Remember, when it kicks the rods out in the lights, oil under the tires isn't much fun. I've seen tons of race cars wadded up each year. Luckily, when it happened to me, I was able to keep mine off the rail! Be safe.
Throttle Body Follies
Q I recently blew the stock 305 in my '88 Chevy Cheyenne. I then bought a 350 four-bolt-main short-block already bored 0.030 over. I had a local speed shop build the engine with my 305 heads from my previous engine. They are bone-stock valves and ports. I also had the shop install a Hypertech Stage II Thermomaster chip to correct the PCM settings from 305 fuel settings to 350 settings. Shortly afterward, my TBI had one of the injectors stick wide open so I just replaced the whole unit. Here lies my problem: I bought a remanufactured TBI from O'Reilly's Auto Parts. They all have had problems running either too rich or too lean (meaning I have warrantied it out several times, five to be exact). I have now managed to get one that performs OK, but I have to have my EGR or it runs too rich. If I drive on the highway it sends a lean code, and when it is cold the engine surges on warm-up at idle. What are my options for this small but irritating problem? Should I buy a brand-new TBI? I found one at Scoggin-Dickey for a decent price. It's a Holley PN H502-6, but I don't want to make another mistake. Any advice would be greatly appreciated, so please help!
Carmen NapieralskiSpringfield, MO
A We have written about this 305-to-350 swap many times before. However, it sounds to me that you have a problem with mix-and-match parts. It's great that you went with the Hypertech chip to move your calibration up to the 350-cid engine. Is it a custom chip or an off-the-shelf chip for a 350-equipped '88 Chevy truck? This makes a huge difference when you go to order any TBI unit. If the Hypertech chip is an off-the-shelf '88 350 chip, it is calibrated to the LO5 350 TBI injector size. The injectors in your throttle body are different sizes between the 305 and 350. The proper PN for the 350 injectors is 19110538, and you will need two. You can easily swap them out, and this should take care of your cold start surge (lean condition) and your lean "check engine" light going down the highway.
The Holley 502-6 direct-replacement TBI unit is a great piece for modified TBI engines. It flows 670 cfm, and the injectors are sized for the stock calibration on a 350 engine. Holley also provides a distribution ring to steer the fuel into the intake manifold to improve cylinder-to-cylinder distribution. The only problem with this TBI is that it uses 2-inch throttle bores. The factory manifold is sized to 111/16-inch bores, and without modifying the manifold you will have a large mismatch.
Make sure your Hypertech chip is calibrated for 350 injector sizes, and the new injectors will straighten out your fueling issues. Good luck.
Sources: holley.com, sdparts.com
If you have technical questions for Kevin McClelland, send him an e-mail at chevyhi@sourceinterlink.com.