I was browsing the Racing Beat website for some oil cooler covers and happened to delve into their exhaust system stuff for the 8. Take a look at;

http://www.racingbeat.com/FRmazda4.htm

It further substantiates from a reliable, knowledgeable source that we should all be suspicious of any aftermarket exhaust claiming to give us any more than 5Hp or so.

Good hunting

Tom

 

you don't just do it for power, but also weight loss.

 

there's just too many variables to know for sure...racing beat is a trustworthy company, and for the most part i believe their claim, but there's always quite a bit you don't know. i've seen dyno charts from equally reputable companies that show much high HP gains for various exhaust systems.

http://rx7.com/RPGReddyRX8exhaust/dynocharts.html

but even that has a midpipe as well, i couldn't find an exhaust only dyno on the site. the fact is there's too many other variables you just dont know when judging a claim like that. if someone told you their ebay mystery chip yielded 45 whp, you'd be skeptical of a high number, no reason to not be skeptical of a low one either.

and weight loss helps too, but most people just do it for looks and sound. which is ok too.

 

I'm personally getting the Greddy for the sound... I miss the agressive exhaust tone I had with my Miata and Borla. If it adds 5-6HP, all the better.

I think the cat is one of the keys to opening things up... I'm also considering the RP "Super Cat" in addition to the exhaust- after hearing a midpipe only, I know I'm not going that route.

 

exhaust systems are tuned for length as well as diameter. Lopping off 1/3 of the length and measuring hp, doesn't tell me a whole lot. Nothing against RB, but they don't describe their scientific process very well, and that's what I picture (the lopping of pipes :p ) when I read their claim.

 

BTW, RB exhaust weighs more than the stock.

 

Yes they do. They tell you they test everything on their engine dyno. It is a water brake system. They begin their tests at 2000 rpm and apply a calculated load to the engine so that it's speed increases by 100 rpm per second. They also take very special care to assure that the testing conditions are accurate right down to temperature. They make a change and do it again. Typically they'll do an original product dyno run, change to the new part, dyno it again, then change back to stock to compare results. In certain circumstances they may once again go back to the second piece again. A-B-A vs A-B-A-B testing.

In addition to dyno testing they also use GPS based equipment that actually tests the acceleration of the car. This is a very good way to tell if something was just nice on paper or if it actually works good in use on the car. I'd say they describe very well how they do things and put more time and effort into it than any other manufacturer. You can't always see all of the performance benefits with just a dyno chart.

 

I wasn't really talking about that part of the process, i guess. Perhaps my statement was too general. But did they attatch an equal length piece of pipe when they removed the catback, or just measure gains with the exhaust ending at the midpipe? Not that it matters greatly, but i have a hard time believing the statement that you can't get more than 3-5hp out of a catback. Even with the best designed factory catback out there. I believe this for some aftermarket systems, but not for every system.

 

Well, I too believe Racing Beat is a reputable company but do not take their word as gold. I also don't take other companies word as gold either. Any company is in business to make money, and you make money by selling product. Some companys approach this by bolstering HP numbers, some in other ways.

I believe there are real gains to be bad from exhuast upgrades. When I installed my B&B there was a noticable difference. When I installed my K&N Typhoon the combination yielded very noticable gains, but I had to remove the Typhoon beacuse of noise and a snapped support arm (design issue I believe).

I'd say your biggest decision maker for an exhaust is the noise level. After that its going to be a personal preference because there are just so many options out there. If weight is a big thing, I know JIC makes a titanium exhaust, but it costs almost $1000. Do you research, and make the choice that fits best with your personal prefs.

 

Okay, perhaps a little off topic but. . . now that I have gone with Hymee's cat back and the Bonez high flow cat is there a way to change the exhaust note without major changes in my setup?

Let me explain: I LOVE the growl, I LOVE the extra gains in power. What I can't stand is the "mad bees in a coffee can" resonance after about 3500 rpms on up the power band.

I thought I had the sound identified as the tin heat shield rattling, but that's not it. Short of adding a glasspack type resonator before the catback, are there any other thoughts? Could it be the monster stainless exhaust tips Hymee tacked on the end of the pipes causing the odd resonance?
I'm at a loss here folks, any thoughts or suggestions appreciated!

 

Did you try the Hymee without the Bonez supercat? I'm guessing the cat is the cause... the one RX8 I heard with just a midpipe and B&B exhaust was like a hive of pissed off hornets at high RPM's... not a pleasant sound. The Bonez shouldn't be that bad, but it's probably causing what you're hearing... I would go to a local exhaust shop and see if you can have a resonator installed betwen the cat and exhaust to minimize it.

 

Without a doubt the highflow cat caused the new "bee" sound. With just the Hymee it sounded great but with minimal performance gain. I'm considering going back to the stock exhaust with the Bonez high flow cat if I can't come up with another solution.

 

The "bees in the coffee can" have been silenced! :D

A 12" resonator has done the trick with no "noticible" loss of performance.
Very happy with the results!!

 

Good to know... I'll remember that when I'm looking at upgrading the cat.

Now, your next assignment is sound clips! :D

 

i liked the sound of the hi flow cat...yes, i had the resonator but it still gets loud after 5k.
a great sound for great driving...under 5 k (meaning when you are with family) it is very moderate.