Hello everyone,
Last week I helped a dude drop a 383ci SBC into his NBS GMT800 2wd 1500. It physically looks alot like my build, except he used an old Holley carb instead of the L31 Fuel injection.
After we got his fired up and driving I decided I've had enough of dealing with the issues that arose with my swap.
My L31 F.I & 0411 PCM was stuck in open loop with no explanation as to why. It was dumping fuel and was non-responsive to Comp tuning. It drank an average of 6-8MPG and didn't deliver the power that my 357ci is capable of producing.
The 0411 PCM required to operate the L31/4L60E isn't 100% compatible with the GMT800 platform and I lost the use & function of my...
Air Conditioning
Oil pressure gauge
Shift/gear indicator in the cluster
Reverse Lights
As well as unleash flashing error messages in the message center for sensors my truck didn't even have.
Check oil level
Check coolant level
The Plan:
Remove the Fuel Injection unit in favor of an old skool carb & manifold. Replace the 0411 PCM with the trucks original 6243 PCM tuned with every single fuel/drivability DTC turned off.
With TPS, CKPS & VSS signal the PCM can still control the 4L60E trans. The only mod/fab work was to adapt a TPS to a carb.
First step: Pull off that injection unit.
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Remove the old plastic vortec gaskets & clean off the silicone before laying down new Fel-pro 1255 gaskets & a couple beads of The Right Stuff silicone. Set the new carb intake manifold straight down onto the block
![Image]()
The Manifold is a Professional Products 52028, split dual plane, air gap design.
I pulled off the drivers valve cover and turned the engine over by hand to DTC or cyl #1 to drop in the Distributor
Since the PCM doesn't need the CPS sensor to run the F.I. (Or to think it's running) I used a Summit Billet aluminum distributor with a standard magnetic trigger, mechanical & vacuum advance.
![Image]()
The Carb of choice is an Edelbrock 1407 750cfm, rodded & jetted for 4% lean for my altitude. Converted to electric choke. The primaries shaft has been modified to run a TPS sensor
![Image]()
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The Carb is mounted backwards on the intake manifold. This will allow the trucks OE throttle cable to mount right up as well as the TPS harness will plug right in.
![Image]()
![Image]()
I don't like those foam air cleaners, but it's all that will fit in that tight space under the cowl.
![Image]()
Made a new upper radiator hose, shortened the Taylor wires for a more snug fit. Routed the throttle cables for a more even flowing path. Mounted the ignition coil on the VC using a hold down bolt
![Image]()
![Image]()
Finished wiring up the ignition. Modified the F.I. fuel lines, a Mallory 4309 fuel pressure regulator is used to get fuel pressure down as well as provide a return line
![Image]()
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Spare Parts Bin:
![Image]()
Here is the first start up after the swap. I didn't adjust ignition timing or carb adjustments, just turned on the key and fired her up.
http://vimeo.com/3075250
There is one catch. because the fuel supply line is 3/8" and the return line is 5/16", the in-tank pump makes 60PSI regulated down to 6 PSI, the excess pressure gets diverted to the return line... Due to it's smaller size the line can't flow that much pressure and it gets backed up and pegs the needle on the PSI gauge.
The fix will be to drop the tank, pull out the in-tank pump and run a electric pump on the frame rail. I found a 72GPH @ 5.75 PSI pump at my parts house and I will have the other half of this project done in a couple of days.
So, why... why a carb?
When I built my SBC I based my build off of a Carcraft article. Project humble Pie. They made 401hp/426 tq with the same engine internals I used. And in another article they built a SBC with the same compression ratio as mine but used a bigger 230/240 cam and made 440HP.... both articles used a Edelbrock 750cfm carb & air-gap manifold to obtain those numbers. Since fuel injection & PCM is no longer an issue... that 23X/24X duration cam looks pretty good right about now.
Was it worth it? IMO, yea. Working on these trucks is more fun than driving them. As well as having a completely unique daily driven pickup.
Cheers ~Mykk
Last week I helped a dude drop a 383ci SBC into his NBS GMT800 2wd 1500. It physically looks alot like my build, except he used an old Holley carb instead of the L31 Fuel injection.
After we got his fired up and driving I decided I've had enough of dealing with the issues that arose with my swap.
My L31 F.I & 0411 PCM was stuck in open loop with no explanation as to why. It was dumping fuel and was non-responsive to Comp tuning. It drank an average of 6-8MPG and didn't deliver the power that my 357ci is capable of producing.
The 0411 PCM required to operate the L31/4L60E isn't 100% compatible with the GMT800 platform and I lost the use & function of my...
Air Conditioning
Oil pressure gauge
Shift/gear indicator in the cluster
Reverse Lights
As well as unleash flashing error messages in the message center for sensors my truck didn't even have.
Check oil level
Check coolant level
The Plan:
Remove the Fuel Injection unit in favor of an old skool carb & manifold. Replace the 0411 PCM with the trucks original 6243 PCM tuned with every single fuel/drivability DTC turned off.
With TPS, CKPS & VSS signal the PCM can still control the 4L60E trans. The only mod/fab work was to adapt a TPS to a carb.
First step: Pull off that injection unit.
Remove the old plastic vortec gaskets & clean off the silicone before laying down new Fel-pro 1255 gaskets & a couple beads of The Right Stuff silicone. Set the new carb intake manifold straight down onto the block
The Manifold is a Professional Products 52028, split dual plane, air gap design.
I pulled off the drivers valve cover and turned the engine over by hand to DTC or cyl #1 to drop in the Distributor
Since the PCM doesn't need the CPS sensor to run the F.I. (Or to think it's running) I used a Summit Billet aluminum distributor with a standard magnetic trigger, mechanical & vacuum advance.
The Carb of choice is an Edelbrock 1407 750cfm, rodded & jetted for 4% lean for my altitude. Converted to electric choke. The primaries shaft has been modified to run a TPS sensor
The Carb is mounted backwards on the intake manifold. This will allow the trucks OE throttle cable to mount right up as well as the TPS harness will plug right in.
I don't like those foam air cleaners, but it's all that will fit in that tight space under the cowl.
Made a new upper radiator hose, shortened the Taylor wires for a more snug fit. Routed the throttle cables for a more even flowing path. Mounted the ignition coil on the VC using a hold down bolt
Finished wiring up the ignition. Modified the F.I. fuel lines, a Mallory 4309 fuel pressure regulator is used to get fuel pressure down as well as provide a return line
Spare Parts Bin:
Here is the first start up after the swap. I didn't adjust ignition timing or carb adjustments, just turned on the key and fired her up.
http://vimeo.com/3075250
There is one catch. because the fuel supply line is 3/8" and the return line is 5/16", the in-tank pump makes 60PSI regulated down to 6 PSI, the excess pressure gets diverted to the return line... Due to it's smaller size the line can't flow that much pressure and it gets backed up and pegs the needle on the PSI gauge.
The fix will be to drop the tank, pull out the in-tank pump and run a electric pump on the frame rail. I found a 72GPH @ 5.75 PSI pump at my parts house and I will have the other half of this project done in a couple of days.
So, why... why a carb?
When I built my SBC I based my build off of a Carcraft article. Project humble Pie. They made 401hp/426 tq with the same engine internals I used. And in another article they built a SBC with the same compression ratio as mine but used a bigger 230/240 cam and made 440HP.... both articles used a Edelbrock 750cfm carb & air-gap manifold to obtain those numbers. Since fuel injection & PCM is no longer an issue... that 23X/24X duration cam looks pretty good right about now.
Was it worth it? IMO, yea. Working on these trucks is more fun than driving them. As well as having a completely unique daily driven pickup.
Cheers ~Mykk
