Terrible Tom <silvereightynine@aol.com> wrote:
> Basic fundimentals review here...
> The suction of multiple pistons pulling air in through open intake
> valves is what keeps vacuum in the manifold.
Yep!
> The throttle blade is what will decrease the amount of vacuum (negative
> air pressure) when the throttle is opened
Yep! There are only two ways to decrease the amount of vacuum -
allow/force more air to flow through the throttle body, or reduce the
amount of air being pulled through the intake valves.
> faster engine RPM with the throttle closed (accelerating and then
> letting off the throttle) will cause more vacuum (higher values of
> negative pressure)
Yep!
> Ok - all that said... I dont see how a restricted exhaust will have any
> sort of effect on intake manifold vaccum?
See my latest agonizing post in this thread for my thoughts on
that process. :-)
> I still think restricted exhaust would cause lower vacuum levels because
> the engine has to fight and push the exhaust out - using more power and
> choaking engine speed... less engine speed means the pistons are moving
> slower and sucking air in slower meaning less vacuum in the manifold....
> Right?
I agree, that's a decent way to think about it. Or, you can
probably simplify it even further if you wanted to and just think
about the engine sucking in air and cramming it out the exhaust. If
it can't force it out the exhaust, it is going to get backed up
(pressurize) and can't suck more air in.
Since an engine is basically a big pump, consider what would happen
if you had a water pump. You've got the suction line down in a well
or pond, and a garden hose attached to the outlet. If you put a kink
in the garden hose, is that going to cause greater suction at the
inlet? Most definitely not. :-) Neither will an engine with a
"kinked" exhaust create more suction (vacuum) in the intake manifold.
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
This archive was generated by hypermail 2b29 : Tue Oct 02 2007 - 15:23:18 EDT