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-   -   Will an Exhaust mod help fuel economy? (https://ecomodder.com/forum/showthread.php/will-exhaust-mod-help-fuel-economy-12895.html)

morkys 04-07-2010 09:22 PM

Will an Exhaust mod help fuel economy?
 
Some say modding the intake ups fuel use because the increase in air causes more fuel to be injected, in a FI car for instance. I would have thought that for a given throttle opening, more air gets in with less pumping losses when you mod your intake. I figured you'd get more power per unit of fuel burned (due to lower pumping losses), and so as long as you drove properly and conservatively, you would increase fuel economy....but, at least a couple of people have noticed that modded intakes always tend to decrease fuel-economy. Ok, for the purpose of arguement, if we assume modding the intake for higher-flow (as in the typical 'better performance' mods) always increases fuel consumption, then what about exhaust mods?

What about modding the exhaust? I know I could get a header and a slighty larger diameter exhaust, complete with mandrel bent pipes and straight-through muffler etc. All else being essentially equal, will modding the exhaust alone produce an increase in fuel-economy? Or is there another approach to exhaust mods that would increase fuel-economy?

Deezler 04-07-2010 09:33 PM

Well, it kind of depends what KIND OF CAR you have, haha.

Your theory is right on, reducing pumping losses should always lead to better FE. The problem is that if you start fooling the vehicle airflow or O2 sensors, you may end up over fueling for no reason (computer is fooled). Also, slapping a big bore intake and exhaust system could actually reduce volumetric efficiency and thus raise pumping losses at certain / lower rpms. Because engine friction rises with rpm, and fuel conversion efficiency is better at lower rpms, this can mean a loss of mpg in everyday driving. So if you have a N/A car I would avoid a completely free-flowing exhaust. If it didn't hurt your FE, it still sure as heck wouldn't pay for itself in fuel savings.

Now, if your car is turbo / super charged, I would say go for it. They nearly always respond well to bigger pipes.

morkys 04-07-2010 10:13 PM

Naturally Aspirated 2001 Corolla CE. 1.8L VVTi and no mods other than a drop-in K & N air-filter, semi-synthetic manual tranny fluid and synthetic engine oil. If I modded the exhaust, it would be a mild mod for smoother flow, not a huge increase in diameter etc. You're right about the increase in size possibly messing with flow and volumetric efficiency at lower RPM's. I'll do some research and plan a mild mod with possibly slightly increased diameter mandrel bent pipes as the main feature for improved flow. I actually wish I could make my car have better MPG on average, but also be able to go fast occasionally, but if that can't be done, I'll lean towards better fuel economy. For a grocery getter, the little Corolla goes fast enough when necessary, which, in reality, is almost never, especially when driving for fuel-economy. I'm glad I found this forum. I feel less crazy now when I see how many KM's I can coast with the engine off....lol... :)

AeroModder 04-07-2010 11:35 PM

Don't bother with larger diameter pipes. You'll see a drop in low-end power from the reduced flow velocity. You're better off going with a higher-flowing muffler and catylitic converter and leaving the stock pipes in place. That's the setup I have.

As it's been stated, reducing pumping losses helps both power and economy.

Ryland 04-07-2010 11:41 PM

It's all about math, lucky for you someone figured out the formula for the correct size for you already!
Autolounge.net | Calculators | Exhaust Pipe Sizing

Frank Lee 04-07-2010 11:55 PM

Dumb auto engineers must not have access to that formula since they persist in putting too small pipes on everything :confused:

2win2rbo 04-07-2010 11:59 PM

Quote:

Originally Posted by Ryland (Post 169693)
It's all about math, lucky for you someone figured out the formula for the correct size for you already!
Autolounge.net | Calculators | Exhaust Pipe Sizing

That's not a bad site. The figure that I got is almost the same as what is installed in mine.

Maestro 05-16-2010 09:11 PM

Intake Restriction and Economy
 
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 running at full throttle, all the time. In order to decrease power output from WOT at a given RPM, you need to decrease the pressure outside the intake valve, thereby allowing less air and fuel to enter the combustion chamber, which will then produce less power than would be done at WOT. The only remaining way to alter power output without changing pressure at the intake valve is by altering the fuel/air ratio. And since the cylinder/piston and intake valve essentially create one big vacuum pump, the way to reduce the pressure outside the intake valve is to create restriction in the intake path. That is THE function of the wonderful device we call a throttle: creating restriction.
So, say your car runs at 1800rpm and 10% throttle at 55mph. If you then go and modify the intake to be less restrictive, you may now need only 8% throttle to maintain this same condition. And the condition that you are maintaining is a certain pressure outside the intake valve. Therefore, in order to maintain the same output you have not changed pumping losses at all, you've simply altered how much restriction is being created by each individual part of the intake. So you are correct in thinking that decreasing intake restrictions would reduce pumping loss at a given throttle position, but what you need to consider is that a reduction in pumping loss on the intake side means more air is now entering the cylinder, and you're producing more power, using more fuel. So to maintain the same RPM/speed/load etc. as before your intake mods, you need to reduce the throttle opening to get back to the same total restriction you had before the mods. If you apply these principles to the performance end of things, the reason intake mods can improve top-end performance becomes clear. If you can now move the same amount of air at 95% throttle that you used to move at 100%, you now have headroom to increase power. (note: intake modification can improve performance below WOT, however any improvement in performance below the throttle position that moves the same amount of air as the pre-modded WOT will be due to harmonics, not reduced flow-restriction)

I would question the assumption that reduced intake restriction hurts fuel economy. Any reduction in economy with such mods is not directly related to the reduced restriction, since as we see above the TOTAL intake restriction must remain the same at a given load. Other factors come into play though; A) intake mods will often be CAI-related, which may reduce economy. B) Throttle position at load is affected, more importantly, it's reduced. Therefore your accelerator is more sensitive, and you may be giving more effective throttle than you used to be without even realizing it.


As mentioned, pipe size is critical in determining MPG loss/gain with exhaust modification. Proper scavenging lowers the pressure beyond the exhaust valve and can increase efficiency. Improper sizing can have the opposite effect, but it is all dependent on the desired efficiency range in terms of RPM's.

2win2rbo 05-16-2010 10:43 PM

^^^ I agree, that is very well said.

ECONORAM 05-16-2010 10:55 PM

What you need to consider is how the exhaust pipes are bent. If they are press-bent, then the pipe diameter is reduced (sometimes dramatically). mandrel bent tubing is the best way to go. It keeps pipe diameter constant, which keeps exhaust velocity constant.

Christ 05-17-2010 12:24 AM

Adding to the mandrel bent exhaust tip (which, apparently, many GM cars have as OE exhaust systems), any curves in the exhaust should be kept to a minimum. Even if you have a mandrel bent exhaust, the flow around a curve is not at a constant diameter. As speed increases, the flow attempts more and more to continue traveling in a straight line. Changing the flow's direction suddenly causes it to "stack up" against the outer radius of the curve, just past the apex (highest point, or center of the arc).

In order to keep exhaust velocity constant (mostly) you actually need more shallow bends (if any at all) and any bends you do have must be smoothly designed and of a larger diameter than the entry pipe, with no more than a 15-18* (I believe) transition step angle (the expansion of the pipe can't be any more than that).

Getting a little complicated, yet?

Ryland 05-17-2010 09:11 AM

You asked about intake, intakes fallow the same rules as exhaust, not the exact same numbers to figure out the ideal size but the same basic rules, if this was not the case you would put your air cleaner right on your throttle body, if you do this you will get the least amount of "restriction" and your car will run poorly and installing a plate with some kind of restriction would not help, just like adding a clogged restricted air filter would not help "but my car needs restriction to run correctly!" is BS created by people who can't read and don't understand math.
Air has mass to it, when you have anything with mass moving it will want to keep moving, air entering your engine is moving in pulses, not a constant flow, your engine and intake are designed to work together in this area, putting to large of an intake on is going to have the same kind of affect as removing your intake altogether, that is part of the idea behind the VVTi, you have a runner for each intake valve and half of the runners are closing off completely at lower engine speeds.

Maestro 05-17-2010 12:38 PM

Quote:

Originally Posted by Ryland (Post 174906)
"but my car needs restriction to run correctly!" is BS created by people who can't read and don't understand math.

Wow. What an incredibly rude thing to say. I guess that will teach me to join a forum and try to be helpful. Thank you sir, for putting me in my place. Fortunately though, I can read and do understand math, so I guess that BS was created by someone else, not me. Your car does not technically need restriction to run "correctly", but it does need restriction to run controllably. Take off your throttle body and see how you do.

I stand by my original post, as well as my decision to largely ignore intake harmonics and focus on explaining total restriction. Intake harmonics are important for performance and can alter throttle position at a given load just as overall reductions in restriction can, however this falls right back into what I said before; if you improve harmonics at a certain load, you've just increased the average pressure outside the intake valve, and you'll just have to decrease throttle position to stay down to the same load you were at previously. You have not helped economy, only performance. Consider the fact that, ultimately, pumping losses are essentially created on the face of the piston, and the only way to alter this loss is to alter the pressure on the face of the piston. To do this, you must affect the amount of FA mixture entering the chamber, and it does not matter to your MPG meter whether this is done through harmonics or restriction, the effect is the same; pulse pressure at the intake valve is varied, and you have to ignite either a denser or thinner FA charge.

Since the majority of the people here are building for economy, not performance, I would say that most can ignore intake harmonics. Economy-wise, intake temperature can help, and realistically, that's it. The physics do not support anything else. A large increase in total intake restriction or alteration in the throttle cable-cam may also help by decreasing accelerator sensitivity, but this would be more an alteration to the driver than the engine.

Ryland 05-17-2010 04:36 PM

Quote:

Originally Posted by Maestro (Post 174939)
Wow. What an incredibly rude thing to say. I guess that will teach me to join a forum and try to be helpful.

Sorry if you were offended, it's just that the design of engine intakes has been studied and written about many times, there are SAE, hotrod engine tuning books, motorcycle engine tuning books, along with web sites on the same topics, all of these sources tend to agree, to big is not good.

Chalupa102 05-17-2010 04:48 PM

I would recommend not going anything larger. On my '05 Toyota Corolla A/T, i had an aftermarket 4-1 header, 1.25" custom exhaust piping from the cat, and an aftermarket muffler installed a few years ago. At the time i did all that, i wasn't really keeping track of gas mileage. A few months ago i switched back to the stock muffler/piping and exhaust manifold and f/e actually went up.

Maestro 05-17-2010 05:54 PM

Quote:

Originally Posted by Ryland (Post 174906)
my car needs restriction to run correctly!" is BS created by people who can't read and don't understand math

Quote:

Originally Posted by Ryland (Post 174986)
all of these sources tend to agree, to big is not good.

Now you are contradicting yourself--as bigger is almost always less restrictive--as well as missing the entire point on the discussion of intakes and economy. Which is that, for the most part, IT DOESN'T MATTER. Certain runner sizes are beneficial for PERFORMANCE due to air velocities and harmonics, which as I mentioned before are not going to affect ECONOMY. I never said bigger was better anyway, nothing remotely like it, in fact.

In any case, you have given me no reason to retract anything I said about total intake restriction and its relationship to efficiency at low loads. I would point out that "all these sources" you are citing are performance oriented, not economy oriented. So until you show all these sources demonstrating how intake modifications affect economy in any way other than the ones I already mentioned or derivatives thereof, I think I'm done here.

Christ 05-17-2010 06:03 PM

SAE is hardly a performance source...

Maestro 05-17-2010 06:18 PM

Quote:

Originally Posted by Christ (Post 175004)
SAE is hardly a performance source...

I'll buy that, to some extent. But for it to matter, you'll have to show a SAE quote showing how intake volume/restriction/whatever, improves economy, rather than (or in addition to) performance. I'm not being sarcastic to say that I would be extremely interested in such a source.

Christ 05-17-2010 06:28 PM

I was just pointing it out for the sake of those who didn't know any better. I don't have a source from SAE, that I know of, regarding intake restriction on any level.

I will note, however, that only for Otto cycle and 2-stroke gasoline engines is an air-throttle actually necessary, and there are actually DI-type gasoline Otto cycle engines which no longer require an intake throttle. Their speed/power is controlled by load and fuel input, like a standard compression ignition engine.

I'm not sure that it's entirely relevant to the OP's question, but you (Maestro) mentioned earlier that throttling restriction was necessary to make an engine run "in a controllable fashion" and didn't clarify any further.

Welcome to EM, by the way. Maybe try a proper introduction?

Maestro 05-17-2010 06:47 PM

Thanks for the welcome! Yes, I should introduce myself. Hello everyone, by the way.

I mentioned in my original post, but yes, it's worth reiterating that the discussion of total intake restriction only applies to the typical throttle bodied, NA engine (though arguably it's even more relevant to supercharging). For those interested, in addition to diesels and DI, there are some interesting gasoline designs employing variable compression and variable valve timing that can largely negate this issue.

comptiger5000 05-18-2010 06:36 AM

Chalupa - What was hurting your FE was the 4-1 header. Those move the power up too far in the RPM range. A fairly long tubed 4-2-1 would be a better choice for FE.

micondie 05-18-2010 08:22 AM

[QUOTE=Maestro;174858] So, say your car runs at 1800rpm and 10% throttle at 55mph. If you then go and modify the intake to be less restrictive, you may now need only 8% throttle to maintain this same condition. And the condition that you are maintaining is a certain pressure outside the intake valve. Therefore, in order to maintain the same output you have not changed pumping losses at all, you've simply altered how much restriction is being created by each individual part of the intake. So you are correct in thinking that decreasing intake restrictions would reduce pumping loss at a given throttle position, but what you need to consider is that a reduction in pumping loss on the intake side means more air is now entering the cylinder, and you're producing more power, using more fuel. So to maintain the same RPM/speed/load etc. as before your intake mods, you need to reduce the throttle opening to get back to the same total restriction you had before the mods.

What jumped out at me while reading this is that if it takes less throttle opening to maintain the same speed then your motor is taking in less air and since you have the same air/fuel ratio, you are using less fuel!
Or is there a flaw in my logic?

Maestro 05-18-2010 08:59 PM

Quote:

Originally Posted by micondie (Post 175082)
What jumped out at me while reading this is that if it takes less throttle opening to maintain the same speed then your motor is taking in less air and since you have the same air/fuel ratio, you are using less fuel! Or is there a flaw in my logic?

Yes, I'm afraid there is a flaw in your logic. Read carefully. What I'm saying is that with reduced restriction elsewhere in the intake, you're now flowing the same amount of air at a lower throttle opening, so nothing really changes.

This is easily visualized if you take it to the extremes. Imaging blocking your intake prior to the throttle body with a plate with a 1/2" hole in it. Imagining you could even support the engine with such a hole, you would need to open your throttle very far to reach the same airflow you would have had without the plate at a smaller throttle opening, however once you open the throttle to achieve the same flow, everything is the same. It works the same in reverse with less restrictions instead of more.

Christ 05-18-2010 10:25 PM

Quote:

Originally Posted by Maestro (Post 175180)
Yes, I'm afraid there is a flaw in your logic. Read carefully. What I'm saying is that with reduced restriction elsewhere in the intake, you're now flowing the same amount of air at a lower throttle opening, so nothing really changes.

This is easily visualized if you take it to the extremes. Imaging blocking your intake prior to the throttle body with a plate with a 1/2" hole in it. Imagining you could even support the engine with such a hole, you would need to open your throttle very far to reach the same airflow you would have had without the plate at a smaller throttle opening, however once you open the throttle to achieve the same flow, everything is the same. It works the same in reverse with less restrictions instead of more.

To oversimplify the concept - The throttle plate is the single largest restriction in your intake system. Excluding small gains in flow velocity from smoothing pipes, and only adhering to basic flow principles, intake mods will only work at or near WOT because of this.

That said, there are other sciences involved that can improve the VE of the engine, thus decreasing it's BSFC via reduced pumping losses. The amount of gain achieved at our levels of operation by such things is essentially non-existent, though, unless the pump itself (engine and auxiliary systems) is tuned as a whole for a specific desired effect.

micondie 05-18-2010 10:50 PM

Quote:

Originally Posted by Maestro (Post 175180)
Yes, I'm afraid there is a flaw in your logic. Read carefully. What I'm saying is that with reduced restriction elsewhere in the intake, you're now flowing the same amount of air at a lower throttle opening, so nothing really changes.

This is easily visualized if you take it to the extremes. Imaging blocking your intake prior to the throttle body with a plate with a 1/2" hole in it. Imagining you could even support the engine with such a hole, you would need to open your throttle very far to reach the same airflow you would have had without the plate at a smaller throttle opening, however once you open the throttle to achieve the same flow, everything is the same. It works the same in reverse with less restrictions instead of more.

Your example doesn't make sense. If you have a restrictior plate with a 1/2" hole before your throttle no extra amount of throttle opening is going to make more air flow through that 1/2" hole. That hole is the limit. Your throttle at idle probably has less air flow than that 1/2" hole but once you reach the flow limit of the hole that's it.

Christ 05-18-2010 10:53 PM

Quote:

Originally Posted by micondie (Post 175197)
Your example doesn't make sense. If you have a restrictior plate with a 1/2" hole before your throttle no extra amount of throttle opening is going to make more air flow through that 1/2" hole. That hole is the limit. Your throttle at idle probably has less air flow than that 1/2" hole but once you reach the flow limit of the hole that's it.

That's exactly what the example said...

If you put a restriction in front of the throttle plate, you have to open the throttle further to get the same amount of air through it under vacuum (this does not apply the same way under boost).

Still, the point is that removing any restriction prior to the intake's throttle butterfly just means that you have to open the throttle that much less to get the same amount of air into it. You're still using the same amount of fuel, regardless.

Maestro 05-18-2010 11:32 PM

Brace Yourself
 
That is why I said to imagine that the hole could even support the engine!

To go to an analogy: Let's say your engine is a pool, and it needs a very particular supply of water to keep you relaxing in your backyard at peak efficiency. Let's say we're supplying this water with a garden hose. And on the end of that hose we have one of those old-fashioned metal sprinkler nozzles that you can screw shut/open. So we run the hose to the pool and adjust this nozzles to provide this perfect amount of water. Then, your annoying neighbor goes and steps on the hose back by the house. A restriction is created, the pressure at the nozzle drops, and you have to open it more to maintain the same flow. The intake issue is the opposite of this. Your intake is like the hose with the neighbor already stepping on it, except in this case, while he's stepping on it everything is perfect. Your pool is happy and your Saturday is wonderful. If you now go and knock your neighbor off (i.e., reduce total intake restriction) you will now have to go back and close up that nozzle (TB) to stay at the flow rate you were at previously. If you don't go close up that nozzle your Saturday will be ruined because your engine ran too fast and you got horrible MPG's.

In general, the restriction of the TB compared to the restrictions of the rest of the intake is huge. Therefore any change in the rest of the intake will likely result in a very small change in TB opening to maintain load. The main point though is that any small change that occurs will not improve your economy, because ultimately you're still filling that pool at the same speed.


To go more technical:

In any case, if we can agree that this hole supports a theoretical engine at idle, that is sufficient for our purposes. You are correct in saying that this hole has a certain limit to the air passage it will allow (given a certain pressure gradient), however, this limit is not directly relevant until we reach it. Let's say that at 500rpm, the engine requires 3/4ths of the air this hole can pass. That would indicate that at 500rpm, this hole is a considerable restriction. Because of this, we do not want to create a great deal more restriction with our throttle body. If we do we will not get sufficient flow. So, let's say we have no idle air control and must supply idle air with throttle opening, and that our hypothetical engine--without this restrictor plate--requires a 2% opening at 500rpm. Now, if we put on this restrictor plate and leave our throttle at 2%, we will no longer be getting enough air into the engine. The reason for this is that while we have not reached the maximum flow that the 1/2" hole can support at atmospheric pressure we have created a significant restriction in front of the throttle body (Incidentally, the effect would be almost entirely the same if we created the restriction behind the TB, though that may just confuse things for now). Because of this restriction we have dropped the pressure gradient across the TB, and therefore we have reduced the amount of air it can flow at 2% opening.

Imagine an intake manifold at vacuum, and the air outside your air filter at atmospheric pressure. There is no single point where this pressure switches; as we move along the intake tract towards the intake valve every restriction to flow is causing a reduction in pressure, eventually subtracting all the way down to your manifold vacuum. On the typical engine, a nearly closed throttle body is by FAR the largest restriction in this system. So, the pressure outside a nearly closed throttle body can be very close to atmospheric, while the pressure just behind it is high vacuum. However, the further away from low-flow conditions (i.e. Idle) that we go, the more other components begin to contribute to restriction. Components are commonly rated for flow at a certain pressure. What is important to note is that this rated pressure is not always the pressure gradient they actually experience in use. Let's say our TB is rated for 600cfm at 14.7psi (atmospheric pressure). That would mean that if we took off every part of the intake aside from the TB and could maintain perfect vacuum in the manifold at 600cfm consumption (which, for the record, we really couldn't) that TB will flow 600cfm. However, as soon as we stick an air filter on that (which, for kicks, lets say has the same flow ratings) we will no longer flow 600cfm, because the pressure across the TB is no longer 14.7psi, it is lower.

The issue with the reductions in intake restriction and economy/throttle position is directly related to this. If we make the intake overall less restrictive, we need to shift more of that restriction to the TB in order to maintain the same flow, i.e., we need to provide less throttle.

Ryland 05-19-2010 07:19 PM

Maestro: if you read books on how an engine really works you will quickly see that how you explained why a "less restrictive intake" is good, why it doesn't really work that way, it would if the air was moving at a constant rate, but it's not so it does not fallow the same rules, the formulas that are out there hold true for people who are tuning for speed and for people who are tuning for peek mileage, why do they work for both? because they take in to account engine speed, an example of this being used in a car is the civic vx, the intake on the 1.5L engine that gets better mileage is smaller around then the intake on the regular 1.5L engine, leave the rest of the engine alone and just swap out the intake for a like intake from the "standard" engine that puts out slightly more HP at near red line and you will see your MPG drop.
Again, the formulas for figuring out your ideal intake and exhaust size have been figured out, tested and published.
I suspect to much time has passed for me to look at what books I've ordered from the library to tell you exactly what SAE books I got the information from, but it is out there and accessible to the public.

Maestro 05-19-2010 08:09 PM

I am well aware of the pulsatile nature of engine flow, as luckily I have read books on how engines really work. Steady flow is difficult enough for many to understand, therefore it is easiest--and quite valid--to ignore pressure waves and the like for an economy-oriented discussion. Also I would note that I never said that a less restrictive intake is good, as you're "quoting" me as saying. You're now quoting me as saying the exact opposite of what I'm saying. And what I'm saying is that reducing intake restriction will not help your economy.

Unfortunately Ryland, to insinuate that I have never read a real book on engines or have no idea how engines work just continues the insulting tone of your previous posts, and I have lost all interest in debating this with you, as it is becoming difficult not to stoop to your level. I wonder if you argue with people like this when not hiding behind a computer? If so, I expect you've been punched in the mouth a few times and deserved it. In any case, Micondie, Christ, others, if you would like to continue the discussion I would be more than happy. Ryland, you will be ignored.

Christ 05-19-2010 08:54 PM

I don't feel like it really needs too much more discussion, honestly... as was stated, the information is readily available to anyone who chooses to look for it, and well, aside from the "black arts" of tuning for pulse length, etc, we've covered it, I think.

ChopsQube 06-08-2010 06:51 PM

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 02-11-2013 03:39 AM

Quote:

Originally Posted by Maestro (Post 174858)
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 02-11-2013 04:32 AM

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 02-11-2013 09:05 AM

Quote:

Originally Posted by ChopsQube (Post 178220)
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 02-11-2013 03:12 PM

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 02-11-2013 04:18 PM

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 02-11-2013 04:44 PM

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 02-11-2013 05:31 PM

Quote:

Originally Posted by Frank Lee (Post 356005)
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 02-11-2013 08:16 PM

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

Tesla 02-11-2013 09:22 PM

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.


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