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Old 07-28-2005, 08:04 PM
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What would you do with stock 781 heads

Ok I have been reading alot about building these heads and going aftermarket. I have read many reasons to go both ways. What would you hotrodders do? Rebuild the 781s or save the cash and buy aftermarket? Thanks

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Old 07-28-2005, 08:20 PM
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Go aftermarket
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Old 07-28-2005, 08:23 PM
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Your talking BBC 781's right? We discussed this last week, but I have 781's on a 496ci it made 500hp/ 600lbft completely stock how much do you want? Do you have the drivetrain/traction setup to support aftermarket heads?
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Old 07-28-2005, 08:44 PM
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I have a TKO 600 tranny. I had a similar post a while ago but never got opinions on what to do as far as this
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Old 07-28-2005, 09:10 PM
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Since there yours and paid for why not build them...? Set of 2.19/1.88 valves and have them cut for them add a good set of springs to match your cam along with some good locks & retainers... A little port matching and on a good short block make 500 HP no problem... Oh and machine work $300 ball park if alot more then find another machinest...

Intakes

Exhaust

Springs, Locks, Retainers


If your wanting to build an all out race motor either move up to 990`s or alum for the weight loss plan...
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Old 07-29-2005, 07:12 AM
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heads

You are not going to find any better head (including the aftermarket head) for a street/ strip big block then the 781 (and other oval port open chamber) heads....

With a set of 2.19 / 1.88 valves and just a tick of port work right under the valves they will work perfect. The flow numbers and cross section area are good on theses heads. They will make a 468 run like the wind thru the mid range.......... Thats where you want it to work in a heavy car.... they also provide excellent throttle response.....

Now if your building a 555 super comp engine then it's a different story....

keith
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Old 07-29-2005, 07:55 AM
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On my 781's
I put in bigger valves (2.19/1.88) then,
A little bowl work to smooth out the valve seat/head interface,
Heavier springs to match the cam,
CompCam roller rockers,
Longer studs required for the roller rockers
Guide plates for 3/8" pushrods
Un-shrouded the bigger valves on a mill by cutting a circle out to the gasket.
Then eyebrow-ed the block by cutting up to the gasket at the location of the valve to match the valve un-shrouding.

Not sure how much more power (if at all) is being made with this head setup, but it sure makes me feel good about it. hahahaha

A bunch of work, but at the time, I had nothing better to do. It would be much easier and might even be cheaper to sell the 781's and buy a new set of World Products oval heads. Do the math and consider your other time commitment's.
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Old 07-29-2005, 11:18 AM
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Are the World heads ported and polished? I have seen complete heads for around $1499 but do they have quality valves, springs etc installed? For around $1,000 I can have these -781 heads complete with manley valves. And of course me doing the porting work. What would you guys do if you were in my boat? My car is street cruiser
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Old 07-29-2005, 12:16 PM
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How much power are you trying to make?

If you are looking for a 400hp/500ftlb 454cid bbc, then I would just do a quality rebuild and install a stronger set of valve springs. Then install a Holley 750, RPM intake, 268 compcam, set of headers, set cr to 8.75 to 9.0:1 with cast pistons, and run it. That would make a nice performance street engine. Just clean up the rough spots in the bowls (under the valves).

If you are looking for more power, then start thinking bigger valves, bigger cam, bigger carb, better rods, better pistons, more compression, and more money.
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Old 07-29-2005, 03:28 PM
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Im looking for 550hp. If I wanted 400hp I would have gone SBC lol
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Old 07-29-2005, 04:44 PM
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Well, technically you would need a head to flow 275cfm on the intake to make 550hp. A 781 will flow that much with bigger valves but at more lift than an after market high performance head. And more lift is harder on the valve train and requires more expensive parts.

If I rememeber correctly, a big valved 781 will flow about 280cfm at 0.600 lift with some bowl work which is about what you need (280 cfm). Don't worry about polishing or port matching too much because it doesn't do much. Head work around the guides and bowls is the best bang for the buck.

You will need a pretty nasty cam for that much power!

There are some good flow data for bbc heads at chevyhiperformance.com.
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Old 07-29-2005, 07:20 PM
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Thanks I will check it out. I guess maybe a aftermarket head is in order? Will the high lift kill the driveability of the engine?
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Old 07-30-2005, 06:59 AM
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Sell them 049's and put the money towards the aftermarket heads, especially if it's going to cost $1K + your time to get them built.
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Old 07-30-2005, 03:43 PM
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It just sucks that when I was looking to build this motor alot if not everyone said the stock heads would be awsome when built. They never did mention that New heads would cost about the same. Now I have 2 pieces of iron that are more likely paper weights now. I wish I knew this before I bought them. I was thinking ebay etc but who wants to pay the ridiculous shipping. I guess Im at a $120 loss once again
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Old 07-30-2005, 05:06 PM
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Re-read this post by Keith. He's a machinist and knows what to suggest. Put some of your own effort in the heads, the feeling of ownership is worth something too. Anyone can buy parts and slap em on, but personally its nice to have some of your own sweat and blood in the mix too. Just my opinion.

Mark



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Originally Posted by k-star
You are not going to find any better head (including the aftermarket head) for a street/ strip big block then the 781 (and other oval port open chamber) heads....

With a set of 2.19 / 1.88 valves and just a tick of port work right under the valves they will work perfect. The flow numbers and cross section area are good on theses heads. They will make a 468 run like the wind thru the mid range.......... Thats where you want it to work in a heavy car.... they also provide excellent throttle response.....

Now if your building a 555 super comp engine then it's a different story....

keith
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