Never happen. No way, no how. That may be what they claim (and yeah, I do see claims like that on their site) but you will never see an improvement anywhere near 25%. I'm not sure how they arrived at this number — either they're being really brazenly deceptive and assigning one rounded mileage percent per final-drive gear ratio percent, or they got this result on some completely dumb car not at all representative of what you're driving. Some kind of hot rod with a 600-cubic-inch engine and twin 4-barrels and a 4.56 rear axle or something like that.

With the car you have, in the type of service you describe, you will be doing very well to achieve a fuel economy improvement of about 12%.

That's not to say you shouldn't do the project, just that you should go into it with realistic expectations.

Plan out your costs and savings carefully. It's fun to build "paper tigers" in your head, multiplying a bunch of swaps and mods by each other to arrive at fantastic fuel economy, but at what cost, and with what real result? How long will it take you in fuel savings to make back $1k in mods? $2k? $3k?

For your planned driving parameters, it looks to me like a good setup would be a 225 engine, lockup automatic transmission with the ordinary rather than the later low-ratio gearset (no, there would still be no point to your six-speeds idea even with the low-ratio gears), overdrive unit, 3.23 rear axle, and P205/70R14 tires. The 3.23 gears with 205/70R14 and a well-tuned 225 will be lively and economical around town, and in third-over your final drive ratio will be around 2.36, giving you an engine speed of just under 1900 rpm @ 60 mph, 2500 rpm @ 80 mph. With careful cam selection and installation and thoughtful configuration of the rest of the engine, this combo should return very good mileage. Note that if your present transmission is in good condition, there's little point in building up a lockup unit just to have the lockup. Not cost-effective; wait til the present trans needs replacement.

Congrats on the purchase. Looks like a great car and I'm sure you'll be good to it.

If you can get another one of those GV units for that price, I'll buy one and kick in $100 extra for you.

From my OD experience, you will gain 5-15% in mileage from the GV alone. It should be a great swap.

Lou

Lou-

Will do.Or if I end up not using the one I am buying,I will sell it to you.No need for the extra 100 though.Just pay what I paid and we would be square,from one slanter to the next!