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Old 05-16-2013, 12:33 PM   #41 (permalink)
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Originally Posted by t vago View Post
[/LIST]Have you ever tried to pull on a piston to create vacuum? It's pretty frickin' hard to do.
Yes, every time I have to change bearings in an engine and the valves are closed for that piston. It's a large volume you're pulling on, takes patience sometimes to bring the piston down to mate it back up to the crank after you change the whole bottom end.

...aaaaand that's why I don't like Triton V8's.

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Old 05-17-2013, 09:07 AM   #42 (permalink)
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There's no way to deactivate just one cylinder on a carbed engine via the fuel system. By playing with fuel mixture on the fly you would be making the entire engine run leaner
I know, and if I had an excellent temperature gauge - one with numbers, for instance - it might be fun to give it a try anyway, leaning past peak head temps like some aircraft pilots do to squeeze the most range out of their tanks. But that would have to be in a car that Sweetie didn't drive, because I'm pretty sure she just wouldn't want it.
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Old 05-17-2013, 09:39 AM   #43 (permalink)
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Originally Posted by Christ View Post
Yes, every time I have to change bearings in an engine and the valves are closed for that piston. It's a large volume you're pulling on, takes patience sometimes to bring the piston down to mate it back up to the crank after you change the whole bottom end.

...aaaaand that's why I don't like Triton V8's.
Don't forget that while it is difficult to pull the piston down on the intake stroke with high manifold vacuum, the volume of air on the piston that you are "stretching" acts like a giant spring and pulls the piston back up on the compression stroke, helping turn the engine and effectively cancelling out any effort it took to pull the piston down.

Throttling losses have to do with the friction of air rushing around a throttle plate and not necessarily with a specific amount of vacuum in a cylinder on the intake stroke.
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Old 05-17-2013, 10:49 AM   #44 (permalink)
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Originally Posted by mechman600 View Post
Don't forget that while it is difficult to pull the piston down on the intake stroke with high manifold vacuum, the volume of air on the piston that you are "stretching" acts like a giant spring and pulls the piston back up on the compression stroke, helping turn the engine and effectively cancelling out any effort it took to pull the piston down.
But, if you're considering a butterfly valve method of trying to deactivate cylinders, that above is only true for the intake and compression strokes. The 3d stroke (that would have been the combustion stroke on a normally working cylinder) would again be subjected to intense vacuum that would be akin to stretching a spring (just as with the 1st stroke). However, the 4th "exhaust" stroke would immediately get rid of that vacuum as the exhaust valve opened up, causing exhaust gases to rush in just as the piston pushed back up to TDC.

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Old 06-03-2013, 03:56 PM   #45 (permalink)
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Quote:
Originally Posted by Christ View Post
Yes, every time I have to change bearings in an engine and the valves are closed for that piston. It's a large volume you're pulling on, takes patience sometimes to bring the piston down to mate it back up to the crank after you change the whole bottom end.

...aaaaand that's why I don't like Triton V8's.



Can't you just remove the spark plug (assuming gas engine) to get the piston to come out easier?
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Old 04-09-2014, 08:32 PM   #46 (permalink)
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Hmm... I'll play devils advocate here, probably because I haven't seen the existing data yet, but this makes sense to me. If we're only running on two cylinders, we only make half the power, and can run the motor much closer to WOT for the same fuel consumed and power outputted. This means reduced pumping losses.

Why won't this work?

If this setup alternated between cylinders 1,3 and 2,4 ever few seconds, it could probably lower overall engine temps and reduce cooling needs. I remember reading about how the Cadillac Northstar cars could run w/o any coolant by cycling off 1/2 of the cylinders at a time and using a bit of fuel to cool the ones that weren't firing; sort of a keep-alive mode until the car made it to the next shop.
Yeah that worked out real great for the north star

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