For the exhaust side, a set of reproduction Ram Air exhaust manifolds-or better yet, 131/44- or 171/48-inch primary headers-twin cats and true 2.5-inch exhaust will free up some power.
As always, good machining is key. Spend more on quality machine work than bolt-on performance parts. This is the opposite of what most hobbyists do!
Fun For 301I'm not new to owning Pontiacs, having had three Grand Ams and a sweet little Fiero, but I've never built one up for show. I have a '78 Grand Prix that I would like to rebuild, but I'm not sure what other Pontiac parts will interchange with my 301ci engine. Will the intake off a 389ci fit on my smaller engine? What about heads? With a 4-inch bore and 3-inch stroke, the 301ci should turn a fair number of rpm.
I have an idea of building my Grand Prix with a GTO Tri-Power setup on it for fun and for the local car shows-something different but still cool. Please don't tell me that I should change the motor out for something bigger. My 301ci is in sweet shape, and I really would like to keep it.
I love your magazine and buy it whenever I can find it on the newsstands. Tony ZatkovicVia Internet
Rocky Rotella responds:The 301ci engine (along with its 265ci brethren) is often considered the redheaded stepchild of the Pontiac-engine family. While it was fairly reliable when operated within its intended range and a decent performer in the right application, the engine was designed for maximum economy, which severely limits performance. Starting with a low-deck block, engineers removed enough material from it and a number of other conventional engine components to just meet minimum durability standards. The end result was a complete engine that weighed just 452 pounds, or anywhere from 150-200 pounds lighter than a traditional Pontiac engine.
While the 301ci configuration may look decent on paper, it was never designed to be a high-rpm engine. The cylinder heads contain small, siamesed intake ports that don't share a traditional common dividing wall. This also carried over to its low-rise intake manifold, which doesn't contain port dividers in the runners as they progress from the plenum. Couple this with the relatively narrow cross-sectional area of the two components, and higher-rpm airflow is greatly degraded, resulting in an engine that doesn't rev much beyond 4,400 rpm.
Installing a Tri-Power or any other conventional Pontiac intake manifold onto the 301ci isn't feasible for the reasons stated above. It might then appear that simply installing a pair of cylinder heads from a larger engine is the answer. While such castings will certainly bolt on, the low-deck design of the 90-degree 301ci block brings the cylinder heads closer to the crankshaft centerline, which in turn requires an intake manifold with shorter runners to maintain proper port alignment. Since aftermarket intake manifolds aren't available, you'd have to modify a conventional Pontiac casting considerably or fabricate another from metal or a composite material.
Should you decided to move forward with the cylinder-head and intake-manifold swap, crankshaft issues would likely prevent you from safely turning the rpm required to achieve maximum performance with the 301's relatively short 3-inch stroke. As part of the weight-saving effort, engineers removed the two central pairs of counterweights from the crankshaft, leaving just one larger weight on each end. This shed nearly 25 pounds but greatly increased the chance for failure at excessive rpm.
With all that said, you are probably wondering what options you have. You may not want to hear it, but these reasons are only a portion of what make replacing an original 301ci with a traditional Pontiac engine so attractive to hobbyists looking for performance boosts. Others, however, are determined to retain the 301ci and want to safely extract as much power from it as possible, and this can be accomplished with a few simple bolt-ons and some careful tuning.
If your Grand Prix's 301ci wasn't originally equipped with a four-barrel intake manifold, installing one and a matching Quadrajet with proper jetting is a must. Have the HEI recalibrated to provide around 24 degrees of mechanical advance by 3,000 rpm with an additional 14-16 degrees of vacuum advance, and set the initial in the 12-14 degree range. A set of 1.65:1-ratio rocker arms will effectively increase valve lift, and if you can remove the heads, have them milled 0.060 inch to boost compression.