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Chevrolet 305 CI Engine Build - Mission 305, Part II

Warning: Think Twice Before Picking on This 305 Camaro

John Nelson Sep 1, 2004
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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.

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1. Turbo City's Tom Miller started off by plugging a scan tool into our '92 RS' computer system, assessing our new Vortec TBI 305's state of tune before making any modifications. Miller told us the Camaro was running "a little rich," but that it was also flat in the midrange.

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.

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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.

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5. The small-block unit utilizes stock 55 lb/hr injectors that have been flow-matched to within 1 percent of each other. An adjustable fuel pressure regulator is also included--Turbo City installs this extra-long knob so adjustments can be easily made.

Miller wouldn't tell us much about his tuning techniques, but he did tell us this: Vortec motors like different timing and fuel curves than Chevys with traditional cylinder heads, and so he starts with a Vortec-specific program, then goes through a process of testing and reprogramming 'til he gets it right. So, how right did he get it?

Miller got The Bitchin' Camaro's tuning pretty right on, we'd have to say. With the high-flow throttle-body in place and Miller's tuning calling the shots, our Vortec-headed '92 RS Camaro jumped up another 27 hp at the rear wheels, coming in at a stout 257 ponies--which translates to 330 at the crank (allowing for the same 22 percent loss factor we used in Part I). Torque-wise, we stayed right where we were before, coming in at 294.96 lb-ft of torque, which translates to a mind-boggling 378 at the crank. Given that The Bitchin' Camaro is making at least 280 rear-wheel lb-ft from 1800 rpm all the way to 4600 rpm, this thing pulls like crazy. It revs right up to six-grand (where it's still making 230 rear-wheel horsepower), and just straight-out flies. Not that we approve of unsanctioned acceleration contests on public roads, but we will say that a '97 SS Camaro and more than one Mustang Cobra have already been abused by our creation (we don't count anything equipped with a wing and a coffee can). We'll get you strip numbers when we can, but for now, the dyno and our right foot tell a helluva wild tale.

Not that we're saying that 305s should become the new basis for performance engines. What we are saying, and a look at the dyno chart should confirm it, is that the often-disdained mini-mouse motors have a lot of potential in them. Mission accomplished.


Superior Automotive Engineering
Anaheim, CA 92801
Turbo City
Orange, CA



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