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Old 09-18-2013, 01:45 PM
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time to restore

i have a 1990 chevy 4x4 sport. its got 300,000 miles and its time to fix him back up. I wanna pull the 350 out and warm it up i wanna know if i can put vortec heads on it? and i also wanna know what i'd have to do to put on a better injection system cause the one i have is the tbi.. its been in my family since new so i wanna restore it.. if i can get any info i'd really appreciate it.. thanks

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Old 09-18-2013, 05:42 PM
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Quote:
Originally Posted by carpetguy View Post
i have a 1990 chevy 4x4 sport. its got 300,000 miles and its time to fix him back up. I wanna pull the 350 out and warm it up i wanna know if i can put vortec heads on it? and i also wanna know what i'd have to do to put on a better injection system cause the one i have is the tbi.. its been in my family since new so i wanna restore it.. if i can get any info i'd really appreciate it.. thanks
Changing from TBI is complex not to mention expensive you quickly stare at 2500-3500 bucks. The scrap yard collection of TPI is getting pretty thin so the price of these is creeping up as well. However, the small 2bbl TBI on the 350 can be replaced with the larger 454 unit at about 600 CFM or the Holley 670 cfm unit. These with 90 pound injectors and no other changes to the truck except for a chip will supply a decently built 350 or 383 to about 360 hp which is possible on Vortec heads without getting tricky beyond what the factory TBI sensors can happily do.

For pistons you'll need some D dish to keep the compression decent for pump fuel. The D shape dish is under the valve pocket, the other side has a step that closes tightly with the sqush/quench step of the Vortec head. This shoves nearly all the mixture in front of the spark plug which nets a fast, clean burn that tolerates compression up around 9 to 9.5 with a decent but not crazy cam. The squish/quench clearance needs to be right at .040 inch or a hair less. You can get there with different combinations of piston crown to deck clearance and gasket thicknesses. The stock deck should be .020 to .025, with a .015 or .019 shim gasket you're right in the neighborhood or a zero deck with a .039 thick composite or some combo in between.

The intake needs to be an Edlebrock Performer RPM with a 4 bbl carb to 2 bbl TBI adapter. If you stay with EGR you'll have to do some external plumbing and an adapter to make it work, not a big deal.

Long tube headers into a duals will take care of getting the exhaust out with no back pressure and will allow the use of dual aftermarket cats if you keep them on the truck.

The best cam for this combo is the Corvette/Z28 roller p/n 12551142 which specs at 203/210 degrees at .050 with a 1.5 rocker moves the valves .446/.450 inch. This thing has a 115 degree LSA which works very well with Manifold Absolute Pressure (MAP) managed EFI like the TBI. This will accept 1.6 rockers however this cam is right on the lift limit of unmodified Vortecs because of contact between the bottom of the spring retainer and top of the guide, this is easily fixed with a little grinding. Check the casing number on you block some of these trucks came with casting that have the provisions for a roller cam. There is no sense in running a flat tappet any more and this is a situation that just keeps getting worse as the detergent chemistry changes and increases in the oil while the ZDDP high pressure additive keeps going away. A two pronged problem where the HP, ZDDP not only goes away but the modern additives scrub any extra you put in off the parts that need it, cause it to coagulate so the filter traps it out. So for the street just forget flat tappet cams. It's cheaper and less hassle to just get a roller block if your's lack the provisions for the roller cam.

Bogie
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Old 09-19-2013, 04:48 AM
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I have recently started using a flow matched pair of 350 CI (5.7L) throttle body injectors in my stock 4.3L V6 throttle body, an adjustable fuel pressure regulator and a TBI Power Plate from CFM Technologies, Inc. (Your high performance 'airflow' parts source for GM / Chevy Tbi / Vortec / Marine + Racing) . The 1988 - early 1991 5.7L V8 and 4.3L V6 throttle bodies are the same and have 44mm (1.750") throttle bores. Those throttle bodies flow about 480 CFM at WOT but can be modified to flow about 500 CFM. I am still using the stock ECM and a stock GM fuel pump.

I sent a spare throttle body to CFM Tech up-front to avoid a $150 core charge. They ported and modified the throttle body for better flow. Send them your throttle body or a spare and you are insured on receiving one that will accept your linkage and TPS. The late-1991 and up Model 220 throttle bodies have different type TPS, the air cleaner does not have an IAT (Intake Air Temperature) valve and the throttle body does not have a vacuum port for one.
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