The Sad State of Motorsports - Performance Q & A

Kevin McClelland Jul 1, 2009 0 Comment(s)

Finally, you could pull your spark plugs and tighten the plug gap down to 0.030 inch to test if the ignition is the problem. This should give you 300-500 more rpm before the engine drops into misfire. We'd step the ignition system up with MSD's finest components for your truck: an MSD 6A (PN 6200), a HEI remote coil (PN 8231), and--for plug-n-play installation--an adapter harness (PN 8877). The 6A will give you the multiple spark at low engine speeds and deliver peak secondary voltage of 45,000 when combined with the coil. This will keep your fire lit as long as you keep your foot in the throttle.

When you have upgraded your ignition system, you should swap out the spark plugs with some a couple heat ranges cooler than stock. The factory plug is much too hot for the increased pressures with the blower. We'd throw in a set of NGK V-power TR5s. Gap them at 0.045 inch. Yes, you will get better life out of a set of iridium or platinum plugs, but the NGKs are affordable, quality plugs that will give you 30,000 miles of great service. Good luck.Sources:,,

Q: I have a 10.2-inch-tall-deck, four-bolt-main, standard-bore Chevy big-block. I would like to use a 427 Chevy crank that I have in this block and a set of 6.700-inch-long rods. Would these rods work? Also, what particular piston would work, staying in the 10.5- to 11.5:1 compression ratio range? I'm looking for 600-700 hp out of this combo. The engine is going into a back-half '69 Camaro, and I'm looking for low 11s to mid 10s. Is this doable? Wilbert CushshonVia email

A: Just about anything is doable, but sometimes you have to ask why you're doing it. Is it just because you have some parts lying around? Using a tall-deck engine in your Camaro poses several problems, with header fitment being at the top. There are very few off-the-shelf headers available for the tall-deck. Since GM Performance Parts released its 572 tall-decks, there are a few headers on the market, but they can be rather pricey. You must really want to use these parts.

Let's get into the internals of the rotating assembly. If you already have these 6.700-inch rods, you'll need a custom piston built with a specific compression height to accommodate this length. The production rods are 6.135 inches long. With the 427 stroke of 3.76 inches, and the 6.700-inch length rod, you will need a compression height on your piston of 1.620 inches. This will give you a zero deck clearance if the block has never been cut. Production compression heights put the piston down in the cylinder approximately 0.020 inch. If you can use the 1.620-inch height, it could save you a few dollars on decking the block. If you're not sure of the deck height of your engine, measure it, or order pistons with a deck height of 1.600 inches and cut the deck to achieve zero deck.

To be in the 10.5:1 compression range, you'll need a piston with a 40cc dome. This will give you 10.84:1 compressions with zero deck clearance with a 118cc combustion chamber head. You could go with a smaller combustion chamber either by milling or by running a more-closed chamber. The only problem with running a closed combustion chamber with standard valve angles is that you limit airflow.

Achieving your 600-700hp bogey with only 427 cid is going to be tough. It will be a race-only package. Why not use the tall-deck to your advantage? You can easily put a 4.250-inch stroker package into the engine and have a 496! It will be a whole lot easier to reach your power and e.t. goals with the extra displacement. The choice is yours.


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