Thread: 305 to 350 swap

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Originally Posted by ceh383

What size tires were on it before? If it was a big jump in size a rear end gear change might be in order....

i was thinking the same thing.... the larger the tires the shorter the gear, unless you're just trying to build a ton of horsepower and waste a lot of gas

if my memory still serves me correctly, the flexplate from a 305 will not work on a 350. a little research on this might save you some time before you swap out the motors.

A computer from a 96 up truck will NOT work with a TBI, the injection control AND the engine sensors are completely different. If you desire to keep the TBI, there are improvements such as an Edelbrock manifold that will work. The TBI computer will need to be changed to meet the larger engine's fuel demand..a 95 350 computer is the simple way or perhaps you can find someone who hacks TBI computers. Figure that your effective gearing was reduced by the ratio of the tire diameters...if the previous tire was 28" dia and you changed to 35" dia, you effectively changed your 3.55 rear gears to a 2.84 gear!
If you had 3.73 rear gears, you effectively changed them to a 2.98....no wonder you dont have any beans.

Like most folks say, the larger increase in tire diameter plus the tire's rotational inertia increase will make your truck a slug, especially if it is an automatic. A steeper set of gears (front and rear if it is a 4wd) will help.

mike in tucson

Originally Posted by robot

A computer from a 96 up truck will NOT work with a TBI, the injection control AND the engine sensors are completely different. If you desire to keep the TBI, there are improvements such as an Edelbrock manifold that will work. The TBI computer will need to be changed to meet the larger engine's fuel demand..a 95 350 computer is the simple way or perhaps you can find someone who hacks TBI computers. Figure that your effective gearing was reduced by the ratio of the tire diameters...if the previous tire was 28" dia and you changed to 35" dia, you effectively changed your 3.55 rear gears to a 2.84 gear!
If you had 3.73 rear gears, you effectively changed them to a 2.98....no wonder you dont have any beans.

Like most folks say, the larger increase in tire diameter plus the tire's rotational inertia increase will make your truck a slug, especially if it is an automatic. A steeper set of gears (front and rear if it is a 4wd) will help.

mike in tucson

Guess I wrote that wrong. I was suggesting changing the computer and all wiring along w/ the Factory Vortech MPFI intake.