Im wanting to build a 512 low deck motor useing a 400 block,but cant decide what piston to use flat top or dome ,any sugestions?Im also useing 440-1 heads and running alcohol

Depends on what you want for compression and what cylinder heads are going to be used.But to answer the question... I like using a flat top piston.

There is no reason for a dome piston if you can get the CR you want with a flat top,alcohol runs best with the CR 15-15.5-1 some go as high as 16-1. Most of the time to get the CR that high you will have to at least run a step dome on your piston.It depends a lot on what CC your heads are,I would have them milled down as much as possible to be able to use a FT or at least keep the dome as small as possible.

Flat top

with a RB 511ci, 0 decked ,flat top piston 7cc valve reilef and 71 cc chambers INDY 440-1 HEADS is 13.1 compression

I have a dome in mine to get the compression up with uncut 440-1's.

I had the domes on a set of cast Iron heads which couldn't be cut to up the compression.

When I build another shortblock I will go with a flat top and mill the heads.

to reach the compression i desired, je made the pistons with an inverted dish. claims it would make better power than a std. recessed dish. i don't know that it does, but thats what i got.

The "inverted dome" piston maintains the squish in the combustion chamber, assuming you have set up the engine with the right clearances. A simple dish takes some of the squish area away on the piston side of the squish area.

Squish means faster flame travel meaning less ignition lead is needed, making more power. Any extra pressure on the piston as it comes up, like what happens when you start the flame early, does negative work. That equals less power.

R.

A flat top with the right piston to head clearance will make more power if the compression ratio is the same, that being said 'm not sure the Indy head has a small enough chamber to get 15:1.

Good Luck!

Thanks guy's for all the info,I know Alcohol likes alot of compression like 15 to 1 but dont know if i can achieve this with flat tops.Machine shop recomended I take 70 thousands off my Indy heads to at least get 13.1 if I use flat tops ,Just dont really want to take that much off a fairly new set of heads,If I go this route how much meat is left on them and how much would I have to take off the intake manifold

One has to take .0123 off the intake for every .010 of the head deck surface or deck of the block.

Where are your pistons now in relation to deck height ?

My 572-13 heads are 60cc no problems what so ever with them,would have no problem at all milling another set down to 60 cc. My pistons set .020 down in the hole and have a .100 step dome and with .042 cooper head gaskets the CR is 15.3-1. The step dome is nothing like the old style large looking dome(TRW L2295)piston,in fact even out of the engine block if you do not have a sharp eye are were not shown they had a dome you would never notice it,it appears to be a flat-top not dome piston.
If I were you I would mill the heads and use step dome pistons and get the max HP out of my engine.

i have 440-1c at 54cc and older indys at 49.5cc so it is doable i would say. i have 11.5 pistons in that are at 13.5. it seems that 10cc off the chamber was around 1 comp point or a bit more than 1.