Used TPI parts are cheap these days. Look for us to dive into this whole budget market wit
Now let's take a look at the TPI motor. As an '85 vintage piece, it's probably still a two-piece rear main seal engine (one-piece rear main seals arrived in 1986), which also means this is a flat-tappet camshaft engine. While neither of these aspects limits the power potential, the multipiece rear main seal and pan gasket assembly are leakers in the best of times. But the real cork in a performance application is the TPI manifold. You didn't mention if the engine was still EFI controlled, but I'll hazard a guess that it still is the case. The quickest way to add power is with a combination of cylinder heads and camshaft. Assuming there is a budget consideration, we'll fall back on the classic Vortec iron head as an inexpensive way to improve power. The stock Vortec head is limited in application with a combination of the small, 64cc combustion chamber and its stock valvespring. Since you are going to rebuild the engine anyway, you could choose an inexpensive hypereutectic piston such as Speed-Pro's ZW423NP30 dished piston that will create a 9:1 compression ratio with the 64cc chamber. You could then raise that compression with a slightly thinner head gasket.
The Vortec heads will also require a different valvespring. Since machine work isn't difficult for you, the best approach is to machine the heads to reduce both the height and diameter of the valveguide boss to accommodate all kinds of decent performance springs. Those who may not want to machine or can't afford this work (which really isn't expensive) could also go to a beehive-style spring like the Comp 26915. This beehive's inside diameter is large enough to fit over the Vortec guide boss while still offering enough retainer-to-seal clearance for a 0.470-inch-lift camshaft. The beehives are not cheap springs, and you will also have to purchase new retainers and keepers to complete the swap.
Before we get into the camshaft, let's complete our induction system. If you go with the Vortec heads, the stock TPI base won't work. Edelbrock makes a Vortec TPI base (PN 3817, $469.95, Summit Racing) that will allow you to retain the TPI configuration. But add high-flow runners and a 52mm throttle-body and you've got around $1,200.00 wrapped up in this arrangement. An alternative might be the Tuned Port Induction Specialties (TPIS) Mini-Ram, which is a short runner manifold similar to an LT-1 intake. TPIS offers this manifold with a Vortec or Fast Burn head base, and the cost is $895.00, but you still need to purchase a fuel rail kit, which is another $360.00-so you're right back at $1,250.00. All these parts will help make your 450 hp, but the cost gets a bit excessive. This kind of research points out why moving to the iron 6.0L engine is more attractive.
Another option for the standard small-block is to add a set of small-block heads like AFR, Brodix, or Edelbrock cylinder heads and then go with a strong carbureted intake or a single-plane EFI manifold that would retain the EFI. We have had great experience with an ACCEL single-plane EFI manifold with the fuel rails (PN 74139, $489.95) using a four-barrel 4150-style throttle-body. This manifold will also require bigger injectors than stock TPI stuff, and those can run around $400.00. You can make more than 600 hp with this manifold. We've made as much as 570 hp with our 420ci small-block with a very conservative mechanical roller cam and an ancient set of AFR 195 heads.
Given the dollar per horsepower of all this Gen I EFI stuff, it begins to make any LS engine look very attractive. One alternative is finding used TPI parts on eBay for much less, which is a great option. I'm not sure if I've made things clearer or just muddied the waters, but at least you have tons of options.
Edelbrock; Torrance, CA
Mr. Gasket (ACCEL)
Tuned Port Induction Specialties (TPIS)