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454 Chevy Big Block Build - Ask Anything

TPI Antics
Rod Walker; Boone, IA: I am a longtime subscriber from your old hometown of Boone, Iowa. I graduated in the class of 1975 from Jefferson with your ex-wife, Susan. I've run the machine shop at Arnold Motor Supply in Boone for the last 16 years. It's a one-man shop with some pretty nice equipment. We do a little bit of everything, from all-aluminum FE motors to 500ci Olds and numerous drag, circle track, truck pulling, and street performance engines. I'm getting ready to redo a street rod deal-a '55 International pickup with the engine and trans out of an '85 TPI Corvette. It's been on the street for a couple of years now and the customer wants more power. He's looking for around 450 hp and a nasty idle. The truck is tubbed with a 3.90 gear, a short-block, hugger headers, and air conditioning. Joe Busch's shop built the truck for this guy, and it's pretty nice. We will freshen the engine, and we're thinking about upgrading the heads, intake, cam, and converter. What can you recommend? Thanks and keep up the good work-your magazine is the best!

Jeff Smith: First off, when I get a tech question from my hometown, it's almost a given that I'll answer it! Boone, Iowa, is also the home of the IMCA Nationals at the Boone Speedway. My friend Blake Hanel and I used to sneak into the pits at the track back when we were in junior high school in the late '60s. To get to your question, Rod, an '85 TPI engine is going to be tough to push up to 450 hp with the existing TPI manifold. Those intakes were originally intended to be used only on a 5.0L engine-back in the '80s the internal GM mindset was aimed at eliminating the V8, and they thought the 5.0L 305 was as big as they ever wanted to go. Things have sure changed for the better for GM performance enthusiasts in the ensuing 25 years, haven't they? You might seriously consider a conversion to a later-model iron-block 6.0L LQ4 LS-style engine as opposed to attempting to make power from a TPI engine. We'll look at the 6.0L LQ4 truck engine alternative, then compare that engine with the mods it will take to make equivalent power from the original TPI motor.

Several years ago, we bought a junkyard iron-block 6.0L engine and installed a GM Performance Parts carbureted intake, a Holley 750 carb, an MSD spark box to run the distributorless ignition, headers, and a mild GM Performance Parts HOT cam (219/228 at 0.050 with 0.525-inch valve lift and a 112-degree lobe-separation angle). The stock LQ4 engine with the carbureted intake and headers made an outstanding 425 hp and 439 lb-ft of torque. Let's emphasize this right here: 425 hp with just an intake and headers! Once we added the camshaft, the power jumped to 483 hp at 6,000 rpm and 450 lb-ft at 5,000 rpm. The total investment if you purchased a used engine and everything new might be roughly $3,500 or less depending on how much of this stuff was used parts. Of course, you could also retain the OE EFI, swap to an LS6-style intake, and have to do a little HPTuners software investment for tuning for the cam, but this is outstanding power in an engine that would be incredibly reliable and powerful. Plus, you're working with 21st century technology. An even simpler version would be a new LS3 crate engine from GMPP, but the cost would be substantially higher with roughly the same power.

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