Race exhausts
 

I'm making an exhaust for my track day/autocross FC to replace my awesome but heavy Racingbeat REV-TII...

(build thread: https://www.rx7club.com/build-thread...turbo-1031251/)

National autocross events have a 100 dB limit so I wanted to get everyone's experience with turbo exhausts and where the line between too loud and too heavy is drawn... and making it handle the heat from a rotary

currently my plan is to run a 3" downpipe to a Burns Stainless 2 stage muffler where the cat used to be and then a 3" all the way to the back with a 90* downturn (that's rotatable to I can point it away from sound meters in a pinch :p: )

what's everyone else running?

i've found that the revII center muffler works really well, and so you may get the best bang for the buck, by just replacing the "cat back" portion with a 3" single and muffler of your choice.

basically with the RB presilencer and any rear muffler you should be under 100db.

its apples to oranges, but on the P port i'm running a borla rear muffler, and its under 103db when its clear and over 103db if there is a cloud.

The rev-tii center resonator is almost 20 lbs... :-/

I'm swapping out the downpipe already so I'd rather keep the rb system whole and sell it...

There is a muffler offer to the IMCA guys called the 95db muffler- it is straight thru, no glass to burn out, 3" in/out, and weighs about 6 lbs, basically they took 2 header collectors and butted them together.
smileysracing.com/shopping/productDetails.aspx?i=116376&c=1294

Gonna try this on my turboed GSLSE, but I have heard before and after on v8 dirt cars. Night and day difference, and very mellow. Not like a cheap glass pack at all

Hmm might be 95 on a V8 or a Turbo Rotary but you put that on a P-port or really any NA rotary and i bet we are right back up above 100 again.

Honestly what knocked the noise down the most on my race car was adding a curved tailpipe out the muffler that angled the exhaust down towards the road at about a 40° angle. It may not look all ricercool, but it gets the job done.

I checked HppRX7's build thread (national auto-x winning SSM FD) and it looks like he's only running a 6"x14" magnaflow and a downturn.

https://www.rx7club.com/build-thread...build-1013942/

So a dual stage burns muffler of roughly the same size and a down turn should be more than enough I think.

On my track only FD I have been using a Borla XR-1 muffler 3in/3out (I think the 40944). My build is a street port to 3574 Aspec turbo kit (short runner, wastegate reconnect with downpipe). The down pipe is 3" (stainless) as is the remaining exhaust piping. I also use a ~60° downturn on a vband. I usually am in the 97 to 98 db range.

Guy

Here is my experience-

I corner weighed my car with RB REV TII and then again after I put on a very light 1mm thick 90mm (3 1/2") turbo back with just one (heavy) Vibrant stealth muffler.

It only saved 26Lbs from the very bottom of the car and it was WAAAAAY louder.

When I ran the RB I used U clamps instead of exhaust donuts and that kept it from swinging into the tires cornering.

The 90mm did get full boost several hundred RPM sooner on my stock hybrid turbo, so if I were replacing the RB I would go bigger diameter than 3".

Two cheap Ebay 3" single turbo backs could be modified into a turbo back dual set up. That is what I would do next time.

I just acquired a KSP/Attain divided wastegate 3" downpipe... so I want to keep that, I'm not sure how much benefit going 3.5" after the downpipe would get me... I might consider it though. it probably can't hurt :p:

According to a forum post the REV-TII weighs 73.1 lbs:
Downpipe: 5.7
Resonator: 17.8
Y-Pipe: 7.4
Muffler (x2): 42.2
Total: 73.1

I have a hard time believing you could only shave 26 lbs by getting rid of two 20 lb mufflers, unless the vibrant muffler was really heavy.

but its in the middle, and as low as you can put it in the car. scientifical testing reveals that better weight distribution > lighter.*

on the P port, i have a 3" band clamp, and i've put everything i can think of on the tailpipe to make it neighbor friendly*2, and adding a second 3" straight through muffler doesn't do much, the turn down basically just directs noise, the thing that helps the most is changing diameter.

i have a dual tip tip thing, and it goes from typical NA with a 3" exhaust loud, to streetable, without affecting drivability. i borrowed my friends buttplug at the track, and its just a 3" pipe with a flat plate on the end with a hole in it, and the engine didn't like that.

so for a turbo car, you may be able to have like a 2.5" tip on the exhaust, and get it quiet.


*we ran spec E30, and those are like a ~1000lbs engine in a danish cookie tin, so they are front heavy. we added ~200lbs of ballast in the trunk to get it up to legal race weight, laptimes dropped.

*2, i drove it up and down the street before sevenstock a couple years ago, and my neighbor walked over and told me it was loud enough to wake the dead. at 2pm the only dead people that are sleeping are vampires…. actually she asked if i had a muffler on it at all, and made a funny face when i told her it had 3

I'm going to have a v-band close to the tip so I can rotate the 90* tip away from microphones so I'll experiment with other types of tips for street driving.

I'm planning on putting the muffler where the RB resonator is for weight distribution.

I have one of the street mufflers from vibrant on the back. Single 3 in/ dual 3 out in flat black. Sounded great when I put it on. 1500 miles later, got real loud. Called vibrant and here is how tht conversation went...

Me- Hi, I installed one of your mufflers one my car, and now it is no longer really a muffler.

Them- oh, I bet you have it on a rotary, right...?

Me- yeah, but it's at the very back of the car. Sounded perfect at first...

Them- yeah, well, um, we never got a muffler to last more than a month on any rotary. If you would like, we can sell you another for a bit less, but it will most likely do the same thing.

Me- "click"

If this were a race application and not street, I would pony up for a Coast Fabrication race muffler. At least then I could repack it in about 10 minutes. We used them on Formula Atlantic and Porsche cup cars. Worked great. Let them run without packing till some one bitches, then you have a choice of stainless mesh or the fiber mat. The fiber was quieter but only lasted for about 2 races

Yeah, that's what I'm getting. I'll get whatever is cheaper between them and burns (They make the burns mufflers and they're close to the same prices). I have a buddy that might have a dealer account with burns...

they actually have a 3rd packing that's semi-unadvertised that they made just for rotaries. But the guy at burns says it doesn't muffle as well, I'm going to start off with the SS Scrubble and repack it with the rotary stuff if I need to later.

This is exactly the same experience I have had with my car with its 3" pipe from the collector on back going through a 3" in out Borla. What I did to make it liveable is to add a Supertrapp tip on the very end of the exhaust for when I am at home and want to load the car. I can adjust the plates to make it quieter and it does do a decent job, but the car is still freakin' loud. I tried it on track once as I was in a hurry to go out and play and the added restriction meant that I couldn't really hear the exhaust all the time, but it did knock about a 1,000 rpm of the top end of the power band.

I am going to try keeping the Borla this year and adding the previously talked about Smiley 95 db inserts and see what that does. I have been racing this car for almost 17 years and have noticed a marked reduction in hearing, even though I use molded earplugs and racers tape over my ears when I race the car.

However, the RX7 is nothing compared to the ex-WC Cougar I have. That V6 with its 13:1 compression, headers and Moroso Spiral muffler is so loud under load that you can hear it from 500 yards away as its really really ear bleeding loud.

Here is a really crappy video of the car and you can see or should I say hear.


What did they just say????

Eric

lol, that's the joke

"what did the rotary racer say to the other rotary racer?"

"what?"

My Vibrant stealth is SS packed and very heavy, but even so it only feels a bit heavier than the RB RevTII midpipe.

My friends do say at night they see the car does shoot little balls of burning steel out that bounce down the road, so I know it won't last forever...but the upside is it should be getting lighter.

I just acquired a KSP/Attain divided wastegate 3" downpipe

Just saw that piece on your build thread. Very nice looking, I would build off that as well since you have it and its a bad ass part.

I did the divorced stock ported wastegate for a while but mine was open air vented with a 2" downturn after I found a separate 2" downpipe/muffler I had made for it was too restrictive.

Running the stock WG actuator and open vented WG I really noticed how weak the WG spring was and gets pushed open easily by exhaust manifold pressure.

I hope you will like what the new HKS actuator does for your boost response if you didn't already have a helper spring on the stock actuator.

Yup- the Stealth 3" in/ dual 3" out flat black is on the back of my car. It was great when we first fired it up. Looked almost stock, sounded real mellow. That went out the window in a hurry.

Funny this about a 6 port, you pull the aux sleeves, and it wants to sound ported, ie loud!

Exhaust is done... and it's pretty loud :p: I have some pretty significant exhaust leaks I think (probably where my EGT probes thread into my exhaust manifold)

I couldn't fit the muffler in the middle where I wanted it (it would have hung down a lot and gotten bashed up by speed bumps) but it's only 6 lbs so it shouldn't bee bad where it is. I hung it closer to the gas tank so it wouldn't swing into the tire I have about an inch of clearance between it and the heat shield on the tire side.

I haven't weighed it yet, but it felt like it should be pretty light:

https://lh5.googleusercontent.com/-C..._171143094.jpg

Looks good, nice welds too

update:

weighed the exhaust tonight.

ceramic coated divorced wastegate downpipe is 11.6 lbs.
the rest of the exhaust is 20.2 lbs.

totaling 31.8 lbs. over 41 lbs lighter than my old 3" racing beat exhaust. :)