I keep seeing people asking questions like "which is the best exhaust?", and "how much power can I expect to get?". I'll try to answer these questions. I'm also going to explain the differences in mufflers and muffler designs so people can make educated buying choices and ask relevant queations. Go use the restroom and grab a snack and an aspirin. I'm going to be very long winded again!

The first issue as to which is the best exhaust is actually a simple answer. They all are! It sounds vauge but you need to understand that different people have different standards. What is the best for Wakeech may be a horrible choice to MikeB. One person may like the fact that one system is nice and shiny while someone else prefers the fact that a different system is stainless steel. Each system will also sound different. Some will be loud, others won't. One person may like it loud and another may not. You get the picture. The best exhaust is the best to you personally and this is a question that only you can answer.

How much power can you expect to get? Again there will be differences in power. However, the RX-8 has proven to this point to have a fairly good muffler on it already so gains may be few to none or there may be a few extra horsepower. Some aftermarket systems actually lose power over stock so be careful! I'll explain why later. Some people are saying that one system makes mroe power than others based on dynos that they have seen. Until someone actually does several tests with different systems on the same car in the same day under the same conditions, we'll never know for sure which one makes the most power. We've seen RX-8 dyno sheets all over the place. It is a little difficult to compare different dyno sheets to each other when the baseline numbers can be so erratic.

Lets look at some differences in muffler designs. For the sake of simplicity we're going to just say there are 3 basic designs. I'm not going to get into any electroinc noise cancelling systems. We have straight through, turbo style, and chambered mufflers. The chambered muffler is what comes on the car from the factory and the style that is also manufactured by Flowmaster and others although theirs are very different. Many aftermarket companies sell straight through designs and this is the style of choice for the ricers. Here's how they are all different.

A chambered muffler is just that, chambered. Air enters into the muffler and hits an open chamber. From there it may split up and go more than one direction. Different muffler styles have different chambers. The 3rd gen RX-7 has a .7 cu. ft. internal area muffler but it had 4 chambers. Some of the internal passages sent air to more than one chamber at a time and then joined them together by way of yet another chamber. This sends air all over the place. Each time it hits a chamber or multiple chambers at different times, some noise is cancelled out. Many people criticise these mufflers for being poor flowing. The RX-8 muffler is twice the size at 1.5 cu. ft. internal volume yet only has 3 chambers. Air enters centrally and then splits to the two outer chambers. This muffler has some heavy packing and its large size help it to control sound very well. This size combined with few chambers and the fact that the total exit area is greater than the entrance area leaves a muffler that flows quite well despite its chambered design.

Straight through mufflers are the choice of many aftermarket companies and of most if not all of the race teams that use mufflers. The problem is that these mufflers come in 2 different styles, louvered core and perforated core. The louvered core is what so many of the ricers use because they have some big companies name stamped on them and they are shiny. Yay (heavy sarcasm). A louvered core has very high restriction despite its straight through design. These mufflers use dimples that protrude into the airstream and grab some of the air and pull it into the outside packing. A simple 2 1/4" straight through louvered core muffler may actually only have less than 2" that is actually straight through. Even this air will be very turbulent and muffle very little. If these mufflers are reversed they flow better but they muffle even worse and still flow like crap. I laugh when kids buy these things to put on their cars. They probably lost some horsepower but the increase in noise is so bad that they feel faster. To make matters worse then they use an insert in the end of the muffler that reduces the area and helps quiet it down some. Manufacturers claim you can leave it in for quiet and then remove it for power when racing. A more accurate term would be that you can use our mufflers full time for less power than stock and be ungodly loud. If you would like a hint of muffling ability you can add the insert and go even slower! Yes, I hate these things.

The preferred straight through muffler is the perforated core. This has nothing blocking airflow. The internal tube is full of holes but they do not interrrupt the airstream. Air still flows through them well while some of the sound gets absorbed by the outer packing as it passes. These are among the loudest types of mufflers. As with any muffler a larger muffler will be more effective at noise suppression.

The 3rd style I'm mentioning is the turbo style muffler. I hate the name turbo muffler because some feel that it either means it was meant for a turbo car or it feels like you have a turbo. Wrong and wrong! The turbo muffler was designed originally as a muffler that was supposed to flow better than stock, deliver improved horsepower, and be a little louder but not overbearing. The problem is that this style is ancient and behind what is currently available today. Basically the air enters the turbo muffler at one end where it flows through a louvered or perforated core tube. This tube has a small amount of packing around it. The air hits a chamber at the far end of the muffler and is forced to turn around and do it again. The air makes 3 total passes before exiting the muffler. When the air hits these open areas at each end of the muffler, it has a hard time turning around since there is nothing to help it in regards to shape. The entrances and exits to these pipes also are very sharp which is also bad for airflow. These mufflers should generally be avoided like last nights beer goggle one night stand. The only exception to this rule is with the Dynomax Superturbo. At the ends of the tubes they do have half sections of pipe in the ends that do help the air turn around and change direction. This greatly reduces back pressure. I used to have 2 perforated core striaght through mufflers on my 2nd gen RX-7. It was very loud. I then tried the Superturbo mufflers from Dynomax. They were very quiet but louder than stock and I noticed no difference in power. If there was a difference it wasn't enough to notice. I sound like a frikin infomercial!

Just because a muffler is chambered doesn't mean that it flows poorly. As I've shown a straight through muffler doesn't necessarily flow good. If you have a chambered muffler that flows 400 cfm but your engine is producing 500 cfm of exhaust flow then obviously there is a restricton. If your muffler flows 500 or more cfm and the engine only requires 500 cfm, does it really matter what style of muffler there is? No! As a simple rule use at least one larger pipe size for a chambered muffler than is currently in use from the engine. If the engine has a 2 1/4" pipe going into the muffler then use a 2 1/2" or larger muffler. These mufflers don't only have larger entrances and exits but also more internal pipe area. This is what helps reduce the back pressure. The most imporatant aspect is that you have a muffler(s) that flow what is needed. Their style is irrelevant if they meet this requirement.

Single vs dual mufflers. Which is better? That too is subject to debate. Once again I'll use the stock RX-8 muffler as an example. It has a single inlet and dual outlets. The total area of the outlets is greater than the area of the inlet. This means that the air slows down inside the muffler. Yes this also means that pressure is greater inside the muffler but it also means that pressure is less in the pipe before the muffler and this helps pull air down the pipe. Since the air slows down inside the muffler there is less of a restriction. Remember that slower air is less air in that particular space and that any passages that the air have to flow through are "effectively" larger. This muffler while not as good as many aftermarket mufflers is quite good considering its very small inlet size. Many othe companies are leaning toward dual muffler. Nothing wrong with this idea and I personally would probably design a system this way myself. When people take a single 2 1/2" pipe (just an example, may be different from actual) and split it into dual 2 1/4" pipes, there is once again an area increase. Even if they were to split into two 2" pipes there would still be an area increase. I find humor in how one company claims more flow because theirs is a 45 degree turn before these mufflers where others are 90 degrees. Lets go back to the available flow vs needed flow statement. While technically true that air doesn't like to turn and that a shallower turn will flow more, in our case that is irrelevant. It isn't a lie though and from an advertising perspective I'd probably say this too. If both systems can flow the required amount of air, it is irrelevant how much more potential one system has over the other. We don't care about potential. We care about needs. The internal muffler designs will play a bigger role in power output anyways. It is benefical to have a mild area increase as the exhaust gets farther away from the engine. It has to do with acoustic pressures and their effects. From a physics standpoint you'd want a smaller pipe the farther you go back! Don't go there! We aren't getting into it here.

I forgot one other type of muffler. It is known as a positive enthalpy muffler. This is what a Spintech muffler is. Spintech uses a different approach to noise cancellation. They have one internal chamber. Lined up in various ways inside this chamber are small 270 degree bend pieces of metal. There is an open edge that catches some of the incoming air and then spins it internally. One wall of this little spiral is perforated and this air leaves through these holes into the back part of the chamber. Since these spirals are spaced out at different locations within the muffler, they each slightly cancel out each other since the same tone is spun at different intervals. These mufflers get more efficient as flow increases. They are actually their least efficient near idle. It is a strange sensation to be in a car equipped with these since you accelerate hard and the tone just doesn't seem to get any louder as rpms increase. There may be a slight rise in volume but not much. These mufflers are virtually indestructible and flow very well with almost no backpressure at all. However they may be too loud for most. these are not quiet mufflers. There was one person here on the forum that had one and liked it but every RX-7 I have ever seen them used on has been ridiculously loud.

Hopefully I've answered some questions. I may have left some things out though. I don't want any manufacturers out there to think that I am saying anything bad about their products. It is just safer to not name any names. What is good in my personal opinion may not be in others eyes. It is subjective and I don't want someone to pass up something that they may enjoy just because I favor another. I just want people to be able to make their own educated decisions. It is hard to write this long without having a rough draft to go over. I'm at the office right now too and should be working. Someone call and buy or sell a house through me!

RG

 

So which is the best exhaust?!



J/K



Thanks for the info!

 

ROTARYGOD

OK I GET THE PICTURE ,

How do i get extra noise out of my existing exhaust , without changing it .

If i am not going to ge ta larger gain in HP i would like to be able to increase sound volume without the large cost .

Please dont tell me to stick screw driver in exhaust ha ha ha .
cheers
michael

 

I never said that aftermarket systems won't get you a gain. Some of them will do better than others.

I was thinking along the lines of a crowbar rather than a screwdriver.

How much extra "noise" do you want? All of the aftermarket systems will give you this. A cheap, simple way is to have the presilencer before the muffler removed or you could take the cat off. If you want some really obnoxiously loud "noise" look into a q-tec electric cutout. That will give you more noise than the law or your ears will allow.

 

Having the pre=silencer removed sounds fine HOW ???? could i do this by myself.

REMOVING THE CAT IS ILLEGAL HEFTY FINE .

How would you amplify existing exhaust note , electronically??? to increase its volume .

cheers
michael

 

I only use a functional cat on my RX-7 one day a year. No fines here.

 

isn't it a fact that the stock exhaust on the RX-8 is pretty good and if you switch all you will get for your $600 is a couple of more HP and a lot more noise?

 

Funny avatar you got there!

You will spend anywhere from a couple hundred to over a thousand dollars on a new exhaust system. Some of them will give you bigger gains than others. Some won't give you gains at all. You may see no gain or you may see a 10 hp gain. I think what you are getting at is that there is little gain per dollar spent and this I will agree with. Also look at how much you are getting for your money with a new intake. Now go look at dollar amount per horsepower with a new ecu. Which one would you rather do first? Remember that everything adds up. Some people place more value on that few hp than others. Nothing is ever a rip off if you agreed to pay for it. Spend your money how you like and give priority to what you feel is best for you. For some it is a new exhaust regardless of price for others it is just better to leave well enough alone.

While I don't have an RX-8, I am planning on buying one in the future. I'm interested to see if there are any changes for 2005 that deal with reliability issues now. I still love the car but personally never buy the first year model due to recalls. When I do buy one however, you can bet that I will install a new exhaust, intake, and ecu and probably a host of other things. I just like to build everything myself. I believe I can at the very least get equal performance for far less money. Everyone is different and that is just me personally.

 

RG,

I know you don't want to name names necessarily, but how can we find out which of the available exhausts are which style? is the Borla a chambered exhaust just like stock? People that have them say they're not that much louder, but in your writeup, it seems to imply that the non-chambered designs don't muffle very well.

In fact, most all of the reviews of cat-back exhausts of any kind tend to downplay any increase in pure volume. Surely they're not all chambered.

jds

 

rx8store exhaust got 12 WHP, thats a crap load for an exhaust..

 

A nonchambered straight through muffler will never be as quiet as the quietest chambered muffler. However the bigger the muffler, the better the sound deadening. Racing Beat sells mufflers for the 1st RX-7 that are straight through designs and actually quite reasonable as far as sound deadening goes. These mufflers have a single in but dual outs. Right after the pipe enters the muffler it splits and now you have 2 tubes getting sound absorption. By having 2-2" outputs vs 1-2.5" output they have increased area which slows down the gasses and gives them a longer amount of time they are in the muffler but more importantly they have increased pipe wall surface area which means there is more exposure to the sound deadening material on the periphery. I am quite frankly amazed at how quiet they actually are. Most of the straight through designs out there will be fairly loud though and I'm willing to bet that the systems for the RX-8 will also be fairly loud. This is a subjective view though and determined by opinion.

When Racing Beat's system comes out, it appears that it will be a chambered system. They understand muffler design very well and know how to design a good flowing system with reasonable output levels. Jim Mederer is a very intelligent person.

I am unsure as to how Borla does it. My hunch tells me chambered but I don't know for sure. Borla makes both chambered as well as unchambered mufflers. David is also a very intelligent person in this respect and he also knows how to design an exhaust system very well.

The Rotary Extreme kit is most likely a straight through design. I doubt that it is a louvered core muffler (thank god!). I have never heard this system so I can't be the judge of voume level. From Chuck's dealings with the rotary community in the past, I can't say anything bad about him. He's an honest guy trying to make an honest living.

Billy Boat (BB) has an exhaust but I know nothing about it.

Greddy will definitely use a straight through design. Their RX-7 systems have always been fairly loud. That's how the aftermarket likes it is Japan apparently.

You can almost bank on the fact that the Japanese aftermarket companies will use straight through designs.

The American companies will be all over the place. Some will use chambered and some won't. If you ask them, I'm sure they'll tell you. They may just make it an overly technical response though!

 

Good info, thanks RG.

jds

 

How much does the stock cat-back weigh? Anyone?

 

Can a mod please sticky this! We've had 3 new exhaust threads that all ask the same thing appear within the last 2 days! Maybe we should just start a new section within the forum called "redundant exhaust questions".

 

ZOOM ZOOM
I cannot imagine needing more exhaust noise. Maybe I spent too much time in tracked vehicles.
If I could not get more than 10% BHP gain with aftermarket exhaust I would pass. I would accept up to 10db increase for that much power, but no more than that. I have a street car and not a race track car. If I were racing I'd use whatever and forget the noise, who cares. But for now, when I have to leave and come home in the middle of the night my family and neighbors are glad I have this phenominally quiet RX-8 that goes like a bat outta he11.

 

does anyone know what systems the HKS and GReddy are using?

 

Straight through. At least that's what they've always used in the past.

 

Does anyone have any sound clips for the Borla exhaust? I would be ever so grateful.
Grace

 

You can find them here.

 

Done, for a while anyway. Good idea. :D

 

Yes, it does a bit. Kinda bugs me too. But I checked, and it is not adjustable. I plan on swinging into a muffler shop one of these days and having them heat up the pipe and tweak it.

 

question, RG....

do the size of the tips have anything to do with performance gains? I think the borla is 3.5'' wheras the greddy is 4.5''..somebody correct me if i'm wrong, i very well could be. point is, the greddy's got wider tips..does that account for anything? I'm still trying to decide between greddy and borla..i've chosen not to look too much into the manufacturer's claimed hp figures, as those can be exaggerated..

i've also read somewhere that the greddy reportedly had a loss of hp over stock, but it wasn't determined whether it was dyno problems or not..

i'm not even sure if you can answer my question, b/c i wouldn't want you to be in a position where you'd be biased to or endorsing a particular exhaust system over the other... Still, i'd just like to have some technical knowledge of each system to make my decision easier.

i've found that i like the sound of these two exhausts the best out of all the other options... and from an appearance standpoint, it really doesn't bother me that the greddy tips are that wide...so, ultimately, what will decide it for me is which will yield the greater hp gains (however modest they may be) i figured if they would only add 5 and 6hp respectively, i'd still like to get the one that has even a 1 hp advantage..

i couldn't find a picture of the borla uninstalled...so i don't know anything about what kind of muffler it would be according to your overview...but there are some pics of the greddy sp2 on that rx7 site..could you please tell me the differences between these two systems?

if you're more comfortable PMing me a response, that's fine with me...

thanks

 

The size of the tips is purely cosmetic.

I overheard a conversation between two ricers one day when I was in Barnes and Noble. They were talking about what mods will give them more power. They quoted the usual hype about a header giving 15, intake giving 10, etc... One of the guys said that a good tip would add about 5-10 more horsepower. I couldn't help it but I started laughing. These guys got so pissed off at me and starting drilling me about what I drive. They made fun of the RX-7 (they both drove Civics) and kept giving me excuses why one of their cars was better than mine. I have a Civic BTW. When the offer came to race all of a sudden they backed down. Where's all of their superior power now? Just a story I thought I'd share.

The Borla muffler is baffled. Greddy probably uses straight through mufflers. They always have. Greddy has also liked really loud exhausts. I don't have anything bad to say about Greddy. They make good products. I personally think their products are overpriced but then again it should be expected that an imported piece will cost more than one made here, so maybe it is fair. I personally think their exhausts are too loud. I like it louder than stock but civilized enough to not draw too much attention.

I don't know which system makes more power since we have never seen an unbiased 3rd party test. I do know that there is a currently available system on the market that supposedly makes less power than stock. I just don't know who's. I guarantee that it isn't Borlas though and even Racing Beat found a gain from theirs (Borla).

 

That's a sad story... How can anyone mock an RX-7 that's almost a sin. Do you know if GReddy and HKS use perforated straight through or other one? Those guys must've been some really dumb ricers cuz even the ricers i know, know what a force the rx-7 is.