John;
You aren't in the Twilight Zone. A race engine can exceed 1.0 VE due to
the effects of tuned intake runners and very well- designed headers. The
exhaust pulse reflected back from the collector into the open exhaust
port and thus the cylinder is a negative pressure-- this literally
"sucks" the incoming charge into the cylinder when both Int & Ex valves
are open at the same time..
Regards, Neil Tucson, AZ
-----Original Message-----
From: owner-land-speed@autox.team.net
[mailto:owner-land-speed@autox.team.net] On Behalf Of John Staiger
Sent: Wednesday, October 04, 2006 2:06 PM
To: land-speed@autox.team.net
Subject: Another stump-the-chump question
Yes - I'm the chump. Since I had a spare minute today, I was playing
with
some numbers and this generated my puzzlement: I have an ex-IRL 4.0L
engine
with certain "published" data - i.e. the GM Race Shop build manual.
When I
model some of the numbers the results are quite bizarre. hence I'm
wondering
what I'm doing wrong.
The build manual lists the following facts; 1) bore=3.661",
stroke=2.85",
maximum RPM=10,500 (limited by rule). Therefore if I apply and old
formula
(theoretical cfm = (displacement * (rpm/2) * VE) / 1728) or 243.54in3
[or
3.99L] x 10,500 / 2 * 1.00 / 1728 where VE = 1.00 or a perfect engine, I
should get the theoretical maximum air flow of the engine [pump] or
739.9cfm.
This is were I mention the last piece of published data -- the GM race
shop
build manual puts the engine air capacity at 925cfm. Further, the hp
specs
and dyno references by several sources fall in line with the 925cfm
number
(more math). So if I go back to the formula above - VE would have to
equal
1.25???? This does not compute... Is this possible. My head hearts.
John
Team Arrow / Team C5LSR
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