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Engine Swap, Ask Anything - February 2013

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Kyle Lutz; Houston, TX: I purchased my first Chevelle more than two years ago. It's been a frame-on restoration. I've read several of your articles over the years and have learned a lot. A while back, you did a piece on building a budget 400 (“How to Build a 400ci SBC Torque Monster for $2,500!” May '11). I'm not sure I can do all of the upgrades that you did but was wondering where I would get the most added horsepower for the least amount of money. The car already has a 400 in it with dual exhaust.

Have you thought about doing a comparison between Edelbrock's EFI conversion and the EZ EFI? I'd like to upgrade to an EFI system, but I am not sure which one would be the most reliable. Any suggestions? You can check out the progression of my car on my website at www.my71chevy.com. Thanks for your input and for writing such a quality magazine.

Jeff Smith: What is it about simple questions that seem easy but can quickly get very complicated? The question of the best-bang-for-your-buck upgrade really depends on a host of variables, but we'll take a shot at it. I dialed up your website and it appears the 400 engine has an Edelbrock intake and cast-iron manifolds. We'll assume for a moment that it's a stock short-block with a stock cam and heads. Our experience with that production 400 showed us that in an effort to pull decent emissions out of these big '70s motors, GM lowered the pistons in the cylinders between 0.060 and 0.080 inch! The stock compression on our 400 with 76cc chambers was a miserable 7.8:1. If you were trying to kill the efficiency of an engine, that's the way to do it. No wonder everybody spit on these engines back in the day. We put 64cc Vortec heads on our original version of the 400 in a marginal attempt to improve the compression, but that only brought the static compression up to around 8.4:1, which isn't even close to what it should be. But with a limited budget, that would the best call. With the stock cam, stock Vortec heads will also help power. As we mentioned in the story, you will need to modify the heads if a cam swap is in the works. As you saw with our engine, it was less than impressive even with the cam and Vortec heads, making barely 400 hp, but at least the torque was decent at 458 lb-ft.

Since your engine is equipped with cast-iron exhaust manifolds, headers and/or an exhaust system are the first things I would suggest changing. Improving on the existing dual exhaust (which is probably a compression-bent 21⁄4-inch system), to a true 2 1⁄2-inch mandrel-bent system will help that 400, even with the iron manifolds. I have personal experience with Flowmaster's American Thunder series of exhaust systems on Chevelles, and they fit very well. This is an entire 21⁄2-inch system with H-pipes, a pair of Super 40 mufflers, tailpipes, hangers, and clamps. You will still need to adapt the lead pipes to exhaust flanges, but that can be handled by a muffler shop. The system is PN 17119 and sells through Summit Racing for $349.95. This is by far the best bang-for-the-buck thing you can do for your car—even if the engine can't really take full advantage of what the system offers. Another company that builds excellent systems designed specifically for a GM A-body is Torque Technologies. They offer several options for both 2-1⁄2 and 3.0-inch systems. They charge a little more (the 21⁄2-inch system is $349, plus mufflers), but you have a choice of several different mufflers. Check 'em out. Because your Chevelle offers the room, you might even consider a 3-inch exhaust system or perhaps a 3-inch system to the muffler and then 21⁄2-inch tailpipes. Torque Technologies offers a system like this complete with either an H- or X-pipe.

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