1973 340, want more power.

Richard McLaughlin said

I have not been in a 12 sec car. 420 hp like you said in a 3000lb car is more than enough.
I want more power simply because I want to have a car that when I tramp it it throws me back in the seat hard and seems extremely fast.
I like the current gears for highway driving. How can I find my exact gear ratio?

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So an all around street machine is basically what you are after. I will say this, if you get 400+, expect to start making suspension/chassis/tire changes. Or you will never put it to the ground. I run 245's on the back of my scamp, and can absolutely burn them at will in any gear. And thats with a snubber and SS springs. I will need to go cal-tracs and spring relocation or even mini tub if I want to really plant it.

The best way to find out gear ratio is to jack it up and put the transmission in neutral. Make a chalk mark on the drive shaft. Then spin the tire. Keep an eye on how many times the tire spins vs how many times the driveshaft spins. That gives you your ratio. EX: If you turn the tire once, and the driveshaft turns 4 times, you're in the 4.10 area. It will also help you tell if you have an open differential or not. If you turn one tire and the other turns the same way, or not at all, that's sure grip. If it turns the other way, open differential. If it is open, you'll have to block the one tire to figure out your ratio.

Your current gears might be great for highway driving. But a gear change will definitely help you get that neck snap you want. Common street gear is between 3.55 - 4.10. But once again, it's all in the whole combination. If you change rear gears, you should get a better converter. If you change cam you should change rear gears and compression. Etc etc etc. It all works together. The best thing you can do is figure out everything about your car. Know every last nut and bolt.