acasanova

Our exhaust systems are built to be quiet and perform adequately. They are not designed to be highflowing, this would result in the obvious tradeoff noise. Why do you think aftermarket exhaust systems perform better than the OE units. The engineers at Toyota know this their priority is a balanced system. Before you post make sense and have some sort of valid argument

niguels

I don't want to make sense MORON, I just want to have fun with people that knows nothing about engineering and do modify their cars losing quietness, LOW RPM TORQUE, and making the iddle rougher in a perfectly working car, just to gain a few horses that show up only in the dyno but that are hard to notice in real world driving.

Probably your car runs always between 4500 and 6500 RPM. Enjoy your ponies. Save money for a new engine.

I am tired on being non-sense. To make sense I am going to stop this by turning off the computer.

Do that makes sense to you? I don't care

oldman

Yes and a Mx-5 likes 2.25 for maximum WOT performance, says nothing about the 99.99999% of the time I just want to drive down the road. I agree with the article but this is NOT the article you posted which clearly stated the 18 PSI was the back pressure of the exhaust and how straight through exhaust is going to get me some big numbers.

The basic fact is most of us have had little Honda 4 bangers with exhaust, intake and larger rims, and most of us have lost to grandma's Accord, Camry whatever too. That blab blab straight through no back pressure exhaust does NOT work where the rubber hits the road and it may barely work in WOT applications that rarely happen.

The Scin tC has a large well flowing OEM exhaust and barring huge cams, headers etc NA, or the above mentioned forced induction there will be little gained but noise from any type of in back of CAT type system, and even a stem to stern optimal build is going to get 15 WHP with stock head and cam NA. This has already been shown with an uncapped race header at WOT. A CAT Header then you are down to say 12 WHP, toss in the optimal exhaust and you are at 10 WHP gain from: header with cat, 2.5 mandrel low restriction exhaust, high flow cat for $1200. While you could save the money and buy a supercharger with a warranty and have buku torque and no blab balb blab sound either. For me I’m waiting for the supercharger, and then maybe a header with CAT. I may give up say 10 to 15 WHP by not running a $1200 system from header back. But the thrill of packing in a sleeper is well worth that. I for one don’t like the blab blab drown of a “performance” exhaust and every performance car I’ve owned I’ve gone through great lengths to have an optimal quite exhaust, which luckily I have bone stock on a tC.

I love the bit about “straight through” core being so much better with flow, yet my favorite packed muffler the dynomax hemi super turbo is the old convoluted path design and no only does it work to quite the exhaust system down to stock Camry levels it has far less backpressure then these straight through jobs that ALLWAYS do a poor job at part throttle drone. You would think this great “straight through” technology doing wonders every OEM would run one especially like say a Z06 Vette and BMW M3. But nope, we all know the OEM runs reverse flow baffled and packed mufflers because they are the only type that work in terms of sound deadening and drone reduction. The day I see an OEM “straight through” design that sounds quite, is the day I’ll change my mind. I see OEM with Iridium and platinum plugs, and syntactic oil, but alas the one of the magic wonders of the automotive world ““straight through” mufflers, goes with the spiral intake turbo, the slick 50, and the Zmax.. Sure straight through mufflers have less back pressure, they also have less sound dampening, and hence are called resonators by the OEM used in conjunction with a normal muffler to dampen harmonics mid stream. Not as a primary rear muffler which is baffled, will always be baffled, has always been baffled.

http://www.dynomax.com/superturbo.stm

and yes that is 410 cfm at 20 inches of water or about .5 PSI and you think you can get less drop / more flow from a "straight through" muffler? The only reason there are fart can mufflers out there is because the is a perception that noise makes power. For me my turbo Integra made 350 Wheel HP with a muffler on it and yes it was Camry quite, my Jetta made 300 ft -lbs to the wheels and yes it was near Camry quite and it used the OEM exhaust with my own hand made down pipe. My Scion tC will be just fine with the factory exhaust upto my listed 225 BHP.

niguels

The whole reason for the backpressure thing is that high rpm cams (like in our cars) have longer intake/exhaust valve overlap.

At high rpms this is great for power, but at low rpms you end up sucking some air/fuel out the exhaust.

A limited amount of backpressure will stop so much air/fuel from
flowing out the exhaust, and create slightly more pressure in the cylinder.

This will improve low/mid rpm torque, iddle, emmissions, and fuel mileage at the
expense of high rpm power, unless the restriction is removed at higher rpms.

FOR THAT REASON the muffler in our cars does incorporate a valve that opens at high RPMS reducing backpressure exactly when the engine needs it.

Now, please stop saying that the people at Magnaflow are EXPERTS because it trashes all the hours that REAL and EXPERT engineers have put in designing a nice car, besides the fact that it sounds silly, poor informed and NON-SENSE.

hahaitzskippy

but dont the engineers work towards

FUEL EFFIENCY, AFFORDABILITY, OPTIMAL POWER, CARB LEGAL?

all in one?

so when toyota designed the exhaust system wouldnt you think that they made the stock exhaust 2.5 inches to meet all of those?

while an aftermarket exhaust burns more fuel making it INEFFIENT, yet it produces more power it will be harder to legalize and the noise level would be TOO MUCH for the average driver.

so what if toyota did it on purpose?

no mean to flame...

i see the importance of backpressure but i also believe to much will restrict HP/TQ

niguels

It is much more complex than that. Actual diameter helps maintain a good escape velocity for the gases. If you increase the diameter of the pipe then you end up reducing the speed of the gases, which is not good. A too small diameter for the pipe would be too restrictive hurting the car's performance.

I agree with you regarding design trade-offs. They have to comply with many restrictions accross the country and specially the ones in California for emmisions and sound levels, but the car is designed to comply with regulations and still perform "sporty" at high RPMS. As a matter of fact the tC qualifies as a low emissions vehicle.

I like my car being quiet, but that is just a matter of tastes.

oldman

right agreed and the compromise is the exhaust after the stock header is sub 10 WHP, which is fine.

The header is OK from the factory and I see maybe 5 to 10 WHP with an optimal header and CAT, once again the factory compromise some HP for a cooler quiter cheaper factory header (twin wall design). I'm sure OEM it was an expensive header to build. Repacement headers may offer 5 to 10 WHP at a cost of $400+ bucks and will run hotter and will be louder due to their single wall design.

So the factory of course has compromises, but it is really a well engineered piece for a $16,000 car. The Scion is HEAVY runs on plain fuel and is just slightly slower then my GS-R Integra which was way lighter, way more expensive and needed high test fuel and was a masterpiece of design.

The Scion is a very impresive piece all in all, and the compromises were few and far between. Any atempt to gain compromise HP will result in louder and for me that is a no no. I don't want noise.

I see the stock exhaust as a near perfect piece, even upto mild supercharger.

sithscripter

A bit of Googling brings up a number of examples (e.g. beater cars) with measured exhaust backpressure >= 15 psi. Scary to think about but I live one sound wall away from the I-5 and every night I hear plenty of excessive backpressure.

I'm not saying this article will qualify Magnaflow for a Nobel prize but it's the first explanation I've read that jibes with my understanding of fluid dynamics, (If you must know, I got a C+ and that was 18 years ago ...) in particular the Bernoulli equation. It also explains the "observed reality" of wide-open exhausts hurting low-end torque.

So if it's all that easy why don't we see aftermarket exhausts bench-tested this way? My tinfoil-hat theory ... only a few companies can afford that kind of testing, and their marketing departments would rather sell exhausts with technical witchcraft.

engifineer

Guys, the key is the proper balance. Too much backpressure takes away from performance, just as too little does. You need bigger exhaust in a non-naturally aspirated engine to allow for the increased air flow. But too little backpressure does have a negative impact.

niguels

Magnaflow's reasoning does not address engine dynamics as the effect of having a high revs engine in whick intake and exhaust lobes overlap for higher rpm performance, they assume the engine behaves the same at any number of RPMs, but the truth is that flow dynamics at low RPMs are different than flow dynamics at high RPMs. For that reason the model they propose is flawed.

For sure they are going to present a theory that backs-up their products, don't they want you to buy their products? is all marketing tactics.

They are just telling half of the truth and manipulating it so that way people believe in their products, something like.... ooohh, how I didn't realize this before?

They play with the ignorance of the people by putting together a writeup that only very few with enough technical background would argue. Result: minimum bad word of muth regarding their products.

Yes, there are gains in horsepower, but everything comes at a price.

If somebody is expecting to install a low restriction exhaust system, being concious of the price (not cheap), low horsepower gains and drawbacks (torque, iddle, noise) then is fine.

At the end... The Beauty is in the eye of the beholder.

oldman

yep

niguels

agreed

cq107

wtf its cheap as hell, take off your muffler and get a muffler shop to make a turn down... $40

idle noise isn't a problem, sure there is some "noise" but if you have the radio on you can't even hear it.
as for low rpm torque "loss", that’s what a manual transmission is for. I highly doubt peak torque has dropped since having no muffler, and I highly doubt peak BHP has increased.
I am an audiophile. I love sound. For me, the noise the car makes now makes driving this car an even bigger joy.
For those interested, I’m going to post some sound clips later tonight (probably close to 11pm PST).

niguels

We never talked about high RPM torque. The loss of torque with a low restriction system occurs at LOW RPMs.

Again, if people don't mind losing torque on the low end for a gain at the high end, then is OK.

sithscripter

In real life (your car moves) your tailpipe is spewing exhaust into the low-pressure wake of your car ... a cutout spews exhaust into the high pressure air cushion created by lift under your car. Not sure how significant this effect is but it's something a dyno can't simulate.

cq107

I never said anything about high rpm torque as well. I said I highly doubt PEAK (or the MAX) torque has dropped.

VERY interesting point. Gotta find some math guru friends and ask them about that...

niguels

ok

oldman

max torque is at 4000 RPM, don't know about you but 95% or more of my time is spent below that range going here and there. Low end torque will go down. I agree with the rest of your statement in general terms.

Yes you can make a cut out for little money, but you ain't even getting a decent tip nor a shop to put on a high quality axle back for $40.00. I can build my own exhaust and have done so. The Scion axle back is um very difficult, you can just go straight back but room for the muffler is limited to some bullet type "straight through" which will be a droner for sure. Or you can go thru a complex curve travers muffler and then a complex curve out, an expensive setup that if not done perfect will rattle. Or you can get a TRD setup with the T muffler. There are some expensive side in side out chamber mufflers too. All in all it ain't cheap to do it right hence IMO the TRD offers the best compromise and minimal WHP IMO.

Look max pressure at the front of the car is say .5 PSI at 120 MPH. Rear trail vacuum is less then that. At say 50 MPH it will drop to immeasurable readings unless you have a namometer. Under the car is a low pressure area too. I would not suggest an exhaust pipe facing straight forward, but there is really no gain from any type of air movement extractor design despite what some tips makers claim. But yes at high speed with the proper placement there is so minimal gains, rule of thumb just don’t face them forward!

JLTD

Actually, Area of a cylinder = PI x Radius ^2 x length. So your example here starts @ 864 sq.in.

Tamago

oh my god, have you ever heard of Pascal's Law?

you're a science-moron..