I have a 93 Suburban 4wd I am considering putting Vortec heads on. What modifications do I need to make? Headers, exhaust, intake? I would like to keep the factory fuel injection if possible. This is going on the original 350 that I am currently rebuilding .030 over with a stock spec cam. Thanks, Chip.  

Chip, lets start with where you live. If Smog testing is a requirement, you need to know that Vortec heads are technically illegal. GM has not sought and exemption from the California Air Resources Board (CARB) nor from the Feds. In California and places that look under the hood the testers often see the different manifold bolt pattern and external EGR and that clues them that someting isn't right, then comes the questions. They'll send you to a techncial referee in the case of Calif. who will inform you that they have to come off unless you're willing to bring the whole machine up to the 1996 Vortec configuration. This is a big and fairly expensive effort. There are many aftermarket heads that are as good or better than Vortecs whose manufacturers have obtained 50 state legal exemptions. Edlebrock, World, Holley come to mind as well as others.

If you live where this level of testing is not a requirement, then putting on Vortecs isn't a big problem. You'll need a TBI to Vortec intake, available from most any speed shop. You'll also have to develop an external EGR source, GM has the basic parts from 96-up Vortec 305/350 engines to make the hookup. This will require a 96-up GM exhaust manifold or if going with headers a Vortec set with the adapter pipe welded to the pipes.

You'll need a new chip as Vortec heads will add about 20% to the power output. The existing chip will be unable to resolve the changes in throttle opening and manifold pressure to the old fuel map. These are fairly expensive.

http://www.fastchip.com/

http://www.hypertech-inc.com/

http://www.superchips.com/

http://www.kcspeed.com/

http://www.jetchip.com/

As long as you're in there you might want to consider a bit more cam. The factory cam is mighty weak, you can go to something with timing similar to the 300 horse 327 cam (3896929) which will really wake up the engine without sacrificing low end torque nor fuel mileage. 

Bogie

We are a smog exempt county in a state with lax enforcement, but I would like to retain the factory TBI. Any other suggestions to improve the torque? Will iron heads and the TBI handle one or two more points of compression and a little more cam like you suggested? This is just a family car and tow vehicle for my 55 when the family goes to nosstalgia drags. Thanks for your assistance, Chip.  

I wish you dropped in here a bit earlier as I rather guess you've already picked pistons and they're probably full dish stockish GM style pistons. The problem is that the piston shape, cylinder head, and camshaft are a set of closely related selections.

For example, high mixture turbulance is a key to high (er) compression without detonation. The combination of a "D" shape dished piston with the Vortec or other "fastburn" type combustion chambered heads is very effective in allowing a higher compression ratio even with a cast iron head. The compression ratio is also related to cam timing where more cam timing allows more compression ratio.

However, the Vortec head raises compression with factory type full dish pistons about a point compared to the Swirl Port heads you have, they also flow better and have more turbulent combustion chambers.

The other downside to Vortec heads is that they are designed to use a port injection induction system. They have no exhaust heat under the carb or in this case TBI. This causes a cold weather problem when the engine is not fully warmed up, this will include formation of ice in the throttle body and resultant rough running and stalling if you live where the weather gets cold and wet.  The Vortec intake manifold does circulate coolant under the carb/TBI zone which helps this problem after the engine warms up. Also, it you have the original aircleaner system with the hot stove inlet provision of drrawing inlet air over the exhaust manifold when the engine is cold will help over come icing.  A set of World S/R or S/R Torquers would provide all the porting and chamber advantages of the Vortec head plus an active exhaust crossover that supports under carb/TBI heat plus an EGR source. These would allow you to use your original GM intake.

If you run without EGR the mixture needs to be richer as the space previously taken up by dead exhaust gas is now air so a little more fuel needs to be tossed in, this is something the guy that blows the new PROM needs to know going in. 

Bogie

I haven't decided on the pistons yet. The block is back from the machine shop and is bored .030. I currently have an older 350 with the later heads on it, so it is driveable. This is going to be a late summer early fall buildup for this year. I am currently building an engine for my 55 and my son and I are building an engine for his 68 Chevelle. So the Suburban's good motor is on the back burner. I can't express enough my appreciation for your knowledge. Thanks bogie, Chip.  

Check these out for pistons

http://www.21cgt.com/FMWebCatalog/default.htm

http://kb-silvolite.com/performance.php?action=start