March 2012 Chevy High Performance Q&A

What’s going on out there?

Kevin McClelland Jan 20, 2012 0 Comment(s)
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Elky Upgrade

Q. My ’86 El Camino has a factory 4.3L V-6 TBI, TH200-R4, and 3.08 rear gear. I’d like to install a 400 small-block, retain the TBI, and change the rear gears to a 3.42:1. Can I use the factory computer without making any changes to it? I know I’ll have to change the heads and intake to work with the TBI. I plan to use stock Vortec heads. Also, could you recommend a mild camshaft that would work with this stock 400 combo? Thanks! 

Eric Patton
Hiram, GA

A. You have a great plan that is somewhat difficult to execute. GM didn’t make it easy to play with the throttle-body fuel-injected engines. These systems are called Speed Density fuel injection. What this means is that the engine is developed, assembled, and dyno-calibrated to generate the fuel and spark map. This calibration is specific for every engine configuration developed. Anytime you change the airflow demand (volumetric efficiency) of a given calibrated engine it requires another complete calibration. Something as subtle as a small performance camshaft and intake manifold will drive the fixed calibration right out of range. Switching from a 4.3L engine to a 6.6L (400 cid) is a 54 percent increase in displacement. You should be able to swap out the calibration chip with the proper cylinder count, displacement, and injector size, and the engine would run. Now, for the engine to be calibrated and run properly, you would need to spend a tremendous amount of time on a chassis dyno to get the fuel and spark tables where you need them. Edelbrock offers calibration for its TBI engine packages that are built around its engine components. It is a complete cylinder head, camshaft, and manifold package, but it is only offered for a 350 displacement. The stock 350 produces about 190 hp at 5,000 rpm, and with the complete heads, manifold, and cam package with calibration, it steps up to the 250hp range. You may be lucky and find a calibration for a large-displacement small-block.

Using the Vortec cylinder heads is going to be a challenge. There isn’t a TBI manifold on the market that offers the Vortec cylinder head bolt pattern. Again, we would suggest using the Edelbrock Performer cylinder heads that will work with the Edelbrock Power Package. Call for more information. These packages are getting some dust on them. The TBI engines have been out of production since 1992 in passenger cars, and since 1995 in trucks. The aftermarket really didn’t step up to the TBI systems in the first place. Many aftermarket companies have moved on from this technology. If you’re going to do something we would do it soon. Good luck.

Source: edelbrock.com

Factory Plumbing

Q. My friend has a completely stock ’65 SS 396 365-horse with a factory Holly 600 vacuum-secondary carburetor. The problem is that he purchased it from an individual and they had to replace the fuel pump, and when they did, they replaced the factory fuel feed lines to the carburetor. Where can he get the factory fuel fittings and line? He has asked around and they said that they don’t carry this fitting, and he would have to make his own. I read your tech section all the time and would like your help on this problem. Thanks for your input.

Roger Bear
Kansas City, MO

A. During our early hot rodding years you couldn’t tell us the factory stuff was good enough for performance use. We would immediately rip off the factory fuel feed lines from the pump to the carburetor and replace it with Holley dual-feed kits from the speed shops. Well, over the years we found that the factory wasn’t that stupid, and that it usually built in a safety factor to allow higher performance. The fuel feed lines for Holley carburetors is a perfect example. Anytime we’re building a street or moderate performing race car, we’ll fabricate the fuel feed system out of steel lines and brass flare nut fittings. They may not be as blingy as steel-braided hose and AN fittings, but they will last forever and perform leak-free forever.

With a lot of these very specialized lines and fittings missing from our muscle cars, YearOne has come to the rescue with reproduction fuel pump-to-carburetor line kits, featuring the correct bends, contours, and lengths. The main piece is a very specific brass three-way fuel block that splits from 3/8-inch feed to two 5/16-inch lines to the carburetor. They offer the kits in both steel (PN RS415), and stainless steel (PN RS415S) for your buddy’s Chevelle. These kits have saved many a restorer from the hacking we did in the early years. Sorry!

Source: yearone.com

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