March 2011 Chevy High Performance Q&A - Performance Q&A

Under Pressure Round II

Kevin McClelland Feb 11, 2011 0 Comment(s)
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A: Over the years, we’ve done just what you’re trying to do. We build the engine with a future goal in mind. We’re currently doing that with an LS2 that we want to turbo in the future. It’s always a compromise either way you build the engine; the camshaft and compression aren’t going to be right for a naturally aspirated operation and you’ll be driving it around for at least a year like this. Will it hurt the engine? Absolutely not. However, you will get very tired of the lack of performanceand more often than not, you never get around to finishing out that planned upgrade. Anything can happen.

How about you build this short-block for a max-performance NA engineand later rebuild the short out of your car for the turbo application? It will cost more, but then you have the opportunity to build it in the future. You may be very pleased with the 383 you build up and never turbo this car and move on to some other project.

Getting back to some engine specifics, you need to pick up a Gen II short-block for a core. The Gen II engines were built between 1992 and 1997. The ’97 Camaro had both LT1s and LS1s. There should be plenty of blocks in the wrecking yards, as the LT1s were an option in the Impalas, Caprices, and Caprice wagons (’92-96) and were standard in the Buick Roadmaster wagons and Cadillac Fleetwood Broughams (’94-96). In the Chevy products, there was the L99 265-cid Gen II that looked just like the Gen II LT1; the way to make sure the car is LT1-equipped is that in the eighth digit of the VIN will be a letter P. Also, cast into the cylinder block right behind the driver-side cylinder head on the bellhousing flange will be the 5.7L. In the Buick and Cadies alone, GM installed more than 135,000 LT1s between ’94 and ’96. Look for the oddballs to pick up a core at a screaming price.

You could build your short at 8.5 to 9:1 compression ratio for your turbocharged build. You could go with a nice naturally aspirated camshaft and swap out the cam when you stick the turbo on it. If you do build the engine with this low of a compression, please stay very conservative with your camshaft selection. If you go with an aggressive profile, you will hate the car until you add your hair dryers. Good luck with the planning and execution of your project.

Let It Bleed

Q: Performance Q&A is one of the first articles I read each month. Can you help me find information on air bleeds and emulsion holes? I have a QFT 750AN DP that gets lean up top. It is on a 383 with an Extreme Energy 274H cam, cleaned up Vortec heads, and a Performer RPM intake. The bottom end is forged, but I am running hypereutectic pistons so I keep the rpm to around 6,000. It is in an Austin Healey kit car used for track days, kind of a Cobra for a Chevy guy. For tuning, I installed an Innovate wideband and disconnected the secondaries. Accelerating at moderate throttle I jetted for 14.5 to 15:1. I then adjusted the power valve restrictors to get 12 to 12.5:1 at full throttle up to 3,000 rpm (half the rpm for half the carb). When I reconnected the secondaries, it was rich so I started dropping secondary jet sizes. When I get it right in the 4,000-5,000 rpm range, it leans out to 13.5 or so at the top. I think I need to reduce the main air bleeds, but I’d like to read up on the subject. When I called QFT they said any good Holley book would help. I currently have an old HP Books Holley Carbs and Manifolds by Urich and Fisher, a newer Super Tuning and Modifying Holleys by Emanuel, and now Hot Holleys by Walordy. They touch on air bleeds and emulsion holes a little, but mainly say, Don’t screw up your carb by messing with them. Can you guide me to a good source of tuning info to minimize my cut and try? Thanks,
Kenneth C. McDonough
Hillsboro, IL


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