Thread: 84 firebird 350 build

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If I owned your car and wanted a little more from it, I'd leave the motor alone for now and change rear gears and converter. Assuming you don't do a lot of high-mile travelling on the freeway, I'd opt for a set of 3.73/4.10 gears and locker in the diff and a 2500-2800 stall converter. I'd use a genuine 10" converter, not a 12" unit with the fins bent over. With these two changes, you'll think you've bolted in another motor. If you dink with the motor first, you're gonna need to change the converter and diff gears anyway, so why not do converter and gears first and maybe leave the motor alone for a while?

If you add a turbo, you really need to know the static compression ratio of the motor so that you know the limit of boost to use. I would not turbo a motor that was over 8.5:1 static compression ratio because of the risk of detonation on pump gas. I would want to disassemble the motor to widen the ring end gap and tighten up the squish/quench to prevent detonation and maybe even change pistons, depending on what pistons you used in the rebuild.

"Port and polish" is a term left over from the '60's. We still port heads and we still polish the exhaust ports, but the intake ports are normally left about as rough as a lady's steel fingernail file. It has been found that this works better than a perfectly smooth intake port. We have also found out that cutting the head and intake ports to match the gaskets is a waste of time and a waste of performance. When you cut the head and intake material to match the opening in the gasket, you create a port that resembles an Anaconda snake that has swallowed a pig, in the side view of the port. As the fuel/air mixture passes this point, it senses an increased volume and slows down. As the charge of mixture slows down, fuel that was formerly held in suspension, drops out of suspension. This leaves a lean mixture to be pulled into the intake port until the next time the intake valve opens and sucks up the wet fuel from the port floor. So, you have a lean mixture, then a rich mxture, then a lean mixture, then a rich mixture an so on an so on. If you just leave the intake and heads alone and hope for the best, you will get the best results.

As a matter of airflow research, the lion's share of the mixture flows right down the center anyway, so the ports being a little mismatched around the edges will not hurt a lot. You can set this right in your mind by thinking about a stream or small river. The major part of the water goes right down the middle, with the water at the shore and at the bottom of the stream moving very little or not at all. Same thing, doesn't matter if it's air or water. Same physics.
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