[Gmecm] L31 Questions part 2

Mon Mar 14 20:45:11 UTC 2005

The injectors are definitely a limiting factor for these motors.  The 96
small-blocks for trucks, i.e., 5.0L (RPO L30, 305 cid), and the 5.7L (RPO
L31, 350 cid), are in fact sequential central port injected engines. GM
refers to this as "SCPI". These engines use a group of eight injectors
molded together at the top of the intake manifold, with a tube and poppet
valve from the bottom of each injector down to it's respective port.  I
believe the 305 injectors are 19 lb/hr while the 350 injectors are 22
lb/hr. The fuel pressure regulators are already about topped out at 60 psi.

For any serious power increases, their is no more head room with the stock
injectors, and with the unique central manifold location, no clear path to
larger injectors without some sort of custom manifold being created.  Their
is one interesting exception to this.  GM produced a marine version of this
motor that had a different intake manifold.  This manifold utilized
external injectors.  These manifolds are rare and hard to come by, but if
you can get your hands on one, the possibilities for increased injector
sizes are limited only by the injector, not the manifold or mounting
location.

Also, the marine manifolds have no mounting provisions for an EGR valve, or
an EVAP system, have no manifold vacuum tap for power brakes, and need some
modifications to be able to utilize an automotive thermostat and automotive
water pump, but these limitations can be overcome if you are determined.
Using a later Gen III "divorced" EGR valve, and drilling and tapping a
vacuum tap, and drilling and tapping the unused manifold bosses for the
automotive water pump functions is straight forward enough.  The more
difficult task seems to me obtaining a marine manifold assembly in the
first place.

Here is a link to the marine version for more info -

http://www.gm.com/automotive/gmpowertrain/engines/specialized/marine/2004_5700_marine.pdf

             Michael Kaczmar                                               
             <abbynrml94 at yahoo                                             
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Thanks to all for the feedback. I am glad to see there is something out
there now. These trucks are very pentiful, and are damn nice truck
engines. I have seen several powertrains in the boneyards for <$500
engine and trans. It'll be nice to snatch one up.  If I get one of
these motors, I want to put more cam in it. Question is, can the stock
injectors handle more flow, or are they marginal at best already? I
figure I can crank up fuel pressure to a point, but are these injectors
specialized and hard to come by? Run in a different impedence range?
Make this system hard to modify or adapt a more common intake onto?? If
I can use standard injectors I'd like to adapt an LT1 intake and fuel
rails onto it (it has been done before)
Are there larger injectors available?

Michael Kaczmar
Creator 77/94/95/96 Caprice a.k.a. Frankenstein LT1/MN6
2004 Impulse Blue GTO, LS1/M12
53 F-100 5.0/T5, Mustang II, T-bird IRS.....
see http://www.geocities.com/abbynrml94 for project pics!!

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