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Old 04-10-2014, 08:02 PM   #41 (permalink)
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My old car had a straight-through aftermarket exhaust on it when I bought it; I put up with it for a few years and then replaced it with stock. Until someone can point to credible evidence that a straight-through design will increase fuel economy, I'll stick with stock and enjoy my quiet car
They don't. In fact they (and single fat pipes) can seriously damage economy. The only benefit they give is at maxpower/rpm (Wide open throttle)

Otto engines need back pressure at low speeds or they run badly/stall. You'e be better off working out what rpms the engine runs and and tuning the extract pipes so the valve opening impulse is reflected back to the exhaust port out of phase, for the next opening at the most common speed (It provides a suction effect). That's what tuned exhausts on 2 strokes do.

You can tune for multiple engine speeds by using paralleled varying lengths, but space and weight become issues.

As the Prius uses Miller cycle (effectively a short stroked inlet stroke via extremely late inlet valve closure), even that might badly affect the economy. This is the kind of thing which requires decent computational power and a lot of dyno testing to verify any changes.

I'm a little surprised that Toyota isn't taking an interest in what hypermilers do in order to roll changes that work into their halo cars.

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Old 04-10-2014, 08:18 PM   #42 (permalink)
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Quote:
Originally Posted by stoatwblr View Post
They don't. In fact they (and single fat pipes) can seriously damage economy. The only benefit they give is at maxpower/rpm (Wide open throttle)

Otto engines need back pressure at low speeds or they run badly/stall. You'e be better off working out what rpms the engine runs and and tuning the extract pipes so the valve opening impulse is reflected back to the exhaust port out of phase, for the next opening at the most common speed (It provides a suction effect). That's what tuned exhausts on 2 strokes do.

You can tune for multiple engine speeds by using paralleled varying lengths, but space and weight become issues.

As the Prius uses Miller cycle (effectively a short stroked inlet stroke via extremely late inlet valve closure), even that might badly affect the economy. This is the kind of thing which requires decent computational power and a lot of dyno testing to verify any changes.

I'm a little surprised that Toyota isn't taking an interest in what hypermilers do in order to roll changes that work into their halo cars.

Not true ever and at all. Back pressure is a myth. Ideally you want a properly sized exhaust so that the flow(speed too) of the gases will assist in pulling exhaust through the system. I agree with your explanation, but back pressure is a no go, there may be pressure build up(i know there is) but it's not a desired effect.
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Old 04-11-2014, 08:13 AM   #43 (permalink)
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Not true ever and at all. Back pressure is a myth. Ideally you want a properly sized exhaust so that the flow(speed too) of the gases will assist in pulling exhaust through the system. I agree with your explanation, but back pressure is a no go, there may be pressure build up(i know there is) but it's not a desired effect.
You're quite right. It's a combination of inertia of the exhaust flow pulling gass through and impulse reflection management, but it's a useful myth to hold on to for general rule of thumb work.

There's also some benefit in ensuring that gases "swirl" or rotate down the pipes instead of trying to have laminar flow, but that kind of mod is well out of the range of simple "knock it up and see how it goes".
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Old 04-11-2014, 01:08 PM   #44 (permalink)
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Can you do a write-up on how you did those mirror covers? They look slick.
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Old 04-13-2014, 03:40 PM   #45 (permalink)
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Can you do a write-up on how you did those mirror covers? They look slick.
Unfortunately, I didn't get any pictures, but the process was very easy, especially compared to my old car (where I had to cut the mirrors off their bases, fiberglass over the hole and attach the plastic piece with the threaded rods so I could attach it back to the car). On the Prius, there are three bolts that thread from the inside of the door into the mirror base, a rubber gasket, and the mirror itself. Simply remove the mirror by undoing the bolts, trace the outline of the gasket onto a piece of aluminum, attach the bolts through the gasket to nuts with lock washers, and silicon the aluminum plate to the rubber gasket.
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Old 04-14-2014, 11:26 AM   #46 (permalink)
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My understand of straight thru muffler vs oem.
Straight Less weight, Less physical size, Less restriction, straight thru exhaust flow and no baffles

Oem
More weight, larger physical size, and has baffles for sound............
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Old 04-20-2014, 12:53 AM   #47 (permalink)
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New best tank...65mpg!
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Old 04-21-2014, 09:03 AM   #48 (permalink)
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Very nice. Congrats.
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Old 04-23-2014, 09:10 PM   #49 (permalink)
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Aaaand...one mirror down, one to go:





haha! my car lives across the street!
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Old 04-24-2014, 08:18 PM   #50 (permalink)
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No photos of the mirrors from the inside POV of the driver or passenger side or seat?

Straight pipe all the way baby. I had it on my geo metro and my insight. Gives the cars more balls ie torque.

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