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One of the very best swaps you can ever make is replacing a TH350 or TH400 with a TH700R4. When I bought my 454" powered '71 I knew the TH400 would have to go because of the horrendous fuel mileage I would get. So after plunking down $350 at the local wrecking yard I came home with a totally worn out TH700R4 out of a 1991 van.
To tolerate the extra torque of the 454" I rebuilt the TH700R4 with performance aftermarket parts then made the swap in only one day; the total cost being around $1700 (which included the drive shaft cutting, the new tail housing with a mount pad, and heavy duty torque converter).
With the TH700R4 I can cruise at 70 mph at only 1800 rpm and get around 16 to 17 mpg; about 4 more than I would have gotten with the TH400. Fish was the first SmokinVette member to swap one in and I was the second. And since I made the swap several others have made the swap. Why run an obsolete transmission when the fantastic 30% overdrive TH700R4's exist?
To tolerate the extra torque of the 454" I rebuilt the TH700R4 with performance aftermarket parts then made the swap in only one day; the total cost being around $1700 (which included the drive shaft cutting, the new tail housing with a mount pad, and heavy duty torque converter).
With the TH700R4 I can cruise at 70 mph at only 1800 rpm and get around 16 to 17 mpg; about 4 more than I would have gotten with the TH400. Fish was the first SmokinVette member to swap one in and I was the second. And since I made the swap several others have made the swap. Why run an obsolete transmission when the fantastic 30% overdrive TH700R4's exist?