high flow exhaust = 3-5% mpg gain?

[some_other_dave]

Some high-dollar cars do have variable exhaust manifolds as well. Or at least exhausts that are changed on the fly. I can think of at least one Porsche and at least one Ferrari that were set up that way. Oh, and a few more street cars that have an "extra noise" button you push to change the exhaust note.

That's not to mention thousands of ricers with "dump pipes" or "cutouts" that make tons of noise and no extra power.

Intakes are pretty clean and low-temperature things. In a modern car, they are transporting clean cool air. You can make moving parts that will move freely and seal nicely for a long, long time. Exhausts are a very hot, wet, dirty environment with acids and soot and all kinds of nasty stuff in them. It is tough to make articulating parts that will last a long time moving freely and sealing well.

-soD

[roflwaffle]

Originally Posted by dcb

Please cite your sources, or admit your mistake.

It's not a mistake, just out of context (Use the search Luke! ). Mazda seems to have designed their exhaust manifold to minimize the amount of hot gases left in the cylinder, and along with other changes this allows them to increase the CR w/o knock, which is where the mileage improvement comes from.

[user removed]

Originally Posted by roflwaffle

It's not a mistake, just out of context (Use the search Luke! ). Mazda seems to have designed their exhaust manifold to minimize the amount of hot gases left in the cylinder, and along with other changes this allows them to increase the CR w/o knock, which is where the mileage improvement comes from.

Green Car Congress: 2012 Mazda3 to offer new SKYACTIV gasoline direct injection engine and SKYACTIV automatic transmission

It seems that they are claiming the 4-2-1 exhaust is one of the factors that allows them to run a 14 to 1 compression ratio.

While it may or may not be a high flow exhaust as the OP thinks improves FE, it may be both or it may not. Certainly looks like a high flow system but I would think it is more designed for low speed efficiency since everything else seems to be pointed in that direction.

regards
Mech

[robertwb70]

Originally Posted by Old Mechanic

I would think it is more designed for low speed efficiency since everything else seems to be pointed in that direction.

I doubt that, I bet peak power is still north of 6,000 RPMs like just about every other engine these days...

[dcb]

Originally Posted by roflwaffle

It's not a mistake, just out of context (Use the search Luke! ).

It is the claimers job to provide context, internet is a big place with lots of contradicting information.

Originally Posted by tjts1

...High FE is goes from 33 to 40. ...
Who says exhaust work can't yield FE?

From the waffle link, the engine sees "%15 improvements in mpg".

And the exhaust mods are listed under "Anti-knock", and force retarded ignition as well.

So it still doesn't add up from several angles.

[roflwaffle]

No it's not, at least not in this case. I took me all of one search and three links to find the information from Mazda. It's also not high flow, but high scavenging that allows higher CR.

[robertwb70]

Their website is tauting the highest compression gasoline engine and the lowest compression diesel engine...both with 14 to 1.

[NHRABill]

This post went awry... From a statement of changing exhaust and tires to see fe improvement to the defense of sorry don't believe anything till it is proven.

Don't take this the wrong way but the prove it defense is childish. Engines are very complex and depending on the setup and combination you are using an exhaust can hurt or help you. Some engines sacrifice performance for smoothness or quiet some sacrifice fro performance and still others are tuned for efficiency from the factory. Can they be changed? Yes. Can improvements be made? Yes. But it depends on what areas you are looking to improve.

Depending on the test and your needs changing the exhaust to suit your driving style can yield an improvement. Welding up a set of equal length or long tube headers is nothing new, porting and polishing your heads , intake runners or plenum are things that also improve the engine flow increase performance and power. Do I need to prove this or can I use that this common knowledge to any shade tree mechanic or person who likes to work on cars. Increased engine performance takes less gas fro a vehicle to get to seed using less fuel but when at speed it consumes more gas quickly negating the initial improvement in efficiency.

I increased the exhaust size on my truck because it rarely goes more than 50 miles in a week. The top city speed is 40mph on my daily drive and my OD gear won't switch till I hit 45mph. the gain in torque by the larger exhaust was a welcome addition to my situation.

There is no correct formula that applies to every engine they all have variables.

[suspectnumber961]

I had one of these on a Nissan 3.0L V6 and it had a good sound...not too loud and crisp. It only went thru the cat...then the tip. These have some fiberglass in them.

Pacesetter Monza Style Resonator Tips - JCWhitney

Problem being that they are not ss...so it rusted out in maybe 2 years or so.

Saw something similar in a parts store in ss for much less.


Check out the Borla XS...more power than a straight pipe...and also at lower rpms...

http://www.mustang50magazine.com/tec...o_numbers.html

[Christ]

Originally Posted by jtbo

Modern cars take heat from exhaust and use that to heat cabin, at least some European cars have such system, but that does of course increase efficiency too.

That Mazda exhaust looks quite complex, would be interesting to have some tech analyse from it as I would like to know how it works, that is what I would like to know from everything actually

It's a small profile 4-2-1 long runner, equal length header with integral catalytic converter.

The bends are so mild that they shouldn't interrupt flow much, if at all. It's designed for scavenging, and to keep flow rates high within the tubing.