Detonation issues

[46flattie]

I've been struggling w/some detonation in my 401 when I tip into the throttle when cruising...for a hill, to pass w/o downshifting, etc. especially if I have my M416 trailer on loaded w/gear. I have a hard time thinking I'm too lean w/the carb jetting in the mid-range....I have richened the mixture up w/o much change. I run the heaviest step up spring to make the needles pull up into power mode as early as possible. However, I can make the detonation lessen or go away when the secondaries open. I run premium 100% of the time (92 - 93 oct). It seems worse in the summer, but engine temp is normal. I know ethanol is suppose to make octane, but I've been wonder if the "up to 10%" ethanol isn't maybe some of the issue. Maybe you guys have some tips for me.

engine specs:

401
30 over
TRW forged pistons (2380)
Summit K8600 cam, straight up
Eldelbrock performer intake
Dog leg port 58 cc heads - Mild porting, mostly just cleaned-up the big stuff and a little radius work, milled .010"
Edelbrock 600 carb (running the 8" set-up springs and primary jet/rod combo is fairly rich - stage 3 - 12%, secondaries stage 2-8% rich) I know it's a small carb, but I like the drivability on and off-road.
BullTear HEI distributor - stock...vac adv running manifold vac
Tried running a total adv of 32 - 33, but have had to back it down a fair amount to eliminate detonation

Vehicle:

Jeep CJ-8
3.73 gears
33x10.50 tires
about 2300 rpm at 60mph



I been thinking about recurving the dist...slowing down the mech. adv in the mid range...or maybe I am just trying to run too much total adv? Maybe too much compression for pump gas...I/m estimating about 9.25 - 9.5 to 1, but never measured.

THanks!

[tufcj]

My AMX 390 had a detonation problem when I first got it running. I found the Vacuum was pulling in too much advance. I'm running a Mallory Unilite. I'm running compression right around 10:1, polished/ported 291C heads, and a fairly large cam (290 duration @ .520 lift). I'm running 18 degrees initial timing, pulling in 18 more mechanical by 3000 RPM, vacuum advance disconnected. Runs great like that, and no driveability problems.

You might just pull/plug the vacuum and see if the problem goes away. No problem driving without a vacuum advance.

Bob
tufcj

[46flattie]

Interesting....this spring I found that the vacuum advance had leak and replaced it (and I have a fair amount of vacuum due to running a small carb). My detonation was not really noticable until I put the trailer on the back for my last trip....

[46flattie]

Disconnecting the vacuum adv made an improvement...I'm running 32 degrees total w/o much issue and have gained back a bunch of HP (from the seat of the pants perspective). Put my trailer on (w/only a partial load) and it seems good. Tomorrow, I'll be fully loaded and we'll see what I can get away with.


Thanks!