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Index > Engine/Drivetrain > Thread: 77 repu exaust--the pipe that ends in mid air?
Thread: 77 repu exaust--the pipe that ends in mid air? [' This thread is 2 pages long: (1) 2 ']
repujar


Newbie
Posts: 3
posted April 21, 2002 06:17 PM

77 repu exaust--the pipe that ends in mid air?

What is the purpose of the small exaust pipe that has no muffler or anything attatched. Just inherited a 77 repu I dont know if there is anything supposed to be attatched to this pipe or not. I do know that it is loud because of this. Some of the parts on this may be from an RX7

any replys appreciated

       
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repuguru


Redlining
Posts: 319
posted April 21, 2002 07:03 PM

Its a fresh air return that works with the thremal reactor and the heat exchanger in you exhaust.

       
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repujar


Newbie
Posts: 3
posted April 22, 2002 09:58 PM

Thank you

That explains a lot. Then there should not be a lot of exaust coning out of it should there? there seems to be exaust and no fresh air intake. Should there be a valve or something at the expanded connector near the end of it or somewhere? I dont mind the exaust Varoooooooooooom but my neighbors and others behind me on the freeway likely dont appreciate it. would a hi flow muffler work? please excuse me my truck might be blue but Im greener than a cows teeth in spring.

Thanks repujar

       
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rotarynews


Moderator
Too Many Rotary Websites
Posts: 206
posted April 24, 2002 03:39 PM

For My reference (and yours too)

If you were to get a full exhaust system on the REPU, it'd eliminate that pipe... Header going into a pre-silencer, going into a muffler should be quite enough for most (unless you have an open muffler) Just check your local smog laws before you do this... otherwise you might need to get a cat put on with an air pipe from the air pump... if you live in a smog check free area, go wild :)

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repujar


Newbie
Posts: 3
posted April 24, 2002 08:36 PM

20-year-old smog

Thanks much all.

Smog not a problem---yet. Just recently changed the law. 20 years n older no smog test. I was just concerned about how a change in flow would affect the ports on the block. I do know that the exaust system seems a lot hotter than pistion engines. Thermal reactor accounts for that I guess.

Again thanks,

       
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Tom93R1


Redlining
Posts: 458
posted April 28, 2002 10:10 AM

That pipe is supposed to be there? Weird... When I got my '74 with a mostly dead, all 3 apex seals on rear rotor completely gone, 12A that pipe did nothing but shoot blue flame about 6" out. I thought it was a failed attempt at freeing up the exhaust a little or something. I guess when half of the engine is doing nothing but passing unburned fuel into the exhaust some things don't work as they were intended.
____________


'74 lawn-green
4-port 13b
Weber 48DCO
Racing Beat Header
Magnaflow
resonator/amplifier
really loud!

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repuguru


Redlining
Posts: 319
posted April 28, 2002 12:34 PM

Yes most of the ones I come accross with the exhaust still intact have a tendencey to blow exhaust from the tube.

I have never tried to restore an exhaust system. Most seem to worn out,rusted, or blown from backfiring that something must be replaced.

If absolute power is not a must get an 81-85 RX7 muffler from a junk yard. You'd be surprised how many good ones are out there. Eliminate the heat exchanger and old muffler and replumb from the thermal back thru the RX7 muffler out the back. You can probably do this for less than $100 bucks and be rest assured the muffler will live and be resonably quite.
____________
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

       
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Rob


Newbie
Posts: 3
posted May 03, 2002 12:50 AM

The smaller pipe that ends back by the muffler should only be blowing hot air. The air pump on a stock rotary serves two functions, part is injected into the exhaust via nozzles in the exhaust ports, the rest is used to cool the exhaust reactor. A stock exhaust reactor is like water cooled manifolds on a boat but uses the air to cool. Pulling the air pump will reduce parasitic loss on the engine but you will eventually crack the thermal reactor due to heat build up. A header is the best solution although be sure to use mufflers designed for rotary engines unless you like lots of noise...
____________
Later, Rob

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Klaus43


Rotorhead
Posts: 1259
posted May 08, 2002 12:18 PM

Why mess around?

...just get the header on there & redo everything from there on back! Pre-silenced or not, a straight shot is best, and be sure to maintain whatever you build 'cause that pulse can eventually loosen mounts, etc... do bear in mind very few non-rotary specific mufflers survive for long...and a plugged exhaust system can be damaging to your motor! --K.

       
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Tom93R1


Redlining
Posts: 458
posted May 08, 2002 01:33 PM

Haw big of a difference will a header make for power? I am thinking of getting one for my REPU. I think I may have to stick a high flow cat on and run an air pump to meet emissions, would it be worth getting a header if I need a cat?

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rotarynews


Moderator
Too Many Rotary Websites
Posts: 206
posted May 08, 2002 01:54 PM

Headers

Headers are great for making power higher-up... and they help get you up into the powerband faster... Some say there is no low-down power, I disagree, the torque is still there, but the horsepower has moved the whole band up. If I remember correctly, putting on the header in my 86 RX-7 was like putting a lighter fly wheel on, it reved very fast from down low.. when I had both the 9 lb flywheel and header on, the engine would zip to 5k in no time at all.
____________
*rotarynews.com
*FD3s.net
*mazdarepu.com

The best way to predict the future is to invent it!
-- Tom Matano


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rob


Newbie
Posts: 3
posted May 08, 2002 10:23 PM

To Header or....

When I installed a hearder on my 1974 Rotary PU, the difference was amazing, better low end and peak power. The engine was stock although I'd relieved the air cleaner housing, re-jetted the carb, and had electronic ignition, aftermarket leading coil, used stock leading coil on trailing side. I did end up replacing the pipe used by the original muffler shop with heavy wall pipe at a later date but that was to control the 'ting, ting, ting' noise coming through the pipe. At the time few aftermarket rotary mufflers were available that I could afford so I used a used RX-7 muff with excellent results. Since the engine was stock, i.e., no hardened rotor gears, I stayed below 7500 rpm and the small muffler wasn't a problem.
____________
Later, Rob

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Klaus43


Rotorhead
Posts: 1259
posted May 10, 2002 10:32 AM

A header is the single biggest bang-for-the-buck, best thing every rotary engine needs! Worth it with a cat?--you bet! Make it a high-flow cat, to be sure. Powerband: if more low-end is desired, try assembling your own header with the runners meeting up earlier--this has the effect of moving the onset of power down the RPM range--at the expense of topend... hence the 'long dual primary' setup for ported, higher-RPM power motors...
I've often pondered whether anyone has ever explored an 'expansion chamber' exhaust design for the rotary...would seem to make sense...perhaps such an effect figures into the 'long primary' setup as well...while we're at it: was it Paul Yaw had come up with a header that had 'tabs' sticking into the exhaust ports to smooth out the flow, yeilding better power?
Let's hear it for tuned exhaust! Now, what about tuned intake??? Does the new LeMans car still use varied-length intake tubes? How long before we can benefit from/play with all that? Sign me up!

       
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Tom93R1


Redlining
Posts: 458
posted May 11, 2002 10:57 PM

What headers you guys use? Is there really much of a differenve for rotary engine headers? I see the racing beat runs about $187, are there any better deals out there?
____________


'74 lawn-green
4-port 13b
Weber 48DCO
Racing Beat Header
Magnaflow
resonator/amplifier
really loud!

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Jeff20B


Moderator
Posts: 661
posted May 12, 2002 03:07 AM

Tom, the header on my REPU is well over ten years old. It's the road-race style from Racing Beat. Never get a Pace setter header. They will make you wish you'd gotten RB.

       
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Klaus43


Rotorhead
Posts: 1259
posted May 12, 2002 10:22 AM

...that's what I'm running, too...

...the deal with headers: Fit, durability, function. There may be some fine designs out there other than RB, but it sucketh the one that is large when you find out your new header won't clear the firewall, or the steering linkage; also, the RB headers are made from nice, THICK wall tubing--quieter and built to last--, and if you get the 'road race' version w./ seperate collector, it gives you the option of running a short primary or dual long primary setup, depending on what motor and what level of build and application... definitely order the header specific to your REPU! The rx7 one might not fit! Remember also to get the appropriate block-off plates & plugs, and throw that emissions crap that never worked into the trash, or a box if you're a diehard pack-rat like me... :), K.

       
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Jeff20B


Moderator
Posts: 661
posted May 12, 2002 11:28 AM

I think you're right about the proper header. I think I'll swap in the REPU header with the RX-7 exhaust. I'd like to think that either MT or RB could do that for me.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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Tom93R1


Redlining
Posts: 458
posted May 12, 2002 12:08 PM

So somebody actually makes a REPU header? where can I find this?
____________


'74 lawn-green
4-port 13b
Weber 48DCO
Racing Beat Header
Magnaflow
resonator/amplifier
really loud!

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Tom93R1


Redlining
Posts: 458
posted May 12, 2002 12:12 PM

Never mind, I fond it at Mazdatrix. Is there a difference between the exhaust ports on a 4 port and 6 port 13b? I would assume that header is for the 4 port motor.
____________


'74 lawn-green
4-port 13b
Weber 48DCO
Racing Beat Header
Magnaflow
resonator/amplifier
really loud!

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Klaus43


Rotorhead
Posts: 1259
posted May 12, 2002 05:50 PM

The difference is...

...actuation of the fifth and sixth ports. So, yes, make sure you get the right one for your application! Does Mazdatrix still make their own headers, or are they reselling RB? A sage once said, "When you assume, you make an ass out of you and me"... In any event, proper header exhaust is well worth the price on any rotary.

       
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