I have the 68 #16 heads on my 73 400 block. Got front end rebuilt so I can safely drive it now. I took it out last night. It tends to run hot in stop and go traffic, but fine on the road. It also had preignition problems when I shut it down, I have installed an HEI type ignition system and new Boesch platinum 4208 plugs gapped at .035 I have the timing set at 11B. I read the earlier posts and intend to check my water pump clearance. Does the preignition have to do with the running hot around 200 in traffic or is it a seperate issue? Thanks Louie
Sounds like your timing is off several degrees, check that first. Plug gap needs to be wider with HEI, I believe .045. May need to re-curve distributor to cam in your engine. #16's are high compression heads, what octane gas are you using? All these things can contribute to an engine running hot & pinging. Put the highest octane gas you can buy in it, may have to mix some racing fuel or Av-gas in to meet the requirements of your engine. Changing the advance springs to lighter ones may help distributor advance quicker.
Also make sure your idle speed isn't too high. That makes it worse. You can shut off the engine in drive if you have an auto, that'll add a light load and help keep the engine from hurting itself.
I figured since it's common knowledge that HEI requires a .045" plug gap that's what to go with. HEI has a higher voltage spark, thus requiring a wider gap. A closer gap will work, but plug life will suffer.
