The term "straight through" is applied to any muffler that isn't chamber, as in one path of travel directed through tubes only.

I learned something odd yesterday while discussing Kawasakis.

They have a new inline four engine that fires 1 and 4 at the same time, then 90 degrees later fires 2 and 3 at the same time. Then a 540 degree dead spot.

The trick is, they have a timed electric motor that allows the engine to idle.

That's to give you a V-twin type of experience. Meh.

I know there are big gains to be had with a tuned exhaust system, I have made a large gain out of my exhaust system without getting to mathematical at all, my times on the strip have gone from 15.7 seconds to 14.5 seconds.
With the weight of the car etc I worked out thats a 27hp gain just from changing an exhaust and the engine is a mild extend port 12a,
And it was just made up out of exhaust bits I had lying around! nothing scientific about the system at all, imagine the gains if you did get scientific!

What was your old setup and what does your new setup consist of?

The old set up was a set of extractors which joined into a single 2" pipe about a foot behind the fire wall then 2 resonators 1 after the other then went to the original rx7 pipe up and over the diff and into an aftermarket twin pipe muffler,
I chopped the extractors off just before the join into 1 and ran two individual 2" pipes back to the diff with a resonator in each staggered so they fit in there nicely and then collect it into a 3" pipe up and over the diff and into a large 3" straight through Trust muffler, surprisingly its not that loud and increase in power is huge!

Congratulations you just reinvented the RB streetport exhaust there :)
Thats almost exactly how its configured. This setup is better than what you had.
What you had is almost exactly what my old exhaust was.

I had a RE performance exhaust which collected to single pipe and then
connected thru two resonators in series and then went up and over the
axle into a turbo type muffler. Sounded good and last for awhile but the
new (to me) RB setup is worlds different, to the point that my Dell needs
to be tuned different now. The old setup dyned at 134 whp and this new
Rb setup is definitely different, faster maybe, but I know the curve moved
because I can feel it.

Ya if you do anything like that to a rotary to free up the flow of the exhaust you'll see a big difference. Single 2" is too small for the higher rpms. I think that people here are more talking about extracting every last bit of power from exhaust tuning.

i'm almost done fabbing up exhaust 2.0.

exhaust 1.0 is a pacesetter (35"?) into 3" pipe into a glass pack into a borla. too loud, doesn't make power either. additionally the muffler shop put a lot of bends in for no reason, and only 1 hanger, so it'll be dragging on the ground after a few laps....

2.0 is an rb road race header, into a pair of straight thru glasspacks, into an RB collector, into megaphone into the same borla. like the factory comp system, or the RB street port, but shorter

system 2.0 has adopted slip fits, so it is starting @ about a 94" primary, but i can cut pipes until it A) fits the car, and B) makes power C) run out of pipe!. rear muffler will also become slip fit so i can change it when it explodes, or i decide i want a muffler that muffles.

2.0 is all made from stuff lying around, except the glasspacks ($30ea), and has no bends except the header yet

What inlet to outlet size are you going with on the megaphone?

its not much of a megaphone, the collector is 2" O.D. now, id like to make it bigger, like 2.25.

muffler is 3", so at most it only goes up an inch, ideally less than 3/4", its going to be pretty short, like 8-10"

Do you think there would be a benefit from doing a megaphone to say 4" and then bring it back down with a reverse cone to 3"? Burns stainless does things like that and they claim that it makes better power like that ( Don't take in those dimensions but the though of going bigger than doing a reverse cone)

dunno... the ISC system kind of does that... the competition system ends at 4", so it seems like it could work.

how much is the question....

Does the ISC system put a reverse cone after the megaphone right away or is it after their expansion chamber?

after. it LOOKS like an expansion chamber, but i think it ACTS like a megaphone/reverse cone

.

what he said. The exhaust works though. look at my old thread. it works 51whp better than the RB street system. The biggest argument I get is that I didn't have exactly the RB street system. well I did before I replaced it with the apex N1 muffler and I saw not 1 WHP gain with the apex N1 over the RB rear muffler.
I'm not here to fight and I wasn't even going to post in this thread even though my posts were brought up multiple times in an obvious effort to draw me in...
All I'm going to say is my exhaust works on my car and it works well here is the proof.
https://www.rx7club.com/1st-generation-specific-1979-1985-18/racing-beat-exhaust-dyno-compairisons-823229/
I'm going to be switching to the Rotary shack header to see if that makes any difference in power for next race season. i want 200whp out of this engine before I finish my bridge build.

Rotaryshack header did wonders for my car. I saw up to 242whp from my small bridgeport. That was with a less than ideal intake system. I only saw 217whp with the RB road race header Y into single 3" before the rear axle.

I don't even have an expansion chamber. I've ofter wondered how much we could make by adding the expansion chamber.

1. switching the rear muffler didnt do anything? odd...

2. i think you will get your 200rwhp, its so close

Wow, so you only swapped the RB header for the RS header, no other changes
at all and saw an extra 25 whp . Thats says something for the RS header alright.

Of course it cost about 2 or 3x that of a RB one but you got your moneys worth.

TG he had the RB long primary exhasut and he swapped that for the RS header and a 3" exhasut after that, so it's a whole new system, but most people call the RB RR exhasut with a straight through muffler the bee all and end all for exhausts. As Rotary god and i have shown there are many different things that will work and in fact work well it's all in how the system is tuned and to what extent.

Well I hope to have everything ready for my complete exhaust within a couple of weeks, and I'll post up my full review of it here once done. I should be able to do before and after dyno pulls also. Currently I'm at about 160whp with my 12a sp. Well see how megaphoning it, and a bit of expansion chamber will do to it. I would really like to hit over 180whp with it. Also all the crush bent tubing will be replaced mandrel bent.

I really love testing thing.

RG suggested to me that my expansion chamber might not at all be working as an expansion chamber at all, but more like and exhaust box as he as described in this thread. Frankly I don't care how it works, the thing is on my engine, it does. When I get my RShack header I'm just going to run it stright 3" back to see how that does. If it gets me over 200 WHP I'm going to leave it, if not I'm going to try another "expansion chamber" with it to see what it does.

Yes, well thats what I was getting at. It wasn't a straight up header swap that got
him those extra 25 ponies. It was misleading at best to claim it that way. Also its
not even clear the RS header made that big a difference now that we hear that.

The RB exhaust is not the "be all end all" but its a pretty good system that
works for 90% of its users to satisfaction and I expect that is RB goal.

Is there more HP to get by fabbing an exhaust yourself, sure, but then you
have to do it yourself :)

the RB header has a couple of design features that limit hp.

1. its LONG my gsl-se header is 31" nearly everyone recommends 24-26" the RB design is gonna have a lower torque peak, all else equal. nice on the street...

2. it makes sharp bends right out of the engine... i guess fits really well, but its not like there isn't room...

3. equal length. my 12A road race header is equal, within about 1/4" hypers old 13b one wasn't. mine is close enough.

4. small pipe/collector size. dual 2" OD THICK pipe into a 2" OD THICK pipe collector? again fine on a street car, 2.25" would be better... the FC header might be like that, but the 1st gen is small

so for a street car it's great, and they are bulletproof (my 12a header is drinking age)...