BBC Valves

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BBC Valves

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I am building a budget big block. I am considering using stock valves on 781 heads with a solid roller camshaft. How aggressive as far as cam, lift, and ramp intensity could I go on stock valves without worrying about reliability. Thanks in advance.
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Post by maxracesoftware »

you could look at this from a NHRA Stocker point of view ??

..where they have fast, aggressive max-area Lobe profiles, for a certain amount of Lift/Duration...and use stock gram weight, length, stem-diameter valves

i'm sure there are some NHRA Stockers running #781 heads

you would probably want to run a lot more Lift than a Stocker Cam ??

and if you have to buy valves, i'd probably use 2.190 or 2.250 - 1.880 valve sizes in the #781 heads..just would need a little more Bowl and Valve Job work.

also becareful of Piston-to-quench area/deck contact in that exhaust corner with certain Piston domes

the #781's weren't relieved in that area enough to clear most Hi-Perf Piston domes
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Post by Guest »

Thanks for the reply. How good are 781's with large valves and bowl work. I am not sure how much money to put into stock heads. I would like to someday go aftermarket. Is 500-550 HP possible with these heads. How bad do the little valves hurt these heads? Thanks Again!
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Post by maxracesoftware »

Anonymous wrote:Thanks for the reply. How good are 781's with large valves and bowl work. I am not sure how much money to put into stock heads. I would like to someday go aftermarket. Is 500-550 HP possible with these heads. How bad do the little valves hurt these heads? Thanks Again!
500 to 550 HP is easily possible with just average ET Bracket hydraulic or solid lifter Cam

600+ HP with moderate to Hi-Lift Roller Cam

usually make an honest 700+ HP with #781s 2.250-1.880 or 2.300-1.880
valves on 468 cid..with Hi-Lift roller
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Post by Adger Smith »

In response to the BB oval port heads: I have never tried a direct comparison of the big VS little valve. I have only flow tested heads done by other shops & tried to improve them & done flow testing on heads I modified. I have had some very good results with the oval port heads with bigger valves. I use the 2.19 & the 1.88 valves. The chamber wall needs to be moved & radiused on both the intake & Ex & the area Larry mentioned needs some major metal removal. It may hurt the CC of the chamber, but really picks up ex flow. My oval port heads stay with the typical flow #'s of a STD package -2 Brodix & other package heads at low & mid lifts. (.050-.600 average flow is equal or better) They also keep port flowing up in the high veolicity area. Great response! Don't sell these heads short. They work great on smaller cubic inch big blocks. When you get to the larger size BB's the avaliable port size (CC's) becomes a limiting factor. A jet Boat customer tried a set on his 496 & they made great low & mid range torque, moderate HP. When the engine went "over" it just died, out of breath! It is my opinion these heads, if done correctly, can give you good performance for the dollar value.
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Post by lugnut5 »

Adger
When you say your customer with the 496 pushed it "over" can you be a little more specific. I'm in the process of building a 496" with a set of these heads done by John Lingenfelter. I'm going to stay around 10.2:1 comp. These heads on a 461" engine with 10.2:1 comp and a comp cams extreme energy 256@ .050 .666 lift solid roller cam went 10.70 @124 in a 1967 camaro that wieghed 3700 lbs. I shift it at 6400. When I try shifting higher, you can definitly feel it nose over. Is this what your customer did also?
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Post by Adger Smith »

Yes,
I feel the port size with extreme velocity makes the engine suffer at Hi RPM. It does make it a torque monster though. Excellent torque at lower RPM over a wide band.
What I mean by "Going Over" is when you reach the hi end max power the fall off is rather abrupt.

Your combination will like a tight converter & less gear than normal. It will also be hard to dial in air that changes during the course of a race. If the air gets better it will tend to pick up more ET than an engine with port sizes that are larger, or better suited for the 496.
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Post by rfl28 »

the 781's like a 1.800 exh valve also,...a fews years back was trying some tips and formulas from darin morgan@ aetc....decided to try the slightly smaller exh valve,....was'nt disappointed,....usual head prep, unschroud both valves w/ sunnen tool,..4a vj, bronze guides, solid roller just like lugnuts,...3250# '81 camaro w/ 468ci ...10.54 @ 128 ...i believe compression was 10.50:1.....they run out of steam @ 6500 and i agree they would choke a 496...just my thoughts....Bob
stand on it!
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Post by lugnut5 »

Adger,
do you think I would be better off raising the compression (from 10.2:1 to say 12.5 or 13:1) and keep the engine a 468" with these heads, or is it still a good idea to go for the bigger cubic inches with a 496" and stay with the low compression. On another note, I remember John Lingenfelter building a 496 with these heads and produced 612 HP on pump gas.(9.5:1 or 10.2:1). That was back around 1990.
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Post by Adger Smith »

It would depend on your combination of parts you now have & the way your car is set up & how you plan to run it. I try to get most of my customers to use their available parts & not make drastic changes in their combinations.
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