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Old 09-25-2006, 04:52 PM   #1
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exhaust and light foot

i have an 05 chevy cobalt. with hypermilling and my psi to the sidewall max, I am achieving abot 31 mpg city and 39 hwy mpg. would an aftermarket exhaust (pacesetter monza) plus the the k&n drop in filter i have now get me even better mileage?
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Old 09-25-2006, 04:57 PM   #2
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Mehbe, but I'd say go for something that's more likely to increase FE, like a WAI and LRR tires.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 09-25-2006, 04:58 PM   #3
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K & N shows no mpg gains.

http://www.metrompg.com/posts/air-filter-part-1.htm
http://www.metrompg.com/posts/air-filter-part-2.htm

I waould also say no on the pacesetter exhaust. I would perdict no mpg gain or slight loss under normal conditions.
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Old 09-25-2006, 05:07 PM   #4
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k&n showed an improvement for me
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Old 09-25-2006, 05:17 PM   #5
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a larger diameter exhaust will not give you mpg gains as it moves the efficiency of flow to a larger volume of air. if, and only if, the pipe size was the same but flowed better then yes it would improve your fuel economy.

i am interested in the gains you claim from the k&n filter. care to show the evenly averaged graphs with standard deviation?
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Old 09-25-2006, 08:10 PM   #6
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Breathe In, Breathe Out

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Originally Posted by thisisntjared
a larger diameter exhaust will not give you mpg gains as it moves the efficiency of flow to a larger volume of air. if, and only if, the pipe size was the same but flowed better then yes it would improve your fuel economy.

i am interested in the gains you claim from the k&n filter. care to show the evenly averaged graphs with standard deviation?
We need an A-B-A test. Now if you changed it from a dirty filter, any clean filter will improve mileage.

I have a K&N for the simple fact that 1. I already had it from my lead-foot days, and I'm 2. keeping it because it basically lasts the life of the car if maintained.

Regarding the exhaust. I wouldn't take a change on aftermarket. Most engines need backpressure to operate efficiently, despite what the exhaust company tells you.

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Old 09-26-2006, 03:10 AM   #7
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Hi rh77 - ?Most engines need backpressure to operate efficiently?

Without actually deffining the word ?efficiently? I would have to say that this is the most missleading of any comment known in the automotive world.
Ever since hot rodders started changing exhaust systems and mufflers for greater HP there has been this debate.
Well its not really a debate as such , because the facts dont support the statement at all.- but marketing hype tends to sway the thoughts of the general public buyer one way and the other.

A closely related thing also is air filters , do low restriction air filters improver HP and FE.

The answer is both TRUE and FALSE. (to both air filters and aftermarket exhausts)

Start with the example of a standard car with its 2 inch exhaust pipe and normal mufflers.
Not a bad systems with no obvious flow problems.
Then you go and stick a 3 inch stainless steel and mandrel bent system on with hi flow cat and mufflers (maybe $1000+)
Does this give an increase of power and economy.?
Most likely NO.

BUT

Say now we have a car in a very high state of tune engine , longer duration cam , hi flow head , suitable ingnition and fuel maps.
We change from our happy 2 inch system to the 3 inch and there is a massive improvement in HP (and probably a little FE)

The same thing applies to air filters.
Changing to a high flow filter may even degrade FE if the new flow of the filter is beyond what the computer can automatically adjust too.
Also going for a pod type filter may lower HP and FE by sucking in too much hot air.
The standard filter in its air box might actually flow enough for the engine even at full RPM's, and you cant flow more than that.

Unless there is an obvious flow problem with the original gear (crushed exhaust bends to fit into tight places) there may be no gain in going to a hi-flo exhaust system., (same applies to air inlets)

But back to ?Most engines need backpressure to operate efficiently?
A standard engine may drop FE and HP if a hi-flo system is added with no other change.(so here it is TRUE)
With appropriate changes to other systems a hi-flow low back pressure exhaust will increase HP and likely FE too. - (so here that statement is FALSE)

It depends entirely on the WHOLE application.
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Old 09-26-2006, 04:24 AM   #8
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Hot Air (I'm full of it)

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Originally Posted by onegammyleg
Also going for a pod type filter may lower HP and FE by sucking in too much hot air.

But back to ?Most engines need backpressure to operate efficiently?
A standard engine may drop FE and HP if a hi-flo system is added with no other change.(so here it is TRUE)
With appropriate changes to other systems a hi-flow low back pressure exhaust will increase HP and likely FE too. - (so here that statement is FALSE)

It depends entirely on the WHOLE application.
I completely agree, but I was referring to a relatively stock engine focused on FE ("most engines"). Having raced myself (and follow the WRC ) mods to the intake and exhaust will generally provide more horsepower.

I half-way disagree with the blanket statement that hot air decreases FE. I traditionally draw-in 120F-200F intake air temp, which increases FE on my engine (Acura/Honda B18b1) by leaning-out the mixture at cruise. It varies tremendously among makes, models, and vehicles overall -- even its application. It takes a huge hit in power, but it uses less fuel (which has been confirmed in my car using by the Davis "CarChip EX" datalogger, which showed a distinct advantage in fuel trim, directly proportional to the rise in intake air temperature).

RH77
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Old 09-26-2006, 04:45 AM   #9
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Hi rh77 -?It takes a huge hit in power?

Yeah , true , unfortunately then most bury the foot even further resulting in less FE than where they began.
But as you say , there is improvement to be found with the warm air intakes.

More experimentation with warm air is needed tho ---
I used to live in Australia where it gets VERY hot , and underbonnet temperatures can get so extereme it blisters the paint of the engine bay panelwork.
Using a warm air intake under these conditions drops power so excessivley that higher consumption results due to more foot needed to get it to go anywhere..

But then I am talking about perhaps 240F.
You dont open the hood and stick your head in for a look. - It will burn ya widdle eye brows off.

Here where I live now I run warm air year round. (out of the frying pan and into the freezer)
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