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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hey guys im almost done with the build of my 406 sbc it has a series 9000 crankshaft 3.75 stroke with 4.155 pistons -6 with 4 valve reliefs and 5.7 rods it also has brodix ik 200 64cc 2.02 intake 1.96 exhaust heads with .575 max lift springs. Ive tried Cams 12-444-8 and 12-443-8 and the exhaust valve keeps hitting the piston. Should i just take it one step lower? Or is there any other cams you may suggest or what can i do to fix this?
I don't think your cam choice is the issue here.
I wouldn't recommend just dropping down on cam without correcting the underlying issue. Hitting now at static means you'll still be hitting at high rpm with only a slightly "smaller" cam.
I'm thinking either:
1. Cam not degreed properly. could be retarded since exhaust is hitting.
2. Insufficient deck clearance. What does it measure?
3. Wrong valve reliefs in pistons (need to be for conventional 23 deg heads)
Last edited by 86LG4Bird; Oct 21, 2015 at 10:50 AM.
1.96" exhaust valve??? Is that correct or a typo... I'm guessing it's a typo though as I have never seen a 23* sbc with an exhaust valve that large.
If that is correct that is why the exhaust valves are hitting. That is too big for std. common 23* angle sbc parts/install
By "-6 with 4 valve reliefs" I'm guessing you mean 6cc flat tops.
I have found most small cc 4 VR flat tops do not have deep enough valve pockets for big cams. You can sometimes fudge that by installing cam advanced or retarded but that just barley gets you by on 240+ degree cams
I find it best if using flat top pistons to run a 5-8 cc 2 VR piston... Common sense tells you the valve pockets are twice as deep on a 6cc 2 VR piston VS. a 6cc 4 VR piston.
At this point you can fly cut your pistons to make the valve pockets bigger.
But before that, check, measure, measure, measure your deck height, gasket thickness, degree your cam in, etc.
You may get lucky and find that your cam is installed retarded from advertised.
To run my 249/252@.050" .570"/.579" lift cam, I had to use deep 2 valve pocket pistons. Wiseco pro tru 5cc 2VR (it's a 355 cid).
With that I run a .025" in bore at TDC, .015" thick gasket, Brodix IK 200 heads, 2.02"/1.60" valves.
