UTfan01SS

iTrader: (1)

This is a 2004 shortblock, but I am installing some flat top pistons to up the compression ratio and will be using a TSP 228R cam. I currently do not have heads... so I'm weighing my options between the stock 862's or locate a set of 243's or 799's and mill them down .030. So my question is... would this increase my horsepower a good bit or would it be a waste of time? Or would it even work? I believe the valves would clear the bore, correct?

The motor is going in a 89 IROC with a T56 trans...

redtan

iTrader: (5)

Yes they would fit (those actually come stock on later 5.3s) and yes they would increase power. If you can find em for cheap they are worth it.

UTfan01SS

iTrader: (1)

Awesome thanks... what are the differences between the 5.7 243's and the 5.3 243's? Do they use the same combustion chamber and valve size?

redtan

iTrader: (5)

There aren't any differences, they are the same head with a different casting #.

codyvette

iTrader: (24)

Same same

UTfan01SS

iTrader: (1)

Appreciate the help

garygnu

double check you static compression ratio before you mill the heads .

MuhThugga

The 243/799 casting can be worth it, but those heads will typically run in the $400-$500 range used. With milling, you'll probably be looking at a $500-$600 investment total without including any valve job, clean up, springs, and such.

You could also use the 862s and have them worked to accept 2.00 intake valves. That will give you a little bump in power without the higher buy-in price of the 243s.

I just put some stock 862s on a 5.3 with flattop pistons, and I calculated the compression ratio to be around 10.5:1 with OEM .051 gaskets.