Chevrolet 305 CI Engine Build - Mission 305, Part II

To all of you TBI performance fans, we apologize for leaving you hanging for several months now. Other projects, scheduling conflicts, and the occasional gremlin in the works have kept us from bringing you the results of our mission to build one little butt-kicking 305, working from the top-end up. Please refer to Part I in our June '04 issue for all the details of our build at Superior Automotive, but we'll give you the short version here: We put a little more bump in our bumpstick with a Crane custom-ground cam (0.510/0.520, 210/214 at 0.050, 114-degree lobe separation angle), added some heavier-breathing capabilities with ported Vortec heads (252/181-cfm intake and exhaust, respectively), machined them to work with the small 305 bores and a GM Performance Parts Vortec TBI manifold, added a Crane Hi-6 ignition to light the fires, and an Edelbrock exhaust system, from headers to cat-back, to vent the spent gases. And even though we didn't get to add a higher-flow TBI unit or reprogram the Camaro's computer, we still picked up 85 hp and 66 lb-ft of torque. We were impressed, to be sure, but there was more to come.

Mea Culpa, Mea Culpa
Before proceeding, we need to clarify two issues, one minor, one major. The author is solely to blame for any errors in Part I, so address your hate mail and used Ford parts accordingly. First of all, and this point is also taken up in this month's "Letters" column, in Part I we reported that our subject Camaro had a "Kansas-flat" powerband, with all our power gains available throughout the rpm range. Well, above 3,000 rpm, this was essentially true, though our newborn creation did tend to run rich. Below 3,000, our 305 was a lean-running sputterer, struggling to get enough to drink. The car was driveable, and noticeably faster than before, but was hardly in an ideal state of tune. We apologize for not being more precise.

The second, and more serious area, concerns the compression ratio. Again, the author is to blame, writing down incorrect information and going to press with it because of pressing deadlines. So, here's the skinny. We reported that our Vortec castings, which had 0.062-inch milled off the head surface to create a 53cc combustion chamber, would yield a 9.63:1 compression ratio when bolted down atop 0.015-inch Fel-Pro shim gaskets. As I said, we got it wrong--this combination would actually yield a sky-high 10.5:1 compression ratio, and kiss pump gas away forever. The shim gasket is also an iffy proposition if both head and block surfaces are not perfect. In our case, we didn't touch the block, so we were at risk right there. Using a 0.039-inch Fel Pro gasket brought us in at 9.8:1, while going with a 0.051-inch gasket would have brought us in at 9.5:1. Our tuner, Tom Miller of Turbo City in Anaheim, California, recommends 9.6:1 up to 9.8:1 as a target compression ratio for a project such as our TBI 305, so we went for the upper end and headed over to Tom's shop to ensure that our nasty little creation was being properly fed.

Heavy Breathing
From the beginning of our project, Joe Jill of Superior Automotive and Turbo City's Miller compared notes on making our 305 work with Turbo City's new 620-cfm Super Flow throttle-body and computer reprogramming; the main result was the aforementioned custom-ground cam from Crane. Miller specializes in what many other tuners eschew--making power with throttle-body injection setups. Our first step, of course, was to get enough air and fuel into the motor. Turbo City's throttle-body, which should be available by the time you're reading this, took care of that. On the other hand, we also needed that all-important custom ECU Prom chip, giving our Camaro the proper fuel and timing tables to read from, and hence the best possible performance.