4-Rotor FC Build
Senior Member
Joined: Apr 2007
Posts: 308
Likes: 4
From: WA state
there is a lot of noise from the intake too, i fired mine up with no air cleaner and the neighbor came downstairs holding his head.
exhaust is a weird topic, if you looked at the 787B it has nothing fancy, its just 4 equal length pipes into 3" with a small straight thru muffler. its pretty quiet for a race car too. pipes are in the 500mm range, but that's by eye.
theoretically the 4 rotor is quieter than the 2 rotor just because there are less pulsations in the exhaust.
good luck! after finding a header length mine likes, its muffler shopping time
exhaust is a weird topic, if you looked at the 787B it has nothing fancy, its just 4 equal length pipes into 3" with a small straight thru muffler. its pretty quiet for a race car too. pipes are in the 500mm range, but that's by eye.
theoretically the 4 rotor is quieter than the 2 rotor just because there are less pulsations in the exhaust.
good luck! after finding a header length mine likes, its muffler shopping time
Its a glorious sound to behold too!!!!!!
AWESOME BUILD!!!!! Sub'd!!
there is a lot of noise from the intake too, i fired mine up with no air cleaner and the neighbor came downstairs holding his head.
exhaust is a weird topic, if you looked at the 787B it has nothing fancy, its just 4 equal length pipes into 3" with a small straight thru muffler. its pretty quiet for a race car too. pipes are in the 500mm range, but that's by eye.
theoretically the 4 rotor is quieter than the 2 rotor just because there are less pulsations in the exhaust.
good luck! after finding a header length mine likes, its muffler shopping time
exhaust is a weird topic, if you looked at the 787B it has nothing fancy, its just 4 equal length pipes into 3" with a small straight thru muffler. its pretty quiet for a race car too. pipes are in the 500mm range, but that's by eye.
theoretically the 4 rotor is quieter than the 2 rotor just because there are less pulsations in the exhaust.
good luck! after finding a header length mine likes, its muffler shopping time
Thread Starter
Joined: Oct 2010
Posts: 605
Likes: 13
From: The Netherlands
I agree, if 4-rotors didn't sound so cool I probably wouldn't be building one 
Anyway there has been some small progress, I've been busy with some side projects but managed to do a little progress.
The middle stationairy gear is coming along ok, the gears are fitted in the coupling piece and the oiling channels have been drilled.
Looks like a small and easy part to fabricate, but oh boy it isn't. It's so hard to keep all tolerances and dimensions in check. Best thing would be to fabricate a new one-piece stationairy gear out of billet material but I don't have the equipment to do so. This will work though.
Also started modifying the center iron. I removed the oil filler neck and machined part of the topside of the iron flat. There is a casting hole which I machined out, there will be a hollow tube here that supply's oil to the center stationairy gear.
Then I sealed off the oil filler neck hole and made an insert that fits into the iron. A threaded hole will be cut in this insert at an angle to hold the hollow oiling tube. The insert is still pretty large but it will be machined down. It's held in place by the pressfit, some loctide and 2 small welds.
Anyway there has been some small progress, I've been busy with some side projects but managed to do a little progress.
The middle stationairy gear is coming along ok, the gears are fitted in the coupling piece and the oiling channels have been drilled.
Looks like a small and easy part to fabricate, but oh boy it isn't. It's so hard to keep all tolerances and dimensions in check. Best thing would be to fabricate a new one-piece stationairy gear out of billet material but I don't have the equipment to do so. This will work though.
Also started modifying the center iron. I removed the oil filler neck and machined part of the topside of the iron flat. There is a casting hole which I machined out, there will be a hollow tube here that supply's oil to the center stationairy gear.
Then I sealed off the oil filler neck hole and made an insert that fits into the iron. A threaded hole will be cut in this insert at an angle to hold the hollow oiling tube. The insert is still pretty large but it will be machined down. It's held in place by the pressfit, some loctide and 2 small welds.
Joined: Mar 2001
Posts: 31,835
Likes: 3,233
From: https://www2.mazda.com/en/100th/
Ummm, how do u figure that the 787B or any 4 rotor is QUIETER than a 2 rotor?! Have u HEARD any of the numerous vids or heard LIVE?! I've heard the BMI Racing 4 rotor Rx-8, LIVE and lemme tell ya its DEAFENING!!! U literally cannot hear ANY of the cars on track @ ALL!! Up close or from the grandstands!!!! I know BMI bumped their exhaust up to a massive 4.5" and gained 50+ HP!!
Its a glorious sound to behold too!!!!!!
AWESOME BUILD!!!!! Sub'd!!
Its a glorious sound to behold too!!!!!!
AWESOME BUILD!!!!! Sub'd!!
this year they actually RACED the 787's and its not any louder than the Jaguars.
the 4 rotors do sound awesome though...
and i tried to put my fist in the 787B's tail pipe, and it doesn't fit, its 80-85mm tops. which is a lot smaller than i would have thought
i've seen/heard the BMI car too, its WAY louder than the 787, and it doesn't sound very good either IMO.
they have brought the 787B and all the other toys to the montery historics since 2001, and they go to sevenstock too, so i've heard em all on track together a lot actually.
this year they actually RACED the 787's and its not any louder than the Jaguars.
the 4 rotors do sound awesome though...
and i tried to put my fist in the 787B's tail pipe, and it doesn't fit, its 80-85mm tops. which is a lot smaller than i would have thought
i've seen/heard the BMI car too, its WAY louder than the 787, and it doesn't sound very good either IMO.
this year they actually RACED the 787's and its not any louder than the Jaguars.
the 4 rotors do sound awesome though...
and i tried to put my fist in the 787B's tail pipe, and it doesn't fit, its 80-85mm tops. which is a lot smaller than i would have thought
i've seen/heard the BMI car too, its WAY louder than the 787, and it doesn't sound very good either IMO.
Thread Starter
Joined: Oct 2010
Posts: 605
Likes: 13
From: The Netherlands
Fiddled some more with the center stat gear today, finally happy with the result
Just a quick check of the gear backlash, nice even backlash all the way round. I really really need to clean my rotors though
Also started on machining the e-shaft, doesn't look all bling yet but wait and see. Expect some more updates on this soon.
I used stainless 316 filler.
The insert is high grade c45 steel which is crappy to weld, and the cast iron is even worse so I'm not even going to bother with a normal filler material, I'd get a porous weld for sure. I found that stainless wire doesn't get porous as easily. It's still not a very strong weld but will do.
Just a quick check of the gear backlash, nice even backlash all the way round. I really really need to clean my rotors though
Also started on machining the e-shaft, doesn't look all bling yet but wait and see. Expect some more updates on this soon.
The insert is high grade c45 steel which is crappy to weld, and the cast iron is even worse so I'm not even going to bother with a normal filler material, I'd get a porous weld for sure. I found that stainless wire doesn't get porous as easily. It's still not a very strong weld but will do.
http://www.pulseperformance.co.nz/in...p?page=product
Last edited by RotaryEvolution; Dec 5, 2011 at 09:38 AM.
Thread Starter
Joined: Oct 2010
Posts: 605
Likes: 13
From: The Netherlands
Worked on the e-shaft all evening, with nothing to show for it. 
I'm having difficulties machining the e-shaft. Turns out you need mad skills to make a precision e-shaft with old manual machines, who could've guessed
I'll get it right though, but it's a steep learning curve for sure, I normally don't do this sort of jobs.
The problem was when machining the bearing surface for the #3 rotor the shaft would bend a bit when it was being machined. This has to do with the way it's mounted in the lathe. I tried my best by machining it at low rpm's and not tightening the 2 centers together too much but It still was a bit off. It's ok if it's not 100% accurate because the shaft will be ground but if it's off by too much the grinding shop won't be able to grind it to stock size. Then you'll have to use oversized bearings, which I don't think exist for a rotary. I ended up making a fixture to measure the exact stroke of the shaft and straightening it. It's fine now but I need to figure out how to machine the #4 rotor bearing surface. That one can't be straightened.
I think that $13000 is worth every penny If I asked an normal hourly wage my e-shaft and bits would probably be just as expensive.
I'm having difficulties machining the e-shaft. Turns out you need mad skills to make a precision e-shaft with old manual machines, who could've guessed
I'll get it right though, but it's a steep learning curve for sure, I normally don't do this sort of jobs.
The problem was when machining the bearing surface for the #3 rotor the shaft would bend a bit when it was being machined. This has to do with the way it's mounted in the lathe. I tried my best by machining it at low rpm's and not tightening the 2 centers together too much but It still was a bit off. It's ok if it's not 100% accurate because the shaft will be ground but if it's off by too much the grinding shop won't be able to grind it to stock size. Then you'll have to use oversized bearings, which I don't think exist for a rotary. I ended up making a fixture to measure the exact stroke of the shaft and straightening it. It's fine now but I need to figure out how to machine the #4 rotor bearing surface. That one can't be straightened.
there's already companies that sell 4 rotors, and in your local country much closer. would be nice if they were affordable for most people but i doubt that's going to happen. you can probably get one setup and running for about a minimum of $25k while doing a lot of the work yourself. IIRC PPRE sells the kit for $13000.
http://www.pulseperformance.co.nz/in...p?page=product
http://www.pulseperformance.co.nz/in...p?page=product
If I asked an normal hourly wage my e-shaft and bits would probably be just as expensive.