Gas Mileage Question

What's the difference between the gas mileage of a 98 Safari 4.3 Ltr Vtech 6, (and what ever stock tranny was in it), and a 1st gen with a 350, (400 hp), and a turbo 400 tranny, highway and city driving.

Anyone think they could ball park that one off the top of their heads?

Off the top of my head the Safari about 20-22mpg's. A early with a V8 about 10-15 mpg. I think the biggest differants is the Safari has a overdrive trans. My 69 with a 307 runs 3600 rpm's @ 70 mph with a turbo350. The Safari w/ a overdrive trans I bet runs about 2200 rpm's @ 70 mph

Van or car running a small block and a turbo 350/auto the rear gear ratio is an important factor in hwy mpg. Bill

1st Gen meaning my van, (66G10). And I haven't checked the rear gear yet, but with my 250 I could go 110km tops on the highway so I assume that tells you something. I'm trying to understand how much more it will cost in gas to have the turbo 400 tranny vs a tranny with an overdrive gear.

I know the V8 will cost more but is the difference between over drive and no over drive the same as saying at a 1:1 gearing ratio, (Highest Turbo 400 gear), it cost $100 and at a 1:0.7, (200r4 overdrive gear), it will cost $70.

Is it that easy to calculate, or are there other factors to consider that make more than a negligible difference?

While I'm saving a few bucks on a great deal on this Turbo 400, am I going to be paying $30 more per tank on every road trip?

Heavy

Heavy Pants you hit the nail on the head. Getting a overdrive tran may cost more, but it will be cheaper in the long run

Remember = We are pushing an iron Box thru the air-not a good thing - and the rear axle ratio is very important as is the final drive (trans-overdrive) ratio in trans. The higher we go on rear axle ratios- IE:= 350-1 to say 300-1 ratios - tjhe more throttle opening we must have to achieve the same speed result! lower gas mileage when we change both from origional-except when having a really low rear axle ratio -IE:= 4.11-1 . Therefore - look @ overall driving - in city or on highways - where will you be using the most. if you might have say a 3.50-1 rear- change the tranny to an overdrive -1st> see how you like it & mileage u get?? Then to rear axle ratios. Also - consider the engine design- 6 cyl. or V-8 & the power they will give you?? For my 5 cents - keep the rear & change the tranny -and compute the RPM drop= 1st with the tranny(new) ratio. to see where the rpm range will be with the rear ratio.

This is an area that I am going to have to look at at some time also. I have the 318 v8 and the stock Auto tranny that was in the truck from factory, but also know that I have 3.91 gears in the rear end, so milage is not great. I have been trying to figure out how many gas stops it would be to hit the Bakers show in MI.

Remember this- when using an overdrive trans and in OD- u can figure a 30% reduction in rear gear ratio-give or take a little.---so if u change the rear gearset ratio to a higher ratio-IE:= 4.11-1 to 300.-1 that carb opening is gonna be larger (more fuel usage) for the same speed/ in final gear= Therefore =reducing the fuel mileage -