Thread: 327 with 305 heads

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I know this is a hot rod car site but .........I have a 1969 327 in my speed boat. I just rebuilt the bottom end of the engine. The person that I got the boat from put 305 heads on the 327. It is supposed to have more compression. I don't know if they work any better or not. I kinda of wished he had left it alone. The engine runs nice and has lots of low end , but when it is wide open I get a bad spark knock. If you back off the throttle just a hair it goes away. The engine is set up with electronic ignition a edelbrock torker 2 intake and a edelbrock performer 600 carb. I just would like someones opinion on the 305 heads and if they would be causing my spark knock. Base timing is at 8 deg btdc and full is supposed to be 32 deg. Thanks

You can't back off your timing a couple of degrees to get rid of the knock? Run high octane fuel or octane additives? Colder plugs?

Ok- the 305 heads are causing the problem due to the excess shrouding. If the builder had of looked up thru the bottom of the block with the heads in place he would have seen that the 305 heads sit offset instead of centered on the bore. If you want the higher compression heads than spend the money for a set of darts, or just go back to the factory heads.

if it was me i would not be to quick to pull the 305 heads, i mean i would not want 305 heads on my car but in a boat unless you race it why not try and use them. how is the timming chain ? i have know people to run 283 heads, on 350s with out any knock. but with the old heads exhaust seats may not last as long on the new gas. but you could ad in some lead or a little two stroke oil. if you're 327 is an old small crank its worth more

techinspector1 is right. Your 305 heads have a 58cc comp chamber and you are making too much compression for the crappy pump gas from the pump. Seen this done on a 350 before. Compression that was 150 to 160 lbs jumped to 210 and ran like crap on pumped gas when worked hard.