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Your mileage seems on the low side of average. Certainly where you drive and how you drive will have an effect of fuel mileage as will the condition of the truck and whether you have an automatic or a stick. Being a 92 it probably has some high mileage on it, in which case if it has an automatic the transmission it’s probably in need of service. Also, if it’s an automatic I don’t know whether or not your getting overdrive and converter lock up.
Your search for power is going to be constrained by the need, or not, to pass emission testing. This will largely determine how much cam and compression you can get away with. The other constraint is the condition of the engine. Putting improved heads and a hotter cam on a tired bottom end invites early failure of the short block and if equipped with a high mileage automatic it also will give up quickly, often with in a couple, three weeks of the new more powerful engine. So you need to plan this out carefully.
Vortec heads are good choice for power and will also improve fuel mileage because they have improved porting on both the intake and exhaust. They’re good for a 20/30 hp increase over the swirl ports currently on your engine. They also have a very efficient combustion chamber. These features are now common to a host of GM and aftermarket heads both in aluminum and cast iron. With an aluminum head you can push the compression up another point while maintaining NOx emission levels and maintaining the same fuel grade as the lower compression cast iron head. You need to work up a reasonable cost estimate for the Vortecs against aftermarket heads if your going to do any modifications to the Vortecs to accommodate higher lifts, stronger springs, screw in studs, and pushrod guide plates. These things combined with the extra cost of a Vortec compatible intake can quickly add up to the cost of on over the counter aftermarket head that can use your existing intake or a less expensive non Vortec intake.
The cam is more tied to emissions testing than anything else. With TBI and emissions testing your rather restricted as to how crazy you can get. Edlebrock sells a kit for these TBI motors that includes a flat tappet cam with 195 I and 214 E degrees @ .050. This tells you where they are willing to go with an emissions engine. You can probably run a cam like the 96 up Vortecs with 204 I and 210 E degrees @ .050 and remain quite emissions testing safe. Beyond that point your treading on thinner and thinner margins. The TPI engines and later sequential injection systems cam push the cam timing up with relatively good prospects of passing an emissions test as the port systems are much tighter to the engine’s requirements and less raw fuel is tossed out during the overlap. If you have an AIR system, it will cover some of that overlap fuel loss to the exhaust and burn it in the manifold/header.
Your block will determine which cam you can use, being a 92 it’s a mixed bag, it could already have a roller, but probably doesn't. If it isn’t roller equipped, then it may or may not, have provisions for a factory roller. If it has provisions in the valley to accept the spider and higher lifter bores along with the thrust plate provision behind the cam gear, then you can put in a factory roller even if it’s currently running a flat tappet cam. If these provisions are absent than the only choice with this block is an after market roller cam and lifters. The only way to find this stuff out is to go in. Probably the first thing is to pull a push rod and measure it. If it's 7.8 inches you have a flat tappet cam, if it's 7.2 (these are give or take a couple thou measurements) it's a roller. If you have a flat tappet, you still don't know if the block is provisioned for a roller or not, so you need to pull the intake. If it's a roller provisioned block with a flat tappet cam, you'll see three bosses above the main oil galley casting and tappet bores that are higher than the lifter. If that stuff is there you can use a factory roller cam kit, if not you'd have to go to the aftermarket for a roller cam and lifters which is more expensive.
You can really run any 4 barrel type intake with TBI, all that’s required is an adapter. Hunting around will turn up some over the counter units, I know Holley used to make them. However, building one at home is not difficult. You can build an adapter from at least ¼ inch, preferably 3/8s inch, aluminum plate with a saber saw to cut the profile, an electric drill with a piloted hole saw to cut the throttle bores and a suitable twist drill and tap to make the TBI’s mounting bolt holes.
The Holley model 502-6 TBI at 670 cfm with a 2 inch throttle can be adapted for use with any TBI engine. Same goes for a junk yard unit from the 454 truck engine. In either case you may need to trim the capacity of the injector, see the Holley web site, and add an adjustable regulator. But the main effort of accommodating the large TBI unit is accomplished in the chip. A custom chip made for your specific modifications is a requirement you cannot side step.
Here’s some URLs to help you out
Computer Chips:
http://www.fastchip.com/
http://www.hypertech-inc.com/
http://www.jetchip.com/
http://www.kcspeed.com/
http://www.superchips.com/
Fuel Injection:
http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSFI/FMSFI.html
http://www.turbocity.com/
http://www.edelbrock.com/
http://www.rancefi.com/
http://www.arizonatpi.com/
http://www.fuelinjection.com/
Bogie
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