I'm very new here. And would like to get your expert opinions. 75 vert. stock L48, th400 trans. with 3.08 rear. I have not been able to spin my tires yet. I do love the gas milage and low rpm at hwy speeds. What ratio should I change to, to get more off the line?

Any lower gear will give you better off the line. If your looking for stop jousting, 3.70 or 3.73 is a great street gear, but you loose some top end. If you do a lot of freeway driving gas mileage will suffer. There is a calculator/technical section on the website: "ifitsfast.com". This calculator will help you determine gear ratios, rpms, and mph.
I will be installing a 3.55 in mine over the next couple of weeks. I would rather have the 3.70, but could not pass on the price of the 3.55 gear set.

Try this clickable link: http://ifitsfast.com

Sarge

What set up are you presently running, engine,trans,rear?

I've got a 350 that has been enhanced a bit. Turbo 350 trans. with a TCI shift kit, 2200rpm B&M stall converter (to be installed), and 3.36 gears (currently). The rear has a lot of miles on it, so I will be rebuilding it and installing the 3.55 gears. Mine doesn't light up the tires either, but I don't want it too. I want it to tranfer weight and go. Not sit and spin...

I went with the 3:90.....go with 3:70 and dont forget to change the speed-o gear in the trans.

if you plan on modifying the engine in the future, such as carb, exhaust, intake, then i'm going to suggest the idea of keeping the 3.08's. Sure, it won't spin now, but it would probly cost less to more take off power through the engine, that way you can keep your decent mileage. Terrible mileage is a horrible reason to not drive our old cars, just my 2 cents.

sorry, "cost less to get more take off"

Thanks for all the replys. Hey Sstanford- I had my 78 rebuilt and changed from 3.70 to 3.36 at Corvette perfections, Complete rebuild and ratio change at no extra charge. $400.00. Gary Watson owns the Co. and is just great.- I might do some slight engine mods. first on the 75 and see how it goes. I have it out today, getting new soft top on.

Hey thanks for the info. I have someone locally that is going to change the gears out for me. I bought a rebuild kit off of e-bay for $90 and got the gears in another trade. I'll have it all done for around $200.00 by the time the dust settles. I hate to park it to do the work! I've had the new torque converter for 2 months. I'd rather be in the seat, than under it right now.