[Diy_efi] crankcase vacuum control

[Adam Wade]

--- Jack Vines <jackv at ambassadorprograms.org> wrote:

> The crankcase pumping losses are real when a
> crankcase has positive pressure, which can happen,
> especially on a high-boost, high-rpm turbo
> engine.

Again, I find that very hard to believe, since for
every cylinder going down, you have one going up, so
there is a net effect on the bottoms of the pistons of
zero.

I can believe the ring sealing issue, and I can
believe the aerated oil issue for parts that might
have windage issues with the oil (spray- or
plash-lubed parts, crankshaft).

> That is why dry-sump systems have as many as 4-5
> scavenge stages and only one pressure stage.

Well, there are a lot of reasons for that in most
cases, including mutiple oil pickup points, as was
described by a gracious race engine tuner last night

> It becomes a vacuum pump and maintains a vacuum
> in all parts of the engine.

ITYM "crankcase".


In any case, I have yet to see it make any difference
on the dyno with newer high-performance motorcycles,
and I fond the "40-50 horsepower" claim a bit hard to
swallow without back-to-back dyno runs with no other
differences on an eddy current dyno.

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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