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Discussion Starter #1
Could the ICE horsepower be increased by disconnecting the snorkel tubing that connects to the air cleaner inlet? It seems the ICE could then inhale through its mouth instead of a restricted nose. Air would still be filtered through the pleated filter and the other filter(?) in the air cleaner cover but it would be allowed to pass less restricted, which might increase horsepower. How wrong is this idea? Anyway, what is the purpose of the snorkel tubing that directs air into the air cleaner?

Also, after about 200,000 mi., I may want to work on getting the ICE to exhale easier for a little added fun once the newness of the car has gone away, you know, to make more noise and maybe make more get-up-and-go.

The exhaust system has four vessels with connecting pipe. I would appreciate an explanation of what each vessel is. I assume the first two vessels are catalytic converters in series. I have no guess as to the purpose of the third vessel. The fourth vessel is the muffler. Would it be possible to put a cutout just past the second catalytic converter which is down stream of the oxygen sensor and still pass emission standards? I figure bypassing the last two vessels of the exhaust system would help the ICE exhale and increase the horsepower. Of course, a pipe would have to be attached to the cutout to allow the exhaust to exit from behind the car. Again, how wrong is this idea?
 

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The vessel you don't recognize is probably the hydrocarbon adsorber. It should have a vacuum hose connection used to switch between cold and hot operation. When the engine is cold and creating excess hydrocarbons, it grabs them. When the engine (and therefore the catalytic converter) is hot, it releases them for final "burn" in the catalytic converter. It's probably the second cannister from the engine. I think the order is cat, HC adsorber, cat, muffler. Removing either cat or the HC adsorber will invalidate your SULEV status. Removing the muffler will draw attention (from the police for example).

Opening up the exhaust system will probably give you less of a horsepower increase than you expect due to the Atkinson cycle engine.

I'm not sure what you're aiming for here. I doubt there's anything you could do to the gasoline side of things to impress the guy in the Mustang next to you.
 

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Your proposed changes will decrease power, not increase it. This is the age of computer controls. Unless the computer controls can compensate for changes to the intake restriction (vacuum signal) and the backpressure (exhaust and valve timing dependent) you will cause more problems than anything else.

For this engine, reducing intake restriction will reduce the vacuum signal, causing the engine to run rich, wasting gas and increasing emissions. This will actually reduce the amount of air during the intake stroke. The exhaust side can be more forgiving, but this application is designed to operate at a specific backpressure, which results in a good intake draw, and good outlet flow, and effective combustion chamber scavenging during the exhaust stroke. Other applications which do see advantages have significant intake restrictions or have aftermarket reprogramming capability (chips or special ECMs) which alter the spark timing and injector on-time to take advantage of changes to the intake or exhaust. You do not have that luxury with this application, and with the Atkinson cycle, you can more quickly mess things up if you alter the combustion efficiency. Remember, the Atkinson cycle gives up low-end torque to allow for peak efficiency at higher RPM. This loss is offset by the electric motor. If you alter the torque curve or horsepower peak location you will likely see a significant power reduction, not any increase. Also note that most of what I have said here is exactly what Toyota did with the 2004 engine versus the 2003. They changed the valve timing to generate the power curve they wanted. As I understand it, there really isn't much more to gain without some radical changes. Regardless, unless you alter the valve timing, you are limited by the Atkinson cycle's operational characteristics.
 

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Trying to second guess the Toyota engineers seems to have quickly diminishing returns when it comes to the drive train in this car.
 

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When you were a child, did you break all of your toys by "fixing" them as soon as you got bored?

Please don't screw up your Prius!
 

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Discussion Starter #6
I broke lot of toys while growing up. However, we didn't get to the moon without breaking a few designs in attempts to make the final product better. I guess it is my scientific nature to explore new ideas and to ask "what if". I don't plan to start tinkering with my Prius for a couple thousand miles, but if the newness is worn off by then, I probably won't be able to resist some sort of tinkering.
 

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Discussion Starter #7
Buggman said:
I broke lot of toys while growing up. However, we didn't get to the moon without breaking a few designs in attempts to make the final product better. I guess it is my scientific nature to explore new ideas and to ask "what if". I don't plan to start tinkering with my Prius for a couple thousand miles, but if the newness is worn off by then, I probably won't be able to resist some sort of tinkering.
Oops.

What I meant to say was a couple hundred thousand miles.
 

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Joel said:
Trying to second guess the Toyota engineers seems to have quickly diminishing returns when it comes to the drive train in this car.
However, I think you might be able to increase engine power somehow while sacrificing quietness and drivability. This is done all the time for Hondas and other cars by aftermarket "tuners". The right exhaust system mods might somehow give you an extra horsepower or three, but you would need some dyno testing to come up with a good improvement.
 

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autoxic said:
Joel said:
Trying to second guess the Toyota engineers seems to have quickly diminishing returns when it comes to the drive train in this car.
However, I think you might be able to increase engine power somehow while sacrificing quietness and drivability. This is done all the time for Hondas and other cars by aftermarket "tuners". The right exhaust system mods might somehow give you an extra horsepower or three, but you would need some dyno testing to come up with a good improvement.
But please keep in mind that the 2004 Prius uses the Atkinson/Miller combustion cycle, rather than the traditional Otto cycle. Making changes such as those proposed could in fact reduce horsepower.

But if you're really planning to wait 200,000 miles before making modifications, I guess it doesn't matter much if you mess it up with your tuning. By then, there should be plenty of qualified and experienced Prius mechanics available to de-tune your car and get you out of hot water.
 

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If it ain't broke, BREAK IT?? Going to the moon had little involved where folks arbitrarily just TRIED SOMETHING irespective of its scientific validity. Sure a lot of instances of thinking out of the box were incorporated but no "lets try this and see what happens even though we don't have a clue as to the underlying science." Until or unless one develops an understanding of the science and engineering on which something is based, how are yo going to inprove it. I don't think the probabilities are in favor of pseudo-random changes resulting in improvement.

Any sufficiently advanced technology is indistinguishable from magic. Until or unless most of what the Toyota engineers have done in the Prius is well understood by the would be "hot rodder", the liklihood of "improving" on it, especially with a mindset attuned to a different technology, is quite slim.

IMHO this is the case BUT by all means give it thought and when the economics permit, mess with it and see what you can do. I'd be thrilled to read of someone's outstanding success in improving on the Prius HP, mileage, or both , especially if driveability were not too adversly impacted.

:D Pat :D
 
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