Manifold Pressure (was:How to get 300bhp at 1.0bar)

[russ southerlin <russ.s.southerlin@ast.lmco.com>]

It was said by one of our esteemed colleagues:

>Therefore I think that even a normally aspirated car with a slightly
>restricted intake could have 1.0 BAR of intake pressure at wide open
>throttle. All this assumes we are at sea level of course.
>
 
I was always under the impression that a NA motor would exhibit negative
manifold pressure (vacuum) under all conditions.  I think the MFA on my
car
will tell me what the manifold pressure is (anyone with a MFA should be
able to do this, there is a ritual involved though).  I'll have to
check.


Bob Davis  

Bob,
The point I was trying to make was a NA car runing at wide open throttle
(WOT) is theoritically (with no intake restriction) running at 1.0
atmosphere of intake pressure. Think of it as the "pressure" or "weight"
of the atmosphere is pushing the air into your engine as the piston goes
down. 

Now if your intake has some restrictions, which all intake systems have
(air filter, valves, intake plumbing etc.), then your engine would have
a slight vacuum at WOT. I'm not sure what is a typical value for this
WOT vacuum but I know I've run engines with a vacuum gage and at WOT the
gage reads pretty darn close to 0.0 (granted the gage is reading inches
of mercury which means the WOT vacuum value is too small for the range
of the gage).

The point I was also making was that 1.0 BAR is 0.98692 atmospheres so
if you had a intake with less than 0.01308 (1.0-0.98692) atmospheres of
equivalent restriction, which would be about 0.190 psi (0.01308*14.504),
then you could be running at 1.0 BAR of intake pressure at WOT.