Hi, I have a 72 350 2-bolt main that I am building for my Elky. When I bought the short block, it had no flywheel/flexplate. so here are my questions:

1. What is the difference between a flywheel and a flexplate?
2. how many teeth, does it matter?
3. will I be able to use my 305 starter?
4. how can I tell if the crank is internal or external balance?

Thanx for any help on this.

A flywheel is used with a standard shift and a flexplate bolts the engine to the torque converter. number of teeth????? it depends on the starter snout and bendix you have---internally balanced or externally---if its a 350 it should be internally balanced, if you are installing a stroker kit it can be either depending on the crankshaft used---small block 400's are exernally balanced.................Dan

If it's a 72 350, it is internally balanced, has a two piece rear main seal, the crank has the larger diameter flexplate/flywheel flange (which means a flexplate or flywheel from a newer one piece rear main seal Gen II engine will not fit) and it uses a starter for a 153tooth flexplate/flywheel. Only 400 cubic inch small blocks were externally balanced and used 168tooth flexplates/flywheels back then. Unless of course the motor had a newer rotating assembly installed in it using an adapter to a one piece rear main seal...which then means "all bets are off," but it's not likely! If the casting number on the block is 3970010 (69-80), you have a higher nickel content block, which is a stronger block. they were drilled to accept both 2 or 4 bolt main caps. It may also be a 3970014 (70-76) or 6259425 (69-76) casting, which is still good...just less nickel in the casting. Your starter off your 305 will work. Chances are it came out of a passenger car...but not a Z-28, Vette or a truck or then it would more than likely have 4 bolt main caps and be the 3970010 casting. The flexplate from your 305 will fit...however, your better off purchasing a newer flexplate...your current one may cause some headaches if it's worn (teeth) warped or even cracked. A 168 tooth flywheel or flexplate off a 396/427 can be installed, but for your purposes, I wouldn't do it...this is more for guys that want to run an 11" clutch with a manual trans or a 400 THD trans. If you do buy a new flexplate, I would get an SFI approved flexplate if your going to build this 350 for performance purposes. What are your plans for a torque converter and trans?

What are your plans for a torque converter and trans?

I will be using a stock converter with a TH200-4r trans.

Ok, new question: do the LS series engine use aluminum flexplates? if so could I use one? I think I already know the answer though :-( . just figured I'd take a shot.

I've never heard of an aluminum flexplate, only aluminum flywheels. An LS motor is a completely different animal.

P.S. Late '86 up 350s (such as the LO5 TBI motor used in trucks and vans) are also externally balanced.