I checked and slightly advanced idle today. I also added some 100 octane to my tank. With disconnected vacuum advance I'm at 11* at idle and 34* total at about 3250rpm. Response is MUCH better with this slight advancement in timing but just a tiny bit of detonation immediately after each shift at wot even with the additional 100 octane. I also believe carbon is still slowly burning off pistons. Pictures attached. I'm considering running 25% racing fuel with my premium this year to stop the detonation and hopefully clear more carbon. Adjustment thoughts anyone?
I warmed up the motor and sprayed a quart of water with a bit of seafoam down the carb with my paint gun at about 2000 rpm. Then took it out for a spirited drive. Runs great. Oil change soon. Inspection camera photo doesn't show much of a difference. I'm done spraying water down my engine.
I never expected my 72 350 would need some racing gas just by changing to 30 over silvolite pistons and a 284-88h cam. It doesn't even perform that much better in the 1/4 mile. A bit of a mystery to me. It always did 15s in the 90s with a wiped intake lobe since 1973. I'm going to have to do an ET check again soon.
What are the cam specs for that cam? What is youir compression? If you have a three keyway timing sprocket you can retard 4 degrees to lower Dynamic compression.
Not sure of exact compression. Stock was advertised 8.5 silvolite pistons were supposed to raise that a little. Good idea...... "Cloyes patented 3-Keyway crank sprocket allows adjustment of the crankshaft timing by ± 4°. Remember: The camshaft angle is half of the crankshaft angle, therefore the camshaft will correspondingly advance or retard by ± 2°"
I don't know but guessing higher than I think. But then my ET should have improved noticeably. ...... I'm overall very happy with performance just thinking there may be more left on the table.
Those pistons look like the 3.0V6 flatops. Usually around 10.5 to one and if the block or heads were skimmed could be your issue.
It would be nice not to have to add racing gas every tank but would it make a noticeable negative effect on performance by retarding the sprocket?
Do you know your IN and EX centerline for that cam to see if there is advance built in? Even though the cam only moves half the crank speed and the Advance and Retard is in crank degrees the cam specs are also in crank degrees.
I am wondering if my particular block accidentally had a bit more compression originally from the factory. (Stock 15sec 1/4 mile ETs with 90k and wiped intake lobe back in the 90s) I didn't take any measurements when it was apart so hard to tell what true compression is.
By retarding the cam you will move the RPM range up and the Dynamic compression down and not need the race gas. With the higher compression and no detonation it will wake up quite a bit.
