I purchased my Formula 20 months ago. Originally from factory 305 TPI / 5-speed. Person I bought it from said motor had been switched to a 350. Have some buddies that recently converted theirs to this set up and wanted to burn a copy of my custom chip. Low and behold...it has original 305 chip, never modified. My car runs good, so what do I have? To hard to get to the stamp on the block, and don't want to pay for dyno, so what other way can I tell?

check the # on the heads. Although people do put 305 heads on the 350. A 350 will run with the 305 chip. I used one before having a chip burnt.

first off, a dyno means nothing, IMHO. A slightly built 305 vs a bone stock 350 could put out the same numbers. Heres an easy way, climb under the car. Position yourself under your starter and look up. There are 3 digits stamped on the SIDE of the BLOCK. Pretty much centered on the block. Take that number and do a search for that number, and "engine block" within 30 seconds you should find a list of engine blocks and sizes. If you just cant seem to find the block number (maybe caked over with dirt, or just cant see it, i know some blocks just are hard to read) you can always pull off your heads and measure the bore... aside from that... not much you can do. 305 and 350 blocks are IDENTICAL on the outside.

Not identical if '87-up. If it is one of these later blocks, then when you look down behind the drivers side head, you'll find either 5.0LG or 5.7LG cast there. 5.0 is 305, 5.7 is 350.

Yeah...a friend of mine is rebuilding his motor and he showed me where the stamp is, but there is to much crap in the way for me to see mine.

A friend at work just told me about some kind of gauge (BDP or something), that you can install in place of the number one spark plug. It measures the volume of the cylinder when you crank the motor. With that info, you can determine motor size.
Has anyone heard of this and what that tool is called?

I GOT ONE! haha well kinda the place i work for is selling one. Its call a P & G. Its used by racing bodies to determine the ci of the motors in competition. New are over 1000 bucks and not many places even have them new or used. You can check around with race tracks around you to see if any one has one you could use. but alot easer would be to check some numbers on the block / heads. You can see a P&G here at our web site even tho the pic isnt good. http://performance-enterprises.com/p...s/forsale.html its one of the very first listings as you scroll down. Its basically just a cylinder with markings on the that measure the ci of the cylinder in question. As you spin the engine with the starter air pushes something up the P&G to measure the ci.

Get the front of the car up in the air so you can (safely) crawl under it. Take a light with you, look for three digits cast into the side of the block. They are fairly large and easy to see. Those are the last 3 digits of the block casting #'s. That is enough to determine if it is a 305 or 350.

You could also pull a valve cover and get the head casting #. But, that will only tell you if you have 305, 350, or some other heads.