I know 36* total timing is where you want to be on a small block Chevy. How important is being around 50-52* with vaccum hooked up? I mean what if you get 48 or so.

 

It's really no big deal. As long as the timing provides good performance and the engine doesn't rattle it self to death, that will do.

BigBlockk

Later.....

 

50-52º is optimum but 48º will work.
What vacuum can did you end up installing?

 

Generally, the closer you can get to about 52 degrees at light throttle cruise, the better your fuel economy will be. But I doubt you'll see any measurable or practical difference between 48 and 52. The important thing is to not get the total combined timing up above 54. Above 54, the engine will start to "buck" and "jerk" at cruise from the over-advanced condition. For this reason, I recommend a target of 50-52 degrees. But 48 will work just great.
Lars

 

we need to clarify the meaning of " total timing". this forum is the only place i have ever heard of anybody anywhere running 50* of timing! total timing IS with the vac line hooked up.
base timing
centrifigal timing
and finally vac advance
these three things are " total timing "
not 36* and then hook up the vac

 

Corvettes engines are different, its OK to run that much as long as the engine stays in a corvette.
Its also OK to have 4 choices of numbers to pick that way your bound to come close to one of them, so you can call it a day and go in the house and read the Wall street journal!
Example:
"My name is John and I have a red Corvette and the timing is set at 12. Is this OK?
Response: yes red Corvettes can run 12."
Example:
"My name is Bob I have a blue corvette and I run 36 degrees of timing is this OK?
Response" yes blue Corvettes run 36."
Example:
"My white vette runs 52 degrees of timing on Tuesdays is this OK.
Response: White one can only run 52 on even days other wises you have to add the 4 different way of timing a vette and add them togather and thats your timing."

 

initial lead and then add whats built in the distributor gives you your total.

 

I ended up using a accel dist. My "all in" is 3600 so i will have to change the springs. The vac can is adjustable so thats why I wondered if 48* was ok.

 

So total timing is not what I thought intial + centrifigal ?? Im confused ...... redC3

 

no, the 36 deg all in by say 2800rpm is the initial + centrifugal...then when you add the vacuum and get the vac advance, those 3 add up to the total.

You say your all in was at 3600rpm..thats a little high. What was your all in reading?

 

Total timing is generally accepted to be initial plus centrifugal. Reason for this is that many performance distibutors do not have vacuum advance. Also, total timing is the maximum timing you achieve at WOT at peak power, thus vacuum does not enter into the equation. Total timing (timing without any vacuum advance) on a performance engine (not fast-burn) is generally set to 36 degrees. Any given engine can produce peak power a few degrees either way of this target spec, but 36 is accepted as the general spec. This is without vacuum advance.

Since different vacuum advance control units produce varying amounts of additional timing advance at light throttle, the total combined timing (total timing plus vacuum advance) is usually not specified by any published spec: The spec numbers for the vacuum advance control units are published, but timing is set to 36 degrees total without the vacuum hooked up. You then add in that produced by the vacuum advance. My only rule of thumb on this is to make sure that you cannot get any more than 52-or-so degrees with all combined timing fully slammed in.

If you ran 36 degrees of total combined timing (full centrifugal plus vacuum), it would give you the following results:
Subtract the 16 degrees of vacuum advance from 36 and it gives you 20 degrees of full centrifugal. Since most centrifugal; curves are 20 degrees long, you would get 0 degrees intial timing. That won't work. Total timing is 36 degrees without vacuum advance. That's a fact.

 

Thanks Lars. Thats what I thought.