Well, i finally got my 355 running on Sat. Wo-hoo! So me and my brother set the timing to around 7-8 deg BTDC. So i clamped down the dist and started to walk away and he said that the timing started to advance to like 10, 12, 13 then we quick ran and shut it off. This cannot be normal. I have a used HEI dist that worked 6 months ago that was on the truck that gave me my donor motor. I am at a loss for ideas. What could make the timing advance on its own? When i set the timing i should have the vac. advance disconnected right? Thanks Bob.

 

No it basically won't do that.

What probably happened, was that the idle speed crept up a little bit, just enough to get the centrifugal advance started to advancing; which raised the isle speed; which brought in a little more centrifugal; etc. etc. etc.

You should have the vac advance disconnected, and you should have the idle speed low enough that you are completely out of the range of the centrifugal advance. Once the engine RPM is sufficient to start operating the centrifugal advance, the timing should advance; you're no longer at the static setting.

Ignore the number you are setting the timing to. You don't have a stock motor, so a stock timing spec is not appropriate for your setup. You need a different way to know what to set the timing to, and possibly a different set of specs for your distributor, from whatever it's doing now. It's called "tuning".

I'd suggest setting the static timing to about 34° with the vac advance disconnected, and the engine at 3500 RPM. That's what really matters, is what the engine sees, under actual operating conditions. Then let it idle back down to 700 RPM or less, and see what your static timing is. That's what it needs to be. Then hook the vac adv back up, and go for a test drive. You probably won't believe the difference it will make.

 

I am not so sure that i follow along with the term "static timing", could you please explain. But now that you mention it advanced as the rpms increased, and the idle speed was set incorrectly. Very good thanks RB. -Bob

 

"static timing" = what you set by twiddling the distributor; it's the "rest" point, for when none of the systems are active that dynamically alter the timing in accordance with the engine's current operating conditions

 

I should have been a little more specific. How does one statically time an engine? Thanks -Bob

 

With a timing light and a distributor wrench.

 

Static timing as used by RB83L69 means without the vacuum advance, which is why he said to disconnect the vac adv, hold the engine at about 3500RPM, and set the timing to 34 degrees. then lock down the distributor and see what it's reading at idle. ANd reconnect the vac adv.

That might have worked on his engine, but all of them are different (boththe RPM and the degrees). But the values he gave should be a good ballpark and starting point. Basically the same idea as disconnecting the ESC connector on the cars with computer controlled timing.

 

Right: "static" timing is the position the distributor is set at in relation to the crank, with all of the mechanisms that alter the timing during engine operation, disabled or not in effect.

In addition to this "static" setting, there's "centrifugal" advance, which adds advance based on RPMs; and "vacuum" advance, which adds advance based on lack of load at high speeds, for cruising economy. The "centrifugal" advance tuning is critical for peak engine performance.

"Total" timing is usually given as static, plus centrifugal. For a Vortec-headed engine, it usually wants to be about 34°, give or take a couple (and of course, allowing for any error in your timing marks), for maximum engine power. A typical optimum timing curve for a warmed-up street SBC, would be 12-15° static advance (what you see with the vac advance disconnected, and engine speed below 500 RPM or so); centrifugal advance starting at about 1200 RPM, and increasing smoothly up to the desired 34° of advance by about 2800 RPM; and an additional 12-15° of vacuum advance on top of all that.

You're going to have to do some experimentation and tuning to get yours really perfect; but the numbers and techniques I gave, should give you a good starting point, and a direction to go from there.

 

Alright, now i understand. Set it at 3500 rpm because all of the advance mechanisms will be functioning. So i need to get and adjustable timing light, because mine is fixed, correct? -Bob

 

Either that, or timing tape to fit your harmonic balancer (that's what I'd do).

You want to set it to 34° with the vac adv disconnected; you want it out of the picture so that you're simulating WOT operation.

You tune the centrifugal advance with springs, weights, and cam plates; you tune vac advance with an adjustable vacuum can.

 

on the topic of timing tapes:


i put a summit timing tape on my 400 (8" balancer) when i built it.

it came off.


i said, ok.. it was probly a cheapie... i got a MSD one locally.

it also flew off.

ok, so i got a second MSD one. i made SURE the suface was clean, ect...
it came off.



how the hell do you get them to stay on?!

 

You don't..... you put it on when you need it, and then you take it off and store it. The timing doesn't need continual messing with anyway, and it doesn't just up and change itself, so there's no need for it to be there all the time.

 

its such a pain to put on and take off though.... esp if i want to check it at the track....


im just going to bite the bullet and buy a dial back light...

 

Just mark your balancer with a couple of drops of white paint at various points of interest, and go from there at the track. Don't outsmart yourself.