Gsoleski

I am wondering about what initial or base timing I should be running on my new engine along with the total timing. My engine is nothing serious, its a 355 roller block, 10:1 pistons, lt4 hotcam, vortec heads with bigger valves 60cc chambers springs and 1.6 roller rockers, an RPM intake, quadrajet, and hooker 2460 headers. I do not have the engine in the car yet i'm just trying to get everything planned out. Should I start out with 12 btdc and see how that runs? Or do you think this engine will require more? Also what should my total be? I've heard vortecs like around 32-34 but how does my smaller chamber effect that? Last thing is I will be using a vacuum advance distributor. Should I have smaller springs in it so the timing comes "all in" sooner or should I try the heavier springs? Sorry for the dumb/noobie question but this is my first time doing this.

Also I didn't want to start another "what will my hp be?" thread but does anyone have a guess? Safe to go with 375 crank hp?

sofakingdom

iTrader: (1)

Probably would run better with a little more initial and less centrifugal...

If you get it to 16° initial and back it off to about 18° of centrifugal (34° total), plus about 12° of vac, should be about right. You'll want it to start advancing just off idle (1200 or so) and be all-in at around 2800.

If the engine is lightly loaded (light car, high gear ratio, loose converter) it'll want more advance. Heavier load, less advance.

Gsoleski

So say I had it at 16 initial but total came out to like 36 and i'm aiming for 32, how can I bring the total down? In other words how do I take the unwanted 4 degrees out of the distributor? Or should I just set it up with lighter springs and when it gets to 32 total just tighten down the distributor and not worry about initial?

FRMULA88

retard total mechanical timing 4 degrees by turning the dist. clockwise then and lock it down.

Your initial timing will change to 12, but this is relative to idle speed.

AT WOT there is no vacuum advance (no vacuum at WOT)
only at low RPM /low load conditions (high engine vacuum) will vacuum advance matter.

At those conditions it will add vacuum advance to whatever mechanical advance you may be at on the mechanical curve. it is a way to improve fuel economy at low load / low rpm conditions.

But how much vacuum the engine creates at low RPMs / low loads is directly related to the camshaft.
performance camshafts make less vacuum at low RPM / low load which makes using vacuum advance difficult to impossible depending on the camshaft. This the trade off you make with a carburetor.


One old school trick was to used Rhoads lifters.. because they would bleed off at low RPM and provide more vacuum.
they make roller cam lifters now.. something to consider if you want more engine vacuum for vacuum advance, & power brakes. http://www.rhoadslifters.com/




The lower initial timing should make it easier to start the car

FRMULA88

food for thought..

http://www.rhoadslifters.com/Pages/Articles.html

JaBoT

An aftermarket distributor like an msd or malory (not the hei versions) will allow you to change the amount of total advance.

FRMULA88

Correct, you have to open up the dist. and make some adjustments.

if this is an MSD product & you don't have the instructions you can get them from their website.