[bhill86]

Title says it. Took my 77 T/A for a ride today and on my way back, around the corner from my house where I drive frequently, heading up hill, 25ish mph I stayed in 2nd gear and accelerated up the hill as I normally do and heard detonation. I was in a neighborhood at this point so I had limits to my speed but low rpm acceleration gave the same result the few times I could test it before I got home.

Last time I had a similar issue which, was this past summer, I discovered the mechanical advance mechanism in the aftermarket dizzy that came with the car 10 years ago darn near seized up and was stuck at full advance. I replaced it with a factory unit I happened to have and that seemed to fix the issue then.

I checked the timing tonight, 14° BTDC at around 775rpm (which is where I set it last time so it hasn’t moved nor did mech advance stick again) with vac can disconnected and open carb line plugged. Vac can adds 9-10°. I couldn’t check total tonight tonight cause if noise but it is set for another 20° or so for 34 total plus the can.

SCR is arguably 8.5-8.7ish. I say that because if anyone read a previous thread I posted I had engine work done by two different fellows in the past who each calculated my milled 6x4 heads at different cc’s. Being afraid of detonation in the past, and being inexperienced, I used to use 91-93 octane depending if I could get 93. Realizing that wasn’t necessary, I stuck with 89 up until recently when I filled my last tank with 87 thinking I could probably get away with it easily. My cam is a comp xe262h which I know builds DCR a little but is it enough to cause me detonation issues on 87 octane with 8.5:1 SCR?

Any ideas? Thanks in advance.