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400 sbc horsepower stumped

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400 engine
21K views 56 replies 14 participants last post by  ericnova72 
#1 ·
I have just finished building a 406 sbc stock crank scat 5.7 7/16 cap screw rods speed pro flat top forged pistons 5 cc valve releifs RHS Pro Action aluminum heads 200 cc runners 72 cc chambers howards hydraulic roller cam,241 int-245ex duration @50 . 545 int 565 ex lift 110 lsa matching lifters crane roller rockers 1.5 ratio, rpm intake holley hp ultra 750 dp cfm carb msd streetfire hei.1 3/4 headman headers .
I had it dynoed on a dynatech roller dyno it showed 427 ft lbs of torque at4200 rpm and only 319 hp at 6000 rpm fuel ratio was perfect throughout the run timing was 34 degrees tried with and without vaccum cannister less torque withe the vaccum canister hooked up fuel pressure was steady at 6 psi i cant figure out why these rear wheel numbers were so low am I doing something wrong does she need more air,such as a team g intake maybe or more fuel or cfm any advice.After 1500 miles took her to the track ran a 12.98@ 105.72 mph in a 1980 Z28 with a 3:42 rear and a M21 4 speed and firestone radials was not to impressed but for a daily cruiser not bad i guess. It just seems there should be more power coming out of of her any advice would be helpfull I was thinking about porting the heads an go with a 2.08 intake valve and perhaps a beehive spring set up. Im stumped any help please would really be appreciated.
 
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