I plan on sticking with my 305 V8 with some basic upgrades like a cam, new pistons, etc. I know that those upgrades will likely boost HP and in turn torque, which means I'll need to upgrade the dif too to handle that power without grenading. So what would be the best gear ratio to put out more torque?

 

why not get a 350 and or make a 383?
by the time you buy pistons, and balance the engine and all the other stuff that goes with it, you can just about afford a full reaedy to run rotating kit and have another 100 hp over anything your 305 is going to make..

also, your rear end is fine until you get sticky tires.
then youll find out the week links.
like u joints...driveshaft...transmission.....motor mounts......rear axle.....no subframe connectors....

 

Unfortunately, where I live, the cost of parts are high, so buying a crate 350 would set me back a few grand more than I'd like, and with a 350 I'll need to upgrade or swap my 700r4 transmission, which will be another couple grand. I still need to get the paint work done, a new hood, and any other cosmetic stuff. I don't plan on any more than 300HP at most.
More or less, summed up as best I can, this is a budget build. It'll be easier and more cost effective to upgrade than swap.

 

Well, you could take the same "rotating assy" advice that was given above, and turn your 305 into a 334 stroker, for a chunk of the benefit. But to answer your question:
...that would be "the highest numerical one". The higher the numerical gear ratio, the more torque you will get (at the wheel). That increase in tq comes at the expense of....speed, so the higher numerical gear ratio that you choose, the slower your car will go (at a given RPM in a given gear), so that would be most noticeable on the highway, in top gear, in the form of; higher engine RPM to go the same speed.

In short, loosing speed to gain tq then becomes a compromise, and a good compromise rear end gear ratio for a TPI engine w/700R4 is in the 3.08 to 3.30 range.

EDIT: It looks like you have a LG4, so a good compromise for that engine w/700R4 would be in the 3.2x - 3.5x range, IMO

 

I like the 3:42s i installed in mine-still plenty of highway speed with a t700.I don't know for sure,but a v8 Berlinetta is something GM might have installed 2.73s in...

 

That sounds about right, I'll need to check my spec sheet again to be sure. It's good as is, but just want to make sure my hardware can handle a bit of a power bump without falling apart lol

 

My Berlinetta came with factory 3.08:1 open diff, have the RPO sheet if you need to compare.

I love the 700R4 with the current 3.23:1 rear end I stole out of a 1988 Z28 with posi and disc brakes. At 60 MPH I am spinning around 2000 rpm, 70 around 2200, and ??? around 2500 because the stupid factory speedometer only goes to 85.

I will say that I swapped engines to a ZZ4 then tore it down and built it my way after upgrading the axle years ago so my opinion is biased on that, but I still think that with the deep first gear a 700R4 offers, you aren't gaining much speed by going any deeper than 3.43:1 with the rear axle.

 

My Berlinetta also came with 3.08 gears with an open diff. I also have 3.42 gears with a posi in it now and with the 700r4 with lockup highway was still great even without lockup it was still very nice. Also had a 290 horse 350 crate motor in it from the previous owner so probably similar power wise to your 305 you’re building. Probably 2500rpm going 70mph in the highway. I’m most likely going to put 3.73 gears since I have a whole new set up but I did not regret the 3.42s at all.

 

What converter you planning on running? With a 305 I'd be looking hard at a set of 4.10's and 3500 stall converter

 

I run a 3.73 gear with my 700r-4 and can manage 25mpg on hwy trips with a 350 engine