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Old 11-27-2006, 05:55 PM
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biggest lift on 781 heads?

what is the biggest lift on large port oval 781 heads. still clearing trw 10.5/1 pistons. but what could the heads take biggest valve lift? right now is .575
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Old 11-27-2006, 06:39 PM
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If the heads are stock, with factory rotators and guides. You are pushing the limit at .575. Most of these heads have a short valve spring/retainer setup and it is hard to come up with a spring installed height of 1.875 that is required for much more lift.

Usually I take a rotator eliminator and trim the back of it. Plus use an aftermkt retainer or .050 up lock to get the proper height.

Also, while doing the spring work. I trim about .100 from the guide tops and cut for seals.
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Old 11-27-2006, 07:07 PM
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what is the max flow any one got out of these heads, stock is 256cfm i think. what if you ported them out and put in 2.19/ 1.88 valves. what rpms could they flow up to?? what could be the max port .cfm's
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Old 11-27-2006, 07:25 PM
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I put 2.19 and 1.88 valves and hard ex seats in all 049's and 781's. Bowl hog out to inner seat area, blend sharp edges and open bowl and blend short radius. Port match intake and smooth out top 2/3rds of exh port.

I have never had any flowed tho. Most of the cams I use in these heads are around .620 lift. Any wilder than that and I go for aftermkt 320 heads.
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Old 11-27-2006, 10:01 PM
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Yea what Bob said...

Most people just dont realize the potential of the large oval port heads (781/049 that is...) Many of the bracket guys do though...

Just a shame on how the installed height issues are with them... Wish they were made like the 990 rectangle port heads...
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Old 11-28-2006, 03:35 PM
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I have some cams in the .700" lift range using .875" and .904" tappet diameters for solid flats. I have a customer that is limited to OEM casting in a pull truck class. The 781's with extensive work will reach the low to mid 300 cfm range on the intake side. The class is limited to 470CID limit and these engines get turned to 8000 plus so the cam has to be pretty big.
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