Huffed6,
I have a little gear ratio calculator in a spreadsheet and I ran some numbers so that you can make a better informed decision.
Know that what you gain in first gear you will lose in fourth gear (given that you do not change transmissions)
So given your tire radius as 15.25" and highway cruising speed of 65mph, and a first gear shift point of 30mph, fourth gear ratio of 1-1 and first ratio of 2.20. I will provide the engine speed for a range of final drive ratios.
Ratio 30mph1st 65mph4th
3.08 2239 2205
3.26 2370 2334
3.55 2581 2542
3.73 2712 2671
3.90 2836 2793
4.10 2988 2936
4.56 3315 3265
4.88 3548 3494
Now obviously you will just shift into 2nd gear at a lower speed, but are you willing to spin that new engine that high to be able to go 65mph? If you race it or just drive around town the lower gears (higher numerically) will give you all the adrenalin boost you can stand, but if you were tinking about cruising to a rod run across the state (or country) a gear set closer to the stock ratio will be more pleasant.
Two other things that you may want to include in your decision process. The faster you spin it, the more heat it makes especially with the blower. Are you willing to dramatically increase the cooling capacity of your car?
Also the lower the gear ratio, the "farther" (more rpm) the engine travels for each mile the car travels. As an example, VW busses typically last about 80% as long as a beetle engine if you count the miles on the odometer. In actuality the engines probably complete a similar number of revolutions during their lifetime. How much are you willing to shorten the life of your engine for more first gear acceleration?
One other consideration, I have the impression that the new engine is not actually in the car and running right now. You may find that the new engine makes so much more power that you don't need to change your gearing because your "doggy" takeoff problem has fixed itself. You might wait and see if you need to change gears.
You now have enough information to make the right choice for you.
Good luck.
Steve
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'98 Jeep Cherokee, 4.0
'56 Willys P/U, 226L
