I have an 81 witha 4 barrel carb, how do i know what engine it is?

more than likely a 305 V8 if its the still the original motor.

Any other way to knowwhich engine it is

first look for the cool little factory sticker near the shroud...but if is gone-

Your VIN has encoded within it the displacement of the original motor

Most libraries have Chilton manuals or Motor guides that break down the VIN and what each digit might represent excluding the last few which are stamped in series....

if you have a 13 digit VIN...it is problably the fifth digit

for example, I know 1978-79 was "L" for 350ci

I dont play with too many cars 1980 and up except Corvette, but your next step will be determine if the motor is original or not:

on the passenger side of the front of the motor about where or just below where the head meets the block is a ledge with a large set and a small set of stamped numbers(which should match the last of your VIN) but you will problably have to scrape it clean before it all can be seen.

It is hard to say on that year if you have a 305 or 350 just because it was equipped with a 4barrel....the small block V8 didn't changed much, especially on the outside from, 1958-1987...it theoretically could be anything if it is not the original powerplant, and the only way to really tell then would be to crack open the engine and do an autopsy with an inside micrometer to determine the cylinder bore.

Thanks that was a big help

Well in that year the 350 had a Oil Dipstick on the Driver side the 305s had the Dipstick on the Passenger side.

Ok thanks that helps