TBI requirements for engine upgrade

[NCSTRONGMAN]

I have a low miles 1987 r10 305 - I just went thru a round of upgrades.
350 vortec heads, mild cam, alum weiand intake, long tubes headers and full dual exhuast....NOW its time to address the fuel as i knew i would have to. It already has been upgraded to a 350 throttle body years ago but with the upgrades she needs more fuel....what to do ? I'm not trying to make a race car, just have a balanced running engine that performs when i want it to

- bigger injectors ? stock are 55lb
- Fuel pressure regulator ?
-Higher volume fuel pump ?
- 454 tbi stock ?
- What must be done if anything to the computer ?

exp advice would be greatly appreciated.

 

[Jrgunn5150]

454 TBI's have physically larger bores, and either an 85 or 80lb/hr injectors depending.

However, simply globally dumping more fuel isn't a great solution. Your stock TBI pump should have sufficient volume, they use the same pump on a 454. An adjustable regulator will help, but again, it's a global change.

I would recommend talking with the guy's at Harris Performance to see about getting a chip. Hopefully your cam isn't too wild, because they are very sensitive to duration.

 

[87silveradok20]

Isn't the stock 350 tbi supposed to be good for 350hp or something like that?

 

[NCSTRONGMAN]

cam is not wild. Im likely making near 300 HP, i found some 75-80lb "POLICE INJECTORS' ON LINE. Could i JUST REPLACE THE INJECTORS ON 350 TBI ? My biggest ? is what impact does the stock simple minded computer play ?

 

[Frankenchevy]

cam is not wild. Im likely making near 300 HP, i found some 75-80lb "POLICE INJECTORS' ON LINE. Could i JUST REPLACE THE INJECTORS ON 350 TBI ? My biggest ? is what impact does the stock simple minded computer play ?

have you hooked it up to a computer to log what your AFR is at various points of throttle position? @1987 GMC Jimmy knows quite a bit about TBI setups and data logging/troubleshooting

 

[4WDKC]

cam is not wild. Im likely making near 300 HP, i found some 75-80lb "POLICE INJECTORS' ON LINE. Could i JUST REPLACE THE INJECTORS ON 350 TBI ? My biggest ? is what impact does the stock simple minded computer play ?

wait you put 350 heads on a 305? have you turned the engine over by hand to make sure it spins freely and the valves dont hit the cylinder walls?

Either way you need to tune the ecm, the vortecs require more fuel than stock engine did, cam require more fuel than stock and changing injectors will require you to change the tune to accommodate for the higher rate injectors. You can gamble with adjust fuel pressure to make it run but the issue will be either lean at idle/rich at wot or rich at idle/lean at wot.

 

[Jrgunn5150]

cam is not wild. Im likely making near 300 HP, i found some 75-80lb "POLICE INJECTORS' ON LINE. Could i JUST REPLACE THE INJECTORS ON 350 TBI ? My biggest ? is what impact does the stock simple minded computer play ?

You could just replace the injectors, but I have my doubts that you'll need simply MORE FUEL at every point in the map.

Most likely, you'll need timing, and fuel, at some points in the map, and not so much at others.

 

[4WDKC]

You could just replace the injectors, but I have my doubts that you'll need simply MORE FUEL at every point in the map.

Most likely, you'll need timing, and fuel, at some points in the map, and not so much at others.

Correct the vortec heads use the same amount of fuel at idle/low rpm, mid - high rpm requires more fuel.

 

[Jrgunn5150]

Correct the vortec heads use the same amount of fuel at idle/low rpm, mid - high rpm requires more fuel.

That's what I was getting at by stating larger injectors or adjustable fuel pressure regulators make global changes, but it didn't seem to be registering.

 

[NCSTRONGMAN]

Thanks -I need to have the ecm programmed it seems. Can the reprogram alone get the fuel where it needs to be or will larger injectors also be required ?

 

[Jrgunn5150]

Thanks -I need to have the ecm programmed it seems. Can the reprogram alone get the fuel where it needs to be or will larger injectors also be required ?

I believe a simple remapping will be sufficient, without an wideband and logging, there's no telling. Unfortunately, the TBI systems are pretty primitive.

 

[NCSTRONGMAN]

OK Im basically done with trying to make the tbi work with my truck. I;m at like 80% deciding to go carb, eliminate the damn ecm, o2 sensor requirement, etc

I;m guessing a quadrajet 4 barrell would do the business?
The quad should fit my street warrior intake
What other things beside regulating fuel pressure down to 7psi would be required?

I have a 87 305 custom with vortec heads, mild cam, perf intake, long tube headers and 2.5 full exhaust, stock 350 tbi currently.

 

[NCSTRONGMAN]

secured q 800cfm q -jet from a friend and a rebuild kit - he even had a holley to quad adapter plate - gonna get a fuel press regulator/guage and go from there.

 

[NCSTRONGMAN]

Are their any other things I may run into ? Linkages, etc ? vacuums ?

 

[4WDKC]

Are their any other things I may run into ? Linkages, etc ? vacuums ?

The problem with spacers is they can cause an alignment problem with the cables, i had one on my tbi/vortec but removed it because it put the throttle linkage in an angle I didnt like. Modifying the factory mounts for the cable bracket seems to have moved the cable away from the tbi causing yet another angle that I havent corrected yet. You may have to get an aftermarket bracket to line up with your carb or maybe I bent mine the wrong way. Dont for get you will need a lock up switch for the 700r4 if you have one. New distributor as the factory is controlled by ecm.