Dak

Maybe this has been covered before but here goes. After reading quite a few exhaust threads it seems the consensus is and has been proven that you need 3" after the exhaust port before the bend on your header. Thus bending right after the flange as the RB header does is not a good thing( and seems the main critique of it). I have to think that with RB's rotary experience and history of racing success in the 80's that they know this. Why don't they build their header this way? Is it fitment? Would it not fit in a SA/FB chassis and it just carried over to the FC? Because there is room in the FC to do it.

peejay

There are acres of room in an FB engine bay too. If anything the SA/FB may have more room because I am fairly sure the 1st-gen has more engine offset for clearing the RHD steering box, which is more of a space liability than the FC's steering shaft.

The answer is probably that they determined X to be the best overall header length, and designing it that way allowed the headers to fit to the original midpipes. Or ease of manufacture/packaging. Or that at the expected power levels, it really doesn't matter all that much. Or they were expecting to sell worldwide and they wanted the headers to clear RHD vehicles.

Take your pick and you probably won't be too far off.

j9fd3s

iTrader: (3)

i would add ease of install to the list, you can RnR the header without taking anything else off, like OEM

not sure about ease of manufacture, it wouldn't be any harder to have a 3" section straight out of the engine, although putting the thing on the car would get interesting

peejay

3" of straight per header is half a foot more tubing, at least two more welds to make and grind smooth... In a production environment, you want to minimize the time sinks and materials costs. Add materials, add labor, add multipliers for expected profits per expenditure, we're talking maybe $40-50 more per header. (If something costs $15 more to make in materials and labor, you don't charge only $15 more at retail! That would be silly and a great way to drive down your profit margins.)

How much did SDJ headers cost, again? How much does Defined get for a set of work-of-art headers? How INEXPENSIVE are Racing Beat headers, in comparison? Expensive headers aren't expensive for the hell of it.

fcdrifter13

I think i am the one that sparked this in my thread on the second gen forums. By my math, and i could be wrong, I ended up with a short length of 28.08 with a 6800rpm header design. This seems longer than what a lot of the numbers I have been looking at suggest. I am on a stock port as well and and in the understanding that the header needs to be unequal length unless i read something wrong. If that is correct how to you figure the math for the amount of unequalness(is that a word?)

I am going to build a short style header into an exhaust box with dual mufflers to try and keeps the numbers up but the noise down.

Dak

I had wondered what peoples thoughts on it were before but the thread in the 2nd gen forum had it back on my mind so I started this one here where it seems the n/a gurus reside.

This all makes sense. Looking at there site it is $129 to $148 more for the assembled road race header( depending on which version you get) vs the unassembled kit. That's what they tack on for their labor to assemble it I guess. Maybe for the average user they deceided the performance trade-off is worth it for the cost/ ease of installation aspect. Besides I figure it's issues aren't anything some cutting and welding won't fix. I'm sure some of the people making some good power from a n/a are using a header that started life as a RB header. Except for when a handful of other headers have shown up over the years they have been the only game in town for the most part. I am begining to think if you know how to weld and fabricate or know someone who does their unassembled kit would be a good place to start to build a custom exhaust with.



I may find out one day haow hard the install is, as I mentioned in that other thread. If I ever get a welder and get good at it I think I may just cut mine up and add in the length to the first bend. Though I don't think it is quiet that simple as that will probably make it no longer line up with the presilencer. Oh well that'll be a good time to ditch it and build a long primary system.

Jeff20B

iTrader: (13)

I did a header that had some extra outlet length, made from an RB disassembled kit for Gavin. It made it harder to get the header in and out. Wasn't much, like maybe 1.5" to 2" of straight, but it caused issues with the stock heat shield and possibly the idler arm. I had to trim the heat shield which is not necessary on an RB road race header.

j9fd3s

iTrader: (3)

since the header pipe/flange junction is mid bend it is more a matter of cutting the pipe in a different place than anything else. worst case they have the bender leave more pipe on that one end. so there is no additional welding needed.

j9fd3s

iTrader: (3)

where did you get this info from?

Rxmfn7

iTrader: (4)

Lets just say I could have bought a pretty decent running FC for the price of my 20B header

fcdrifter13

Well the math is from rotarygod for the length, the Dia math was from someone else and the unequalness is something that popped up time to time. Although the math isnt the most important thing, youll basically have to do trail and error.

j9fd3s

iTrader: (3)

did you read the whole thread? there is a disclaimer at the end where it says its wrong

fcdrifter13

Has it been updated. Thats been a while ago i wrote it all down in my note book of many things

j9fd3s

iTrader: (3)

no, you just had to waste your time reading the whole thing

fcdrifter13

Oh lawd i forgot how old it was. 2004, and it goes on with month in between, but you are right.

j9fd3s

iTrader: (3)

i think that anyone can pick up an engineering book and look at the equations and do the math, in fact its a good idea, but what they really learn in engineering school is how to choose the appropriate equation for the situation.

that being said, we know empirically that, 28" is in the ballpark, so its not completely wrong.

fidelity101

iTrader: (11)

I just added 3 feet.

we shall see, I have no dyno and the engine is tired but there is an autoX this Sunday so I will cruise it around a bit and see.

step 1. start over (kind of a common theme recently)


step 2. Add runner length. (approx 3 feet added)


step 3. Add resonator


step 4. add tape?


step 5. stop and compare (while still tacked)


step 6. re-install, inspect for leaks (NONE!)


both headers are RB designed and the street header is absolutely the road race one right before the street header collects you see the slip joint they weld on to the make the change of pipe to the collector, before that they are the same. As stated prior its likely to streamline manufacturing process and cut costs. Like most things.

Dak

Fidelity101 I'm curious about how that system will work as it is almost the same as a setup I had been curious about awhile back in this thread. https://www.rx7club.com/naturally-as...-dual-1027848/

Only difference is it would've split back into duals. I'm debating on a single similar to your setup now though. Either way from what I've read since I'm ported now I need to collect it somewhere so it's more of a mid-collected vs. collecting around the rear axle now.

fidelity101

iTrader: (11)

I wanted the less weight and easier serviceability. I had to quiet my exhaust down per the event coordinators I run with. so I added a resonator but I wanted to remove my rusted *** ancient RB header. So I just did it all at once. if I wanted it to be split it into duals I would not have collected it at all and just bought RB true duals.

Laxfreak3557

How do you like the longer header so far? I've been curious about this length header for awhile as well. Do those rotor shaped RB mufflers work well?

fidelity101

iTrader: (11)

I can hear the individual rotor pulses better, definitely a different sound. It seems to peak tq lower which is good for my application.

RacerJason

iTrader: (5)

Mine:

https://scontent-b-lga.xx.fbcdn.net/...98&oe=54B52E62

https://scontent-a-lga.xx.fbcdn.net/...fc&oe=54B6F389

Stainless, optimal length, long radiuses out of the flange, dual Borla XR1's...

irishrx7

I'm finally at the stage of building the exhaust system on my PP engine and still unsure to go with short or long system. I'm running a rx8 box so I'll have quite a drop in revs with each gear change. So will need good power form 7000 to 9000rpm. Is a long system good for good mid to top and short just for peak hp? Any help guys would be great.

diabolical1

iTrader: (3)

any video or sound clips of it.

j9fd3s

iTrader: (3)

i'm planning on making mine modular, and go to the dyno and see what the engine likes.

i want to buy 3, 4 foot sections of pipe, and cut one in half. this gives me the header 32", header + 2 feet, ~50", header + 4 feet, ~70", and then header +2 foot + 4 foot, which is 90"

that's 4 runs on the dyno...

once you get to the approximate length you can fine tune it a little.

i'm hoping mine wants a shorter header, so i can run more muffler, but i guess we'll see