781 head help - Team Camaro Tech
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post #1 of 3 (permalink) Old Apr 3rd, 11, 09:09 PM Thread Starter
adrian
 
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781 head help

i have 781 bbc head and was wondering how to wake them up. i hear doing sum bowl work and installing bigger valves would bring them to life but is there anything else i need to do, like port and polish or mill anything? they will be put on a 454 that i want to make a street machine and track on weekends. it will have the 781's with bigger valves and bowl work and other recommended wrk yall advise me to do, performer rpm intake, comp cam xe 274/286, Lift .552/.555, 373 gears, hooker headers, and a 750 holley dbl pumper. any idea on what compression il be running and horspower range? block casting number if needed is 361959 and head #336781
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post #2 of 3 (permalink) Old Apr 4th, 11, 07:02 AM
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Bryon
 
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Re: 781 head help

It depends on how much you want to spend. Generally the more you spend, the better they will flow. But if you spend too much, it might have cost the same for a set of aluminum heads that flow OK right out of the box.

68 Camaro SS 396 - 468 BBC now, M21, 12 bolt 3.73 coded housing but w/ 3.31 gears.
Looking for 68 Camaro with body number NOR 181016
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post #3 of 3 (permalink) Old Apr 4th, 11, 10:10 AM
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Ron
 
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Re: 781 head help

781's are Large Oval Ports not Rectangular with approx a 118cc Combustion Chamber (Always CC BBC Heads to ensure the Volume as they have been known to differ). The Guides are Critical and you can install larger 2.19/1.88 Valves with moderate Bowl porting. NOTE that the Larger Valve tend to decrease the Chamber Volumes by a cc or 2 but by the time you un-shroud around the Intake and Venturi approach the Exhaust your back at 118cc's.

With Flat top Pistons the static compression is approx 8:1 - very low for a Performance cam so do not use more then a 266 or 270 cam. Alternately you can use a 396 Close Chamber head with something like a 98cc Chamber Volume over them Flat top pistons to raise the Static compression to approx 9.2:1 and use that 274 cam with close to an 8:1 DCR.

You're best is to replace the pistons with something like Speed Pro L2465F30's with a 25.7cc dome with 781's which will bring the static up to approx 10.2:1 using the ,018" thick steel shim Head Gasket - in which case you can run a verily stout cam like a 278 or 282 providing an 8.2:1 DCR and run Pump Gas - Here is where the 781's really shine if you shell out for a SR Cam ; however, I recommend the XM278H-12 and CC-925 springs with nothing but a Piston Change & 0-Deck for your 1st BBC build as it prepares the Block for Future changes if you so desire. 500+Hp & 6400rpm isn't shabby for relatively Stock 10.2:1 HFT BBC - Roller Rockers (Harland Sharp or CC-Pro-Mags and 2" ARP Rocker Studs are a must spinning over 6000rpm ;o)

You can 0-Deck the block and run a composite .038" Head Gasket - which is handy if you ever go to Alu-Heads. It is important to keep the quench between .034" to .044" with anything over a 9:1 Static Compression - particularly with Iron Heads.

A Cast Crank is just fine to 6400rpm but if you thinking 7000 rpm & 600+Hp you need a Forged one. With prepared 781's, Forged Crank, Auto-Hole Shot to 3.73 Gears and 10.2:1 Static you can get away with a 282 to a 288 SR Cam and put out 600+Hp with 7000rpm revs - of course it's expensive.

You should check that 959 Block as it could possibly be a 4 Bolt with a Steel Crank. NOTE the Engine CODE and find out what type of Vehicle it originally came out of.

PS: Don't post so many threads, members can't keep up to what you have and don't have ;o)

P. Kelley's DCR Calculator and Comp Cams Camquest Software are handy apps to help you design the block and choose a cam:

http://www.empirenet.com/pkelley2/DynamicCR.html

http://www.compcams.com/downloads/register.asp

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Last edited by Z15CAM; Apr 4th, 11 at 01:38 PM.
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