Will an Exhaust mod help fuel economy?

[ChopsQube]

Digging up a somewhat old thread, but I just thought I'd give my 2 cents, which might be wrong, most likely in fact! LOL

Anyway, for our uses in the "eco" world, I would think that modding/changing the intake in front of the throttle body would be pointless.

The reason I say this is because the things that matter and/or make the difference are the intake runners on the other side of the throttle body (the intake manifold) which some of them these days physically change length via rpm. Beyond that, other designs use variable valve timing that again, change via rpm. Both of these designs are for maximizing breathing and top-end power for the "performance guys", yet on the other end also maximizes breathing, power, low-end torque and efficiency on the bottom-end for us "eco guys".

So short of running either of these engine designs at WOT, there's really no point in modding/changing the intake before the throttle body.

At this point, I'm not saying anything about cold air or hot air as I haven't read up on that yet. I've just seen it mentioned here and there on this forum as well as on GasSavers.

Exhaust systems on the other hand should help both performance and efficiency. For improved top-end performance you would most likely go with larger than stock pipes, a 4-1 header, larger free flowing cat, muffler and delete the resonator altogether. For efficiency on the low-end, you would probably go with a Tri-Y long tube header (4-2-1), same size or possibly smaller than stock pipe and free flowing cat, resonator and muffler. Both systems should utilize mandrel bends for near constant flow speed.


Again, I am no expert on any of this. This is all just information I have picked up over the years from all types of sources. To me, it seems to make sense, but like I said, I could be and possibly am wrong.

[kanoshee]

Originally Posted by Maestro

I know exhaust was the main question of the post, but I see this a lot about the intake, and it's rarely really addressed, so I'm moving from lurking to posting around here...

The effects of intake modifications on pumping loss is very commonly misunderstood. The common assumption is that reductions in intake restriction will lead to reduced pumping losses. This is entirely FALSE at all engine loads other than WOT. On the typical NA engine, a certain amount of intake restriction is CRITICAL to running the engine, otherwise you'd be RPM's.

you should really summarize this i read it three times and still can't really understand it lol

[Tesla]

Wouldn't hold my breath on that one otherwise you might suffer pumping losses.
Did you check the dates?

Never the less exhaust and intake flows always make for good discussions, I've read a few of the older discussions and resisted the grave dig, but seeing as you've brought the corpses out I'll throw my 2c in.

I do understand that any restriction prior to the throttle body is irrelevant as the throttle itself is the greatest restriction, but I do wonder if improved airflow after the throttle body can improve combustion and hence economy. The MAF has measured a certain airflow and the ECU will then decide on appropriate fueling via the injectors, that part is set, but how that volume of air is delivered to the cylinder is what governs the pumping loss surely.

If the manifold is smooth and tuned to the engine needs for the desired operating range it will ensure each cylinder can draw the correct amount of air as it's time comes up, but if it is just a basic tube with one inlet and four outlets, then it will present all kinds of pulsations, turbulence, reverse flows etc. forcing the engine to work harder to draw it's required volume and in addition to that there will be significant variation in how much air each cylinder gets, some will burn lean, whilst others will burn rich.

Just because it is running at a slight vacuum doesn't mean that suddenly flow restrictions and turbulence magically disappear, the air doesn't know it's in a slight vacuum, it still continues to behave like air does.

So yes I believe an appropriately designed and streamlined intake post throttle body can improve FE as can a suitably designed exhaust, so aero inside the engine is just as important as that on the car body.

How do you get it perfect?
With just as much trouble as geting the perfectly streamlined form outside the body most likely.

[mcrews]

Originally Posted by ChopsQube

Digging up a somewhat old thread, b

Exhaust systems on the other hand should help both performance and efficiency. For improved top-end performance you would most likely go with larger than stock pipes, a 4-1 header, larger free flowing cat, muffler and delete the resonator altogether. For efficiency on the low-end, you would probably go with a Tri-Y long tube header (4-2-1), same size or possibly smaller than stock pipe and free flowing cat, resonator and muffler. Both systems should utilize mandrel bends for near constant flow speed.


Again, I am no expert on any of this. This is all just information I have picked up over the years from all types of sources. To me, it seems to make sense, but like I said, I could be and possibly am wrong.

Key words underlined and bolded.

first, nothing new there and second it really has no relevance to ecomodding.
As stated before 'top end or wot (wide open throttle) are achieved maybe 1/10 of 1% of all normal driving much less eco-driving. So 'tuning' for that is really just about presonal feelings and not honest day to day driving results
Now if you are hotrodding or racing, great advise.

as for as your low end comments, again key word is 'stock'. Unless you have a rusted out system, there really would be no financial payback in changing uot an exhaust system.
I presonally feel that in 95% of all cars sold (let me limit this to US mamufacturers) in the last 15 yrs have an effeceint exhaust system for conservative driving.

[Tesla]

Here's a couple of articles/papers,
First is one an F150, economy, & power up.

Aftermarket Exhaust Review: A Review of Power and Fuel Economy Improvements with Truck Exhaust Systems


This on is looking at length and bends in pipe on fuel economy.
http://scialert.net/qredirect.php?do...876&linkid=pdf

[Frank Lee]

It should be noted that a lot (most? all?) of these magazine "tests" are really just plugs for the product(s) being pushed by advertisers. Check this out: http://ecomodder.com/forum/showthrea...k-n-10523.html

[Tesla]

I know what you're saying,
and it is true that in most cases aftermarket exhausts are designed for the "Rev Head" who wants to push more through the engine in the pursuit of power, but that is not necesarily the whole story.

It is a fact that OEM exhausts are a compromise in just about every way, economy, performance, noise, space, etc. in no way do they represent state of the art for economy tuning.

An exhaust can be tuned for free flow to get economy, it's not all about big pipes, it's aerodynamics and optimizing flow for a particular set of conditions. Smaller pipes that are properly configured, length and shape can be used to improve engine efficiency but you'd be hard pressed to find an exhaust shop that actually knew what you were talking about.

The article below talks about some of the intricacies of exhaust design, there is very little out there re economy, but maybe that will change over time.

Exhaust System Technology: Science and Implementation of High Performance Exhaust Systems

[Tesla]

Originally Posted by Frank Lee

It should be noted that a lot (most? all?) of these magazine "tests" are really just plugs for the product(s) being pushed by advertisers. Check this out: http://ecomodder.com/forum/showthrea...k-n-10523.html

Just went through the thread, didn't look at the article,
First point it was determined to be "Bogus" by a roomfull of mutually backslapping ecomodders, maybe the claim was dodgy, but I always question myself when I'm around a bunch of people who all agree with me.
Once you get too comfortable with "been there, discussed that" you start to miss the subtle details of new knowledge.

The most I can see from it is their testing was poorly performed and their claims may have been overinflated,

I didn't see anyone do an A-B-A series of testing using K&N replacement vs new OEM paper filter.

I have heard of people claiming better power and economy with a K&N, but not for me.

The issues with K&N are they do flow more = more crap in engine
The oil can leave residue on the MAF sensor resulting in poor engine management, so I stick with OEM paper filter.

Very true that most of these products are performance/power oriented, but the WOT mantra I constantly hear bantered is such a broad generalisation that just gets thrown about willy nilly that it always pricks my ears and I question if the individual has even bothered to consider the information with an open mind.

For me it is an exploration of knowledge, I'd love to have the funds to explore all this, but until then I will just try to understand it.

[Frank Lee]

Then you need to look at the article to verify how bad it was before vilifying the ecomodders' response, correct?

[Tesla]

Had a look at it,
No doubt that it is more of an info-mertial, but that doesn't mean there is no valid information there.

Ever since the world was privatised nearly every scientific paper you read has an agenda and is trying to sell something.

Their testing methods were poor, but there is enough info out there that suggests that in the right hands and on the right vehicle performance modifications can result in improved fuel economy.

That's not to say every performance mod will, but the right ones can.

My main criticism was that there was no refuting the actual claim of improved economy, just the method in which the claim was made.

With my vehicle being a turbo diesel, any improvements in flow directly translate to improved FE, this is a simple factor of the turbo itself being the biggest restriction, although I think even NA diesels benefit as well by reducing restrictions.

Even with gas engines I believe fuel economy can be improved by improving flow, pumping losses can be reduced even at part throttle by a properly designed intake and exhaust system.
It's not all about the size of a pipe and just because you are not running at WOT, doesn't mean your intake and exhaust is performing ideally. I think that's the part that get's me most often is when people declare that as an ecomodder you aren't running full bore, therefore your exhaust and intake can't really be improved and then there is the simple assumption if a bigger exhaust is for performance at WOT then a smaller more restrictive exhaust must automatically give better economy.

Does this tell someone how to go about exhaust improvements, if I was a newbie and wasn't aware of how complex exhaust matching is I'd be inclined to go home and put a 1/2" pipe on my exhaust manifold with the expectation of getting 100mpg.

It takes a bit longer, but better to tell them that with current offerings you will probably get best economy from the OEM design, but there is a possibility of improving on this though it will require you to do a lot of research and become a semi expert on the topic, anyway enough of that.
Appologies to anyone who took my comments personally.