Re: higer ratio diff
Your T-5 5th gear ratio will dictate if a switch to 3:78s will be enough of a difference to offset your expenditures, and the height of your rear tire. For arguments sake, let's assume your 5th gear is a .8 (not the best one). I have 3:54 gears in my roadster w/.8 T-5 and @ 70 I'm at 2500 rpm with a pretty tall rear tire (approx 30"). Gas mileage is hard to figure since I don't have a speedo (and it is off the road at the moment awaiting it's new engine) but if I had to guess I'm probably say around 17-20 MPG as a conservative estimate, US, and at speed. If I babied it I would guess 20-22 MPG. I'm running a "Y" adapter w/2 94s, progressive, former engine was a stock 40 Ford, the new one is a 59, 4" crank, 030 over, stock cam, probably around a 255 cube. Once it's together I now have a GPS so I can calculate gas mileage but that will not help you now - I will post mileage figures then.
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