brcb7tuner

Whatever you do go 2-1. I had a rb road race header with two separate mufflers and it sounded like a four wheeler. So I bought a new flange and welded a vibrant 2"-21/2" collector with a offset in/out magnaflow muffler and it sounds great and all fits perfectly in the space thats under the passenger seat.

088

iTrader: (9)

There is an old thread floating around the interwebs with hp numbers for various exhausts. Here is one example:

http://www.johnr.com/rx7faq/faq3.html

Based on the reported numbers, the answer seems clear. The problem is that the elusive "+24hp" exhaust doesn't exist any longer (if it ever did). I suspect this is actually a system designed by Rotary Engineering for Mariah, and licensed to HKS for mass production. I asked Jim Hagerty about this. He didn't confirm the story, but did mention:

"HKS USA recently went into bankruptcy and has bailed out of the US market. No source of HKS parts is available in the states. We are currently using the Racing Beat exhaust system."

So maybe we need to expand the question: what vendors (as of today) offer FC exhausts (specifically for n/a's) and how good are they (for a stock or streetported application as the OP indicated)? "Good" meaning HP numbers, sound level, quality of construction, etc.

Racing Beat - yes
HKS - RIP
Mindtrain - RIP
Rotary Engineering - RIP
Greddy - ?
Corksport - ?
A'Pexi single - yes, but I have discouraging dyno data
A'Pexi dual - yes (but no data)
Mazdatrix - no, all I see is RB on their site
Borla - haven't seen any new units for sale
OBX - ?
Pacesetter - ?
AWR - offers header only

what else?

Perhaps someone who attended Seven Stock can chime in. What exhaust vendors showed up, alive and still kicking...?

I'm personally interested in the same application as the OP. I have a Rotary Engineering (RE) exhaust on my racecar, but I'm looking to put something decent (finally) on my street FC as well. Based on dyno results, I haven't come across anything better than the RE. I'm not sure what makes it perform. Is it the Y section (looks stockish in design, but a little larger diameter)? Is it the mufflers (I can't go cutting one open and ruin my only good exhaust)?

I could just get the RB and be done with it. But, I'd like to know what other options are still out there, i.e., new units available for sale.

j9fd3s

iTrader: (3)

on my street FC's ive actually gone the other way. i took a good hard look at the stock parts, and taken a measurement or two.

so the stock system. the exhaust port outlets on the engine are about 48mm, the stock manifold is 50mm and the RB header is 43mm. so the stock port/manifold have an anti reversion property, and when you bolt on the RB header you loose this. the RB pipe size is fine, but it doesn't match the ports well at all on an 86+ 13B.

second the stock exhaust manifold is a 50mm outlet, but on an S5 the inlet to the downpipe is only 43mm! they used 50mm ID pipe, but its welded on the inside. S4 is welded on the outside. so you can either buy the RB downpipe or spend some time with the grinder....

the stock cat back is 55mm and splits into 2 40mm (maybe its 45?) pipes. the HKS is larger and splits into 2x50 mm pipes.

the stock mufflers are baffled, the HKS are straight thru.

my vert is running stock, but ground out to 50mm into an HKS cat back, and it helped, but i'd be surprised if it was a 10hp gain.

i think the good +1 would just be to move to 60mm ID piping, a header that didn't suck and muffler(s) that could flow enough. i tested backpressure in my S4 and it was easy, and very informative, but the S5 doesn't have a spot stock so its not as easy.

spiff-d

On my 87 FC I ran this:



I had no cats or resonators and an OEM manifold. There was a performance gain, and it was noticable but let's face it - it was still slow as *****.

For my 1991 Vert I'll be buying the same system, running 2 3/4 to 3" from the header to the mufflers - no cats, no resonators. I had zero complaints with it and really enjoyed the sound.

Kstout24

iTrader: (1)

I have a large diameter HKS system with a cat delete, it looks nice, sounds great, and performs amazing

Lebel

iTrader: (4)

I have a small streetport on my s4, looking to run single exhaust. I see A'pexi is a good choice. What you guys think?

088

iTrader: (9)

I had the A'pexi GT Spec on a streetported s5 n/a and it lost power vs stock catback, even after fuel tuning. On a previous FC, I ran the A'pexi N1 single, but never tested it at the dyno. They also make a 'dual N1' system; no idea about its performance, however.

GREAZERLOU

iTrader: (2)

wow, lotta opinions! Heres my 2 bits...

Before anything, a streetport cant take full advantage of 55mm EFI throttle bodies! If its gonna be a street car or auto x car, go with 48mm ITBs. A 48mm Weber-style EFI throttle body will outflow a 48mm Weber carburetor (the "recommended" size for a streetport) because of the absence of the venturi system. You basically want the smallest ITB thatll meet the max airflow requirements of your port job so you get the most hp out of it as well as a broad powerband which is good for a street car or small auto x course.

If your going drag racing, or dont care about low end power, start with 50mm ITBs and step them up from there. Thats a lot of air for a streetport. And if you still wanna go bigger, then do so. Just remember that the bigger you go the narrower & "peakier" the powerband gets.

Anyway, that being said, you gotta choose an exhaust configuration...
1. header/collector with single piping back to a single muffler
2. road-race header, dual piping all the way to the back into a single muffler
3. "true-dual" front to back

Ive personally had all 3 setups on a streetport (GSL SE) with a side draft 44mm Mikuni and can tell you that setup #2 made the most power on my car.

I originally started with an RB header/collector with 2.5" piping to a 3" round Ultrafo. Not much power down low but definitely powerful in the mid/upper rpm range and sounded awesome (and loud!).

Then the talk was all about "true duals" so I followed the trend and chopped the collector off my header, ran a second 2.5" pipe to dual 2.5" Dynomax Super Turbos. Power on the bottom end was still bad but I did gain a little up top and it sounded BADASS!!! Thats always been my all-time favorite setup even though the mufflers didnt really last that long.

Then I did some research (bought a copy of "How to Modify Your RX7 and actually READ the original Racing Beat technical manual that I had in my stack of magazines), downsized my piping diameter to 2.25" (even though they recommend 2" piping) and put just one of my 2.5" Super Turbos back on. It was a night and day difference. I had more power down low and in the midrange and about the same power up top. Ever since then ive always been a believer in running that configuration on a stock or streetport motor.

Now, all these setups only had 1 main muffler (2 in the case of my "true dual") and nothing else in betweeen that and the header... SUPER LOUD!!! If you dont mind that then thats my recommendation. You can add more straight-through type mufflers/presilencers/resonators between the header & main muffler if you need it more quiet. Either way, the principles behind tuned length primary pipes/collectors realative to port configuration still apply.

FWIW thats my experience... butt dyno on the streets of Sylmar and the "stop light 500" way back when I was into that kinda thing. Good Luck!!!

Lukas B.

how does it sound? ive been wanting to get one but i dont have 1 grand to spend on just an exhaust

Dak

The RB True Dual setup?
racing beat true duals - YouTube