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Old 06-18-2012, 12:39 AM   #1 (permalink)
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Reducing throttling losses?

I've in the past maintained that, for gasoline engines, intake losses are composed of pumping losses, of which intake manifold vacuum is the result; and throttling losses, which is the energy required to suck air past a very inefficient blockage. Most people have either implied or concluded that throttling losses are negligible compared to pumping losses. Others lump throttling losses right into pumping losses, and with reason: The throttle itself helps to cause intake manifold vacuum, right? How would one go about separating the two effects if they're intertwined? I've even lumped this in, on other threads of mine, so as to simplify explanations.

Well, now I'm going to ask: What if throttling losses are significant? What if they can be lowered? And I'm going to refer to these quick Paint drawings:



Here is a simplified representation of my throttle body. Causing air to be sucked past the two circled little openings at either end of the throttle plate will take a lot of energy. This energy is taken from the mechanical energy that the engine just got done developing. Since the openings are so small, the incoming air is going to be accelerated a great deal while inside the small openings. This airflow will have a high average velocity, and that will translate into a lot of turbulence immediately past the throttle plate.

Note the interesting little curve at the bottom, where the lower throttle plate edge is at. I suspect that Dodge put that there in order to aid in driveability, and to reduce throttling losses at slightly-open throttle conditions.

Now, to my proposal: Put a wedge on the lower throttle plate, like this:



Note that effectively, we've gone from two small openings to one small opening. The wedge blocks the lower throttle plate opening. Obviously, to get as much air into the engine as before, we would have to... open the throttle. Which leads to picture 3:



Note that the upper opening has widened a bit, and that the lower opening remains closed. There should be a bit less turbulence just past the throttle plate, since the wider top opening should allow the incoming air to have a lower average velocity, which will lessen the turbulence behind the throttle plate.

I am going to be testing this idea. I found a throttle plate with a wedge from a junked Volvo 850, and it happens to have the exact same minimum and maximum diameters as the throttle plate in my truck's throttle body. I've already adapted the Volvo plate to my truck's throttle body, and have taken the truck on an initial test run composed of about 85% city driving. Results are promising.

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Old 06-18-2012, 01:37 AM   #2 (permalink)
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Quote:
Originally Posted by t vago View Post
Note the interesting little curve at the bottom, where the lower throttle plate edge is at. I suspect that Dodge put that there in order to aid in driveability, and to reduce throttling losses at slightly-open throttle conditions.
i always suspected it was for a more progressive throttle opening
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Old 06-18-2012, 02:26 AM   #3 (permalink)
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CV carbs.
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Old 06-18-2012, 02:36 AM   #4 (permalink)
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Controllable intake valve throttling.
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Old 06-18-2012, 02:39 AM   #5 (permalink)
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There, now you have the simple solution and the not-so-simple-but-much-more-effective-and-elegant-solution.
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Old 06-18-2012, 02:43 AM   #6 (permalink)
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Back in the stone age I read BMW was playing with throttle-via-intake valve. I wonder what ever came of it...
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Old 06-18-2012, 02:45 AM   #7 (permalink)
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Lots of paperwork and time/expense.
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Old 06-18-2012, 02:51 AM   #8 (permalink)
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They still use it. Problem is it's complicated and noisy and a bee-yotch to maintain, supposedly. There's still a throttle plate, just in case the system fails and defaults back to normal valve operation.

-

Always wondered if you could do throttle-less more cheaply... like say, using an intake tube that's flexible, and having bladders control tube diameter...
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Old 06-18-2012, 03:55 AM   #9 (permalink)
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Valvetronic - Wikipedia, the free encyclopedia

Requires a vacuum pump, because there is no manifold vacuum. It has a throttle plate for startup (that goes wide open once the valvetronic takes over) and emergencies (in case the valvetronic craps out).
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Old 06-18-2012, 10:53 AM   #10 (permalink)
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If my interpretation of my limited reading is correct, a similar system (to Valvetronic) is used on the MINIs.

The wedge throttle sounds intriguing. The idea could be extended further, so that there is only one gap for air to go through at all times, instead of just at very low throttle openings. The slide valves used in some race cars would be one way to do that--the throttle plate slides out of the way instead of rotating out of the way. The intent in a race car, of course, was to eliminate the restriction from the open throttle plate, but it would give you only the one opening.

Perhaps an iris? That would be quite mechanically complex though.

Neat ideas to play with.

I look forward to seeing the results of your testing!

-soD

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