Injector Math

Mon Mar 22 15:09:09 GMT 1999

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simplest method i can think of to "get in the ballpark" w/ estimating
horsepower is to ask the cam grinder.  it's been my experience that
for "standard" combinations of carb/intake/heads/exhaust they can
often tell you exactly what power to expect -- indeed, a dyno sheet
is frequently available, as they actually test their cam(s) to determine
what works best with what.  some pieces work lots better than do
some others ...  do avail yourself of this expensive and hard-won
knowledge!

as to the bumpstick itself, i'd suggest asking about a "negative overlap"
cam.  the cam grinder you want to do biz with will know what this
is and how to tailor it to your situation.  the minor added expense of
getting a true custom cam will be more than offset by the results.
IIRC, the latest tt porsche awd turbo used a neg overlap cam.

once you are in the ballpark for the n/a condition, calculate the power
in the boosted condition, eg:
  HP == hp * ( (14.7 + 10 ) / 14.7 )
        == hp * ( 1.68 )
yes, this will produce a number that is very much higher than what
will actually obtain (no losses due to intake heating, etc) but you
_want_ a high estimate to avoid any chance of a lean condition.
next, do the bsfc to pounds conversion per your formulas, then
correct for injector duty cycle.

Frederic Breitwieser wrote:

> Greetings, as most of you know by now, I'm building an
> efi-based mopar stroker engine using a turned down 440 crank
> combined with a .030 over 383 block, for a total
> displacement of 431 cubes.  With the below math, I'm trying
> to caluclate several things.
>
> Approximate HP/Torque to be expected from the motor, both
> N/A as well as boosted (10 lbs of boost max), the
> appropriate injector size for a sequential-based injection
> system, as well as cfm of air required at 5000 RPM naturally
> aspirated as well as with 10lbs of boost.  Yes, I'm having
> fun.  Anyhoo:
>

<snip>

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<HTML>

simplest method i can think of to "get in the ballpark" w/ estimating
 horsepower is to ask the cam grinder.&nbsp; it's been my experience
that
 for "standard" combinations of carb/intake/heads/exhaust they can
 often tell you exactly what power to expect -- indeed, a dyno
sheet
 is frequently available, as they actually test their cam(s) to determine
 what works best with what.&nbsp; some pieces work lots better than
do
 some others ...&nbsp; do avail yourself of this expensive and hard-won
 knowledge!

as to the bumpstick itself, i'd suggest asking about a "negative overlap"
 cam.&nbsp; the cam grinder you want to do biz with will know what this
 is and how to tailor it to your situation.&nbsp; the minor added expense
of
 getting a true custom cam will be more than offset by the results.
 IIRC, the latest tt porsche awd turbo used a neg overlap cam.

once you are in the ballpark for the n/a condition, calculate the power
 in the boosted condition, eg:
 &nbsp; HP == hp * ( (14.7 + 10 ) / 14.7 )
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; == hp * ( 1.68 )
 yes, this will produce a number that is very much higher than what
 will actually obtain (no losses due to intake heating, etc) but you
 _want_ a high estimate to avoid any chance of a lean condition.
 next, do the bsfc to pounds conversion per your formulas, then
 correct for injector duty cycle.
 &nbsp;
 &nbsp;

Frederic Breitwieser wrote:
<BLOCKQUOTE TYPE=CITE>Greetings, as most of you know by now, I'm building
an
 efi-based mopar stroker engine using a turned down 440 crank
 combined with a .030 over 383 block, for a total
 displacement of 431 cubes.&nbsp; With the below math, I'm trying
 to caluclate several things.

<P>Approximate HP/Torque to be expected from the motor, both
<BR>N/A as well as boosted (10 lbs of boost max), the
<BR>appropriate injector size for a sequential-based injection
<BR>system, as well as cfm of air required at 5000 RPM naturally
<BR>aspirated as well as with 10lbs of boost.&nbsp; Yes, I'm having
<BR>fun.&nbsp; Anyhoo:
<BR>&nbsp;</BLOCKQUOTE>
&lt;snip></HTML>

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