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Old 01-12-2012, 08:42 PM   #31 (permalink)
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where can I pick up my diploma.......

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Second: Grille Block
http://ecomodder.com/forum/showthrea...e-10912-2.html

Third: Full underbelly pan
http://ecomodder.com/forum/showthrea...q45-11402.html

Fourth: rear skirts and 30.4mpg on trip!
http://ecomodder.com/forum/showthrea...tml#post247938
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Old 01-12-2012, 08:55 PM   #32 (permalink)
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...assuming you're complaining about me, I humbly refer you to the 'Auto Shop Series' article, "Header Science," in the November 1973-issue of HOT ROD Magazine, pages 114-118 (wink,wink).

...from the dust-bin: http://ecomodder.com/forum/163178-post22.html



...here's something recent from Prof. Richard Hathaway: http://www.google.com/url?sa=t&rct=j...qO7gvQTH9kfoWw

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Old 01-13-2012, 08:29 AM   #33 (permalink)
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All of this works in theory on a single cylinder with a single pipe terminating into the atmosphere at a fixed point. With multiple cylinders exhausting into a common manifold, which later join a common collector pipe, I would think that the physics might get a little more complex. For example, an exhaust charge from one of the front cylinders on my transverse-mounted V6 would leave the cylinder into the manifold. The Pipe expands at the point where the other two pipes converge into a single pipe, which bolts to the crossover (and I don't even know how that flows into the rear manifold). From there, the pipe expands again where the rear manifold attaches to the collector pipe. Farther down the line there is a resonator, I think (big coffee-can-looking-thing before the cat), where the pipe expands greatly, then reduces again to 2". It then flows into the cat, expands again, and reduces again back to 2". Front there it moves into the muffler, where the pipe this time reduces slightly, expands inside the muffler, then reduces again to go out the tailpipe. That's a lot of "biggers and smallers" which I think pretty much get rid of any pressure wave charging effects beyond the resonator.

Back on the subject of tailpipe restriction, my thinking is that reducing the pipe diameter at the point that it terminates into the atmosphere increases the velocity of the exiting exhaust gases and reduces the amount of open area that atmospheric pressure can exert directly to the end of the pipe. If that is the case, then a butterfly valve would be ineffective to create this type of effect. Instead, one would want to simply reduce the tailpipe diameter. OR, perhaps a flapper or check valve with a fixed spring pressure which could effectively allow only enough open area to permit exhaust to flow out at a set velocity over a broad range of engine speeds.

Just my thinking out loud here, I might be totally wrong.
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Old 01-13-2012, 10:53 AM   #34 (permalink)
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...lookup "Helmholtz Resonator" and "quarter-wave shorted stubs" and you'll find that length tuning can also be used to ensure that exhaust pulses from one cyclinder do not interfere with exhaust pulses from another; it's all about timing and lengths; been proven over-and-over again with use of "Tri-Y" headers, first on WWI airplanes, then on cars.

...lookup "acoustic impedance" and "collectors for headers" for applied information about how/what happens as the hot, high-pressure, exhaust gas slug sudden encounters a change in media (ie: confines of pipe to open atmosphere).


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Old 01-13-2012, 04:03 PM   #35 (permalink)
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Quote:
Originally Posted by abogart View Post

Just my thinking out loud here, I might be totally wrong.
Hmm.. Your car nearly has the aerodynamic properties of a golf ball.
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Old 01-13-2012, 05:06 PM   #36 (permalink)
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Quote:
Originally Posted by toc View Post
Hmm.. Your car nearly has the aerodynamic properties of a golf ball.
...hopefully, without the weight of all that clay!



Used car salesman sez: "...That's not hail damage sir, that's automotive aero-dynamic dimpling!"
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Old 01-14-2012, 08:30 PM   #37 (permalink)
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For those who are interested, here are the abbreviated, simplified, Intake and Exhaust "tuning" equations:

LENGTH...acoustic tuning:

• L(int) = [IOIC Vs(int)]/RPM = (X 1100)/RPM 3"

• L(exh) = [EOIO Vs(exh)]/RPM = (120 1800)/RPM 1"

...where:

L(int) = Length, atmosphere to intake valve, inches.
L(exh) = Length, exhaust valve to collector, inches.
IOIC = Camshaft Intake Open-to-Intake Close (see X below), degrees.
EOIO = Camshaft Exhaust Open-to-Intake Open (120 typical), degrees.
RPM = Engine speed where acoustic "tuned."
Vs(int) = Velocity of sound at 85F (intake air temperature) is 1100 feet-per-second.
Vs(exh) = Velocity of sound at 1000F (mean exhaust gas temperature) is 1800 feet-per-second (gasoline), varies with type of fuel.
X = Intake camshaft timing: 90 (max.race); 85 (race); 77 (high-perf); 72 (stock), degrees.

DIAMETER (inside pipe)...mass tuning:

• dia(int) = BSQRT[(RPM S)/(360 Vg)], inches

• dia(exh) = BSQRT[(RPM S)/(360 Vg)], inches

...where:

dia(int) = Intake runner diameter, inches; same cross-sectional area as intake manifold opening.
dia(exh) = Exhaust pipe inside-diameter, inches.
RPM = Engine speed where mass "tuned."
B = Piston BORE diameter, inches.
S = Crankshaft STROKE, inches.
Vg = Velocity of gas slug (intake or exhaust): 300 (race); 260 (hp); 245 (street); 240 (stock), feet-per-second. Limiting criteria, Mach index Z 0.6 (Vg 300 fps).

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Old 01-15-2012, 07:02 AM   #38 (permalink)
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Quote:
Originally Posted by toc View Post
Hmm.. Your car nearly has the aerodynamic properties of a golf ball.
Hehe, well if that's the case, maybe I should put a few more dents in it!
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Old 02-26-2012, 04:24 AM   #39 (permalink)
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I love it when educated people post links to articles or post equations but ignore so many other obvious variables when it comes to a specific engine, driving style, altitude where the poster lives, etc etc etc. Just because something was demonstrated once given a certain set of conditions doesn't necessarily mean it's going to have the same results once nearly ALL of the conditions are different. That said, some of you also want to jump to tiny details while ignoring the general rules.

Le sigh.

OP, generally speaking: you probably won't see much of a difference on your particular vehicles with the modifications you're listing. I've installed 2.25" exhaust systems on 1.8L SOHC 8V engines and seen dyno verified gains across the entire rev range, so I'm hard pressed to think you'd see LESS power as someone suggested. That said, this was not done for economy. Another trap people get into is they tend to drive the car harder to hear the intake and exhaust, therefore canceling out any potential gains.

While the factory airbox and exhaust is restrictive by design (erring toward a quiet cabin and driver comfort), neither those engines you have nor the way you're driving them (ecomodding) are trying to pass more CFM of air through them than the factory parts can handle. I doubt you're hitting a point of restriction yet until you're at WOT bouncing off the rev limiter. But at 1,900 RPM cruising, you won't see significant gains from those parts...that's my educated guess. They can flow a certain amount of air for a given RPM, and I don't think you're asking them to flow anywhere near their limits yet. It's at THAT point where those parts become beneficial. I wouldn't waste the money on the exhaust, that's for sure...I wouldn't want the added drone in my daily driver. But for the low cost of a DIY intake system, I'm gonna do it for ****s and giggles to pass the time on a Sunday.

Note though, that many hypermilers are on factory intakes and exhausts getting double the EPA MPG's for their cars. There are bigger fish to fry.

But hey, I'm just a nut job with a 3" exhaust on a 2.3L. No, that's not the eco car. That's the corn-fed weekend car.
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Old 02-26-2012, 06:26 AM   #40 (permalink)
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Quote:
Originally Posted by SoCalMP5 View Post
They can flow a certain amount of air for a given RPM, and I don't think you're asking them to flow anywhere near their limits yet. It's at THAT point where those parts become beneficial.

THIS is nailing the nail on the head and a clear explanation. as a hypermiler you keep your engine at lower RPM and throttle position and thus aren't flowing as much volume intake/exhaust. That's not to say that there ISN'T any benefit to modifying these parts, just that the return benefit is going to be less than one might expect. Unless your down to splitting hairs, there are better places to invest your time/money.

best of luck!

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