i'm hoping this is the area fred wanted to talk about next...

on my PP ive basically switched from a collected 3" system to a short 2" dual system.

the 3" system has construction flaws, so the engine really likes the dual. velocity is way up, so is noise.

the plan is to collect it.

a megaphone will slow everything down, but will that let the (poor) muffler work better?

 

Which engine are you wanting to run this on? I'm confused when you say you want to go from a collected system to a dual system yet you plan to collect it. Which is it?

A megaphone amplifies. By the time the noise gets to the muffler, it will be much louder than without the megaphone. A muffler can only quiet so much. If you start at a higher number, you finish at a higher one too.

If you really want to have some fun lets talk about exhaust tone vs collector location!

 

this is on the 12A PP, i had a short header into 3". executed poorly, so that its too restrictive even at idle, not quiet either.

so i took it off, and put the other header on, with a short center section and 2 long glasspacks. next step is to tow the thing over to a muffler shop and finish it with a collector and rear muffler, so it'll be a long primary system.

the engine really responded to the "dual" system. its louder, revs faster, there is now some SERIOUS energy in the exhaust.

the problem is noise, i really have my doubts that putting a muffler on the rear is going to make it quiet enough even for the track.

maybe i'm a candidate for your exhaust box?

 

Here's a noise tip. The farther forward a collector is, the easier it is to muffle. Of course the tone also changes as a result and the farther forward the collector is, the higher pitched the exhaust note. If you've ever heard true duals (collected at infinity as I like to call it) compared to a standard setup, you know how very different they sound. As you move the collection point farther and farther back, it gets closer and closer to this tone which is somewhere between a poorly running Harley crossed with a poorly running lawnmower.

A peripheral port engine will actually work quite well to a true dual setup up to about 6000 rpm or so. Above that though and it'll fall on it's face. You might actually want a different type of system in which it stays a true dual and then a butterfly valve in a crossover pipe, much like an H-pipe on a V8 exhaust system, opens at a preset rpm and gives you the top end power. Rob Golden actually tried a system like this on an engine a while ago. He didn't go into too much detail but he did say when the valve opened that it was like a rocket engine on the back of the car suddenly kicked in. I'd imagine you'd want the total length to the valve face to be equal to that of a tuned length header from exhaust port to the "crotch" of the collector.

It shouldn't be hard at all to try this design out. You'd even want to put the collector before the presilencers. You'll still have fun trying to muffle it but power should be pretty nice. A couple of Dynomax superturbo mufflers would probably be fine. Make sure that you use 2 of them and that they have a 2-1/2" through size so you'll get good flow.

 

rob golden used to work at the same dealership before me, and had (has?) this infamous REPU with an MFR 13B PP engine, 0-100 in 2 dealership lengths...

we're thinking on similar lines, i was looking at those mufflers too....

when you say move the collector forward you mean shorten the header?

you're making me want to tow it up to my friends shop and just try things on the dyno until we go deaf...

 

The more you quiet a pport by restricting it with mufflers, the more power you rob from it which defeats the porting to begin with. If this is driven on the street, I would recommend running 3" exhaust from the header collector and then into a RB 3" pre silencer and then back to a high flow 3- 3.5 " RB muffler. Any more than that and your power will start to drop. Don't run a dual system on a pport. This is one of the reasons why pports are not very desireable for street/quiet applications.

 

Hey j9fd3s,
this may mean something or it may mean absolutely nothing, but many, many moons ago when i set up my first 13B in my Rx-7 at the time, while my brother and i were doing the initial tuning on it, i remember revving it and then it misfired and immediately the exhaust note changed. when i checked, the muffler had physically ripped open. it was a Super Turbo muffler ... i think it was a 2-1/4" (it may have been just 2", but i honestly don't remember). my 13B was stock ports with a 48 DHLA.

i've been watching this thread since you started it, but have refrained from comment simply because i don't feel i have anything useful to contribute. i haven't had the pleasure of messing with a PP thus far. at any rate, i'm not knocking Dynomax, i actually love them. i put a 2-1/2" Super Turbo on after that incident and it performed beautifully for the next 4 and half years. my only caution is to size it carefully for your PP.

 

by the way, maybe i should clarify. i meant that only if you're going to try collecting early again. if you are already set on running duals, then i'd imagine dual 2-1/2" Super Turbos as presilencers running into a massive main muffler should be just fine.

 

I've seen a stock muffler split at the seam on a stock engine before. I was just getting a Megasquirt setup on another guys car and at that point it was running very rich. We were having hesitation issues and as we were driving and I was trying to get it sorted out, the car had the loudest backfire I had ever heard. It sounded like someone fired off a shotgun from inside the hatch. The exhaust note was noticably louder. The right muffler split right down the middle. Funny sight.

 

Any type of muffler that has packing or insulation material inside will blow out with a pport in a matter of a few miles. My friend even blew up a Borla XR-1 with his drag all motor rx7 pport.

 

we melted an RB 3" presilencer on the ITS car

 

I think this might be pictures of the car Rotarygod was referring to...

 

That's the one! That was damn funny!

A turbo muffler won't blow out of it has enough flow. In the case of a 2nd gen, 2 of them with 2-1/2" of total flow area isn't an issue. Muffler material and construction is the only thing left as an issue if flow isn't. On Brad's car he had stock mufflers and was running so rich that unburned fuel was condensing IN the muffler. It lit!

 

The funny thing is, the packing doesn't seem to do anything for noise.

I exploded a turbo muffler within a day of installing it. There's pics somewhere. basically never install anything that isn't straight-through OR designed specifically for rotaries.

 

My magnaflow 4" round straight thru mufflers are packed with fiberglass that melts with my handheld propane torch. Which only goes up to 190*F. These mufflers started off great and the repu was totally quiet - only heard fumes rushing out of the tailpipe. Now it's loud as ****.

 

It's all in the muffler design & material. I make aluminium rear mufflers that last at least 3 drag seasons before they need repacking. They're straight thru design so they have no back pressure but lower the db's considerably. Sound levels are under 100db with a full exhaust. Exhaust config is the long primary system - twin 2in pipes collected near the diff with 2x s/s packed resonators on each primary, then into the 3in alloy muffler.
With these full exhausts we're making over 300rwhp in street cars running carbed 13B PP's. They run mid 11's on the quarter in street trim with DOT tires.
The highest hp we've tuned with a full street exhaust is 335rwhp but that was an injected 13B PP.
Typically we'll see 125+ db at the intake, and under 100db at the tail pipe.

 

http://www.rx8club.com/showthread.ph...ffler+cut+open

thought that was interesting, rx8 does make similar power to the 12a PP..

 

In other news, you cannot boil water with propane.

 

Reminds me of when I had my old 79 and did mechanical secondaries:

 

Oh, I also wanted to throw this in there too, not sure if it would help much: