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Old 10-22-2005, 05:44 PM
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Jmark Jmark is offline
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Swapping to 700r4 worth it?

I need some opinions from all you tranny experts please.
My truck is a '77 1/2 ton with a metal shell camper. Its not a tank but it is an older heavy truck.
Current engine is a mild 350 with a th350 tranny. I built both about a year ago. Both are fine. My gears are 3.41 and my tires are 31" tall. My current rpm at 65 is 2600. My driving is probably split between in town (40-45) and in town freeway at 55-60. On trips, I try to keep my speed at or below 65.

The problem is my fuel milage stinks. I"ve spent a lot of time tuning and re-jetting the carb and have managed to increase my milage about 1.5 mpg overall. I still only get 9.8 in town with the A/C on and highway is 13+ with A/C and no load in the truck. I sometimes pull a Coleman tent trailer or my boat, neither weigh that much and I don't use them much either.

I"m wondering about finding a good 700 core and building another (my second) tranny for my truck. I currently have the 9" tail shaft so I won't have to make any drive shaft mods and because i'm running a stock Qjet carb, I "should" be able to hook up the TV cable easily.
Do you think it would be worth it from a milage standpoint?
I like the lower first gear for sure, that would be great with my 3.41 gears, but i'm concerned about lugging down the engine with the 4th gear OD and the lock-up converter. I know I can lock out the converter until I hit the freeways, but I selected my cam for optimum hp and torque at cruise speed, which is right at 2600-2700 rpm, although it pulls real good down to about 2000rpm.

If I have to "get into it" more to keep it going, I'll end up in the bottom step of the metering rods and kill any milage increase from the lower rpms. Any thoughts are appreciated.

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