I would like to make my exhaust as light as possible while keeping the volume down. I was thinking about an exhaust that exits the passenger side in front of the rear wheel. Does anybody have a suggestion for a single muffler that will not kill HP while also "muffling"?
Second question: Can anybody tell me if the Bilsteins for an FC are rebuildable? DO they have a gland nut, or are they welded or crimped? It is important that this is clarified due to the new Chumpcar rules.
Thanks!
Rob R.
What decibel rating do you need to meet?
I suggest you call Bilstein on the second question. I suspect they changed over time. The Bilsteins for the Miata did iirc...
I am struggling to think of how to make a "quiet" non-turbocharged RX-7 with an exhaust that short. I'm just not sure how the muffler would fit anywhere.
You can't shut up an na rx7 in that distance without strangling it.
I'm not sure if you knew, but the 1986-1988 2nd gen NA RX-7 uses exhaust backpressure to open the 5th and 6th ports. If you put on a free flowing exhaust you run the risk of not having enough back pressure to open the ports and your engine will choke around 4krpms.
The 1989-1991 2nd Gen RX-7 uses the smog pump to achieve the same thing. So exhaust backpressure is a non issue there...
For the early years you have two options: Remove the actuators and safety wire the ports open. Supposedly this kills your low end torque, but my butt dyno never noticed and as you're going to be running it at 10/10ths in a lemons race I doubt you'll be low enough in the RPM range to bother.
The other option (and this could go for both early and late years) is rotary resurrections "Electric port conversion"
On my 1986, I used racing beat headers, a corksport pre-silencer (cat elimination) for a 1988-1991, and an Apexi G3 cat-back (I don't think it's offered anymore) with something like 3-in piping. It was heavier than crap and still pretty loud when the baffle was removed.
On the bright side, I can tell you it was pretty "unrestrictive" as far as flow goes. The nut my engine swallowed was found in the tip of the exhaust pipe (wedged in the removable baffle).
In reply to wvumtnbkr:
Not sure what gland nut is but I can take a picture of mine for you if you like. Just point me in the right direction.
Basically, does the top or bottom of the strut look like you could disassemble the internals with a tool (even if it is a specialized tool)?
Secondly, what WOULD you folks recommend to loose weight in the exhaust?
The exhaust is currently a header going to a borla catback exhaust. I would like to make the exhaust a single for weight reasons.
In other words, I need to stay less than 86 dB and loose some weight without loosing HP.
Yes, I am aware of the port issue (they are wired open because the car never sees less than 4K rpm anyway).
Thanks!
Rob R.
What about one of those mugen style twin loop mufflers? I don't know if it could deal with the heat.
A turbo should quiet it down a bunch. Aaron Cake had a hugely long writeup about bolting an s4 turbo to an s4 NA engine, and I bet it wouldn't eat your budget too much. After that maybe some sort of cherry bomb stuffed in the tunnel? (unless you can move that Borla muffler way forward to eliminate piping)
we ran a turbo before. It is not so good with fuel and a bit temperamental. We will not be going back for now.
The problem with the borla is that it is dual exhaust. Anybody know what diameter piping and what muffler I could use (single) to make a single exhaust?
wvumtnbkr wrote: Basically, does the top or bottom of the strut look like you could disassemble the internals with a tool (even if it is a specialized tool)? Secondly, what WOULD you folks recommend to loose weight in the exhaust? The exhaust is currently a header going to a borla catback exhaust. I would like to make the exhaust a single for weight reasons. In other words, I need to stay less than 86 dB and loose some weight without loosing HP. Yes, I am aware of the port issue (they are wired open because the car never sees less than 4K rpm anyway). Thanks! Rob R.
ohhh that I don't know. I think they can rebuild it but I don't think I can rebuild it kind of deal...
Titanium exhaust is your answer, but ask your wallet first. A friend of mine ran an aluminum one on his rx8 STX car and it would not hold up. 89DB is hard with 1 muffler. I'm was about 97db with 1 muffler, now I have a resonator.
Estey recommended me the morosso spiral flow, worked real well, good compactness and definitely brought the Dbs down. Hard to tell on the inside though, exterior wise is noticeable.
Also if you got them wired open just remove them and the whole rod/actuator system then jb weld a dime on the hole where the rods would bolt to on the LIM, fits perfectly. Or puddy them up for better/smooth flow if you want to keep them in.
You're kind of stuck on the header part because they are all heavy as sin and thick metal for the heat they generate, especially in your conditions.
This is a dumb idea but what about running a turbo? don't hook it up to anything, just let it act as a muffler and make cool turbo noises.
Fabricate a titanium exhaust that's modeled after the racing beat exhaust? I know the racing beat flows well and is still pretty quiet. Aside from that route I'm not sure how you will quiet the rotary and add lightness.
I might need to experiment with this a bit...
P.S. I forgot, the sleeves are removed. JB weld on the LIM too.
crap. I want a lightweight exhuast in the worst way. (or lighter anyway).
titanium is your answer then, its the worst way but only worst way because its so damn expensive and finding a welder who will do it might be a challenge.
Just think of a long heavy exhaust as a performance benefit, it's part of the engine and you need it if you want to make a lot of power.
Knurled wrote: Just think of a long heavy exhaust as a performance benefit, it's part of the engine and you need it if you want to make a lot of power.
what he said.
i think you are barking up the wrong tree with your exhaust crusade.
It's a Rotary. Lightweight and simple exhaust and still meeting noise requirements at most tracks are generally mutually exclusive when dealing wi off the shelf parts.
The options are to find other areas in the car to lose weight (hole saws and dimple/flanging tools can help a lot, check out Loosecannon's MG build for example), swap the rotary out for something lime a V6/V8 which can be quieted with some simple exhaust solutions or spend a ton of money on titanium and making it all by hand, not too mention pissing all over the cheap endurance racing series rules you might be running with.
Can always try a turn down but a rotary always wants to be heard, May want to look elsewhere and no offence but the easiest place to loose weight is from the driver.
JtspellS wrote: Can always try a turn down but a rotary always wants to be heard, May want to look elsewhere and no offence but the easiest place to loose weight is from the driver.
Ouch, that last bit hurts 
To clarify, I think we are in the short rows of lightening the car. I just felt that a dual exhuast is heavy and not necessary. Apparently, it is somewhat necessary!
Exhuasts are "free" according to the rules.
No swaps. I like the reliability of the rotary.
What about the glass? Sunroof delete (if equipped) what's the rule on interior?
it has a windshield (becuase of wipers being necessary for alot of races).
No other glass. Lexan rear hatch. aluminum hood. Doors gutted and all brackets cut off. All "2 ply" steel in the back of the car removed down to "1 ply".
No dash board. No HVAC systems. No power steering. 1 race seat and a cage.
Sunroof and all interior materials removed, aluminum panel in it's place.
Tail lights and marker lights and headlights removed. LED taillights (trailer lights) in place of stop lights.
Hmmmmm, drop the subframe and grind down excess? Possibly think about heim joints in place of tie rods? Weigh upper and lower suspension bits between aftermarket?
I mean you can go to extremes and cut your rotors to absolute minimum on all corners as well, guess it depends how extreme you want to get, you already are over half way there.
I don't know about rotaries, but how about running a cat? When I had my Civic with a waaayyyy too loud exhaust, putting a catalytic converter quieted it down noticeably. Your easy weight savings seem to be mostly done.
i take it this is frowned upon?
Rotaries don't like catalytic converters. Well, let me clarify. Cats rob power from rotaries, and using the wrong cat can result in a melted/clogged cat that will rob power and kill your engine.
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