1996 LT4 Chevy Corvette Bullet Engine - Under Pressure

Performance Q&A

Kevin McClelland Dec 1, 2006 0 Comment(s)

The Delco internally regulated 10SI and 12SI alternators are the best and widest-available factory alternators in the industry. They are what the aftermarket has grabbed up and converted to one-wire-style alternators. The 10SI alternators were introduced back in '70 for limited use and were in most GM vehicles by '74. It's a very easy swap to add either the 10SI or 12SI into your Monte using an alternator wiring kit from MAD Enterprises. Mark Hamilton has done it again with a complete, very straightforward instruction manual, explaining changes to the factory wiring harness. All the factory GM connectors, wire terminals, and shrinkable tubing, 8 feet of 8-gauge Tuff-Wire for the main power feed, and a diode to prevent engine run-on are included in the kit. Mark doesn't sell alternators, but he has sourced out the correct 10SI and 12SI alternators for purchase. For a 63-amp 10SI alternator, pick one up for a '78 Camaro with air conditioning, and for a 94-amp 12SI model, ask for an '84 Camaro with an L69 H.O. 305. You can get these at any auto-parts store across the country. This prevents you from being stranded out on a cruise or a long road trip. Also, Mark recommends not going with a one-wire-style alternator. The factory three-wire system will sense the load on the electrical system and charge accordingly. To pick up the alternator kit, it's sold under PN ALT-1.

Whip It. Whip It Good
Q I have an '01 Silverado with a 4.8L Gen III engine in it-not the typical vehicle for a CHP reader. I have gotten a tune, put in some electric fans, and am in the process of installing headers and building a custom exhaust.

I thought that I should get a baseline dyno run before all this. The truck has a 72-inch driveshaft. You might see where I'm going here-with my setup in Third gear (1:1), I got up to 5,000 rpm/124 mph...when time all but stopped as I heard a huge boom and saw my driveshaft drop into view and rattle around under the truck! The trans was toast. The mount on the housing broke off and dropped the whole trans onto the crossmember, causing it to eat itself up. I have a new trans ordered, so that's not my concern. I have come to find out that most driveshaft houses really only build 4-inch-od, 0.125-inch-thick driveshafts in 72-inch lengths. This has a lower critical speed (4,900 rpm) than my stock 5-inch-od, 0.083-inch-thick driveshaft (6,200 rpm). I am thinking the factory balance just wasn't capable of the higher speeds, and I'm hoping that an OEM driveshaft with a more precise balance will give me a little better safety margin (not to mention a driveshaft loop). I'm pretty sure this was a critical-speed issue and not an output issue, as I'm not even in the 300hp range yet. Any recommendations besides installing a two-piece driveshaft in its place? Thanks.Andrew GreifBallston Lake, NY

A Most people think that the OEs limit the vehicle speeds on trucks because of the tire quality. Well, with your electronic tune and eliminating the 100- to 105-mph top-speed limiter, you have met your driveshaft! I'm sure that you would rather have been introduced in another fashion. Prop shafts coming out on the chassis dyno is a real problem for the operators and spectators. There's a ton of energy in that shaft when it comes loose; look at the underside of your truck at the evidence of its attack on your trans.

Driveshaft critical speed is based on the length, material weight, and diameter. Yes, your driveshaft balance could have just driven it over the edge and started the whip that finished you off. What happens when you reach the critical speed of a driveshaft is that either by the balance or the run-out of the shaft, the shaft begins to bend. As the shaft speed increases, this bending creates an even greater imbalance, and the shaft shortens and pulls itself out of the transmission at the slip-yoke. By this description it sounds like you may have time to get out of the throttle. But as soon as the shaft begins to bend, it's all over!

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