305 Small Block Engine Build - The Other Small-Block

Richard Holdener Jul 1, 2010 0 Comment(s)

There are obviously ways to reduce the cost of upgrading a 305, by either porting the stock 305 heads or substituting a set of Vortec iron heads for the slightly more expensive Trick Flow aluminum heads. The downside of porting the stock heads is that they will never equal the flow of the Trick Flow heads, nor will the porting eliminate the potential for cracking (305 heads are thin, weak and prone to cracking, especially if you overheat engine). The Vortec heads are stronger than the 305s, but have their downside as well. The problem with the Vortec head swap is that extra work is required to allow for reasonable cam timing (above 0.450 lift). The extra work and expense required to accept any reasonable performance cam needs to be taken into consideration when considering the Vortec heads, as does the fact that (like the stock 305s), they are heavy lumps of cast iron that will be more prone to detonation than modern aluminum heads. This is a case of you get what you pay for, and the dedicated 305 heads from Trick Flow Specialties are a worthwhile investment.

The last obstacle in our 305 upgrade was the induction system. It was certainly possible to top the new Trick Flow heads and Comp cam with the stock Q-jet intake and carb, but we chose to replace them with a dual-plane, aluminum intake from ProComp along with our favorite dyno carb, the Holley 750 HP series. A low-cost alternative to the 750 HP will provide equal performance at this power level, but the 750 was on hand at Westech and was easy to tune thanks to an external Percy's Adjust-a-Jet system. Make sure to measure the available hood clearance when selecting a high-rise intake like the air-gap-style from ProComp.

With everything bolted in place, we ran the 305 in anger and were rewarded with peak numbers of 362 hp at 5,800 rpm and 353 lb-ft of torque at 4,500 rpm. Torque production with the upgrades exceeded 340 lb-ft from 3,500 rpm to 5,500 rpm, making for not only a broad torque curve but a 305 that no longer fell on its face after 5,000 rpm.

Measured peak to peak, we improved the power output by 138 hp and by over 170 hp out at 6,000 rpm. If 360 hp isn't enough, we certainly could coax 400 hp out of this combination by upping the compression (milling the heads) and/or stepping up in cam timing, but you start to trade-off things like idle quality, drivability and low-speed response for the stronger mid-range and top-end charge.

RPM - HP TQ (Stock LG4) - HP TQ (Modified LG4)

2,500 - 149 313 - NA NA
2,700 - 157 306 - NA NA
2,900 - 169 306 - 181 327
3,100 - 182 308 - 194 329
3,300 - 199 308 - 209 333
3,500 - 203 304 - 226 340
3,700 - 210 299 - 244 346
3,900 - 217 292 - 260 350
4,100 - 221 283 - 273 349
4,300 - 223 272 - 286 350
4,500 - 224 261 - 300 353
4,700 - 224 250 - 314 351
4,900 - 219 234 - 328 351
5,100 - 214 220 - 339 349
5,300 - 205 203 - 348 345
5,500 - 195 186 - 355 339
5,700 - 186 171 - 357 329
5,900 - NA NA - 359 319
6,100 - NA NA - 358 308
6,300 - NA NA - 349 291

Sources

Trick Flow Specialties
Tallmadge, OH 44278
330-630-1555
www.trickflow.com
Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
The Carb Shop
Ontario, CA
909-947-3575
CustomCarbs.com
Pro Comp Electronics
Ontario, CA 91761
909-605-1123
www.procompelectronics.com

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