When are forged pistons needed?

Ok so via my other threa I have Keith Craft AFR 185 CNC heads on order. They are being set up for my hydro flat tappet cam and I am using scorpion 1.72 full roller rockers. My current pistons are about .05 in the hole yielding 9:1 compression with .042 gaskets. They are currently inexpensive fedral mogul cast .040 pistons with 4 eye reliefs.


I plan to do mostly street driving with some 1/8 mile racing about 10-20 times per year for fun. I will be shifting around 6k due to where my cam is making power.


At what point do I say..."time to take the short block apart even though it has only 10k miles and have flat top forged pistons installed."

Is this even necessary with the projected 340-375hp at the crank? The block is a 1968 mexican block by the way due to the c8 code. I am guessing it will cost $1200 or so to purchase the pistons and have them balanced and installed. Maybe a little off...If I can get away with it I will leave things well enough alone and wait a few years until I can order an assembled 347 short block and just swap the top end onto it and roll...

You do NOT have to replace your pistons for the engine you have described-- Save your money for something else.


JOE SHERMAN RACING ENGINES

only if you plan to bolt a power adder on. (nos/super or turbo charger)
you should be just fine with what you have.

if i were to change anything it would be the quench height. have the block decked about .040"

You don't need forged pistons until the stresses or pressures on the piston go above "normal" levels. 6500 RPM or 11:1 is where I would draw the line for myself but I tend to be conservative.

Thanks guys that is what I was thining.


Also, I have heard many people tell me .05 in the hole is not optimal for quench and I will have issues with ping etc... I did have some pinging issues before but I fixed it by running 9 initial timing and 38 total. This time I will have the car dyno tuned.


Anyways, I talked to John Kaase Racing and Keith Craft Racing and they both said they build engines with .05-.06 in the hole piston configurations and it is totally fine especially on this smal of an engine for street/strip use. Interesting subject though.

I think if I get the intake port matched and the heads on and engine tuned...I could run a 3000 converter and get some drag radials and hopefully run low 8's in the 1/8 and low 13's in the 1/4 at least! On my puny street tires and 2000 converter maybe mid 8's?


Thanks guys.

Ok,this is just me, but I'm thinking you've gone overboard on the CNC heads instead of getting rid of the flat tappet cam and using "regular" heads. On the other hand,I'm also a big fan of using what you have. Just to answer your question,you need forged pistons about 1 millisecond before your cast pistons fail. No,really!

With the AFR 185's assuming they have 2.02/1.6 valves I would worry more about valve to piston clearance,depending on cam size,than whether or not the pistons are forged.