cannot figure out my spark knock.
 

i have a 13b street ported , 51mm weber, rb header. i just switched to a direct fire ignition only on th eleading plugs. i also put a strait through muffler on which made a huge difference in power. now if i let it pull all the way through 3rd gear it starts to spark knock at about 6k. i have retarded the timing several times with no improvement and my air fuel gauge is not going lean. whats the deal? i autox this car several times a year and want to make sure this is fixed before i damage anything.
any help???

what octane of fuel are you using? try using an octane booster or up the grade of fuel to see if thats your problem. I f not I am guessing its your spark setup you have going on. just play a game of guess and check ;)

what octain fuel should i use?

Trailings not switched?


-Ted

only the leading are direct fire. the trailing is running from the stock ignitor and distributer cap and rotor. the leading is being fired by the 2 lead coil off a 2nd gen.

What heat range plugs are you using? For a race motor, you should be using at least an NGK 10 (cold) or 11 (very cold) plug. Too hot of a plug will cause problems.

What is your timing now set at? If you hold the motor steady at 4000 rpm, how many degrees of timing do you now have?

I think more importantly what is the timing doing where you're experiencing knock. Is there a mechanical advance? It doesn't really matter what the timing is at idle when you're shooting it with a timing light if your setup is allowing for too much advance under load. When we're setting up our race engines we'll confirm the timing across the rev range on a chassis dyno. If it wasn't knocking on the old setup and it is now I'd say the problem lies within what you've changed. Confirm what the timing is doing across the rev range under load and make corrections accordingly.