Chevy LT1 Head Questions - Performance Q&A

Kevin McClelland Jun 1, 2009 0 Comment(s)

In mid-1987, GM improved the TH700R-4 transmissions with an increased number of vanes in the front pump to stabilize line pressure and volume. GM increased the spline count to the input shaft at the same time. This was a great improvement to this transmission, giving it better durability and life. If your Camaro is equipped with the original transmission, it's very safe to say it is a 27-spline input. If you're still in doubt, get the trans code off the side of the case and give Ken Casey a call at Burt Chevy (800.345.5744). He can identify the trans for you from the factory ID numbers. The only problem with this is when the trans has been rebuilt and modified with later-model components. Good luck with your Camaro project.


She Be Lean
Q: I have an '84 Camaro with a 350 that has been bored and flat-decked. It has World Sportsman II 72cc heads, a Lunati Voodoo cam (PN 60101), Speed-Pro flat-top pistons, an Edelbrock Performer RPM intake, and a Holley 670 Street Avenger carb. The distributor is a stock HEI with vacuum advance out of a '77 Camaro. It runs great when the weather is warm, but as soon as it cools down to 55 degrees, it surges cruising down the road and falls on its face when accelerating, and I have to ride the clutch when I take off or it will die. I have considered fuel injection, but it is a little cost-prohibitive. Also, I'm going to install a Mallory Hyfire 6 EXL soon, but I don't know if that will help or not. Can you please give me some ideas on what I can do to give it better cold-weather drivability? I don't want my car to have to sit for six months every year. Thank you very much for any help.
Mike Kennedy
Via email

A: What you have is a lean condition. When the ambient temperature is higher than 55 degrees, you have just enough fuel to satisfy the engine's fueling requirements. When the temp drops, the air density increases and you have more oxygen in the inlet air. This leads to the lean surge you're feeling, the bog when you try to accelerate, and the stumble on take-off while slipping the clutch. Going to a stronger, hotter ignition system can help fire a lean mixture. But it sounds like you need to increase your jetting.

First, make sure that when the carb was installed, the float level and idle feed screws were set properly. If the float level is low or the idle feeds are on the lean side, this would also give you lean stumble conditions. Check out Holley's online FAQs for the correct information on adjusting your Holley 4150 model carb. If the adjustments are correct, we'd increase the primary jet size by two. I would also increase the accelerator squirter from the factory 0.028 inch up to 0.031 inch. This will aid in the initial step on the throttle. With these two changes, you should be able to make it through the winter.

Also, if your calibration is this sensitive, we bet it's too lean for max performance during the summer. Adjusting the jetting of a carburetor is a very subjective adjustment based on the experience of the tuner. The folks at Innovate Motorsports have brought us affordable wideband O2 sensors to help dramatically with any tuning. The LC-1 kit gives you the wideband O2, wiring, software (PC), and cabling to your PC to know for sure that you have the proper calibration. Also offered are dash-mounted gauges to give you convenient, real-time AFR. Check out Innovate's online forums to help the novice tuner dial in his car.



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