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sbc spark knock

8818 Views 3 Replies 3 Participants Last post by  6sally6
just installed a 350-30over with dart 202 steel heads, edelbrock air gap intake, edelbrock 650 carb, large cam-specs unknown, stock hei distributor,msd 6al, 10:1 compression, approx 400hp.running 91 octane gas. my problem is spark knock at medium acceleration. total timing is at 30 deg at 3500 rpm. should i back off the timing--should i try installing a curve kit --should i be using vac advance on a motor like this with low vacuum. any advice would be greatly appreciated
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It might be the cam.........

If it has early closing of the intake valve to get "more power under the curve"(whatever that means) it may be building a lot of cylinder pressure causing the knock. Hey...I'm no cam expert....know just enough to be dangerous. Really need to know the cam specs/particulars to help diagnose. I would try all the above to see if you can stop the spark knock. Start by moving the initial timing back. Then experiment with the vacuum advance. try ported and unport vacuum. See if either makes a difference. With the initial advance back some...try some lighter springs and see if the total timing can get to 34/36 degree by 2500rpm...withOUT knock.
This has been discussed many times.There are at least 4 different balancer and timing mark location on small blk chevy,Has the balancer slipped etc.How many cc are the heads, is it o deck
Good come back........

IF he used an old balancer it could have indeed slipped, therefore, the marks are off and engine possibly out of whack! I WOULD HAVE spent a little more and got a new(or known "good") balancer and had the assembly..including the balancer balanced at the machine shop while they were doing the work. Just eliminates "things" that could cause problems later.
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