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Old 10-04-2005, 12:13 AM
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781 heads

can I get some help. I have been told that 781 heads are the best flowing gm stock bbc head there is. Is there any trueth to this. If so great if not I need some help choosing some heads for a bbc. 496

Thanks,

Chris

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Old 10-04-2005, 12:41 AM
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IMO the 3993820 is a better head. It has the same ports 256/114 but 113 cc chamber instead of the 118.

Personally I use the 3909802 101 cc chamber. I flowed them with a Victor Jr intake.

If I go to anything else. I would buy the Edelbrock 60459 Perf/RPm 110 cc chamber with 290/110 ports. The problem is you need to buy special pistons for the semi-open chambers if you won't to get higher compression than flat tops.
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Old 10-04-2005, 08:32 AM
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Yes, the 781's are good flowing heads. So are the 049's.

I measured the ports on my 781 to be about 255cc with combustion chamber volume of 120cc. I also have a set of 802's and those only measured 240cc on the intake ports with 110cc combustion chambers.

fyi, I had a big set of valves put in a set of 802's and got it to flow about 255 intake/199 exhaust at 0.500".

I think you will need the bigger chamber heads if you want to make a 496 that is pump gas friendly.

I believe the 496 kits were designed to work with 120cc chambers. 110 cc chambers will really kick the compression ratio up on a 496. So, it depends on your application. Read the 496 kit specs to determine the compression ratio that it will make with a certain cc head. I guess 8.5 to 9 cr 496 with a 120cc head, which is about perfect for a BBC with pump gas and a cam between 205 and 225 duration.

I think a stock set of 781's would be good for a low rpm 496 with 9:1 cr and a mild to moderate cam. If you plan on revving over 5500 rpms then consider adding bigger valves and doing some port work to the 781's or any other factory head you use. But it may be cheaper just to get a set of World Products oval port iron head street heads (1300.00).

The new AFR street oval port head would be the best but cost about 2000.00 for the set.
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Old 10-04-2005, 10:02 AM
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heads

A little more info on the end usage of this engine would help....

The 781,049 and like heads are an excellent choice for heavy cars, and cam be made to work well with just some minor changes. I would up the valves to 2.19"/ 1.88" this will give you a good cross section are under the valve. and allow the heads to move some more air. The exhause ports are all ready big so they need no work there. The intakes are about perfect for this valve size...

I know guys running these heads on basic 454's in 3500lb car going mid to low 10's on just motor, no spray.. so they do work...

Keith
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Old 10-04-2005, 10:05 AM
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I wil be putting the 496 in a jeep for mud drags
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Old 10-04-2005, 10:11 AM
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heads

I assume that it's a light jeep, maybe 2500lbs or less..

Is this something you do from a dead stop or is it from a float??? what kind of rpms do you expect to see????

Keith
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Old 10-04-2005, 10:18 AM
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its from a dead stop the jeep weighs approx. 2500 lbs I would like to see 6000- 6500 om the rpm side
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Old 10-04-2005, 10:34 AM
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Are you limited on compression, cam (roller, flat tappet) intake, carb etc????

Are you considering the stock heads because of cost???

Keith
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Old 10-04-2005, 10:37 AM
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I have no limitations and yes I am using them because of cost. I am on a budget. atleast thats what my wife says. lol
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Old 10-04-2005, 12:01 PM
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what can I do to make them flow really well
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Old 10-04-2005, 12:07 PM
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heads

In your application i wouldn't do anything to them except the larger valves like i mentioned and just bowl work up to the new valve seats....

Keith
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Old 10-04-2005, 12:41 PM
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and if they're off, port the intake/exhaust and polish the chambers. Its not that hard, just do it and be glad you did.
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Old 10-04-2005, 12:50 PM
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heads

You do-not want to do any porting on the exhaust side of theses heads... You can polish them up if you like but do-not remove any metal....

The only way i would touch the intakes is if you have access to a flow bench and someone that can point you towards the correct location to remove metal...

Keith
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Old 10-04-2005, 01:09 PM
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ok great thanks




,

Chris
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Old 10-04-2005, 03:32 PM
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When bigger valves are added it would be a good idea to unshoud the valves a little. That is, grind the combustion chamber wall away from the valve 0.020 or 0.030" at the point the valve comes closest to the combustion chamber wall.

Then clean up the area directly under the valve at the valve seat/head interface.

Some mild block eyebrowing is also a cheap flow improvment.

Make sure to get the proper valve springs for the cam you are going to use.
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