Neither of these are great choices. I have a set of 350 smog heads, 1.94 valves, nothing special (I forget the casting number but they're basically the best of the crappy heads) The other set is from a L69 (305HO) They have smaller chambers and valves but I have a set of new 1.94 valves lying around here somewhere in the box. Their casting number last digits is 416 (not 461 as I was hoping). That's the choices nothing more, nothing less.
It's going on a 350 BTW, I haven't picked out the cam or pistons yet but I'm shooting for about 9.7 or so.
If you don't mind, I'd like to keep the conversation to those 2 heads. Thanks.

 

The 416's actually have some of the biggest runners of any SBC head ever made, 165/59cc ports.

 

Throw the smogger heads away.

Do your part to help eliminate this disgrace from the planet. Help destroy the collective memory of 165 HP 350s.

If you're one of those environmental recycling types, take them to the scrap yard to be melted down.

Now, on to what to do with the heads you keep:

The 416 heads will give you ALOT of compression if you're not careful.

They come out to around 61-62 cc after unshrouding for the the larger valves (without which, your flow will actually decrease with the 1.94", as opposed to the 1.84"). At 62cc, with the pistons .025" in the hole (stock deck clearance) and a .039" head gasket, and 6cc double-eyebrow valve reliefs in the pistons, you'll get just over 10:1. With a 12cc dish and the same clearances and stuff, it's about 9.4:1. If you get flat-top with 6cc VR pistons with the normal extra .020" or so of "rebuilder" deck clearance (Speed Pro for example), with .039" head gaskets, you'll end up with about 9.6:1, and no "quench" whatsoever (.080"-.085" instead of the .035"-.040" you'd need).

I detect "budget" in here somewhere. Therefore the real actual correct solution is probably not in the stars for you. That would be to run the 416s, deck the block to 9.000", and get "custom" pistons without the "rebuilder" extra deck clearance (JE, SRP, Venolia, Arias, Mahle, etc.) and a 14-15cc "reverse dome" dish.

 

Yes, the evil "B" word has raised it's ugly head in here. I try to console myself by knowing I'll at least be picking up something from my old 305HO. Now, If I go with the 9.4, then My thoughts would be to run a shorter duration higher lift cam to get some of that back. I know I'll have to watch the C/R.

 

http://kb-silvolite.com/calc.php?action=comp

Using the calculator above, I got:

9.2:1 CR with 74cc heads
10.25:1 ------- 64cc heads
10.5:1 --------- 62cc heads

and 9.8:1 CR with dished pistons and 62cc heads.

All those calcs are with 4.030" bore and .040 piston/head clearance.

Something to keep in mind... is whether or not there is a head upgrade in your future, in which case you would probably want to build your block around a set of flattop pistons.
If your plan is to upgrade later, the smogger heads, milled down a few thou, can be acceptable.
Your car won't be a slug with those heads, unless you're comparing it to a car with HP heads.
The point is, if you use every trick in the book to get your CR up, you can get acceptable performance out of smog heads... or at least acceptable enough that they'd qualify as being a set of substitute heads til you get something better.
I think it's wise to invest your $$ into a blueprinted shortblock that's compatible with a set of high CR aftermarket heads.
And don't throw your smog heads away til you're sure you have no use for them.

 

I would much prefer to use a dished piston with a hi C/R head than use a pop up piston. I think that system works much better.

 

That's kind of funny; using that calculator, putting in 6cc for the valve reliefs, .025" for the stock deck clearance, 4.165" gasket bore diameter, 74cc heads, and a .030" over 350, I come up with 8.7:1 CR. A half-point lower.

I think somebody isn't putting in all of the numbers that go into the whole deal. In particular, that calculator asks for "piston-to-head" distance, which is the head gasket thickness, plus the "deck clearance". Which is .025" stock, and about .045-.050" with most replacement pistons. That means, the CR you quoted, is off by however far omitting that extra .045" - .050" will throw it.

Putting in 62cc heads, it gives exactly the same result as the one I was using. Imagine that.

Numbers all seem to work that way. They don't lie. But incomplete ones, or mis-interpreting them, produces mistakes. This is a typical sort of thing that causes motors not to run as expected. Or, conversely, it's how people say "I've got a 10.7:1 350, runs fine on 87 octane". Maybe it runs OK on 87; but that's because they don't actually have what they say they have.

 

I was calculating a .040" piston to head clearance, which would be a zero deck with a .040" thick gasket.

Head vol - 74cc
piston vol - 6cc
gsk thick - .04"
gsk bore - 4.1"
deck cl - 0"
stroke - 3.48"

= 9.2:1 cr

Time after time, same results

 

So, it looks like I'll be doing the "sitting bull" port job on the 416's then.

 

If you sweep out the chambers for new 1.94 x 1.60" valves you have the chamber size you're looking for. (using the 305 head as a base)
If you sweep out the chambers to fit 2.02x1.60's you end up about 64-65cc's.
I like the 1.94x 1.60" combo for this head.

Your old 1.5" exhaust valves probabily won't be sericeable anyways.

You also have the option of using the 76cc smog heads
The 441's 336's 920's are perfered. If yours are 624's or 882's then use the 305 heads.

Shave them .060", install 2.02"x 1.60s" and use a .015" thick shim gasket.
The finished chamber will be 69, 70cc's

Which will get you 9.7:1 using RB's parameters. (.025" deck height with the thin gasket)

 

Just curious about that .015 gasket...

I was thinking about using one once, but when I called summit I was told that it's a race only gasket.
I'm not sure what that might mean, but the guy made it sound like it wouldn't work on anything but a race motor.

 

After rereading this, I just have to ask
Do different browsers show a different calculator than the one on my monitor?
The calculator I'm seeing asks for 7 pieces of data to compute the static CR

Head Vol
Piston Vol
Gasket Thickness
Gasket Bore
Cyl Bore
Deck Clearance
Stroke

So am I not doing it right, by entering -0- into the 'Deck Clearance' box, if the block is zero decked?
Cause it sounds an awful lot like RB is saying the gasket thickness is supposed to be added onto that value before entering it as 'Deck Clearance'