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Old 03-10-2012, 07:45 PM
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336781 Heads With Flat Top Pistons

Have A 454 With Flat Top Pistons ,SLR Cam. Lift Is 532-522 Duration Is 282-292,with Roller Rockers . Had Some Head Trouble, They Were 702's Now Have 336781 Open Chamber Heads . 206-172 Valves Will This Combination Work Just As Well ? Thanks....................gus

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Old 03-10-2012, 09:22 PM
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flat tops and 781s make a pretty low CR
i dont know what cc the old heads were
have the 781s and/or the block been cut/milled ?

but it will probably work ok with that cam



*I am no expert
there are a few guys on here that know more than me
maybe they will chime in
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Old 03-10-2012, 10:20 PM
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The 702's Are 98 Cc . The 781 Are Supposed To Be 113 Cc. The Block Has'nt Been Decked ,but The Heads I'm Not Sure About As They Are Still At The Head Shop &the Bore Is Still Stock. Thanks For The Comeback...........gus
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Old 03-11-2012, 10:11 AM
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Quote:
Originally Posted by GUS00
The 702's Are 98 Cc . The 781 Are Supposed To Be 113 Cc. The Block Has'nt Been Decked ,but The Heads I'm Not Sure About As They Are Still At The Head Shop &the Bore Is Still Stock. Thanks For The Comeback...........gus
the 781s are more like 118 - 120 cc
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Old 03-11-2012, 10:41 AM
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I dont know what the deck height or the volume of piston or head gasket thickness is gonna be but the flatops with those heads will make that big block sick (wont go!) compresiion,Ithink ,will be in the 8:1 range at best...
Try to get some closed chamber heads or change pistons.
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Old 10-19-2012, 10:06 PM
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How much can I mill the 781s down .They have 219 188 valves now .I want to try them on a 454 with a comp extreme marine cam - lift-544-547 duration 226-236 & flat top pistons. stock bore & deck. .......
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Old 07-02-2013, 02:11 PM
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This is an old thread I know ... but I have just researched this as well, and this is what I think I have found for my setup:

454 bored .030 = 4.280" bore x 4.00" stroke

Clevite Forged flat-tops, P/N 224-2519.030
Specs in the Clevite catalog say these have a -4.9cc dome volume and that the stock deck clearance is .025" (My block was decked what my machinist only described as "minimally" ... approx .005, so I'm using .020")
Comp.Distance is 1.640"

336781 Cyl heads.
ALMOST ALL lists that I have found say these are 113cc.

Felpro Permatorque head gaskets have a compressed thickness of .039"

So, using Summit's compression calculator with these numbers:
4.280 (Bore)
4.00 (Stroke)
113 (Cyl Head Volume)
4.9 (Dome Volume)
0.020 (Deck Clearance)
0.039 (Compressed Gasket Thickness)
8 (# of Cylinders)

... I get a CR of 8.15:1
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Old 07-02-2013, 03:11 PM
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I get 8.7 with 113cc head.
All the 781 I have done were 188cc to 122cc.
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Old 07-02-2013, 03:18 PM
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Quote:
Originally Posted by lmsport View Post
I get 8.7 with 113cc head.
All the 781 I have done were 188cc to 122cc.
188cc ???


Duke
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Old 07-02-2013, 03:34 PM
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Typo i"m sure. Most average about 120 cc. stock.. I don't know where they are getting the 113 figure.
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Old 07-02-2013, 04:01 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Typo i"m sure. Most average about 120 cc. stock.. I don't know where they are getting the 113 figure.
Well, these are a few of the places that I found:

Chevymania Casting and Suffix Tables

Chevrolet Big Block Cylinder Head Casting Numbers

Big Block Chevy Engine Parts casting numbers and Identification

Looking on Google, though, there are websites that list them as 118cc ...
Mortec web archive


Has anyone actually cc'd these heads for themselves?
They sure seem to be popular (as far as cast heads go ...)

Last edited by 66GMC; 07-02-2013 at 04:11 PM.
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Old 07-02-2013, 07:40 PM
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Quote:
Originally Posted by 66GMC View Post
Well, these are a few of the places that I found:

Chevymania Casting and Suffix Tables

Chevrolet Big Block Cylinder Head Casting Numbers

Big Block Chevy Engine Parts casting numbers and Identification

Looking on Google, though, there are websites that list them as 118cc ...
Mortec web archive


Has anyone actually cc'd these heads for themselves?
They sure seem to be popular (as far as cast heads go ...)

I read all three of the above sources. LOTS of incorrect information on them..

Example. 049 heads are also listed as 113cc. They are in actuality 120-122..
Another example. Stated in article that tall deck 427 trucks had 7/16" rod bolts. Completely false!

Plus many more. In this case don't believe what is printed..

Yes, I have actually cc'd many BBC heads and they are usually larger than GM stated spec.. I usually start with a .005" cut before measuring the chambers. A sloppy repair valve job can add cc's of volume to the chamber. Sink that valve/seat and add combustion chamber volume..
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Old 07-02-2013, 08:44 PM
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781's with flat tops

If you build a high performance 454 with flat tops, you're gonna have a turd. You need at least 10:1 for any decent performance with those heads especially if you don't open them up with bigger valves and porting. If you have to run low octane go 9.25:1. You have to use domes with those heads. Make sure you get the right pistons for the open chamber heads, don't get pistons for a earlier closed chamber head. If you go large on the cam and spread the lobe separation angle out, you might go 10.5:1 without detonation provided you keep the timing conservative. The heads are not the best but will make some serious HP with good compression ratios. I've built two, one for a car with a roller w/10.5:1 on 93 octane and a one for a boat ~9.25:1 with a milder flat tappet cam and it doesn't rattle on 87 octane.
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Old 07-12-2013, 10:33 PM
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I'm not real crazy, obviously, about discarding my brand new forged flat-tops.

I've just located a set of closed-chamber #3931063 heads, which according to that Mortec achive, are 101cc

Using Summit's compression calculator with these numbers:
4.280 (Bore)
4.00 (Stroke)
101 (Cyl Head Volume)
4.9 (Dome Volume)
0.020 (Deck Clearance)
0.039 (Compressed Gasket Thickness)
8 (# of Cylinders)

... I'm seeing a result of 8.87:1

Can I expect any improvement with my present cam, or should I back it back down at least one level, maybe 2?

The same guy that has the heads has a 454 block bored .060, a set of pistons, rods, and steel crank.


Also has a spread-bore Holley and Weiand Intake


That stuff looks a little sketchy to me, but the ask is $1100.00 for the whole lot. I'm thinking there is almost enough there to build and sell another mill ... or is this just throwing more good money after bad?

I guess it's always hard to give up "known good" parts (even if they might not be a good match) for a bunch of unassembled "unknowns".

Worth the risk? I'm going to go and have a look ... probably on Sunday.
Depending on what he will want for he heads seperately ... I may start with that.

PS.
If I do go with his block, piston, crank, heads ...
4.310 (Bore)
4.00 (Stroke)
101 (Cyl Head Volume)
-0.100 (Dome Volume)
0.025 (?) (Deck Clearance)
0.039 (Compressed Gasket Thickness)
8 (# of Cylinders)

...I'm still only seeing a result of 9.24:1
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Old 07-13-2013, 06:28 AM
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Known good parts??? Consider the possibility he is selling this combo for the same issues hoping to find someone who doesn't know better. Cut to the chase,your bottom line is you do get what you pay for.
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