Qingdao

iTrader: (3)

With my engine under control (finally). I've decided its time to trash the 3" drain pipe and get a good exhaust system. A system that will just bolt together. Not that I am apposed to welding... I'm just lazy and my welds are BEUTIFUL... they work. I want a BEUTIFUL thing

I want to do the RB setup, but for the price of the products I don't want to order the wrong thing.

I already have the "streetable headers" seen here...
RX7 1975-1985: Exhaust - Headers: Streetable Header - 81-85 RX-7 13B 4PT -



One of my questions is which pre silencer should I get?

I am running the RB holly intake manifold so I don't need the 6th port actuators from the exhaust, but I am hesitant to get one of the 12A presilencers because I'm concerned they will not bolt together.


My second question is do I need a catalitc converter "test pipe" or some kind of strait pipe to go in between anything? Or does the pre silencer bolt from the headers and also to the power pulse muffler I plan on getting?


This is for the S model SA22c chasis BTW.

Qingdao

iTrader: (3)

Wait... I think I just answered my second question....

In the complete system description on the RB site it says you need to use your stock conecting pipe...

DAMN I'm gonna have to weld...

Jeff20B

iTrader: (13)

Can I stop you right there?

Many rotorheads, including myself and rotarygod, have discovered that any time you do a "long primary" exhaust on a rotary, you gain a lot of low end torque and high end power compared with any short primary. rotarygod was quoted as saying (I'm paraphrasing) "when I went from a long primary to a short collected system, I lost power everywhere". I too have experienced this twice.

Specifically in the blue car when I swapped from an RB classic "streetport" (long primary) exhaust over to a collected system using the RB collected header you posted above, yeah I lost power everywhere. It used to pull hard up past 7k with the race prepped Nikki on the long primary, but then stopped pulling at 6500 with the short collected system. Then I swapped in a stock carb and it once again was able to pull up to 7k albeit at a slower rate. In other words the bigger carb wanted the bigger exhaust while the smaller carb is ok with the smaller exhaust. And smaller power is the result. The smaller exhaust bascially doesn't run out of breath quite as soon in the RPM range when it got the smaller carb, but the bigger carb quickly caused the exhaust to become a bottleneck by 6500. Does that explanation make sense?

This next story is about an S4 NA engine that went into the red REPU first for test running, then went into the white REPU. The red one had a long primary and had excellent low end torque. I was quite impressed knowing that all 6 ports were open all the time as it was a carbed setup. Plenty of power everywhere! But it lost all power everywhere when I swapped it into the other REPU which had a single pipe exhaust system. To make matters worse, it also had a typical R5 13B exhaust manifold which looks identical to any 81-83 FB manifold, just with a 13cm stud hole spacing instead of the 12A 12cm spacing. This exhaust used to have an RB collected 2" REPU header a while back, and I seem to recal it was still too small back then too as it just didn't have the wow factor like the current long primary in the red truck does.

Exhaust plays a HUGE role in rotary engine behavior. Much bigger than I imagined it would. You have to get it right for it to work right. Any idiot can build a loud exhaut on a rotary as the engines are inherantly noisy, but it takes some careful planning to create a quiet exhaust that also flows a lot, and I believe... no I know a long primary with a proper final muffler is ther answer.

Believe me when I say that collected header of yours with its 2" outlet is hurting power. At the very least chop it off and add a 2.5" collector like the FC headers. By the way I threw one of those FC headers, modified to fit, in the GLC and now I wish I'd gone long primary in it. Oh well. When the Magnaflow being used as a presilencer croaks, and it will this close to the engine, I'll go long primary with two custom made 2" core presilencers set side by side under the passenger seat area. The primaries will run the entire length of the center section, corssong over in the middle and collect right in front of the mid muffler which sits just in front of the axle housing. I have to use a mid muffler as there is not enough room for a big muffler after the rearend, just another medium sized one. So technically it would be more of a medium primary, as the car is really short, but you do what you can.

By the way, a long primary exhaust is louder than a short primary. Take my REPU for example. It has two mufflers after the long primary center section. Again because of the noise, but this time it ended up really quiet. If I had to do it all over again, I'd have splurged on a real RB powerpulse muffler installed after the rearend and just the two presilencers in the center section. It would be a truly long primary exhaust. The RB powerpulse is fully capable of quieting things down without need of a second main muffler.

So whatever you do, be prepared for a little more noise if you go long primary, but it's not much more. I had way more noise from a 3" drain pipe exhaust in the blue car with a short collected header than I did from the REPU's long primary when it only had one main muffler, before I added the second one.

Since you're gonna have to weld anyway, and were planning on buying a presilencer? You said? Go for at least a short collected 2.5" system which uses the RB 2.5" presilencer. But that is kind of a lot of money in my opinion. I'd rather buy the materials to fab up two 2" presilencers with 4" shells and stagger them just like RB does, so I can have a much better long primary system. But you'll need a good muffler if you like things quiet like a typical RB system. That's what I like.

Oh I just reread your post. It looks like you are getting a powerpulse muffler. Then by all means get the 81-82 muffler because it has the dual inlet that collects to a single 2.375" OD (or 2.25" ID) feeding into the muffler. Then you can fab your center section like I talked about. Long primary! By the way it's not hard to add a dual pipe flange to a collected header. I've done it a few times. You chop it where the two pipes are the same distance apart as the holes in the flange. Easy.

In closing, remember the difference between long primary vs short collected systems is HUGE. Infact once the red REPU gets a turbo setup, the long primary is going to the white one so the S4 NA can once again breath like it was meant to.

Sgt.Stinkfist

iTrader: (6)

agree 100%. I am sort of cheap and prefer to fab up what I can. So when I did my S4 swap I needed a new exhaust and did exactly this. Luckily my car is an 82 and the PO already had a full RB streetable system, so I was already set for the dual inlet muffler. I then dismantled my collected RB header and fab'd up a simple dual 2" from header to muffler... granted I took it 1 step further by splitting the flange at the engine to make it fit the 13b's wider bolt spread

DreamInRotary

iTrader: (49)

Love the post Jeff, I will be considering heavily my options on the 12a now. Thanks!

t_g_farrell

iTrader: (1)

I can second that opinion of Jeffs on the long primary. I originally had the RE short primary
system from back in the day. I bought a used RB SP system complete with the header and
power pulse muffler for $400.00 2 years ago. Difference is night and day. I need to get on a
dyno and see the difference but with the old exhaust and my Dell it dropped off sharply at
around 6500 RPMs. This new system is much better and has better torque down low as well.

Qingdao

iTrader: (3)

Eh... bump it... I'll just trash my whole setup and dump the $1000 or so on the complete long primary system.

I must have the FC header pipe because it is a 2.5 outlet.

Jeff20B

iTrader: (13)

You do? Does it even fit the 1st gen chassis? It didn't fit the REPU chassis when I tested it, but the REPU is compatible with 1st gen headers.

You'll love the 1000 dollar RB exhaust. I love mine. The only thing that would get me to change it would be a turbo setup where 3" makes sense.

Qingdao

iTrader: (3)

Well... I didn't messure it, but Damn if it isn't big. Bigger than my recently **** can'd 12A RB headers. Now you have me curious enough to messure it. It does have a bung for an O2 sensor.

I kinda wanted the long primary from the get go, but I guess I just needed a little encouragement to push me over the edge to get it. I don't plan on turbo ever; too much piping for an otherwise simplistic car. I have thought hard about the SC though. In which case a very open exhaust like the long primary system would be benificial.

Kansasrx7

Now dose the long vs. short apply to a non ported motor also? Im looking at exhaust next and was just planning on the standard RB short complete system but this thread is making me rethink. But with no plans of even porting this 13b and the only intake mod with be a high flow filter will I see the same gain from a long system vs. if I were to buy the short?

Jeff20B

iTrader: (13)

Yeah, my FC header that went into the GLC had an O2 bung (I had to fill it in and weld in a new one to make it fit the car hehe). I don't know if any 1st gen headers came with them but from what I've seen, they didn't.

84stock set a record with a Camden and his RB long primary exhaust. What does that tell you?

Kansasrx7, the 6 port 13B in your car has a lot of total port area. It needs a free flowing exhaust.

Have you read about the gains RB got back in the 80s when they tested a GSL-SE? Just installing the long primary exhaust netted them an additional 21HP taking the stock GSL-SE from 135HP to 156. Then they threw on one of their dellortos and got an additional 21HP to total 177. Not bad eh? I plan to throw a weber 45DCOE in the white REPU when I swap in the long primary. I'd like to get 177 but we'll see how it goes.

We know the stock GSL-SE intake is a little limited, but a good air filter can help. j9fd3s maxed out a GSL-SE once. He might be able to add to this thread if he sees it tomorrow.

Another idea would be to grab an S5 NA intake manifold and make it fit. You gotta grind the top of the rear plate down a bit. hornbm installed one on his GSL-SE but I don't know the details. I just remember it ran well with decent power.

Qingdao

iTrader: (3)

I just stuck an O2 sensor in mine and ran it to a cheezy AFR gauge.

j9fd3s

iTrader: (3)

lol! yes i had a couple engines and a couple different exhausts in it, and i did have the stock gsl-se fuel system maxed out, and actually since then i've had a couple of FC's and arrived at a good cheap street system.

so whats the recipe you ask? i used the RB street port system... with an FC block, the FC block has larger ports. later i ran a GSL-SE block with 9.7 rotors, and it was easily down 15hp.

i also ran the regular RB exhaust, and this post was actually going to touch on how the two are not really apples to apples. between the short exhaust and the long exhaust, peak power is about the same, however the longer primary exhaust makes much more low end and midrange.

so the apples to apples part? its simple both headers are 2" OD pipe, and the long system collects into a 2 3/8" (i think) pipe, which is just about right for a stock 13B. the short system collects into a 2" pipe. i think if you ran the short header into a 2.25" or 2.5" pipe it would perform much better

on an FC block both systems can be improved by port matching the header to the block. the FC block has 48mm exhaust ports, but the header is only 43mm, having a big mismatch right at the engine like that is bad.

good cheap street system? whats that? on the FC, since the RB header has a poor match to the exhaust ports, and its a length that gives a torque peak at the same place as stock, it doesn't do much for power. it turns out that the stock FC manifold has a good port match, and the exit is 50mm, which seems to be just right for a stock engine, its the smallest size that works. so the cheap street FC system is to run the stock FC manifold, it fits on a 1st gen, btw. into something like this RX7 1986-1992: Exhaust - Race Pipes: Down Pipe - 86-91 RX-7 - into either a presilencer or a cat, and then into a muffler/mufflers of your choice. you get 90% there but its simple, potentially emissions friendly, and it works with the stock tune on the ECU (the S5 ecu is a little lean under 4500)

Qingdao

iTrader: (3)

Alrighty...

Has anyone taken the long primary headers/mid pipes and made a dual all the way back exhaust?

Like two seperate canisters after the mid pipes.

I'd love the super low idle and distinctive pops alternating between sides


Thats an exhaust I'd put some effort into!

wankel=awesome

Did just that with 2 flow masters and 2.25" pipe a few years ago on my gsl. Sounded godly, but was loud as hell and threw a random fireball every shutdown. Damn modded nikki would turn those flowmasters into bombs!!

Jeff20B

iTrader: (13)

A true dual exhaust might sound really good if you use the right mufflers and enough of them. Who is their right mind would use blownmasters on a rotary anyway?

wankel=awesome

Like most things I buy, the flow masters were a smoking deal lol. 2 40 series for 50 bucks, couldnt resist.

LizardFC

iTrader: (1)

While were on rotary exhausts, what about turbo applications? Obviously true dual and long primary are out since it has to collect at or before the turbo, and the backpressure from the turbo changes the whole equation. But how? Is there any difference from say... a short collected manifold like the stock S4/S5 vs. an aftermarket with a foot of dual pipes before the turbo? And does the overall length of the system play as much of a role?

j9fd3s

iTrader: (3)

yep! the old school guys prefer this. they think that a muffler AND header collector adds too much restriction. so a dual gives up scavenging and is low backpressure.

my friend ran duals on his bridgeported Rx3, it put down 230rwhp@9600rpm, which is where the dyno stops, curve was still climbing AND AND it was quiet enough to street, and he did, it was his DD for years

peejay

The S4 is supposed to be better for power production than the S5. There's a lot of surface area in the S5 and that hurts flow.

I can attest that a quickly matched S4 manifold on a GSL-SE engine is worth the trouble. And that if you have the means to do it, don't even bother putting the GSL-SE intake manifold on, it's a total dog.

I mean, wait, the S5 and GSL-SE manifolds are AWESOME! I have two of one and thee of the other, they're the best, I'll sell them to you at such a deal...

As for exhaust, the long primary system was the best money I ever spent, period. On anything. The only downside is that it feels like the rear muffler weighs more than a transmission and the midpipe is even heavier than that, but even then it's sooooo worth it.

But here, here, listen to the difference!

Short header, 2.5" exhaust system with two straight through mufflers:

RB exhaust, no loss in power output at all:

Qingdao

iTrader: (3)

Is Rotary Works exhaust any good?

At half the price of the RB Road race headers it seems cool.

EDIT:

O/T, but can you bolt a 12A front cover to a 13B? or with my next engine am I just gonna have to hunt down a GSL-SE front cover?

Nicholas P.

iTrader: (1)

I would honestly just buy a racing beat header. You can get them used alot cheaper these days.

(I bought one used back in 06 for $60.00)

Qingdao

iTrader: (3)

Yeah, I've seen a couple on here for a good price... I'm in no rush (its not like I don't have an exhaust).

I might wait for DGRR.

j9fd3s

iTrader: (3)

i think the RW header would be good except its 2.25", its probably too big

the only difference between the gsl-se front cover and the 12A is the metering pump bolt pattern

Qingdao

iTrader: (3)

Performance drop in the larger size? I'm just gonna make my own duel exhuast*, and not buy the full RB (cause I took a better look at my budget LOL).



* I'm gonna buy new mufflers and pipes as apposed to whatever I could find in my buddy's yard.