781 heads for BBC - Nova Tech
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  #1  
Old Nov 20th, 10, 12:26 PM
lil2004gmc lil2004gmc is offline
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Default 781 heads for BBC

Can anyone tell me if the 781 Heads are any good. Are the square, rectangle, or Oval. I am kind of new to chevys and I have always own Oldsmobile. I sold my W30 this summer that Ihad for 18 years since high school. So Chevy heads are alittle of a mystery to me.
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  #2  
Old Nov 20th, 10, 02:06 PM
bbdeuce bbdeuce is offline
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Default Re: 781 heads for BBC

454 oval port cast iron peanut. They are okay smog heads. If they are ready to go fine but if you have to put money in them I would pass.
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Old Nov 20th, 10, 02:08 PM
lil2004gmc lil2004gmc is offline
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Default Re: 781 heads for BBC

now how do I know if these are the 781 heads. is there a casting number and where is it....
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Old Nov 20th, 10, 03:33 PM
bracketchev1221 bracketchev1221 is offline
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Default Re: 781 heads for BBC

They are great heads. They are the best GM street head made. It is an open chamber oval port, not the peanut port that is a 236 casting head. If you pull the valve cover the number is cast onto the intake runner. It will be the last 3 numbers of the casting. I had a set on a 408 big block (396 +.060) and made just over 500 hp on 93 octane gas at 6800 rpm.
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Old Nov 20th, 10, 03:42 PM
lil2004gmc lil2004gmc is offline
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Default Re: 781 heads for BBC

ok thank you.
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  #6  
Old Nov 20th, 10, 04:17 PM
Big Dave Big Dave is online now
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Default Re: 781 heads for BBC

Like Ray stated aqbove; this was the last PASS (aka Oval Port) head made before the "Peanut Port" heads where introduced in 1975. It replaced the earlier '820 PASS head in 1974 and went out of production in early 1975. It has a small (for a BBC) 113.4 cc combustion chamber, and the standard small valves used on all PASS heads of 2.06" intake/1.72" exhaust. On top of a 1974 454 short block it makes 235 horsepower. Note that these valves are the same size as installed in aftermarket SBC heads; so increasing the size of the valves can wake these heads up when combined with a pocket port job and a set of free breathing headers.

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Old Nov 20th, 10, 04:37 PM
lil2004gmc lil2004gmc is offline
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Default Re: 781 heads for BBC

From what the guy told me I think he said the valves were replaced with 219 intake and 188 exhaust. Does this sound right and is it a good combo for these heads. Also if I wanted to keep these oval port heads. What would be the largest i could go for valves.
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Old Nov 20th, 10, 04:41 PM
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Default Re: 781 heads for BBC

2.19" intake and 1.88" exhaust is a great improvement (the BBC head is hampered by a poor exhaust port). The 2.19" could be replaced with a 2.25" or a 2.30" intake valve if you wanted to install new valve seats.

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Old Nov 20th, 10, 04:44 PM
lil2004gmc lil2004gmc is offline
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Default Re: 781 heads for BBC

what would be the average cost of adding the larger valves.
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  #10  
Old Nov 20th, 10, 09:01 PM
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Default Re: 781 heads for BBC

Depends upon where your average machinist works. In my neck of the woods it costs about $250 to $270 to cut and press in the new seats and perform a five angle valve job.

This price doesn't include the $116 for eight new Manley 2.250" 11/32" dia stem stainless steel tuliped intake valves (11874-8), or the valve guides if they need to be replaced with sil-bronze (Manley 42158-32 $84 plus labor).

This is why as expensive as new big block heads appear to be when you look at the price of them; you will discover if you add up the price of all of the features of the aftermarket heads being installed into your current 1974 heads (the new aftermarket heads also enjoy the benifiit of being computer designed using new fluid dynamic wet flow modeling) that they are about the same cost.

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  #11  
Old Nov 22nd, 10, 09:25 AM
bracketchev1221 bracketchev1221 is offline
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Default Re: 781 heads for BBC

Mine had 2.19/1.88 valves.
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