timing for 285 horse good wrench crate motor

[diggerbob]

about 15 years ago, I bought a 285 hp, 350 crate motor at a chevy dealer and put it in my truck. I didn't get any documentation with it at the time other than a single page that gave a few key specs ( it is 8.8 to 1 compression). I put a HEI in it and set the timing at 10 degress @ 800 rpm which is what the one page spec sheet said to do.

At high way speeds, I can hear a little knocking so I think I may be getting too much advance at wide open throttle. The specs for 330 hp engine that gm makes today says that this engine should be at 32 degrees at WOT (vacuum plus centrifugal advance) and the specs for the 290 hp engine also says 32 degrees at WOT but using centrifugal advance only. My question: Do I need a vacuum advance on my engine or should I just go with the centrifugal only? I am going to have my mechanic buddy recurve my distributor if necessary to eliminate knocking but I thought I would see if anyone here knows about this crate motor and whether or not is was designed for centrifugal plus vacuum advance or just centrifugal...

[kwmech]

Keep the vacuum advance for a smoother transition and drop the timing to 8 and see what happens. Way easier to try it and see

[67 cst swb]

Here is what I do.
Using a timing light.
Start at 8 degrees, once everything is tightened down, take it out in the street/parking lot/wherever...
From a slow rolling start... floor it for a good hard acceleration... if it doesn't ping or clatter. Go back and advance it 2 degrees and repeat...
Again, from a slow rolling start... floor it for a good hard acceleration... if it doesn't ping or clatter. Go back and advance it 2 more degrees
Repeat this over and over...
Now... once it starts to ping or clatter... back it off 2 degrees (to where it didn't ping/clatter) then leave it there.
Keep in mind there are numerous things that effect this such, as quality of fuel, octane of fuel, advance built into the distributor (typical is 24 degrees at full advance), etc...

But this is essentially giving the engine "what it wants" with the variables as they are at present time.
If you start running better or worse fuels... this will need addressed
If you change distributors... this will need addressed
If you start messing with and adjusting the advance built into the distributor... then your on your own on that one.

This is always how I have known to time a vehicle regardless of what the factory spec timing calls for.
How can a crate engine used in California (sea level) with 89 octane fuel be set at the same timing mark as the same crate engine in Denver (5280feet) use a ethanol blend of 92 octane. My opinion is... they can't.

note: use at your own risk. I will NOT be responsible for accidents, burnouts, back fires threw carburetor or any engine damage do to unknown variables.

[CST10]

I use straight mechanical advance. No vacuum advance. I use 91 octane gas and set it like the post above. Vacuum advance is better for gas mileage though.

[airdale94]

You shouldn't get any knock with 10 degrees. I would check the springs on the mechanical advance. Maybe put some stiffer ones on them.

Also is it wide open throttle or just highway. If it's just highway depending on the distributor, aftermarkets will have a adjustable vacuum advance that you could back off a little.

[67 chevelle]

I like around 12 initial and 34 total , another thing that can cause pinging is a lean condition , if you have changed your carb , intake , pcv , or have a brake booster issue , any of these along whit many other can cause this , one way to check for leaks is spraying carb clean at suspected leaks with the engine running , the engine will smooth out or rpm will increase if you hit a leak