BJYM and my modified BJYM is now online

[Walter Sherwin]

>I've uploaded my BJYM code which is for a '95 Chevy 1/2 ton truck, 350
>(5.7L), 4L60E, AC, 3.73 rear gears.
>
>My modified code contains mods for the following "enhancements".
>
>Replaced stock block with a 4 bolt splayed cap block
>Cola Crank
>Eagle Rods
>Ross Racing Pistons with 11.4:1 cr
>Total Seal Rings
>AirFlow Research  195 Heads w/2.05 and 1.88 valves
>Comp Cams Hydraulic Roller camshaft  - .512 I  &  .532 E lift, 220 & 224 @
>.050, 114 lobe sep
>B&M Power Charger 144 Super Charger making 9 lbs boost at the manifold
>Holley 610 cfm throttle body
>Fluid Dampr
>Doug Thorley Headders
>3" Exhaust
>And a 4L60E that's on it's 3rd clutch set, 2nd Torque converter, and 2nd
>Input shaft and housing assembly in 42,800 miles.
>And to give you a better idea how I drive this thing, it's on its 3rd set
>of tires too. :)
>
>My modified chip has a 900 rpm idle, 6000 rpm shift points (or
>thereabouts), and quite a bit of timing.  The fuel is whacky, as the B&M
>kit increases fuel pressure with boost, and the Map sensor rides in the
>90-100% range 95% of the time.
>
>Things that I don't like about my chip:
>
>1. Error code 32:  EGR..... I don't have an EGR anymore, yet the SES light
>comes on daily to remind me that it still isn't there.
>
>2. The over rich fuel condition on upshifting under full throttle.
>Problem comes from the high boost/fuel pressure, and I don't think it can
>be solved via ecm.
>
>3.  A choke setting that's too rich on startup.
>
>Enjoy!
>




Greetings!



Sounds like you have one neat truck.  I've got a 91 454SS (C1500)  running
about 1 bar of boost on pump gas.  A couple of things in your summary caught
my eye................

1) Are you really running 11.4:1 compression ratio with 9psig boost?  With
what, rocket fuel :)

2) With the airflow potential of your base motor, you might want to consider
stepping up to something like a 177 or a 174 Roots?  You could spin it
slower, and probably get more air, and cooler air.  Or, have you thought
about a Whipple style screw charger?  Way more air and way cooler!  They can
be reached at 1-209-442-1261.

3) You said that you have a 610 CFM Holley TBI?  Does it use Holley style
injectors or the GM Rochester style injectors?  Sounds like you have a
rising rate fuel pressure regulator method of adding boost enrichment fuel?
Be careful with the Holley type injectors, because they can hydraulically
lock shut at 18+ psig fuel pressure.  This problem is even worse under hot,
or low voltage conditions.  The Rochesters are good for up to 60 psig.

4) Where is your MAP sensor port location?  Below the supercharger, or below
the TBI but above the supercharger?

5)  It is fairly easy to get rid of the rising rate regulator scheme, if you
want to "trick"  the calibration somewhat.   You can either rescale the cal
for a 2-bar sensor (lots of work, and I don't recommend it) or continue to
use the stock 1-bar, below the TBI, and model the engine as a very "large"
engine, with equally "large" injectors.  You will need to know a few
specific addresses, but I am sure that they are available through the DIY
page.

Here's how it works.........................Consider your 144 as an "air
pump", with its own RPM dependant VE curves.  Use the 1-bar Map sensor,
below the TBI, together with engine RPM, to step through the normal software
VE tables. You want to make the software "think" that the base engine
displacement is much greater than 350 cubic inches, say 700 cubic inches for
sake of illustration.   You also want to raise the base fuel pressure at the
injectors, to a constant level at which you would have sufficient fuel mass
flow to feed your engine at a VE table value of  "FF" at the highest RPM
breakpoint of the tables.  So as to avoid excessive base fuel pressure, you
could at the same time step up to BBC injectors which are available in
either 80# or 90# flavours, and will drop in wherever a Rochester injector
previously resided.  Let's assume 30 psi, with 80# BBC injectors, which will
give you about 250#/HR maximum injection delivery.

Now, adjust the main injector scaling variable in the software (probably
KNEGRCST) so as to "tell" the software that you have a 700 cubic inch engine
with 250 #/HR injection capacity, instead of the stock setting of 350 cubic
inches and 110#/HR.  You must also change the EGR mass table values, in a
similar ratiometric fashion, if you have not disabled EGR through the
software.  (There are ways to disable the EGR, which would also correct your
Code 32 problem.  Someone on the DIY page should be able to help).  As an
example, my KNEGRCST was formed as the product of  "1461.5 * (one cylinder
volume in litres/injector rate in gm per second)".

Once these things are complete, you can use the software VE table values to
"cut-down" the fuel delivery rates, to match your engine's fuel
requirements.  No codes, no problems, and very consistent control over the
fuel, once everything is dialed-in.

Too bad I can't give you any more specific details, but I have no idea of
what BJYM consists of.  I use this method in my truck, to control about
700HP and about 560#/Hr of injection capacity.  But, my PCM and software are
different.  Good luck, and stay in touch!



Walt.