cr250r

iTrader: (4)

Hi guys i have a set of 853 heads going on a forged turbo 5.3l im wondering just how big of an exhaust valve you can fit into these heads im going to do a DIY port job clean uo the castings and maybe pay a shop to polish the combustion chamber and open them up a bit to drop my compression to around 9.25 or 9.0 i work in the army as a helicopter engine mechanic (4yrs) dont be afraid to talk theories here

96capricemgr

iTrader: (1)

Don't bother.

KCS

iTrader: (20)

The seat is 1.60" OD, so that's the max I would go without swapping out the seat inserts.

cr250r

iTrader: (4)

So 1.6 max if not go that big why not?

KCS

iTrader: (20)

I would. Most of the time, the stock exhaust valves crack right below the tip so I replace them when they do. 1.6" exhaust valves aren't that expensive and the boosted setups will love the extra area when that valve cracks open.

cr250r

iTrader: (4)

Right thats what i was thinking i know the turbo will do the work on the intake side and thinking if i can get the exhaust out faster maybe small effect on turbo spool top end hp

cr250r

iTrader: (4)

How much would a 1.6 valve increase the flow on the exhaust side?

KCS

iTrader: (20)

Way too many variables to say. The valvejob profile, valve shape, throat, bore, etc all comes into play.