I have a pair of fly wheels from 1990 Mercruiser 330 hp (454) inboards and replacement 496HO's. I/O's
Are these the same and were the 454's internal balance or external.
I was going to use the ones from my old motors if they are the same..

454's are external.
Don't know about the 496 but I do know that between the Mark IV and the Gen V 454's there is a difference. It's small but enough that I wouldn't swap the 2.

they are MKIV so these are external bal. the new motors are 8.1 496.
also are the flywheels the same between inboard/outboard and inboard motors.

As for a I/O and a inboard it all depends where the starter is installed. An inboard the ring gear is on the outside and I/O it's on the inside (because the starter is mounted to the block). Some you can just pull off the ring gear and put it on the other side but not flywheels can do this.

/f_inscreenname thanks I just confirmed them and you were correct. Since the flywheel from my MKIV blocks appear to have a counter balance built in them with a few drill holes I assume they are External Balance correct?
So can the flywheel be neutral balanced.

counter weight on the flywheel is external
It can be neutral balanced but you would be better off just buying a natural flywheel. Just bought one for a 427 stroker I'm building. 78.00 bucks

http://www.summitracing.com/search?S...ord=atp%20z296

IF you are installing 496HO engines, you need to use the flywheel that came with them. If you will be using a TOP mount starter like a transmission boat, or inboard, then you need this flywheel.

http://www.michiganmotorz.com/inboar...nes-p-626.html

If it is for an I/O, you need this one.

http://www.michiganmotorz.com/sternd...nes-p-627.html

If its an I/O with bottom mount starter, you may be able to get a flywheel from a GM 8.1L truck engine. Like this

http://www.carpartkings.com/rhinopac...el-167576.html

[QUOTE=MILD THUNDER;4055263]IF you are installing 496HO engines, you need to use the flywheel that came with them. If you will be using a TOP mount starter like a transmission boat, or inboard, then you need this flywheel.

http://www.michiganmotorz.com/inboar...nes-p-626.html


This is the application that I am doing.. Can I just change ring gear on an I/O to the other side so it would work with top mount starter?

yes, as long as the flywheel is machined on both sides, mine were not from GM gen VI marine engines, I had a machine shop cut the other side and I put the ring gear on and was fine...best to use flywheel that came with the engines...

why is it best to use the flywheel that came with the engine?