Car Craft magazine builds a 325 horsepower 305 small block Chevy V8
In the March 1999 issue of Car Craft magazine, a project was begun; to build a 305 small block up using readily available off the shelf parts and see how powerful it could be made. The reasoning behind this was that the 305 was the power plant in MANY, MANY GM cars and trucks and why yank a good motor (what have I been telling you all?) when a good motor was already there?
Base Dyno of Mule Engine- 145bhp @ 4000rpm / 165 lbs-ft torque @ 4200rpm
The first step was to take a 'donated' 305 out of a '82 Camaro. The 305 had 80,000 miles on the clock, 8.6:1 CR, and a grossly mild hydraulic cam. As such, the stock LG4 wheezed out a less than astounding 145 net (read at the flywheel, not the rear wheels) horsepower at 4000 rpm and only 165 lbs-ft of torque at 4200, as installed in the Camaro, complete with dinky exhaust pipes and the dysfunctional catalytic converter. For the rest of the tests, headers (type and diameter unspecified) with 3 inch dual pipes feeding Flowmaster (type unspecified) mufflers were used. A noncomputer HEI with 22 degrees of initial advance in the distributor was also used in this and all following tests of the dyno mule and the engine was run on 89 octane (readily available) gasoline.
Full Performance Exhaust System- 197.3bhp @ 4600rpm / 261.3 lbs-ft torque @ 3100rpm
With the headers, 3" dual exhaust, and high performance Flowmaster mufflers installed, no other mods (other than some timing and carb tuning), the motor's power and torque took a noticeable jump! It was noted that the headers alone were probably worth 30 or so horsepower, proving once again that the exhaust manifolds on the LG4 / L03 are for paperweight use only.
Add Edelbrock Performer EGR Intake Manifold- 216.6bhp @ 4200rpm / 284.8 lbs-ft torque @ 3300rpm
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Add Edelbrock Performer RPM Intake Manifold- 230.9bhp @ 4800rpm / 285.2 lbs-ft torque @ 3300rpm
With the addition of Edelbrock's Performer EGR aluminum intake manifold (with the EGR blocked off), horsepower climbed a very noticeable 19.3hp and the peak RPM dropped to 4200rpm, much more real world. Average power through the power band improved by 14.9hp along the curve and 21.2 lbs-ft of torque. Moving over to the Performer RPM intake manifold, horsepower jumped up 14.3hp but at a much higher RPM band. Torque barely moved (barely noticeable, about half a pound at most!). (It should be noted that the Performer RPM manifold is taller than the stock or Performer EGR manifold, and you might run into hood clearance problems. This manifold will not fit under a stock 3rdGen hood (like a base Camaro, Firebird, etc.) as far as I know and understand.)
Add Edelbrock Victor Jr. single plane intake manifold- 225bhp @ 4700rpm / 276.3 lbs-ft torque @ 3600rpm
With the addition of the Edelbrock Victor Jr. single plane intake manifold, power dropped somewhat. With the Q-jet carb, the Victor Jr. gave up both horsepower and torque. With a Holley double pumper 750cfm carb on the Victor Jr. appeared to be closer to the Q-jet / Performer RPM manifold combination. This was surprising since the single plane manifold should appear, at first glance, to be the worst combination you could bolt onto the 305. The testers decided that the Performer manifolds were the better choice since they offered better low end throttle response and power.
Add Comp Cams Xtreme Energy CS XE 262H-10 camshaft- 269.8bhp @ 5100rpm / 291.1 lbs-ft torque @ 3600rpm
With the choice to go with the Comp Cams Xtreme Energy CS XE 262H-10 hydraullic flat tappet stick, the engine saw an increase in horsepower of 41.9hp with virtually no losss of peak torque. That was with 16 degrees of iniitial timing. The torque was smoothed out over the power band and the camshaft seemed to really pull past 3300rpm. Power was moved up 400rpm than the stock unit. The Edelbrock Victor Jr. intake and Holley was retained for this power figure.
Add GM L31 Vortec Heads- 324.7bhp @ 5800rpm / 316.5 lbs-ft torque @ 4800rpm
Adding the L31 GM Vortec heads to the Victor / Holley combo above netted this figure. The heads had to be extensively worked in order to get them to install correctly with this engine. The Vortec heads have a unique intake manifold bolt pattern requiring a special and costly GM or aftermarket intake. Indeed, the Edelbrock Performer Vortec aluminum manifold is almost 40% more expensive than the regular Performer manifold! The valve cover bolt holes are the centerbolt design, meaning that early blocks and installations will have to switch over to the post-'87 center bolt valve cover design and late-model guided rocker arms. The heads have a volume of 64cc which will require milling in order to avoid compression loss on a 305, and the larger-diameter chamber outline requires that you use 350 head gaskets, a solution which could also cause a loss of compression. Car Craft milled the heads 0.045 inches and used a thin 0.015 inch head gasket to bypass these possible problems. With this work done, CC managed to maintain a CR of 10.0:1 on the small block with no detonation problems, even using 89 octane gas, once the L31 Vortec heads were installed. 1.6 ratio rocker arms added a few hp and lbs-ft of torque but not enough to warrant the expense.
Add World Products S/R Torquer heads- 297.6bhp @ 5500rpm / 308 lbs-ft torque @ 3900rpm
Adding a pair of World Products S/R Torquer heads using the Edelbrock Victor Jr. and Holley combo netted this figure. While this figure can't be compared to fairly to the 325hp / 316 lbs-ft torque of the Vortec heads due mainly to the different intake manifold design, this is still very strong for a small bore motor like the 305. It was noted that with this combo, you could hunt 5.0 liter Mustangs easily. Other observations were that the Super Victor Jr. and the Performer RPM probably wouldn't fit under stock hoods, and that a dual plane (such as the tried and true Performer EGR) manifold would be best for street duty on this engine.