XDEEDUBBX

this combined with a supercat will be extremely loud. But on a turbo, it will quiet down a little.

nycgps

iTrader: (1)

This exhaust is on my list of *add-ons*

but wont be able to get it b4 my trip to Asia (in summer)

scsi

has anyone mentioned its Hi-Power, not Hi-Flow?

anyway, looks good

Moostafa29

I agree that this car does not need dual exhausts, but I can't get over the look of something missing on the rear.

chickenwafer

iTrader: (9)

Yeah, I suck. Hi-Powwa is right

Missing the dual tips isn't that big of a deal. I mean, a lot of people out there think it's a "downgrade" to go from a dual to a single. But honestly, this system weights over 11-lbs less than stock, makes more RWHP (Yes, if even in only single digit numbers, it's still MORE), but the biggest thing is it is designed to SUPPORT more horsepower if you go FI and have increased exhaust gas flow.

Those were some of the key selling points for me; weight, turbo future, awesome sound, made by HKS, and price.
I was originally looking and nearly bought the JIC Magic Sparton 2 catback with the titanium muffler for $1300+ shipping. With this exhaust I saved over $900 bucks I can put towards something else (which I did; a custom carputer, Hymee sCANalyser, ProSport gauges, etc)

I can't wait to get this on! Damn I wish I had a freakin garage!!!

scsi

but the JIC titanium exhaust isnt 3"... perhaps it should be compared against the turboxs or something

besides, the JIC dual is lighter than the HKS single. i guess what we really need is a 3" full titanium single exit exhaust

Digital_Damage

Man that would be expensive, but I would be interested.

You might as well stop trying to have a logical discussion with him. He is not capable of it. I gave up a long time ago.

He is a fan boy plain and simple.

For those that might be interested in an actual discussion:
It is simple physics; if you remove the cat the most restrictive item at that point is the muffler. If you have an exhaust with the same dia. pipe and two mufflers you will be able to expel more CFPS than a single can.

The weight saving is an appealing aspect of this exhaust the only question I have about it is; if they were going for a high performing weight/balance minded exhaust why did they not have it come out the passenger side? Would it require more or greater angle bends?

XDEEDUBBX

ok brain damage, you have to result into name calling right how mature of you. is this another unsuccessful attempt at protecting the turbo xs exhaust? who's being the fanboy now? look at my signature again fanboy and tell me who the fanboy is?

The pipe routing for the single side exhaust is much better as far as bent angles go. The rx8's stock exhaust starts off as a single pipe, then hits a wall, which then breaks it down to 2 pipes. Now, use your simple physics, which would flow better?
btw, the jic exhaust that was on the turbo 8 measured at 80mm vs the hks hi power which measures at 75mm

engineers at hks have fully tested the single pipe to minimize the bends and this design was what worked out the best and made the most power out of everything they tried.

chickenwafer

iTrader: (9)

Yes, the muffler is the most restrictive if the cat is removed. But a muffler is still a flow restriction. So how do two mufflers restrict LESS than one? Sure they can flow more volume (CFM), but the enigne is putting the same volume of air flow as it did before, so that doesn't matter.
Not to mention with a single-outlet, you have a pretty *straight* shot to the rear muffler, whereas on a split system, you have a Y-Pipe and more compluited bends, which is another flow restriction.
If you take your idea to the extreme, you want an exhaust system with 24 mufflers and 12 Y-Pipes because it can handle more volume. That is one huge *** flow restirction.
Our idea taken to the extreme would be a single pipe with no muffler. Who's gonna make more HP?

I really don't want to get in an argument about this because fighting on the internet is just dumb. I just want to have an intellegent conversation (with no name calling, because we aren't in High School anymore, please. We don't need an internet dick-measuring contest....) I just want to know where you are coming from. No disrespect intended.......

XDEEDUBBX

thank you chicken...btw, it was designed on the left side because it took less of a bend due to the differential. If it went out the passenger side the bend would have been more close to 90 degrees vs. a 45 degree bend on the driver side

Wanganrx8

I really didn't understand how 2 mufflers, and bent piping flow more either. It's a simple straight pipe with one canister, that should flow way more than the 8's traditional dual mufflered exhaust. the whole exhuast system on the 8 never made sense to me, it should of been a single pipe from the start, it's a small displacing motor so why would it even need dual exhaust? (yes, i know the exhaust isn't even really dual)

lazi

i'll jus say. HKS all the way.

lazi

i've had the JIC exhaust before. i was pleased with it, but didnt notice the gains untill i got the HKS exhaust, the reason why i say this is because i believe i lost power in my JIC exhaust, and gained it from the HKS. fanman also had this problem with the JIC exhaust as well and had power loss, the craftmanship of the HKS is far beyond, and will give the peak of HP that is there to free up

XDEEDUBBX

the FD never came in a dual exhaust, what makes the 8 special that it needs two?

Digital_Damage

None taken, I just attempted to point out a flaw in the assumption that a single can is going to have a higher rate of flow. Instead of a logical discussion he decided to get cute.

Back to the subject at hand.

I was also under the assumption that the less bends the better, then I did some research into flow and pressure. Found out I was wrong.

I'm not sure how much air the engine puts out (I asked this in another thread and no one could give me an answer). But if the engine generates any positive pressure in the exhaust then the number of bends is negated because the pressure will be the determining factor in forcing the gas out.

So if it does have pressure then the larger openings (or more) will be able to expel more gas.

If the engine does not generate enough gas to pressurize the exhaust then the larger openings (or more) will not help.

I guess an analogy would be this,

You have one hose with one filter on the end of it.

You have another hose that splits at a Y and has two filters at the end.

Which hose is going to generate more filtered water?

Wanganrx8

this is just an assumption so i could be completely wrong but maybe mazda did it because most modern sports cars do have dual exhaust, so it's maybe just a styling issue and doesn't have any purpose beyond that.

Red Devil

At redline, the NA Renesis puts out ~26-27lbs/min. Confirmed that number myself with Cobb a few months ago, and works out to calc'ing the Renesis as a 2.6 liter.



Also, to build on comments regarding the JIC vs. HKS and which provides more power, I personally don't see the JIC losing power unless it is more restrictive than the OEM cat back. The Renesis has no overlap, so the rules of exhaust tuning based on engines with overlap - pretty sure that's every other engine on the market today - don't apply.

I've read a lot about members claiming a loss of power from one exhaust to the next, but never a dyno to back this up. And a +/- on the dyno of a few hp from one to the next doesn't prove a thing. The only two dynos that I've seen that appear to correlate are the ones from TurboXS and RX7.com. Both found comparable starting hp figures and reported comparable gains from a mid pipe/ cat back combination of around 18-20whp.

If someone wants to call BS on those, that's fine, if they want to quote Racing Beat about minimal gains - that's fine too. I'm more of pulling a lot of threads together and summizing them here.

Digital_Damage

Thanks, I was looking all over for that info!

XDEEDUBBX

to be quite honest with you, the dynoing was done on fanmans car. You can ask him about it directly , i wasnt there to see it at all. He might even have the figures available to give out.

lazi

yeah. fanman should have some figures, he dyno'd it and lost power with he JIC titanium i believe

scsi

i still say we need a single full titanium exhaust it should be cheaper than the current full titanium dual right?

maybe even dolphin tip, J's racing style

Red Devil

I've got nothing wrong with Fanman's statements, but for me to believe it I'd have to see some sort of dyno from several members on one exhaust before believing it lost hp. This is why I used the TurboXS and RX7.com example...they're not directly affiliated (that I'm aware of) yet got similar numbers. I can tangibly believe there's something going on there. Even if I was surprised by the large gains they achieved.

XDEEDUBBX

haha that would be nice, i would love to have it wrapped in a carbon fiber skin as well, just like the other hks single outlet exhausts. maybe i can bug them to do it..

scsi

lets shoot for a 12lb catback

chickenwafer

iTrader: (9)

Digital Damage: I did some flow calculations on the Renny while trying to figure a turbocharger on a compressor map. So I naturally did the flow rate for NA first then the boosted flow rate at ~ 12 psi.

First you have to make the Renny 2.6L for the equations because the math is centered around piston engines (which suck! BOO! LOL)

To figure airflow in LB/FT per min you need to know you Mass Flow Rate (MFR). To get your MFR, you have to know your Volumetric Flow Rate (VFR).

For VFR @ redline: 2.6L equals 159.6ci @ 9000 rpm= 382.3 CFM at redline.
Your Mass Flow Rate (MFR) will vary by what elevation you live. But I live in Phoenix which is pretty close to sea level (which is 14.7 psi ambient), so I used 14.2 psi as an *estimate* of my ambient air pressure.

MFR= [2.703 x Ambient (14.2psia) x VFR (382.3 CFM]/(Outside temp [85F]+460)=26.92 LB/MIN of air flow for the Reneisis at redline for my specific conditons.

Then just to have fun I plugged that MFR back in the *rough* equation of figuring crankshaft horsepower.

Crankshaft HP= (MFR)(60)/(A/F)(BSFC). BSFC is your Brake Specific Fuel Consumption. The typical street engine is within 0.5-0.7. And A/F is obvious your Air/Fuel ratio.

Using this formula is arrived at EXACTLY 230 crank HP using the figured MFR, which is crazy close to the what is probably is. Assuming 20% driveline loose, that would put me at 184-rwhp, which is only 4-rwhp off from what I dynoed at. So it's pretty damn close for a math equation.

ANYWAY; the airflow for the Renesis at redline is roughly 26-27 lbs/min.

I also figured later with a properly sized compressor running 75% efficent and an intercooler; at 9psi I would generate around 323-rwhp!