Andrew7dg

So I was hoping to get this car moving under its own power (1982 gs w 12a) and as I was moving it in the shed the main cat falls off. So looking under the car I wanted to take the down pipe and the smaller cat off and the bolts broke from the exhaust manifold to the down pipe.

Time for a new exhaust....

Looking at rb website gives all sorts of options of full or partial kits. Just for the header though they want $288. Full exhaust $800

However they had another option that intrigued me. The disassembled rr headers for only $150. I am a welder/fabricator at my work and could save a little money by going with this kit however I don't know how to design the rest as this design is a dual design in contrast to the street able header. I am trying to budget money for other stuff for the car and this was a little unexpected cost.

What would people recommend to do after the dual header? I do plan to do some racing and auto cross so it shouldn't be designed too loud.

Also what are people's opinions on header wrap?

Cookboy

iTrader: (10)

Do plan to do much street driving? I just got rid of a cobbled together system which was quieter and to my mind sounded better than the RB long primary system I now have. It was the RB header, then RB presilencer, then a 2" Magnapack where the midpipe was with a 2.5" single in dual out Borla pro XS. The borla and Magnaflow pieces were 165.00 or so combined on amazon. The stock mazda tips fit right in the borla, it looked almost stock.
For best performance the long primary is best, but obviously will be more money.

NCross

iTrader: (18)

I would use the dual pipe RB pieces to weld your own together. You want to ad 2-3 inches of straight piping straight out of the engine before it bends. Then Id probably run your long piping to a RB universal silencer on each run and and finally end with a universal RB muffler with a dumpy tip. It will be a hair louder than a standard Power Pulse single exhaust system, but will have a great sound and more power.

j9fd3s

iTrader: (3)

you have many different options for an exhaust. the traditional favorite is the long primary system, where the two header tubes are joined around the rear axle, about 90-120" pipe length.

its competition is the short system, 24-32".

the short system will outpower the long by a couple percent, usually, but the long system makes a lot more low end and midrange.

if you can weld, get the header kit.

for the middle bit, RB actually sells 2" thickwall pipe for a good price. the thickwall pipe help keeps the noise down a bit.

and if you're lazy, just connect it to this Power Pulse RX-7 Muffler for 81-82 RX-7 - Racing Beat and call it done.

project7s

iTrader: (5)

Hmmm I didn't know the short system made more power, I always thought it was the other way around?

Also any idea of where to get a stainless dumpy tip like the aussies use?

Andrew7dg

Rotary Tech Tips: Exhaust System Configurations

Here is RB explanation on the long vs short

Here is the mid pipe

Street Port Center Section for 79-85 RX-7 - Racing Beat

But what I don't get is the tail section. It goes to two 2" (from the midpipe) to two 1.75" Tail pipe?

This seems mis matched

j9fd3s

iTrader: (3)

it is, but the further back in the system, the less it matters. or if you like, the further back in the system the less diameter you need

Jeff20B

iTrader: (13)

Because it cools down (contracts) and you need smaller pipes back there to keep velocity up. The way RB did it is correct but I would have prefered a smoother transition.

Andrew7dg

Ahhh.. The 1.75 is correct

So if I were designing my own system, around the axles area drop the size of the pipe to 1.75. I could smooth out the transition a little at the end of the mid section instead of a sudden flange transition.

j9fd3s

iTrader: (3)

or you could just leave it 2"... not very important either way

Jeff20B

iTrader: (13)

Yeah, it's 11 gauge thickwall 2" so that's 1.75"ID. The powerpulse muffler tubes are actually 14 gauge 1.6" (1.5"ID) before they collect into a single 2.375" (2.25"ID) that is maybe 16 gauge.

79RX7GUY

I pieced together my exhaust from a NOS pacesetter header I found (basically the same as the RB race header). Then had a local exhaust shop bend some heavy gauge 2" pipe back to a RB streetport muffler (the dual inlet one). I run it on the street daily in the summer and have never been bothered by the cops about it. Its loud enough to enjoy the sound of the 12A but not loud enough to be annoying or get me in trouble. Noticed a considerable difference in top end pull too!

Jeff20B

iTrader: (13)

I don't know about that for high RPM but yes the low end is undeniable. I've tried it both ways with superchargers and NA. Actually several ways. My findings are that a long primary beats a short collected every time. Of course no dyno to prove it, but the seat of pants says the long primary wins.

Let's see, I've tried short collected collecting into three sizes: 2", 2.5" and 3" across several platforms and engines. Then I tried custom long primaries collecting at 2.5" and 3", and also RB's long primary which collects at 2.375" which is basically the same ID as RB's thickwall 2.5" as they both have a 2.25" ID. The long primary wins every time.

By the way, the long primary collecting at 3" was on a freind's REPU with a 7" Camden. It didn't work that well - was noisy and didn't seem to enhance low end torque over the crappy manifold dumping into 3" it had before (some shop out in Spokane did these Obamanations of exhaust back in the 90s or early 80s I think). Same volume (noise) level as before too. Just sounded slightly like more character vs the dumb loud drone of the manifold. Not recommended.

I've tested long primaries and short collecteds in REPUs where a loss of low end torque is noticible, and in 1st gens. I even tried short collected 3" vs long primary 2.5" on the 20B and the long primary won. That was three RB thickwall pipes collecting into a dinky 2.5" and it was more powerful than the short collected 3". I had the same experience on a 13B with a Camden where the short collected 3" was a dog but the long primary was awesome (same exact components actually - this 3" exhaust has been around - now it's on my turbo where 3" makes sense).

What does that tell you? Tells me all these poor guys doing a short collected 3" based on flawed logic/info are leaving some (a lot of) power on the table. Do they have the time/resorces to swap to a long primary for testing and comparisons? Probably not.

But as they say, every engine is different. lol

I know the requirements for a peripheral port are going to be different from a side port, but most guys here aren't daily driving a p-port so... GO long primary!

j9fd3s

iTrader: (3)

[QUOTE=Jeff20B;11832618 the seat of pants says the long primary wins.[/QUOTE]

i agree there. i had both the long and the short system on my GSL-SE and power up top was really close, but the long system had so much more bottom end, it was an easy choice.

the short system felt like it made a couple more hp maybe 500rpm higher, but the long system was like 10-15 hp more at 3000rpm, easy choice.

i dunno about the P port, right now its got a long system too!

t_g_farrell

iTrader: (1)

I went from my old RE short primary to the RB SP (long primary) a few years ago and the power feels better
across the entire RPM range. Top end still seems to see a limit at around 7K but I suspect thats the stock port
limiting me there.

I also now switched to my fat nikki which has yielded even more low rpm grunt and it revs up to 8K really fast
compared to the Dell I was running before. I need to get this dynoed again to compare it to the old RE setup and
the Dell. It would be interesting to see the curve for torque now.