What is the actual combustion chamber size on #781 big block cylnder heads???? Most places have them listed at 113cc. Always thought they were basically same head as the #049 which alot of places have listed also at 113cc, but due to a recent post seem to be more like 121cc. Was just wondering if #781 are also really 121cc chambers. Im putting a 454 together with TRW #2349 pistons and a set of non surfaced #781's. At 119cc it lists as 9.99 comp ratio. But if there 113cc comp ratio would be a bit on the high side............THANX

my 049s measured at 121-123cc depending on which chamber I measure. This was after some unshrouding around the exhaust valve and polishing the chambers.

I'd say they were around 119cc before I touched them...

114cc 781, and 118cc 049 is my understanding. I'm sure someone will jump in here and correct me. smile.gif

well I just had bigger valves put in, and when I got them home I cc'ed them.

One head had 3@114cc and 1@113. The other head came in at 3@114 and 1@115.

These are 781 heads 2.19/ 1.88.

I have a couple of sets of 781's they are around 120-122cc. My 049's originally was about the same as the 781 until I milled them .040". Now they are 113-114.

I think it means we have to cc each head b/c I suspect they vary all over the place..

And the -049's probably do too.

pdq

every 781 or 049 i've seen has been 120-122cc. i've had 2 sets of 781's and one set of 049's.

My 781's were about 120 before milling. You really have to cc them to be sure.

Troy.

PDQ, and not only one of a set of heads. Particularly if they've been dusted in the past. To wit, I had one head that measured 1.5cc on average bigger. So we dusted that one down an additional .005-.007" to get the two heads much closer in chamber size.

DON'T ASSUME!

whoops

depends on how many valve jobs they have had, how many times they have been resurfaced, ect.

For the minimal cost of having a cylinder head or machine shop check the CC's you can know for sure.

you need to know actual CC so that you can know Actual compression, so that you can make an Accurate choice on which cam to use.

Just as well you should know actual deck height, the area around the piston/above the top ring, the gasket cc's.

You should also know the actual stroke, but some dont want to take it that far. Some GM cranks are so far off, that if you were to grind them on an index they wont clean up without going wayyy under.

I cc'd several of the chambers in both of my old virgin, big valve, SB -461's to make sure the end ones weren't different then the rest.. And they did vary a schosh, like 66 to 66.3, but mostly right at 66 cc's

I figure the same should apply to the BB heads too. That way we would know for sure!!

pdq67