flowmaster super 40... FE impact?

[tasdrouille]

I don't think you'll see a difference. Diesels, which do not have throttles, have a lot more gasses passing through the system at all times than a similarly sized throttled gas engine. That makes them more sensible to back pressure and negative boost. Yet, at least for TDIs, people removing everything from the turbo back do not generally report increased FE. There probably is an advantage, but it's probably 1-2% or less.

[NachtRitter]

Hmmm... guess I'll scratch the fart can off my mods list...

[ConnClark]

Originally Posted by Daox

Frank and PaleMelanesian are completely right. You won't see any improvement in FE from replacing your muffler. Your car will just be louder, thats all.

Not true.

Lower back pressure means less work for the engine to expel gases from the cylinders on the exhaust stroke.

A common misconception is that that an increase in manifold vacuum due to increased throttling to maintan the same power offsets any gains due to more work being required by the engine to pull the fresh air charge into the cylinder. Since the crank case is connected to the intake manifold via the pcv valve any increase in the manifold vacuum increases the vacuum in the crank case eliminating any extra work needed to pull the fresh charge into the cylinder.

The crank case vacuum does however increase the work required by the piston to expel the spent charge again however this is countered by the increase in power due to the higher pressure differential across the piston on the power stroke.

Another side benefit is that the mass of air thrown around by the under side of the pistons in the crank case is reduced (I can't remember the technical term used to describe this effect). At higher rpms this reduction in air mass reduces drag on the engine.

The end result is a net gain in power (actually a reduction of a losses ) for the same amount of fuel burned.

[Frank Lee]

bla bla... so has anyone gotten better fe cuz uh pulling the muffler off? Dint think so.

[Coyote X]

Put the biggest nastiest cam made in it if you are going to swap to a loud exhaust. I never liked the sound of a stock engine with loud exhaust. It needs a lope to it Then you can start taking it to the track and really have some fun with it.

My Camaro sound clips, clip #2 is stock engine with a loud exhaust. It sounded like every other Camaro and I thought it sucked. But I only had it like that for a week or two before the cam got installed. Clip #3 is with the cam, so with a cam like that it is ok to be loud. Also the cam/other mods dropped me from 28mpg to 15mpg driven normally. So being on ecomodder with a car like that is kind of pointless. But I guess if you want a loud farty/raspy type sound with a stock aluminum engine go for it if that is what you like, everyone has different tastes But it at best won't change your mileage at worst it will drop your mileage. Unless something is wrong with the exhaust on it now you won't see a gain.

[Christ]

Swap headers for something with scavenging and higher flow than stock, use high flow (CARB approved) cats, 60mm piping, and run it into a truly blended y-pipe (not the chevy "under the tranny pan" BS). You might see a gain of 1%, but it will sound A CRAPTONNE better, and you'll have more power when you want to use it.

This is of course provided you're running a stock engine with next to no current modifications, and it's either a V6 or V8 with a naturally crappy OEM exhaust.

[tasdrouille]

Originally Posted by ConnClark

Not true.

Lower back pressure means less work for the engine to expel gases from the cylinders on the exhaust stroke.

It's funny when people talk about back pressure or pressure drop in the piping of charged engines. The condition they talk about is almost always at WOT. Sure, that stock exhaust is very restrictive, at WOT near redline. My IC have a 3 psi drop, at max boost over 4k rpm, but the drop does not even register on the gauge under normal highway driving.

[malibuguy]

it really depends on how ****ty the stock exhaust design is & of course how you drive it, most of the time, if your staying below say like 2500rpm, & barley using any throttle, your not going to see gains for the most part, vice versa, heavy throttle, loads, towing, etc would benifit from a properly designed exhaust

[PaleMelanesian]

Originally Posted by tasdrouille

It's funny when people talk about back pressure or pressure drop in the piping of charged engines. The condition they talk about is almost always at WOT. Sure, that stock exhaust is very restrictive, at WOT near redline. My IC have a 3 psi drop, at max boost over 4k rpm, but the drop does not even register on the gauge under normal highway driving.

Quoted for Truth.

[Christ]

Originally Posted by PaleMelanesian

Quoted for Truth.

Umm.. not exactly. While it may be so miniscule(sp) that it isn't NOTICEable at low-load/low-rpm, fixing any restriction in your intake tract will actually promote better airflow anyway. Plus, you don't magically have 3lbs of pressure loss at full load/high RPM... it builds up to that.. meaning that at normal load/mid RPM, you might have .3PSI of boost restriction (pressure loss/drop)

Part of that pressure drop is not even restriction though, it's just b/c the air charge is more dense when it comes out than it was when it goes in! That adds a whole new dynamic to the equation. If you have a rubber ball, that just barely fits into something, so that it applies pressure on the circumference of a circle, then you nearly instantly drop it's temperature by 30% or more (depending on the setup), it will fall out of that compression fit, which shows that it's not putting as much pressure against the circle. (Or any, in this case.)

Anyway, that's why I suggested a full header and such... the scavenging effect will actually increase airflow, rather than "unrestrict" it, and the full length tube headers usually increase low-mid torque as well.