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To answer the original question, I have a 455 with an almost stock Buick Grand National transmission behind my 72 455 and 3.42 gear.
List of mods:
Billet servo
larger boost valve
larger reverse boost valve
Raybestos blue plate clutches
Kevlar band
Transgo shift improver (valve body only kit)
Pros, 15.5 miles to the gallon in mix driving conditions. Cruise RPMs are below 2000RPM. Bolts right into the stock 400 Turbo locations with a 350 Turbo driveshaft.
Cons, this particular set-up doesn't down shift from 4th until below 30 miles per hour. The Bowtie Overdrive cable corrector may fix this problem but I just live with it. Also second gear holds on too long with this Transgo kit and big servo. Last, the exhaust note is at drone levels at 60 MPH because of the lower RPM.
I only have about 500 miles on this trans and I haven't given it too much of a beating to see how it will hold up.
Ask yourself what you want. Try to have a ride in someone elses car before you decide. You may decide that a 400 Turbo will do all you need instead of the extra gas mileage. How long can you drive the car before you pay for that 200 4R with the "gas savings"? It may take a while with the limited driving you will probably be doing.
James
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