I am about to build my motor and i am aiming for a 9.5 compression ratio. The heads i have are 400 heads with 1.94 and 1.5 valves and 76cc chambers. Speed Pro makes some dome pistons that will give me a 9.3 ratio. Or i could buy a set of 083's that have 1.94 and 1.5 and 64cc and with flat top pistons it will give me a 9.72 ratio. My budget wont allow aftermarket heads so thats not an option. My main concern is will i be able to run some decent pump gas, like mid grade, and not hurt the motor.

 

Well I do believe that my year (1990 TPI) came with a 9.3-9.5 compression ratio and I have 083's with valve reliefs. Guess your flat tops are what is giving you the extra few hundredths. I'd say it's as close as you will get though. I run 89 octane with my setup with a 9.5 cr and 12* timing advance, so I think you might be fine with that setup and a stock timing at 6*.

 

best of the two are the 083 L98 heads. they have hardened exhaust seats for unleaded gas. The old 400 heads won't. Use flat tops with 64cc heads.

 

They are flat top four valve reliefs, from speed pro. On Summits site it says that those pistons with 64cc chambers will give me a 9.68 comp ratio. With that ratio will i be able to run 89 octane safetly? See here Speed-Pro Power Forged Pistons: TRW-L2256F20 - summitracing.com

 

don't trust those stupid charts, 64cc heads = 9.68CR.... Is the motor on the stand now?
check your piston depth, and decide on your head gasket. That'll tell what true CR you'll have at the end of the day.
9.5:1 should be ok.

porting the heads at all? might want to polish the combustion chambers a bit. Also what cam?

 

You'd be better off with 083 heads, 64cc chambers, and dished pistons with 9.0:1 CR than you ever could be running whatever compression you can imagine with stock 400 heads. Those things are terrible. Unless you need a door stop or boat anchor, get rid of them. It doesn't make a lick of sense to get new pistons to raise the CR with stock 400 heads.

 

Im using Felpro Permatorq Head gaskets and a comp XE 226/230 duration 477/480 lift cam. The motor still has to get sent to the machine shop but i was offered the heads and wanted to decide now before they got away.

 

Another vote for the L-98 heads over the old "bathtub chamber" 400 heads.

I calculate your compression at 9.6:1 with no decking of the block (pistons sitting .025" in the hole with 6cc worth of valve reliefs) and a .039" Fel Pro head gasket (9cc). I assume you're boring 20-over on the block due to the 'f-20' on the tail end of your piston part number.

If you're concerned that might be a bit high (I wouldn't be concerned, personally) you can get some slightly dished pistons (-12cc is a very common dish size) and use some thinner head gaskets (GMPP .028" compressed thickness composite head gaskets work well and are inexpensive) to get you down to 9.25:1

 

I was talking to a friend of mine who is a old hot rodder and he said that the L98's would not atamize as well due to swirl porting.

 

he's on crack.
He may be thinking about TBI swirl port heads. But they atomize better, they just don't flow as well at high RPMs. The L98 heads will outflow those old school paperweight heads you've got.