Piston Slap: Of extra gears and HEI dreams for Buick powertrains?

Rob writes: 

I’ve got a 1968 Buick small-block 350 in my car. Should I invest in an high energy ignition (HEI) distributor?

One more question: The car has an original Powerglide transmission with about 1500 miles on it since being rebuilt. Any real advantage to upgrading?

Sajeev answers: 

Each of those upgrades can be seen as an “investment” with “real advantage” aplenty. These words may ring hollow to the purist, and that’s fine. But for those of us who lack concours-quality vehicles in our collection, both HEI and a transmission upfitting are fantastic choices with immediate and long-term benefits.

The swap to GM’s electric, high-energy ignition (HEI) is easy and offers that aforementioned long-term benefit: since finding replacement points of respectable quality is getting difficult, this conversion eliminates a point of failure. The HEI assembly is bulky, but clearance issues with most factory Buick air-cleaners (GS350 cold-air affairs aside) are unlikely on a small-block Buick. (And for other small-block engines, the aftermarket makes “HEI offset” air cleaners.)

With all the pros and so few cons, it’s hard to say no to an HEI upgrade.

Your transmission question implies the more complicated task of upgrading to a three-plus-speed automatic transmission. The benefits will be immediate: The extra gear before the Powerglide’s 1-to-1 top gear improves acceleration around town, and likely nets you better fuel economy, because you’ll need less throttle in the process.

The gearbox to make this happen easily is GM’s three-speed TH-350, because it is almost a perfect drop-in. Just get one with the same overall length. Conversion kits are plentiful, to boot, but your application may have unique items that need addressing (crossmember modification, flex-plate differences, to name a few).

There might be a little trick to getting the shifter into first gear, but this video shows it can be done. No matter, the upgrade is totally worth the effort for just about any GM product with a Powerglide from the factory. The maximum benefit comes from adding a GM overdrive transmission to your Buick 350, be it a 700R4, 200R4, or the newer ones with electronic controls. (Or the modern ones with six or more gears, if so inclined.) But those are not necessarily worth the time and effort; the three-speed swap probably offers far more bang for the buck for most of us.

Bottom line? I’d do the HEI swap now, and consider the notion of collecting parts for a TH-350 swap.

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