between the lights.

 

So I didn't make it to the track last weekend, didn't have all the materials for the intake, and didn't want to rush, so I took the old beemer. Today I continiued, as there is a Rotary meeting next Saturday I want to try and get to.

I got the cold air intake done. It's not perfect, as I did the 20% time 80% result thing, and traded my computer for a bit of cardboard. I drilled a hole next to the radiator and ran a 76mm flexible hose to the front bumper, and fitted a k&n filter in there.





So far everything seems good, intake noise is much much quieter


Yes I could, but this was easier.

 

You aren't concerned that having a plenum will counteract the harmonic benefits of ITBs unless the plenum volume and shape is meticulously designed for your specific setup? Are you sure the rear ITBs are getting proper flow? Doing it that way does make it considerably easier to keep intake temps down and give a good source for MAP signal but... You should definitely do some dyno runs with is on and off to see the results!

 

I would personally run MUCH longer intake runners. 18"+. You might be surprised.

 

Nah, not that concerned. It's not the most equal flowing design, but I don't think it matters that much (I have dual wideband and EGT sensors to check this). It's a pretty large (102mm) tube with not that much airflow going through it, so probably not that much pressure drop. It doesn't help with MAP, as it doesn't see vaccuum, the aluminium bit is always at ambient pressure. It's like a carburetor hat.

Anyway, MAT temps are now pretty awesome, car drives much better, so for now I''m keeping it


That's really long! Maybe I'll try it!, It's around 14" now, and max power is over 8k, so pretty high for stock internals.



So today was great! , There was this rotary meeting about 80 miles away, so I drove the RX-7 there, did some tuning along the way, got the full load mapping dialed in, it's making pretty good power now. It wants a lot of fuel! Duty cycle with the ID1000's is around 90%, and I lose power and EGT's rise when I lean it out.

Made it to the meeting fine, lot's of nice cars! Did some time attack sessions on this short autocross-like track, only 1st and 2nd gear were used. Not the best track for my car, there's no torque, only top end power, and the turbo 2 transmission sucks at shifting 1-2 all the time at 9000rpm. I hammered on the 9000rpm limiter a lot



Made the trip back as well!, got around 23mpg, which is better than my old RX8 did

 

That sounds AWESOME 7-9,000rpm!

 

I saw you tearing up the track 😎. The sound was good!

 

Thanks! Yeah it's pretty awesome

Put some miles on it last week, no issues. It could do with a longer intake, and the transmission and clutch suck, but I don't think I'm going to do too much about it. Probably better to start tinkering on the 4-rotor engine again

 

Sounds like the better plan

 

I knew this thread was going to be good the moment I saw the machines... I cannot wait to get to the last page...