hey guys i recently rebuilt the 305 in my 89 t/a...........while i had the engine apart i got the heads ported i also put on some headers...distributor....and plug wires.............well so far this year its run a best of 15.33 at 90.somethin mph which isnt qiute as fast as i was hoping for so im gonna change the rearend gears to 3.73s and maybe a new converter......so what i want to ask all of u is how much et does a conveter shave off? thanks for any replys i appreciate it

 

A properly matched converter will get the engine rpm quickly up into the powerband where the engine can do the most amount of work in the shortest amount of time. Too high of a stall speed can be just as bad as too low.

How much ET a converter will shave off depends on a lot of different parts combinations. A good 1/4 mile run should have a converter that has less than 10% slip. Without changing anything else except my diff gears, my ET stayed roughly the same however the converter slip was very different. The higher the slippage, the more heat it will build in the oil which will cause lots of other problems. With 4.57 gears, my converter had 13% slip. With 4.86 gears, the slip is less than 4%. My converter stalls at 6000 rpm and I shift at 7400 rpm.

For street/strip use, a converter should stall about 500 rpm into the powerband. For a full race converter, the stall speed should be about 1000 rpm into the powerband. If your camcard says the powerband is 2000-6500 then you would want a converter with around a 2500 stall speed. This is only a ballpark number. The only way to know the exact stall speed the engine should have is to put the engine on an engine dyno and see where the torque curve is.