Opinions??

depends how many cc your heads are? How big the motor will be and what CR you are going for

If you can get the desired CR w/o having to resort to a domed piston, the flat-top will have better combustion characteristics. That's why the approach has been to use smaller chamber volumes in order to rely less on filling the void w/ a dome that gets in the way of the flame front.

I agree with Brad.
If you can cut the heads to get the CR you want, I like the flat top piston. But there is nothing wrong with a dome if you need it. Make sure the piston has a good cut out near the spark plug, IMO.

A 499 with a flat top piston at zero deck and 68cc heads (5cc valve reliefs) should put the engine just over 13 CR (~13.3). I have run that CR with both 110 octane gasoline and alky.

My SR heads are 70cc's, zero deck 499 and right on at 13:1. I also run 110 gas.

With the Indy chamber configuration your best bet is stay with a flat top piston for many reasons,a few is better flame propagation(ignition and burn characteristics),lighter pistons as well as detonation control.With a dome piston,depending on the design it shrouds the spark and contains it in the plug notch area.

My experience, if you can get the compression you want, is to stay with flat tops. Generally, in my opinion, you will make more power with less timing and if using a production block, that is a good thing.

My 493 with 14cc ross domes ran well, but it made the fastest times on the track with 38/40 degrees of timing. My 572 flat top ross engine only need 30 degrees to make the most on the dyno, but it ran the fastest MPH with 32 degrees.

anyway, a long winded relply.................to say flat tops

Anyone ever mill a domed to flat top??

Be sure to measure the piston thickness to determine the amont that can be removed from the dome.Look at the inside of the piston to see if the dome is recessed towards the top.

My Ross were recessed and compuflow only felt he could have removed half of the 14cc dome. It would require some precise measurements, but should not be a problem doing the actual machine work.

I cut my cylinder heads down to 62 CC which allowed me to use a very small dome to get 15 to 1 compression. that seems to work pretty good.I think the dome is only about. 0.080 high.

My 572 runs flat top 14.8-1. 32 degrees. Makes decent power,9.02@151,3350lbs
Doug

My Mega 540 came with domed pistons despite me telling the {now gone} jerk Indy salesman that I wanted 13.0-1 on my 440-1 540 kit. I will cut those pistons flat the first opportunity if I don't dish it to 10-1 instead. C-16 vs 110 at half the price and easier to get.

All the comments on flame propagation, quench effect being ruined, trapping unburned mixture, were pretty obvious to me when I looked at the domes and the chambers and thought about the quench flow with that damn hump in the way.

Let's talk about a guide for that quench flow toward the plug or ??? Cut into the flat of the head? Easy mill job or hand.

Wouldn't a lathe be more appropriate due to easier fixtureing? I am gonna get the Diamonds I have flt topped and that was how I thought it could be done easiest.

My ears are buzzing right now from doing a set of KB quench domes flat with a die grinder, very low budget thing here though. Just trying to make them work with a magnum head and not going for any real precise piston head clearance. Local machine shop said $300, for that price I could buy a different piston so an hour later the set I had on the shelf work.

Dave,
I have often imagined a fixture that would hold a piston and let you use a router with a carbide bit to face off the top of pistons.

With a little jig work one could maybe even make valve reliefs.

I've also heard of a guy welding in part of the chamber on a 360 head, surfacing with a die grinder, to create a squish area. Happened in Idaho.

R.

I did that with a router once, just put the pistons on rods in the block. I lost that carbide and have not been able to find another flat ended one aluminum cutting one like that. I tried it with a round ended one and it was NOT happy cutting that hypereutectic material that way.