Mathius

So I've been trying to figure out what would be the best way to setup an exhaust system from scratch?
I'm building a rally port (racing street port) 12a, and it's getting dropped into a 78' Datsun 510. So I can't just use a bolt in kit.

I'm curious though.
What would be the best performance wise?
A true dual setup. Would and X-pipe help or hinder performance?
Would a large diameter single exhaust (like a 3") be better, or worse than duals?
Would a smaller diameter single exhaust (2.5 or 2.25") create a more friendly powerband?
Does back pressure make much difference in a ported Rotary?

I could go on.
But these questions have been on my mind a lot lately, and I wanna know what everyone else's take on this is?

Qingdao

iTrader: (3)

2.5'll do it fine. There is no need for much more N/A IMPO. Not for a street port at least.

True duel is what I would do; just cause if you can get the idle low enough it would sound wicked. But performance suggests a cross over or x pipe as far from the engine as possible.

Mathius

So if I go 3" it wouldn't really hurt anything right?
The port I'm using is a huge street port. It's the biggest that pineapple racing makes. It's a step down from a Bridgeport.
Or would a 3" kill off some bottom end.
I just want to make use of all the power I can squeak out of it..

Mathius

I'm not against a 2.5" system. It just seems small to me considering the 2" primaries on the header I have. Or any header for that matter.
Though the smaller the pipe, the cheaper.. lol

j9fd3s

iTrader: (3)

if it was mine, i would do the following:

buy the racing beat dissassembled header kit. this lets you fit the header pipe to the engine so that the pipe is straight, the assembled headers meet the engine mid bend.

for header length its up to you, if you had infinite time, you'd go to the dyno and try different lengths, if not pick one of RB's lengths that fits the car.

after the header, 2.5" pipe is fine, you could probably even do 2.25, if it was fairly straight.

for mufflers, the larger they are the quieter it will be, all things being equal.

Mathius

Well I actually have a Pacesetter header, it came with the motor. It has a 2.5" single collector, and 2" primaries. I thought I would just run it to save money.
The primary tubes seem pretty long. But I haven't seen a RB header in person to make a comparison?
The pacesetter seems to fit the Datsun pretty well. Not sure if a RB header would fit the same?
But at the same time I'm not to worried about hacking up this header if I need to mod it when I get it all together.
As of right now I'm kinda leaning toward a 2.5 single system.
Then keep my options open if it seems restrictive...

I just had to ask if a bigger pipe size would be better?
I'm not really sure how much back pressure these motors like.. I do like the dual idea to though. I'm keeping that option on the table. But the length of it has me a bit worried. I'd have to think it would kill off a bit of power in a full length system.

Jeff20B

iTrader: (13)

I like long primary systems but I doubt you could fit one in a 510. Just go with 2.5" single pipe system, and use the longest mufflers that will fit.

These do not like backpressure. Stockports tolerate it better than ported engines. Exhaust gas velocity is what you want.

Mathius

Ok so I had to look at that header. That would work..
But I'd be reinventing a perfectly good wheel so to speak.
The bonus to the RB road race disassembled header being the dual outlet.
I found a good article from Australia about 12a exhaust. It basically explains how diameter + length = exhaust velocity.
A major factor being back pressure. To much can hinder the scavenging effect, and cause a loss in performance.
A naturally aspirated motor needs that "lack" of back pessure to properly clear the chamber on each rotation. (Like a 2 stroke piston motor).
This is even more important where overlapping ports can cause blowback on the ignition cycle. Like Extended, or Bridge ports.
It makes sense to me, but where is the happy medium??

j9fd3s

iTrader: (3)

the happy medium is what will actually fit in the car and be quiet enough to use on the street.

plus the engine actually doesn't care too much, its not picky about header lengths, we run long or short. long is 90-120" and short is about 32" because thats a store bought length.

t_g_farrell

iTrader: (1)

Don't spend much time or money on the pacesetter, as it will burn through pretty quickly. The RB stuff is made to a thickness that can withstand the exhaust heat of a screaming rotary.

Mathius

I'm kinda starting to wonder if it is a pacesetter?
It's old.. It's a full length piece. No stamps on it anywhere. I was told it was a pacesetter when I got the motor.
I'll post a pic of it when the sun comes up. Maybe someone can identify it for me? But seeing that I have it, I'd rather put money elsewhere right now, than buy another header.

Mathius

So I had to dig it out of the snow.
But can anyone identify this header? Was told it was a Pacesetter. Theres no stamps, or any markings on it at all.
kinda starting to think someone made it?

sa7

iTrader: (13)

Definitely a pacesetter header.. with what looks like an extra length of exhaust welded to it

j9fd3s

iTrader: (3)

it is a pacesetter, but if you're building the whole car, and it fits i'd just run it, one less thing to worry about.

LongDuck

Yep, had a Pacesetter on my 80LS and it lasted about a year of DD. Exhaust gas temps being what they are, it will fail by blowtorching a hole in one of the 90deg bends right out of the engine, usually the back one, because its closer to the exhaust port.

The RB header on my SE has been going strong for 20yrs now, still sounds great. I have no doubt it will go 20 more. The only issue I had with RB parts was a seized bolt on the presilencer that sheared off. Bought a new one and started using copper antiseize on threads.

Mathius

Oh I have absolutely no problem with Racingbeat parts.
I'm just a cheap *****.. lol
But maybe I'll bite on a new header if it will fail that fast.
Plus if I buy that Racingbeat disassembled kit, I can fit it better. Not just have it half-assed..

t_g_farrell

iTrader: (1)

Now you're talkin sense. Make a build thread for us so we can follow along.

Mazdax605

iTrader: (5)

I have a brand new unused RB disassembled 12A header kit for sale if you are interested. I'll sell for less than new from RB.

Mathius

I might hit you up on that. Send me a message..
Wouldn't be able to buy it till after the new year though, and shipping prices to Canada are always a crap shoot..

Mathius

Ok.
So I figured out what I'm doing for pipe size, and what to use for a header.
So what should I use for a muffler??
I'm doing a rather large port, and a big *** exhaust port. It's gonna be pretty loud!
I'm planning to run a mid pipe resonator, but don't really want to use a big *** 3 chamber muffler..
What's the common take on decent flowing "quietish" mufflers??

t_g_farrell

iTrader: (1)

Racing Beat muffler if you can fit one. Most others will burn up or blow apart from backfires.

Mathius

So just the universal muffler?
Universal Muffler, 2.5-inch ID for RX7 1975-1985 - Racing Beat
Do you recommnd the pre silencer? I want to still have some sound, there is such a thing as to quiet.. lol
I'm just running a single 2.5 inch pipe. Was thinking a quality resonator would work with a good muffler?

chainreaction

I bought the Racing Beat header flange and built my header using 2 1/4" ID sprinkler pipe. It's about double the thickness of regular exhaust pipe, so it takes the heat better. It is also easy to have bent on a standard exhaust bender. It also helps to deaden some of the exhaust noise.

peejay

3" will create backpressure from a lack of velocity.

You really can't beat the long primary setup for noise reduction and power generation.

FWIW, I had a huge streetport Turbo II block engine and I didn't make much more power with a 2.5" exhaust than with the factory 1 7/8" exhaust. It mostly just droned more.

Mathius

That's actually a pretty good idea!

Thanx for the info.
I'm kinda gaining a bit more knowledge toward understanding how much heat, and noise these motors actually make..
I'm gonna buy the RB disassembled header kit, and I'll have to see what I can dig up for heavy wall pipe?
I'll end up running sched 40 gas pipe for longevity.. lol