6G Celicas Forums

I take it you guys didn't actually read the entire post, then.

Backpressure happens with big pipes or small. How it happens is just different.

I'll repeat myself: Big pipes have lower initial backpressure, but quickly create turbulence (a form of backpressure) because they let the gas expand, cool and slow down.

Big pipes have backpressure.
It's the equivalent, roughly, of a river getting blocked up by ice. The engine is then spending too much energy trying to push exhaust gases out of the pipe because the expanded, cooler gas is acting like an ice dam.

Small pipes have backpressure.
Small pipes can't accommodate all the exhaust gas coming out, and it bottlenecks.

Backpressure is bad, period. Flow velocity is good, and is what allows engines to run efficiently. Big pipes mess up flow velocity by allowing the exhaust gas to slow down. Small pipes mess up flow velocity by not allowing the exhaust gas to enough space to move.

Turbos need larger pipes because for the same engine size, they pump out more exhaust gases. Which only makes sense, they're burning more fuel and air. The presence of the turbo in the exhaust stream also changes the equation, as that lower initial backpressure of large pipes is utilized in concert with the initial high flow velocity from the engine to improve turbo response -- there's a pressure differential emphasized by larger pipes.

AHHH all that stuff about backpressure and what not is causing my simple minded brain to explode!! PERIOD PERIOD!!!! Slap on a loud muffler and drive around. If you don't like it loud get a silencer (I can't even spell now Thanks a lot!). PERIOD PERIOD!!!

Galcobar, you're telling me that and engine that doesn't have any exhaust at all, completely removed manifold and everything, it still creats backpressure? Your arguement makes a lot of sence. Different exhaust sizes completely makes since how big and smaller for different rpms and what not. But you just can't tell me there is some back pressure at low rpms on a car with no manifold or anything.

there wouldn't be backpressure w/o a manifold because it would just dump out immediately, but who would be able to handle the noise, the smell, and the white trashiness

You'll note I never made any comments about backpressure without an exhaust.

So, let me clarify -- exhaust systems have backpressure (except at that perfect pairing of RPM and pipe size where the amount of exhaust exactly matches the capacity of the piping). The problem occurs when the exhaust exits the engine and enters the exhaust system. It's still got all that pipe to travel through, which is where letting gas slow down is the problem. You end up with the fast-moving gas coming out of the engine slamming into the cooler, slower-moving gas still in the pipes.

No pipes, no logjam of fast versus slow exhaust.

Interestingly, it's actually possible to improve peak engine performance with a properly designed exhaust system, as it can improve scavenging (creates a vacuum that actually pulls the exhaust gas out of the combustion chamber).

2-stroke engines on the other hand need backpressure to run properly, this might be where the, dare i
say "myth", that 4-stroke engines need backpressure originated?

I'm not saying that i'm right, but what Galcobar says makes most sense to me.

i'm open to other statements

Get ready for a complete mind melt because I'm going to explain something that most people don't consider let alone even know about: Resonance. The Celica actually has two resonators, one in the intake and one in the exhaust. Both intake and exhaust tracts act similarly in terms of resonance but each of them use resonance a little differently.

When a valve opens in the head a shock wave is produced because of the differential in pressure that exists between the inside of the combustion chamber and the intake/exhaust track. This shock wave is negative pressure and travels (at the speed of sound) all the way to the end of the tract where it meets the atmosphere. The pressure difference that it encounters there creates another shock wave, this time positive, which goes back down the tract until it reaches the valve again. If this positive shock wave hits the valve when it's open it will result in pushing whatever gases are in the tract into the cylinder. This is a good thing in the intake tract where you want more fuel/air mixture dumped into the cylinder. It's quit the opposite in the exhaust system where you want the gas in the cylinder sucked out. Therefore you want the pulse in the exhaust system to hit right before the valve opens so when it does the gases in the cylinder are sucked out or "scavenged" by the now leaving shock wave. The frequency at which this happens changes with the RPM. When an engine has a "flat spot" at a certain RPM this is a likely culprit.

I'm sure the engineers at Toyota spent countless hours designing the intake and exhaust tracts to be a good compromise between performance, economy, reliability, emissions, etc. When one part or another is changed from it messes with the resonance and possibly something else needs to be done to correct it if you want to maintain that stock compromise. Most of us don't so we give up a little economy or take some power away from one part of the horsepower curve and give it to another. What's important here is the volume of the given tract. If the exhaust diameter grows the increased volume of the pipe should come out of some other part in the system. This is an over simplification but I hope you get the picture.

I believe the celica has two on the intake, one big resonator in the driver side fender and one small one on the throttle body intake pipe.

Nice explaination
I always thought the resonators were to muffle the sound of the intake.

-------------------------------------------------------------------------------------------------------------


on a totaly unconstructive argument, fart cans are for ricers.
(no offense to fart can owners, heh)


-------------------------------------------------------------------------------------------------------------

what if you had small pipe going from header to resonator and a bigger (.25" or .5" more) pipe going from resonator to muffler? what kind of effect would that have?

to revive from the dead as I didn't want to post in the official custom thread...

this member says he has drone on the freeway at 75 mph and im assuming he's at 3,600 rpm on the freeway. (225/45R17 tires with a 3sge beams motor which is same motor as mine)

I have a 57mm exhaust with 14 inch magnaflow resonator and magnaflow chambered 57mm inlet/outlet muffler



question is how much more hp can a straight through muffler be over the chambered design?

has anyone ever seen the inside of the magnaflow chambered muffler?

my plan is to get 2.5 inch piping after 57mm magnaflow resonator so it mates up with a 2.5 inch inlet/outlet magnaflow straight thru muffler. Since richee3 has droning at 75mph on freeway and he has catalytic converter will the sound be different for me if since I won't be installing catalytic converter? plus he has the vibrant ultra quiet resonator so it's a bit weird that his drones.

the vibrant straight thru muffler has an oval body of 5x9
magnaflow straight thru muffler has an oval body of 4x9

both mufflers and the same length and width. so in essence they should sound the same right?

This post has been edited by BonzaiCelica: Feb 7, 2013 - 2:38 AM

i wish someone would eliminate the term back pressure.

back pressure is bad, back pressure belongs to old spy movies where someone sneaks up to the tail car and rams a potato spud into the tail pipe so that it cant start.

the only reason why we have exhausts is to direct noise and emissions away from the cabin. if not for that, our headers would dump out the side of the car.

pulse extraction and scavenging are features of specially designed systems which may look like they impede flow, but actually assist in power production (or rather minimise loss of power due to manditory exhaust system) but DO NOT call this back pressure.

say if you get airbourne and land on your front pipe and squash it... theres your ever so valuable back pressure... go jump on a dyno and collect ur extra 20hp.

Also, to whoever says they lost power by freeing up their exhaust, its for one of these two reasons

1. the new exhaust (merges, header length, pipe diameter) doesn't match the flow dynamics of the engine (displacement/cam) OR

2. the new exhaust does match up, but the ECU isn't retuned to match.

Bonzai Its weird that anyone should have drone above the rev limiter

Afaik DaaaaaaaaaaaaaaaaaaaNunNunNunNunNunNunNunNunNunNunNunNunNunN
un isn't called drone. LOL

Drone is around 3000-4000 revs where the rumble of the exhaust reverberates and it sounds like its oscillating

Its the job of the harmonic balancer to remove the vibrations but it doesnt do it all. Polyurethane engine mounts definitely do not help.

what ever drone thats left is usually taken care of by a very effective factory exhaust muffler system

wait haha i totally type that wrong read it again please its suppose to say 75mph and 3600 rpm. hahah

Yea I was gunna say why are you cruising at 7500 RPM at 75 (or whatever rpm it said before)

I know that oscillating sound all too well...

To answer your questions, yes they will sound completely different.

Decat brings on a whole new set of sounds , drone seems unavoidable unless u go back to a small diameter and stock muffler.

The chambered muffler really does dampen a broad spectrum of sound including that ear drum hammering drone, the aftermarket ones comprise a small amount of sound dampening for full flow like a straight pipe would give

As far as back pressure goes, I know our engines don't need it, but doesn't it help with gas mileage on N/A cars?

What size is the exhaust pipe on a USDM 6th gen Celica GT?

No. Backpressure is an inelegant reference to the amount of energy required to move exhaust out of the engine. The higher the backpressure, the harder the exhaust is to move.

Backpressure means one of two things: either burnt fuel is left in the combustion chamber because backpressure is preventing exhaust from exiting the engine quickly, which reduces the production of power, or; energy which could have gone towards turning the wheels is instead being used to help the pistons push the exhaust gas out of the engine.

Either way, you end up burning more gas to get the same performance.

Small pipes are used by the factory because most driving is done at low RPMs, with low exhaust flow. The idea is to minimize backpressure (precisely opposite of what you're asking) where the engine spends most of its time. There's no point in strapping a three-inch pipe onto an engine to achieve peak efficiency at 7000 RPM when the engine actually spends 90 per cent of its time below 3000 RPM producing only enough exhaust to efficiently use a one-inch pipe. To achieve a range of reasonable efficiency, the exhaust system ends up with a compromise size of say two inches.

This post has been edited by Galcobar: Feb 12, 2013 - 1:11 AM

2 inches